PRT vs PRS

[Tom Bachman]

where can I find the differences between the PRT and the PRS machines? I just responded to a guy who has an older 48/96 PRT machine, but now realize this is the older technology.

Who can spread some light on this for me. The price point seems to be good for the size of machine. Here at school we purchased a used BT32 and I've decided that I probably need a CNC machine in my shop at home. :D

[Brady Watson]

PRS has I-beam gantry & hardened rails, plus depending on vintage, PRTs are all steel. I prefer a PRT over a PRS personally because the steel tables are way stiffer than the aluminum extruded ones.

Find out what control box the tool has, when it was made & I'll see what other info I can give you.

-B

[coryatjohn]

>> because the steel tables are way stiffer than the aluminum extruded ones

Brady - Does this really matter? How much flex can there be in the PRS machine when cutting a sheet of plywood? How much less would a steel table machine be?

[ken_rychlik]

I've had both and got slightly better cutting on the prs. Both have good and bad points. The hardened rails of a prs help, but the motor adjustment on them is more of a pain. The bits are easier to change on a prs, but the spindle in the center of the gantry is more stable on the prt. The aluminum table sides of a prt have more flex than a prt with steel sides. The prt had more gantry flex because of the design. I've gone on to another brand, but if I went back to a bot, it would be custom made. Steel frame, hardened rails, spring loaded motors to the racks,,, kind of a frankenbot.

[MogulTx]

Tom,

I have owned a PRT, a couple PRS' and a PRS Alpha. I would tell you that you can do a lot of inexpensive learning on a PRT. They are good machines. You can also upgrade the control box and drive motors if you want to (pricey, but would not break the average person). If you have a ton of ewxperience on a shopbot and intend to run it 8 hours a day, 5-6 days a week, I would probably hold out for a PRS Alpha and pay the additional thousands for it.... If you think you will run it an hour or two a day, a couple times a week ( which is where I started about 3 years ago)... I would think the PRT would be great.

It is tough to tell you that this system or that system is going to serve you best- economically and from a performance standpoint. But there is nothing wrong with starting with a PRT and using it for a year or two and then selling it and upgrading. Thus far, they have been steady on price and very good on performance. And shopbot is excellent at suporting them and the newer machines...

You have to look at the dollars you will spend, what your budget is, what number of hours you think you might run the machine, what "facilities" you have available, etc... and make your decision..... But give us some idea of your considerations. We all have opinions and are pretty fair in applying them. We will help if we can.

Merry Christmas.

Monty

[Tom Bachman]

Well, guys this is the machine in question.

http://www.talkshopbot.com/forum/showthread.php?t=18735

I'm new to CNC, we just bought a BT32 at the school where I teach Cabinet and furnituremaking. I do some custom cabinetry on the side and since the acquisition of the CNC at school, I've been on the look for an intro machine. This one is actually bigger than I was anticipating starting with, but it looks to be in decent shape and the price and location appear to be OK.

With a machine this size I would look at using it to cut cabinet parts and joinery and making so signs as well. Really, I'm not sure what all I am going to be able to do with this machine. I will be retiring fro teaching within a year or two and am really looking for something to "keep me busy".

Thanks in advance for all your help and insight.

[Brady Watson]

It's going to need some upgrades for you to be happy with it. You'll want either the 4G or RBK upgrade ($1500/$2800) and possibly a spindle. Without pics I cannot get very specific with recommendations or concerns.

-B

[richards]

Every machine is a tool and every tool has limitations. In my toolbox, I have a variety of hammers. On the shelf, I still have more than a dozen routers. Many types of hammers are within easy reach. Knowing what each tool was designed to do and knowing the limitations of each tool and then not exceeding the tool's ability to perform the job that it can do, is the secret.

I owned a PRT-Alpha. My good friend, Jeff, owns a PRS-Alpha. With a belt-drive transmission (and later the Alpha 7.2:1 geared motors) on the PRT, cuts made on either machine were more than acceptable as long as we let the cutter cut without trying to turn the Shopbot's frame into a pretzel. Both Jeff and I saw advantages to the other's machine, but neither of us felt cheated.

Enjoy using any of Shopbot's machines. If you like to tinker, you'll probably add a "feature" or two, but right out of the crate, all Shopbots are amazing machines.

[curtiss]

PRS has I-beam gantry & hardened rails, plus depending on vintage, PRTs are all steel. I prefer a PRT over a PRS personally because the steel tables are way stiffer than the aluminum extruded ones.

-B

Nice to have ...something nice... said about a PRT, if they are NOT as stiff, why did they go to the aluminum rails ?

[Brady Watson]

Nice to have ...something nice... said about a PRT, if they are NOT as stiff, why did they go to the aluminum rails ?

Consistency. The AL extrusions are WAY more consistent dimensionally and for straightness than C-channel A36 steel. Camber, twist and other issues created a lot of waste in the production process, which is why SB went to extrusions. The extrusions are also more pleasing to the eye then C-channel. But...A steel framed 4x8 PRT has 4 legs. A new PRS 4x8 has 6 legs. If they could get away with 4, they wouldn't put $ix on them. ;)

I like the PRT better than the PRS for my needs. Yes, the open I-beam gantry is nice, but it has a high center of gravity. I change tools at around X24, Y12 and this is comfortable for me - but others prefer to change tools down at Y24, X12 and this can be cumbersome. Non-4G/Alpha PRTs (with gold unistrut) need to be welded up. The 4G+ gantry is nice, stays square and is easy to adjust/square if needed. The lower center of gravity of the PRT gantry gives better mechanical advantage than the PRS one - which is why I still run a PRT with 4G gantry & 7.2 Alphas...

I'm still rolling on original angle iron rails. Few get that most SBs never even had true angle iron rails on their machine, but rather soft, malleable bent rails that will get roll forged and worn out after a few years. Real angle wears incredibly well. My tool was so large that it would not fit in the bender, so they used real angle. Glad they did. SB does offer REALLY NICE hardened rails, including the angle - pre-punched for the rail screws & bolts for PRTs. If your PRTs rails are worn out, it's worth an inquiry.

-B

[Tom Bachman]

This is additional information that I received.

Did these machines not come with design and control software when new?


The Bot is all original - meaning I haven't updated anything except add a vacuum table. It did everything I asked of it, so never saw the need to update. I've learned that I should have done an upgrade or two. It is loaded with Mastercam X software. $5,000 just for a license. You'd have to be offline to use it. They get cranky if it is used by anyone other than the licensee. It is difficult to operate. Overkill. But all that was available in 03-04. As far as tooling...There is about a dozen router bits that come with it.

I assume that MasterCAM X is control software...or is it design....or does it do both?

[srwtlc]

MasterCam X is design software. Original purchase around mid '01, it would have likely included VectorCam for design/machine code software.

Control software in it's current config would be no higher than version 3.4.27/Windows or version 2.39/Dos Win95/98.

I'd also check to see if it has the direct drive motors or 3.6:1 gear box motors. My original PRT came with direct drive and I later upgraded to the 3.6:1 gear box ones for much improved cuts.

[Brady Watson]

Tom,
As Scott points out - ask him for the numbers on the end plate of the stepper motors. Non-Gearbox versions are a bit too coarse without some type of belt reduction.

Also, consider upgrading to VCarve Pro to shorten your learning curve and to generate toolpaths for CNC routing. MasterCAM is geared towards metal milling and lacks certain strategies and tools.

You may also want to hold out for a newer machine that is turn key with newer software.

-B

[Tom Bachman]

Tom,
As Scott points out - ask him for the numbers on the end plate of the stepper motors. Non-Gearbox versions are a bit too coarse without some type of belt reduction.

Also, consider upgrading to VCarve Pro to shorten your learning curve and to generate toolpaths for CNC routing. MasterCAM is geared towards metal milling and lacks certain strategies and tools.

You may also want to hold out for a newer machine that is turn key with newer software.

-B

I've already begun to think just this!

Thanks, Tom

[David Iannone]

I have a 2001PRT and am looking to upgrade to the 4g board in the next 6 months. What is the big difference between the 4G upgrade and the RBK box upgrade? Other than the cool looking box it is installed in and the price difference? Do I need to consider the RBK upgrade instead?

[Tom Bachman]

Here are the numbers off the motors that he sent me.

the Model# on the Step Motors is:
A6497-9412KTG

With everything you guys know about this machine, the upgrades that it needs...software/hardware, what do you think this bot is worth? He's willing to entertain an offer.

[Brady Watson]

Those *should* be 3.6:1 gearbox motors - very similar to the ones used on current tools.

What are the details on the vacuum system? What pump, voltage, 3 phase?, horsepower? Do YOU have 3ph?

-B

[Tom Bachman]

No, I don't have three phase. Not sure about the vac system.

[Brady Watson]

I don't think his asking price is out of line. This of course is without even seeing the tool or asking important questions - but he only cut foam with it and light use since 2008.

The fact of the matter is, you could buy his tool & spend $150 on Cut2D and be making money from day 1. It is cheaper than a hobby machine and it will do real work - albeit slower than a newer SB. Than again it is only 25-30% the cost of a new machine.

If you just 'want' a CNC and want to tinker & fart around, then it is perfect for that. If you need a machine to make a living or do production work, then I would consider a newer tool & lean towards an Alpha model. That machine will do everything the new ones will, just a bit slower & perhaps with a little less resolution on very small parts. Aside from this - it'll handle whatever you throw at it.

Comparing cost of entry with this tool vs a new tool, you may want to consider taking that price difference and paying someone to train you at your shop to get you going. ShopBot can provide this service for you. It is a WAY better value than attending classes in Durham. Nothing like training on your tool in your shop on your stuff with 100% of the attention. It will propel you 6 months+ ahead of where you'd be learning on your own. Just a thought...

-B