Standard vs alpha

[dan_nelson]

Im a one man shop looking to get into a bot.I have no cnc experience.Should i think about starting out with a standard with a high hp spindle and up grading at a later date with the faster alpha up grades? I will be using the machine for panel prosessing and carving. Looking at a 96x60x6 thanks for your help.

[Gary Campbell]

Dan...
If you are going to cut cabinet panels for a living, I strongly reccommend the Alpha. There are other features other than just the speed to consider. The Alpha IS the professional machine.

IF I was on a budget, I would rather have an Alpha with a router than a standard with a spindle.

The power that is required for panel processing, especially drilling, are right at the limits for the standard. Even tho it is said that the Standard can do all that the Alpha can, only slower, is not 100% accurate.

Panel processing, cutting hardwoods and drilling hard materials, especially Melamine are best left to the full power machines.

I have cut with both the PRStandard and Alpha. I own an Alpha 9660.
Gary

[gene]

Dan,
I do panels with mine and i got the alpha because the alpha has a closed motor system meaning if it looses a step it will stop. If a standard looses steps you dont know until the parts are finished and no good. Check the for sale area on the site , i think i have seen one . also i think that you can re register it with shopbot and get support from them. Check with them and if i am wrong i am sure i will be told so SOON !

[richards]

Dan,

Check with Shopbot before going any further. Ted recently announced that the PRS-Standard will use a new motor/driver combination from Oriental Motor.

The new motor/driver is open-loop, meaning that it doesn't have the "alpha" that lets it catch-up when steps are missed, but that feature has caused me just as much product loss as missed steps would have simply because it usually leaves a divot in the part when the motor/driver goes into "alpha" mode.

Assuming that the new motor/driver is the Oriental Motor RBK series, it looks like a very good package, especially if Ted ordered a geared motor.

The advantage over the PK29x motors and the Gecko G20x drivers is that the RBK series is sold as a unit directly from Oriental Motor. The catalog price is about 35% higher for the RBK package than it is for the PK29x / G20x parts, but the PK29x / G20x needs additional parts and pieces before it can be used.

The big question to me is whether the new motor/driver uses a gearbox or whether it is a 1:1 drive like the original PRT-Alpha (pre-7.2:1 geared motors). My PRT-Alpha when used with the original motors had a terrible chatter problem that left much to be desired in the quality department. After adding a 3:1 belt-drive transmission and then upgrading to the 7.2:1 motors, most of the chatter was eliminated.

[thewoodcrafter]

After owning both I wouldn't even consider a Standard.
I make a living with the machine and a standard just will not do the job I want.
If funds are tight get the Alpha now with a router and upgrade to a spindle later.
Upgrading to an Alpha later is pretty expensive.
Buying a used spindle and VFD would be cheaper.
You will find lots of used machines and some used spindles at way cheaper prices than new here on this forum. If your not leasing, used is the way to go.

[jerry_stanek]

When I checked with Shopbot about upgrading a standard to an alpha the cost was almost the same as if I ordered the alpha over the standard. Shopbot gives you a refund when you ship back the 4g board and drives.

[gerryv]

Mike, I recall recently reading about a kind of hybrid stepper with a built in position sensor. As I recall, it runs in open mode unless a lost-step is detected then somehow responds to address the situation. I thought it was a Vexta but now can't find it. I think it was priced to fall between their closed and open loop units.

[richards]

I'm going to withdraw what I wrote earlier about the new motor/driver (Oriental Motor RBK?) until Shopbot releases some solid information about the entire system. (Everything that I wrote above was based on speculation.) Because I don't know which motor (296/299/291) is being used, which gear box (if any), what voltage power supply (motor/drivers are rated up to 75VDC), diameter of the pinion gear, etc., it's just too soon to speculate, especially when buying a machine at the higher prices.

-----

If anyone gets a kick out of reading motor/driver specifications (like I do), visit www.orientalmotor.com (http://www.orientalmotor.com) and look at the RBK motor/driver section. You'll find that Oriental Motor sells a motor/driver that equals the torque of the Alpha motor/driver that Shopbot sells, so there is no reason that the new PRS-Standard would be less powerful than the Alpha. The 299 size motor/driver is only $68 more than the 296 size motor/driver. The 299 motor has more than 600 oz*in of torque and the 296 motor has more than 300 oz*in of torque.

With a 3:1 belt drive transmission, the 299 would give 1,800 oz*in (112 lb*in or about 50% more than the Alpha 7.2:1 motor which produces 80 lb*in with the gear box Oriental Motor provides).

Bottom line - If the RBK motor/driver selected by Shopbot uses the 299 size motor and if it is equipped with a high quality gearbox that multiplies and transfers ALL of the available torque and if the power supply produces the maximum allowable voltage and if the pinion gears are the same as the Alpha pinion gears and if the steps per revolution selected by the switches on the driver are set at a minimum of 1,000 steps per revolution (to match the Alpha driver), THEN it would appear that Shopbot has advanced the PRS-Standard machine into the real world of CNC machines; otherwise, the PRS-Standard would still be an underpowered, hobby-use only conversation piece that looks good but was never meant to do serious work.

Also, with a 3.6:1 or a 7.2:1 gearbox, the final torque would depend in large part on the components used inside the gearbox. However, I would hope that no one would order the RBK motor attached to the SH style gearbox that was used with the PK296A1A-SG3.6 motors. That Oriental Motor gear box used components that only allowed about 20 lb*in of torque, meaning that the gearbox limited the torque to an unusable level.

With the proper RBK motor/driver, the proper gearbox, the power power supply, and the proper pinion gears, the PRS-Standard machine could easily compete with the PRS-Alpha. It would have the same cutting speed, the same jogging speed, the same accuracy, but it would lack the "Alpha" feature of the the PRS-Alpha machines.

If the lighter duty motor/driver has been selected for the PRS-Standard, I wouldn't use the machine. To me, the lighter motors would put that machine into the hobby class and I just don't see Shopbot users as being hobby class CNC owners. Once they see what can be done with a CNC router, they'll want the machine to DO something more than make light-weight cuts in foam.

[curtiss]

Is not one/ or the main / limiting factor with CNC just what the router bit can handle without breaking ??

Seems like the speeds and feeds for either a PRT, PRS or Alpha would be detemined by the bit and the material being cut.

a side question, At what point does drilling holes with a router start to be excessive for the bearings ?

[Gary Campbell]

Curtis...
in order:

Max speed is a product of bit design, rpm, spindle horsepower, hold down and move speed. When it comes to cabinet parts, for example, a large machine can push a 1/2" bit full depth thru 3/4" plywood between 12 and 15ips. Our machines dont have spindles powerful enough to evacuate chips when cutting that fast, so we could break a bit at a lower cut speed. We also experience flex in our machines when cutting loads are high. (deflection) That is why it is important to have a matched package. IF we put motion components in that had double the speed/power of the Alpha, we couldnt cut much faster than the Alpha and maintain cut quality due to limitation of the frame. If the frame were heavier, then it takes much greater power to overcome inertia. Its a vicious cycle. Short answer is, assuming constant spindle power, and proper speed/move settings, a ShopBot could hardly break a bit larger than 1/4".

Yes, the material being cut and the proper bit determine speed, but the ability of the frame to withstand lateral forces generated by cutting also contributes. That is the reason that the $150K+ machines can cut faster and with better quality than we can with the same bit.

Are you speaking router or spindle? Many spindles, including the HSD that ShopBot sells, are used for industrial operations like mortising. This means that they are used for plunge only by design. This may not be the same for all spindle configurations.

The loads required to drill holes is a production scenario exceed, in my opinion, all bearings supplied with routers sold in the US. Even tho I might use one for this, as many others have, the constant plunging is not what they were designed for. Since a complete PC router costs less than a set of spindle bearings, its no wonder many do this.
Gary

[thewoodcrafter]

Someone correct me if I am wrong but I think you can cut at least 3 times faster with an Alpha over a Standard with the same hold down, bit, spindle and material setup.
That can translate to big savings.

[hh_woodworking]

I do a lot of drilling with my prt and pc set up. Granted I am only drilling 1/8 holes in 1/4 plywood so that will have an impact (not much force is needed). I am drilling about 120000+ holes per year. I run the router at 10,000 and I am on the 3yr for the bearings year 2 on brushes . I also do a fair amount of cutting with it also.
Ed

[Gary Campbell]

Roger..
The SB website lists the move/jog speeds of the alpha at 600/1500 ipm and the standard at 300/500. My personal experience, cutting under load, would have me believe that they are not that close. Onionskin cuts with a 3/8 bit in 3/4 material are done at 480-600 ipm on my alpha and the most I could reliably get out the standard was 200 ipm with a 1/4" bit. I couldnt exceed 450ipm on the jog without an occasional missed step.

Please note that the machine I was running was running at less than optimal voltage, so results may reflect that fact.

I have heard, from a very good source, that the differences in load before the motors "fault" is 50# for the standard and close to 200# for the alpha.

My guess is that 4 times the power and 3-4 times the speed would be pretty close. So, for the hobby or occasional user the standard will work just fine. For a professional user, I consider the Alpha a neccessity.
Gary

[joe]

Dan,

Back on the subject:

What are you expecting to do with a router? Perhaps you could ease into a used unit by looking on this forum. If you look around your area perhaps there is someone who has a CNC for you to look at. I'd post on this forum for a contact.

I'd also suggest looking at other businesses who are doing what you expect to do and get what they have. That way you know what you need.

Good luck,

Joe Crumley
www.normansignco.com (http://www.normansignco.com)

[dan_nelson]

Thanks for all the help fellas, I truely am impressed by all the response and info, I will continue my search for the right machine for my needs

DAN

[gene]

Dispite the speed of cutting and all the other stuff mentioned here if it looses steps and cuts the parts inaccurately what good is the part then? The main reason i bought the alpha was for accuracy , then speed. You will not know that the steps are missing until assembly , Then what. Throw out a cab job? I say bite the bullet and go for the alpha.
Dan , I dont know where you are located but you have a open invitation to my shop and you can test one out. If i am too far find someone close to you and i am sure they will give you the tour as well . if you like e mail me @ cabinetsplusofaugusta@yahoo.com (mailto:cabinetsplusofaugusta@yahoo.com)

[erik_f]

I'm not saying anyone is wrong or debating that the Alpha isn't the better machine, but I think its been about 5 years since I have caused my machine to miss steps. Then again I'm not in a production setup trying to push as fast as possible. This thread makes it sound like the standard is total garbage, which it is not. I agree that the Alpha is better suited for high speed production...but the standard is much more than just a hobby machine.

[richards]

Maybe I just don't get marketing, but why offer an underpowered machine when motors and drivers are available to make both the PRS-Standard and the PRS-Alpha equally able to run at the same speeds?

If the Alpha feature is a benefit, why not let it stand on its own merits without crippling the PRS-Standard?

The older model PK296A1A-SG3.6 motor was a limiting factor. The PK296A2A-SB7.2 motor could have been used that gave 2X the torque and 2X the resolution (additional resolution that was not needed, in my opinion) at the same price. The PK296A2A-SG7.2 motor, when wired half-coil, is by far the better motor for use with the Gecko G203v stepper driver. At 35VDC and 3A, it produces all the available torque that the gear box can handle. The PK296A1A-SG3.6 motor, wired bipolar series, is barely usable with the G203v stepper driver. The inductance is just too high to let that driver/motor combination work properly. If all six wires were available with that motor, it could be wired half-coil, and with a 80VDC power supply, it would have performed much, much better than it does when wired full-coil.

The point that I'm trying to make is that many motor manufacturers make motors that would allow a PRS-Standard to run with the same vim and vigor that the Alpha has. Those that need/want the "Alpha" feature could still order the PRS-Alpha and pay the $750, or more, per motor difference.

A businessman who runs a break-even analysis spreadsheet will get a real eye-opener when he compares a $125,000 machine that includes a 10HP spindle, auto tool changer, high-powered and high capacity hold-down vacuum, that can run at 12-ips, full-depth, one-pass to a PRS-Alpha that needs $30,000 to $40,000 in upgrades and then still runs at 6-IPS and requires two passes, plus sanding or to a PRS-Standard that runs at 3-IPS and requires three or more passes, plus sanding.

A hobbiest might never see the need for speed, but when the final cost is either nothing (PK296A2A-SG7.2 vs PK296A1A-SG3.6) or minimal (RBK296 vs RBK299), why not add real value to the machine and let the "Alpha" feature win adherents on its own merits.

I might be totally out of line making this kind of post, but I bought a PRT-Alpha in 2004 with the anticipation that I could compete with the "big iron" machines. That never happened. I'm lucky to get the scraps that fall from the table of those "big iron" shops. They can deliver a better quality product at a much lower price point than I can, and they can do it while making a decent living, while I struggle to make minimum wage.

Don't get me wrong. The Shopbot is a great machine, but it cannot compete in a "cabinet shop" with the "big iron" machines unless either quality or speed is discounted.

In the high-volume low-price field of cabinet making, the price of the CNC machine is the least important part of the cost/profit matrix.

[Gary Campbell]

Dan...
Nice to talk to you on the phone, hope to hear soon that you are an owner.

Mike...
The difference in retail between the 9648 alpha & standard is $4900. Frames and motion hard parts are the same. This means that the Alpha setup is able to be sold for close to $5k more. For those that can afford the extra features of the alpha, its not a question. $5K more, cuz its worth it! If I were ShopBot, I would choose NOT to put out the standard with the same speed and power. But thats just me.

Eric...
I hope that you dont interpret anything that I said as being negative towards the Standard machine. A 4 by 8 machine that can accomplish most any CNC task for $12K? Borders on magic and kudos to ShopBot. And their Alpha version, with its features for $5k more? Even more impressive. Please be aware that I AM one of those that will try and push most everything as far as possible. At least I try.

That being said, the ShopBot is still an entry level machine in the flatbed CNC world. Our Alpha has features above entry level, I feel, but entry level priced. At the time, the best I could afford and that holds true to present. Please do not confuse "best I can afford" with "what is the best". I most likely may never be able to afford the best that the CNC world has to offer.

Since I have had the opportunity to operate, or stand next to an operator running my files, on 3 "other brand" big iron machines, I can say this: next to them, I consider my Alpha also to be a hobby grade machine. My reasons are: it is lighter,(less than 6,000#) less expensive, ($40K not $200K) and requires assembly. It also has no where near, as Mike says above, the cut quality of the big iron at 1/4 of their speed.

To jump up to the next step in speed and quality will be a large one financially. The reasons why are explained best by Ted in his Article on ShopBot Design decisions: http://www.shopbottools.com/ShopBotdesign.htm He states very well how increases above what we have now will come in exponential increments rather than muliples. There are also many other factors, such as hold down, as I surely wouldnt try to cut twice as fast without a very expensive vac pump, power upgrades to the shop, etc. If it wasnt for ShopBot, I wouldnt own a CNC, and I bet the majority of us here feel the same.

In the long run, we are very happy with our machine, and would be more likely to add another ShopBot than switch to another brand, but I stand by my original recommendation to Dan. That if he is going to cut cabinets for a living, then I recommend the Alpha. So does ShopBot, its all over their front page. Click on any part of the "Professional/Industrial" section and you are directed to the PRSalpha section. I also stand by my term "hobby", in that if you are not cutting cabinets for a living, then it is a hobby. Many hobbies turn into business', but there is a major difference in doing something and getting paid, versus doing nothing else to make your living.

Sorry for the rant, didnt intend to flame your standard.
Gary

[bleeth]

I don't think the difference, and here I am speaking strictly of cabinet making, lies in professional vs. hobbiest. I think the difference lies between low, mid, and high production needs.

If one is in the business of doing 20-30 cabinets per week this can be quite easily handled with a PRS running a single spindle, mid sized vac and producing all parts with a 5mm bit.

If one needs a weekly batch of, say, 50-60 boxes, than an Alpha running the same vacuum and an auxiliary drill setup is the way to go.

If your weekly needs run more to 100 boxes than a tool changer is probably in order as well as a very healthy vac and you are now pushing the max for a Shop bot.

A large production shop has a weekly batch of 150 boxes minimum and will likely do much better with a box system based on a beam saw and a dedicated point-to point machine.

In a shop with only 1-5 employees there is no true need for a CNC beyond what SB produces.

The current PRS has no practical edge quality over an Alpha for cabinet parts, assuming a decent spindle on both, as long as it is not pushed beyond it's means.
I cut with a PRT with geckos and all cabinet parts go straight to the edgebander with no sanding. My reason for upgrading it is speed, not quality.

[shoeshine]

Not to needlessly continue, But I have to put out there that many of us who have a bot at the core of our business are not cabinetmakers.

"I also stand by my term "hobby", in that if you are not cutting cabinets for a living, then it is a hobby."

I guess it's how you define hobby, but I find that a little narrow. For rapid prototypers, luthiers and other instrument makers, fine furniture makers, prop and scenery designers, sign makers, architectural millworkers, and everyone else out there, being called a hobbyist is a bit demeaning to our high level of professionalism and commitment to our craft.

That the speed you can drive a 1/2" bit through a dado defines your needs is fine. But the flexibility and design capabilities of the smaller machines is ideal for many other applications. For my purposes, I would FAR rather have 5 BT48's running in tandem than I would ever have use for a "big iron" machine.

Chris

[gerryv]

VERY well said Chris,

I put myself in the "prototyper" category plus I have a son training in the fine furniture (mostly one offs) category. I spend at leat 50% of my time leaning towards selling my still unused Buddy 32 while I wait for SB to take true 3D seriously - as that's what I personally happen to need, knowing it's not (yet) the biggest CNC market. There, I said it - now I'm in deep poop!

However, that said, I salute SB for their efforts with Project Wizard - a great idea that got ignored, especially considering the new economic reality and the number of guys and gals hurting for business right now. Frankly though, I see the 100,000 garages concept going the same way if they focus too tightly on "systems" that are not truly multi-functional. Dang, I said it again.

It sure is a well built machine though, certainly the best I've ever owned and I've owned quite a lot of machines for different purposes. Now if it would just let me do what I bought it for...

[Gary Campbell]

Dave...
Thank you for saying it better than I was able to.

Chris...
The subject of original post and my response was, by design narrow. I was referring to cabinet cutting only. Please do not twist my words into into negative or demeaning comments towards any craft. By definition, if one is doing anything outside their regular occupation, it is a hobby. Even if their individual skill level surpasses that of the most accomplished professionals, as I am sure many do, by definition, it is still a hobby.

I sincerely do not wish to define my needs by the speed that I can cut, however, my survival may depend on it. Our market has changed and we must find ways to lower our product price to be able to compete. And yes, the speed at which we cut will be a factor, as will our assembly methods, material choices and many other factors. Quite frankly, if we didnt own our ShopBot, we wouldn't be having this conversation as I would be out somewhere looking for work.

I am glad that we can agree on the scenario of multiple ShopBots versus one larger machine. Much less capitol outlay for the same amount of product out the door.

Ain't this fun?
Gary

[erik_f]

The standard can take the heat!!! I suppose it frustrates me when people talk about the standard and alpha as two vastly different machines. The truth of the matter is (like others have said) compared to industrial CNC the Shopbot is a toy in any form. I use my machine for prototyping and lots of one offs. I didn't mean to come across short. I wouldn't ever want to push someone toward a standard when they would be better off with an Alpha, but for me it makes no sense to run an Alpha.

[scottgus]

Just one little input: Go for bigger Z height. When I got my PRTalpha 96x60x12, 2.2HP HSD spindle, I started doing curved cabinet front doors, among other things. I wrote a whole set of programs to generate automatic toolpaths, based off Bill Young's Extruder, that can ball-nose carve a rough curved panel of practically any shape and radius into a ready-to-be-sanded curved door.There is an awful lot of room under a 12" Z. My boss has a 5'x12' Biesse Rover that flies thru panel processing. But it has only 6" Z and he is always complaining because the odd carving project he wants to do won't fit under the gantry. He can't do curved doors on his $150,000 monster, but I can on the little baby in my garage!

As for PRT gantry flex, I plan to make a 7" tall torsion box and transfer my vacuum holddown system into that, so I can reduce my Z to 5" and hopefully reduce flex as well. Cutting climb then conventional reduces errors from machine flex, too. Maybe PRS's are more firm.

But a bigger Z height will pay off in those non-panel jobs you just wish you could have done if you hadn't limited the machine to a 6" Z.

[david_white]

I guess I will put my two cents in . I have A standard and it cuts 5 hr a day . we make radius moulding oak,cherry poplar mdf etc. After the blanks are cut they go into A Mikron moulder to be profiled . The Bot is great and I have rarely had a problem losing steps or any thing else.Before the Bot we used A big iron pin router using pivot points and jigs .The bot has greatly enhanced production.Having said that I would also agree that if you are going to cut cabinet parts the alpha is the way to go.

[richards]

I didn't mean to start a fire-storm when I posted my thoughts. Different businesses have different philosophies about how to market their products. I'm sure that Ted has carefully examined the market, talked with potential customers and then developed the two classes of machines to best meet the needs of the market.

Back when I bought my PRT-Alpha, the Oriental Motor Alpha motor/drivers were substantially more expensive (and more capable) than the other motor/driver packages that Oriental Motor offered. Anyone could go directly to the Oriental Motor web site and see for themselves why the Alpha model cost several thousand dollars more than the standard model.

Because Gecko stepper drivers were not being offered at the time, it was also clearly apparent that buying a motor different than the one supplied by Shopbot could cause difficulties.

So, in short, there was a very valid reason to offer two classes of machines.

Today, with the opportunity to buy Oriental Motor RBK motor/driver sets, the paradigm has changed. Oriental Motor offers a full line of motor drivers at competitive prices. Those motor/drivers can be programmed with a "steps per revolution" setting to work with any conceivable CNC machine. Of all the settings available, 1,000 steps per revolution and 2,000 steps per revolution are just two of the choices, meaning that the RBK can be a drop-in replacement (software wise) for either the Gecko G203v or for the Alpha.

So, because the paradigm has changed because of an offering developed and marketed by Oriental Motor and because Shopbot has decided to use that new motor/driver, there is no longer a need to offer two machines whose greatest difference is torque and speed.

The Alpha motor/driver still has some significant features that the RBK motor/driver does not have, but torque is not one of them and speed is not one of them.

High production shops might need the Alpha feature. They might need an auto-tool changer. They might need an air drill. They would certainly need a spindle and a high volume vacuum hold-down system. Those are all extra-cost features that a "standard" machine buyer would not expect to use or need (except for a spindle).

However, Oriental Motor has solved the problem of torque and speed so that it no longer a high-cost issue.

[erik_f]

No worries...it is good to have people around that understand in so much depth the "under belly" of the CNC and easy upgrades that are cost effective.

[ted]

I have to first apologize for what will probably be a somewhat off-topic posting, since it is going to be a clarification about our new PRSstandard tools that use the Oriental Motor (OM) RBK stepper drivers. Second, I apologize for even mentioning the RBK drives here in the forum earlier, before we got information and photos posted on the website. This little slip has probably fueled a lot more distracting speculation than was necessary.

Before reviewing what we have done, I want to address the suggestion that on the PRSstandard tools we should be using larger motors and belt-box drives to make them more powerful. I addressed this same issue a couple of years ago (http://www.shopbottools.com/teds_report.htm#My%20First%20Post) by way of trying to explain some of our thinking behind the choices we have made in setting up ShopBots the way we have. Since that time, we have evaluated two potential belt-box system for ShopBots. Belt-boxes remain very attractive because they can be fitted to any motor and deliver nice, damped, gear-reduction that is a great match for CNC stepper motors. That said, we have not yet found a durable and robust belt-box at reasonable pricing (see previous discussion on our own attempts to make them ourselves). As pointed out above, OM does not put gearboxes (other than planetary gears) on their larger motors because of an engineering concern with damaging the gears from too much power. They also de-rate some of their gear-motors because of similar concerns.

Thus, for the PRSstandard, in order to keep the cost of entry-level CNC as low as possible in a tool that still performs very well using motors that we have a lot of confidence in -- we use the OM gearhead motors. For ShopBot, OM has specially mated a robust, low-backlash, tapered-hob gearbox to a very well proven motor. The (3.6:1) gearbox and (~3A) motor make a great combination and works very well with the RBK/RBD driver system. We have been shipping these motors with the V4g Control Box and gecko drives for almost 2 years. This combination brought a major improvement to the performance of our 'standard' tools, both new tools and ShopBots that were retrofit (BTW as a matter of info with respect to comments above, the 203v geckos that we ship have been modified by gecko for a better inductance match to both earlier PRT and current PRS motors).

So, moving forward to the new Control Boxes: From a performance point of view, the RBK/RBD drivers offer only slightly better performance than the previous 203 geckos (mostly in having a smooth and predictable power curve). But as pointed out above, they do have a number of additional features that make them very attractive to CNC applications. They make the PRSstandard an even better rounded, basic CNC tool. It's performance in speed, power, smoothness, and resolution is many times better than our similar tools 3-4 years ago. With the standards, it's not so much that we've made compromises as that we've resisted doing a number of things which might increase the performance to a degree, but would also ratchet up the price. The tools cost about $5,000 less than PRSalphas, and we remain very proud of them and believe they are a great option for many.

With respect to the issues of this thread, compared to the PRSstandard, the PRSalpha has more power and a higher resolution. That's because the gearbox has a 7.2:1 reduction (also a tapered-hob, low-backlash). Because of their integrated AC power supply, the alphaStep motors are much higher revving and carry their power much further out in the speed curve. This means they not only have much more power than a standard (because of the gearing), but they carry it to higher cutting speeds (because of the alpha drive). Not only is the step resolution higher, but because it is largely achieved with gearing it will result in smoother cutting and less chatter than resolution achieved through microstepping which gets nonlinear under a load. The high revving motors also allow alphas to have very high jog/positioning speeds, which we actually limit to 30ips for safety reasons. (The top speed of a stepper motor is related to the voltage of the driver, the RBK drives top out at 75volts vs the alphaSteps which are effectively 150volts. This means that at the present the RBK drives do not have the speed capabilities of an alphaStep. Because power drops off gradually at the top of the curve, this also means that alphaSteps deliver more torque at high cutting speeds.)

These considerations are before we take into account the closed-loop nature of the alphaStep. The capability of recovering from lost positioning and stopping if there is a significant problem is important. In production, dull tooling and attempts to push cutters inefficiently fast can result in forces that would cause position loss (and no recovery) without closed-loop feedback. A toolpath may be slightly distorted by the recovery, but cutting will continue accurately -- and in most situations the problem is handled unnoticed. Thus these tools come into their own in demanding production situations.

Hope this answers a few of the questions. I invite you to have a look at the recently posted pictures of the new PRSstandard Control Box.

Ted Hall, ShopBot Tools

[stevevarrow]

Dan
I have recently purchased and installed a 48x96 standard machine with spindle and air drill for use in a low volume production environment.
I had several issues with the new machine including safety issues with the new control box, these are not limited to the spindle and air drill engaging during the powering up process.
I was told by Shopbot to disconnect the spindle from the control box and power it seperately, the effect of this would be that the safety stop would not disconnect the power from the spindle in case of emergency.
I find this advise unacceptable and cannot believe that this new product has undergone proper post production testing, in Europe if I were to disable a factory fitted safety device I could be prosecuted and pay heavy fines or be imprisoned.
In my opinion the latest generation standard machine has no place in a workshop environment in its current configuration.
My advise to you is to consider all your options before making a major purchase and make sure you have all the potential costs of upgrading in writing before you make that purchase.
Steve Varrow, Jalousie, West Indies

[richards]

Ted, I apologize for my post that generated the need for you to respond. Just so I don't do that again, let me post my understanding of the RBK motors vs the Alpha motors.

As a base line, I'll use the figures of the ASM98AA-T7.2 Alpha motors that you shipped as part of the upgrade kit for my PRT-Alpha.

I'll use 10-ips as the desired cut speed, because anything faster puts the torque curve on the downhill side of the shoulder. (For the non-geeks who might be reading along, a stepper motor/driver has a torque curve that when plotted out at various speeds resembles a human shoulder joint. At slower speeds, the plot line stays on the upper part of the shoulder - near the neck, but at some higher speed, the plot line resembles the point of the shoulder. Going even faster, the plot line drops quickly, just like the upper arm when the arm is hanging loosely at your side.)

With a 1.5" pitch diameter pinion gear (30-tooth), each rotation of the shaft drives an axis 4.71". Divide that by the 7.2:1 gearbox, and each time the motor's shaft revolves, the axis moves about 0.654", so to move the axis at the rate of 10-ips, the shaft has to turn about 15 revolutions per second, or about 900 RPM.

I hope that that part of the math is correct.

The RBK motor, because it is driving a 3.6:1 gearbox, needs a shaft speed of about 7.5 revolutions per second, or about 450 RPM.

Given the fact that the Alpha motor is normally run at 1,000 steps per revolution, the RBK motor would have to have its resolution set at 2,000 steps per revolution to get the same resolution per step due to the 2:1 difference of the gearboxes.

Because I have no data on the gearboxes, other than the fact that they are both have the tapered-hob design, I've used torque/speed data from the non-geared motors so that apples can be compared to apples.

The AS98AAE motor/driver shows that at about 900 RPM, the motor produces about 250 oz*in of torque. 1,000 RPM is about the peak RPM for that motor, meaning that at 1,000 RPM, you're right on the pivot point of the shoulder. Multiplying that torque by 7.2 would give about 1,800 oz*in or about 112 lb*in. I was told that the actual torque was closer to 80 lb*in with that gearbox, which would allow the typical loss caused by the design and the materials used.

The RBK296 motor has a different torque curve, as you stated. With a 75VDC power supply, at 450 RPM, it produces about 300 oz*in of torque. At 1,000 RPM it produces about 250 oz*in of torque. Multiplying 300 oz*in by 3.6 gives about 1,080 oz*in. Reducing that by the same factor as the 7.2:1 gearbox gives about 770 oz*in or about 48 lb*in of torque, or about 60% of the torque of the Alpha motor.

The RBK299 motor, with a 75VDC power supply, at 450 RPM, produces about 550 oz*in of torque. At 1,000 RPM it drops to about 350 oz*in of torque. Multiplying 550 oz*in by 3.6 gives about 1,980 oz*in. Reducing that by the same factor as the 7.2:1 gearbox gives about 1,400 oz*in or about 87 lb*in of torque, which is just slightly higher than the Alpha motor.

The conclusions that I would draw from examining the data sheets from Oriental Motor (and doing a little head scratching) is that the smaller RBK296 motor would easily be able to run at 1,000 RPM when fitted with the same tapered-hob 7.2:1 gearbox that the Alpha uses, and because it and the Alpha motor have the same torque at that speed, they should perform equally well.

The larger RBK299 motor could be run at 50% of the speed of the Alpha motor and still have slightly higher torque using the 3.6:1 gearbox. That would also mean that the larger motor would be able to spin at 750 RPM or faster, giving a jog speed of about 15-ips. (Personally, I jog my PRT-Alpha at 15-ips because I *still* haven't mounted sensor targets on the far side of the X and Y axis. After hitting a stop at 20-ips, I slowed the jog speed - hitting a stop once is more than enough. Going slower gives my old body a little more time to hit the E-Stop button.)

Did I compute something incorrectly from the data sheets or did I make the wrong assumption somewhere along the way because it looks like the RBK296AA motor and the ASM98AAE Alpha motor would perform equally well if both motors used the same gearbox? If the 3.6:1 gearbox had to be used with the RBK motor, then the RBK299 motor appears to slightly outperform the Alpha motor, up to about 15-ips. Of course that would still mean that only the Alpha motor would have the "Alpha" mode. If the RBK motor lost steps, there would be NO automatic recovery.

[rb99]

Thank for the info Mike.

RIB

[rhfurniture]

Of course one way to increase drive power with small motors is to use more of them. I have a PRT benchtop (now extended to 48" x 32"), and a while ago I put a second motor on the gantry carriage, which improved things no end, mainly in cut quality. I am now thinking of putting a second motor on on the table carriage which will improve things again. Besides more power, this approach distributes the force, from a single point to 2 ends of a line, which helps considerably with the mechanics.
Now I imagine that a moving gantry machine with 4 smaller motors driving the gantry could work very well.
Sorry - realise this is a going a bit off topic..
R.

[khaos]

I would be concerned that the current drawn might hurt the drivers. Am I of base here? Geckos are tough but ...

[wberminio]

So that I understand clearly,something that is getting more difficult these days,

What would be the advantage of
upgrading from a 2007 PRS Standard drive to these new RBK Stepper drives?

Erminio

[rhfurniture]

Joe - 1 gecko per motor.
Anyway its a bit speculative, as shopbot would need to put extra channels into the control board to cope.
I can do it on my PRT BT by putting in an extra gecko to make 5 - 2+2+1. IIR, I think the old prt boards had 6 channels - X1,X2,Y,Z,A,B.
R.

[khaos]

Got it.

[gerryv]

Even when the second one is set up as a slave?

[erik_f]

Current overload

[richards]

A Gecko G203v requires about 2.5mA of current on it's signal lines (step and direction). It also requires that the signals lines be sourced instead of sinked. Sourcing means that the common is tied to ground and the pulse/signal generator send at least +2.5V for a signal that is ON and 0V for a signal that is OFF.

Depending on the pulse/signal driver chip, you could easily run more than one G203v per signal line, i.e., two Y-axis motors could be driven by the same Y-axis signals, two X-axis motors could be driven by the same X-axis signals, etc.

There is one pitfall. When you use two motors that face each other on the same axis, the motors must turn in opposite directions. To do that, you just reverse the wires going to ONE of the motor's poles (A-pole OR B-pole). If you wanted to have the motors wired exactly alike, you would need to invert the direction signal with a chip similar to the 7404 chip - which costs about $0.50 each.

As far as current goes, your power supply would have to be large enough to handle the extra current requirements. Although I recommend sizing a power supply to produce 100% of the maximum current listed on the Motor's name-plate, most designers agree that having at least 66% of the total current is sufficient because the nature of CNC machines is that all motors rarely are required to work at full capacity at the same time and a motor that is lightly loaded draws significantly less current than a motor that is fully loaded.

[ted]

A couple of comments:

Erminio - there is very little performance difference for a PRSstandard of 2007 to go to the new RBKs. They are nice drivers, but speed and power are about the same as the geckos. The box is prettier and fully sealed, with some new features for I/O, and the power curve a little smoother for the drives. But, we do not see a real need to upgrade. Where the new box may be of interest to some, is that it has a main disconnect switch that handles both the spindle and the tool as well as circuitry to control the router/spindle on-off in files rather than the previous standard manual control.

Mike - Eventually you will probably beat me down on this. But my main point is that while the 299 format motors would provide a nice option, their appeal would depend on either a new and non-OM gearbox or a belt box. We are trying to find one, but we don't have it yet. For the 296 size motors, whether alpha or RBK, the high-speed performance comes down to the voltage they are being driven at. We can run the RBK version at 65v while the alpha are effectively 150v. That means the alphas are capable of twice the speed at power -- and this is before we take into account that we can electronically shift the alphas in jog mode in order to not be constrained by pulse rate limitations.

Finally, there is a comment above to the effect that we suggested disconnecting a safety feature. That's something we would never do. I'm sorry if Steve misunderstood us, but the suggestion that was made to him was a short term fix to actually provide more safety via manual control of the spindle while he waited a week for a new control box we are sending him that is correctly configured to his electrical service situation. It was our mistake to have sent him one of the new PRSstandard control boxes with full spindle control in which the disconnect was not properly configured for his power requirements in the islands. We are trying to get remedied as quickly as possible while not disrupting his production.

Ted Hall, ShopBot Tools

[ted]

And, just an FYI for those who want to use more motors. It should not require any additional channels. The V4g boards on PRTs and all the PRS tools have sufficient source current on the board to drive several gecko, RBK, or alpha drives (as noted above, each new motor needs it's own drive). As Mike points out, you do not really need to worry about direction issues because you can just reverse two wires (we usually suggest the black and the green) on any motor to change it's direction. [Alpha motors are a little more complicated on direction, but we can provide cables that reverse the direction of the motor.]

Ted Hall, ShopBot Tools

[wberminio]

Thanks Ted,

So far my PRS Standard has been prefect for my custom work.My be a bit slower than an Alpha,but a lot faster and more accurate then some employees I've had in the past.

Erminio

[richards]

Ted,

I know that choices are not unlimited when you take a product to market. It appears that you were able to get Oriental Motor to match an existing 3.6:1 TH style gearbox to the RBK296 size motor. Perhaps that gearbox couldn't handle the torque of the 299 size motor. Perhaps they were unwilling to supply you with the 299 and that gearbox. The two motors have the same face-plate dimensions and the same shaft size, so they should have been able to machine 299's shaft to work with the gearbox, but for whatever reason, you ended up with the motor/gearbox/driver combination that you're offering.

Why you use a particular motor/gearbox/driver is no business of mine. As you know, I only test motors, I don't build machines. There is a huge difference between being a designer and a manufacturer. The advantage that I have is that I don't have to worry how one part affects another or whether the entire machine is better off with one component or anther. I just test motors and drivers until I find the optimum settings for a particular motor and a particular driver.

The only technical quibble I have with what you posted is the part about voltages. I totally agree that running a motor with a 150V supply will generate much more torque than running the same motor with 65V. I've qualified that sentence with the words "the same motor".

The motor's inductance is the major factor that determines how much voltage it requires to do its job. For instance, the PK296-01AA motor, is rated 7.7mH when wired half-coil and 30.8mH when wired bipolar series. If we use the formula published by Gecko to find the maximum voltage for that motor, i.e. 32 X SQRT(Inductance), then that motor when wired half-coil could be driven with a power supply that generates up to 88V. On the other hand, when wired bipolar series, that same motor would require a 177V power supply.

Gecko drivers can only be used at 80V or less, so it's easy to see that that motor is not the best motor to use if it is going to be driven by a Gecko.

Another motor that has the same frame size and the same torque ratings is the PK296-01AA. It is rated at 1.5mH when wired half-coil and 6mH when wired bipolar series. That computes to 39V half-coil or 78V bipolar series. That motor is better suited for use with a gecko.

After searching the Oriental Motor web site, I could not find the inductance ratings for either the RBK296 motor or for the ASM98 motor so I have no way to compare voltages and torque except to use the Oriental Motor torque charts, which I did in the earlier post. From the torque charts and assuming that Oriental Motor selected the highest possible voltage that could be used without overheating the motor, i.e. < 80C, then it would appear that the RBK296 motor has about 4mh to 6mH inductance and the ASM98 motor has about 25mH to 30mH inductance.

Lower inductance also means that the motor has to be able to draw more current to produce the same amount of torque. For instance, the 296-1AA motor might be rated to draw 1A while the 296-3AA might be rated to draw 3A or even more.

All of this is just test bench theory. It's interesting to me, but I don't build machines. I leave the building to you.

[richards]

It looks like my editing skills need some work. In the 6th paragraph, I meant to specify the 2nd motor as the PK296-03AA rather than as the PK296-01AA.

The PK296-03AA has 1.5mH inductance when wired half-coil and 6mH inductance when wired bipolar series.

[adrianm]

I'm in the process of ordering a new PRSstandard. I did consider the alpha very strongly but all the additional wiring required (not to mention the unit cost of electricity) would make it a very expensive proposition in my circumstances.

Besides the bottleneck in my shop has always been the human being rather than the CNC and seeing that the standard is about three times faster than my current machine that is only going to continue!

[Gary Campbell]

Adrian...
I am not aware of any additional wiring to the Alpha. There may, depending on the actual configuration, be a heavier wire, but no additional wiring is required.

Each, standard and alpha require:
power for the box (110V)
Power for either spindle or router (spindle requires heavier, and 240V) but thats the same for std or alpha

All the I/O are exactly the same parts (prox, zzero, etc)
The motors are different, but use the same number of wires.

I have just assembled a standard with a spindle and it drew 12 amps when idle, My alpha draws 15 to 17 depending on the load (both with spindle, router may actually draw more at 110V)

I dont believe I would use electric consumption as a selection criteria. This does not take into consideration an already loaded distribution panel. In this case, adding more 110V loads may worsen the condition.
Gary

[adrianm]

Getting a new 100amp supply to the workshop is a lot cheaper than I was initially led to believe by my supplier.

So I've changed the order to an Alpha 96 with a 2.2 spindle.

Thanks for the info about the current consumption.

[Gary Campbell]

Adrian...
Good choice on the 100amp supply. Having good, even better than good, power is an important start. Welcome to the club!
Gary

[nick]

I just want to put my 2 cents into the thread on positive comments about the PRS standards.

I've started a 3D custom carving and sign making shop. I have a 9648 PRS Standard w/ 2.2 spindle.
I typically carve between 2.5 and 3.5 ips. I've used Brady's recommendations for VR setting which I believe helps me reduce step lose.

At the time I bought my CNC, I just couldn't afford the alpha or anything else for that matter so I learned real quick to control and operate the standard with VR settings, cutting speeds, etc within the boundries defined by SB.

I understood what I bought, pro's and con's and worked around the con's and build off of the pro's.

My goal is to try and develop a customer base that demands more performance...That just comes over time. If I am successful in my venture, then I can afford a more expensive CNC...aka alpha, iron horse, etc.

I'm not a cabinet maker so I respect the recommendations on alpha only...

But for me...the standard is starting to put money in my pocket...which it what the goal is...and it does the job it was created for...entry level CNC work.

I would love for it to be faster, more accurate, but for now the standard will have to work.

Most of you understand spec's, variables, inputs/outputs, feeds, speeds, RPM, etc which makes the operation of this equipment called "professional machines". not a label meant for marketing...

I'm just happy that my day job is working with CNC equipment.

Hope that can out right...

[gene]

If the 10 amp service has not been installed yet you may want to see what the cost of 150 or 200 would be. The box is very little cost difference. If you are coming off your house then i understand the 100 amp box .

[adrianm]

I'm in the UK and the 100amp service is the biggest they'll put in without a lot of additional expense.