Ridges while planing surfaces

[joelinkous]

Whether I'm using an Area Clear routine to make a pocket in my material, or I'm planing my table, I'm getting ridges where the cuts overlap. The bit I use for 90% of pocketing is a 1/2" bit with 30% overlap. It's not just ridges though, they are complete changes of elevation between every other cut, sometimes by 1/64" or 1/32". It's similar when planing the spoilboard with a 1" bit w/30% overlap, but it doesn't show on the final product like the pocketing does.

I'd rather not sand the spoilboard down or I'd have an unlevel table again, and most planing of my material is usually accompanied by some very fine/complex v-carving where any minor deviations caused by sanding could ruin it. Am I splitting hairs here? I'm not sure whether to simply deal with it with sanding or other finish work, or if there's a way to remedy it during the CNC process.

I think it has to do with the cutting direction of the bit in relation to the direction of the current cut causing different stresses on the Z motor, but how would I fix it?

[richards]

Joe,
About a year ago a bunch of us had a lot of fun talking about making the Z-axis perpendicular to the table top. You can find the thread here. (http://www.talkshopbot.com/forum/show.cgi?tpc=7&post=40868#POST40868)

Although there was a lot of kidding going on, you should be able to find good information on how to eliminate the ridges that you're getting.

[scottcox]

And be sure to check out Kip Steven's Z-Leveling solution in this thread (http://www.talkshopbot.com/forum/messages/312/20708.html?1185334832)

[drodda]

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7765

Here is what I did to solve this on my machine. I still can't figure why shopbot does not supply a simple thing like this on all machines?

Simple Outriggers would make everyones headaches go away.

These were installed as a simple test. I was going to make a more permanent set later if this worked. It worked so well that I have never replaced them.

-D

[rick_woodward]

Well,Dave. I'd say that was a stroke of genius there. Simple, very effective and a perfect solution. Looks like a very easy way to dial in. Thank you VERY much for posting that. I call that a Winner !

[olecrafty]

Thanks for the pic.s Dave. Much better than my method.

[joelinkous]

So, from what I see by the braces on your Z mount, I assume the issue deals with the Z mount itself flexing, and the braces keep it rigid?

[drodda]

The fine threaded bolts on all four corners allow you to adjust the tilt in all directions of the Z in the Y carriage. You can tilt it very precisely from front to back or side to side then you tighten your 3/4" bolts to hold it in place. I would use heavier angle if done over as this one had a little flex in the angle. If you were to weld the angle to the side of the Z it would be better also.

-D

[harryball]

That's ingenious... I think I can adapt what I already have to work something along those lines!

Robert

[paco]

This is something that I have found some time ago here. Unfortunately, I cannot remember who did it... sorry. I'm planning something like it.


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7767

I would add that squaring the Z and squaring the router/spindle may be two different things... router mounting can be off when the Z rail assembly if square.

This is my router mounting adapter. Once the Z rail assembly was as square as possible, I squared the router mounting as perfect I could.


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[waynelocke]

Dave,
What an elegant solution. I was just getting ready to address this and was giving Rube a run for his money. Thanks also to Paco. Here are some pics of my iteration and the setup I use to set the Z. I didn't have to use the mallet once and was able to dial it in to within several thousandths over the about 8" diameter of the indicator setup. What wasted effort I have spent over the years without this. Thank you Dave and Paco.
Wayne

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[Brady Watson]

Question: Just out of curiosity, how often do you have the need to adjust the Z axis?

I only ask because it's one of those things that you 'set & forget'. Unless you do something like change the Z attachment position or REALLY make a big boo-boo and crash into something, the Z axis doesn't usually go out of perpendicular with the table. It's cool to see all the different contraptions that people come up with to set the Z axis (and I say if you like it & it works, go for it). I've probably setup or tuned 40 ShopBots of various models and configurations and have adjusted the Z with nothing more than a high quality level. The machine cuts dead on after the adjustment is made, with zero marks that you can see or feel with your hand. I guess I am just puzzled about what is so difficult about using a level to get things right. I must admit that when I setup my Bot for the 1st time, I thought using a level was hokey...but I have yet to find any method that is quicker or better (that's just me).

A while back a friend of mine gave me a trammel meant to be used on a Bridgeport vertical mill for setting the head perpendicular to the cast iron table (the head tilts in BOTH directions on a BP). I tried the trammel setup on the Bot after replacing the Z pinion & adjusting the mounting position & v-rollers...all the time thinking that it would be on par with the level. It wasn't...the Z was way out compared to a level & I had to re-adjust using the level to get it right again...Go figure!


For those that want to use a level (otherwise ignore below) to set the Z up, there are a few things that you must do/have in order for it to work:

1) Your table must be dead level.

2) PRTAlpha style gantries need to have the 5 bolts on either side of the Z loosened. Just one bank of 5 is fine. Otherwise you will wind up fighting the Y extrusion and pull the Z towers all over the place, or worse yet, spread the towers apart.

3) You need a GOOD quality 2' or 4' wood laminated level. A torpedo or aluminum one doesn't cut it.

4) Level to the T-rail ONLY...not the 2X2 tower. Make sure the surface of the T is clean & stickers/decals will influence the reading.

5) Get the infamous 'side to side' adjustment set and snug the top two 3/4" bolts down 1st. Then do the bottoms, turning each a little at a time. If you crank one side down too much it will pull it out of alignment.

6) Clamping the level to the T-rail makes life much easier.

7) Tighten up the bank of 5 bolts.


-B

[drodda]

Brady,

How can you have a dead level table if you can't get your Z set in the first place?

Seems to me that shopbot could weld this outrigger on the Z in the first place instead of telling you to get a freind to hold that heavy z as you tighten it in place? They lost me when they said to use a rubber mallet to adjust in the instructions when I received my new machine? Unfortunately most of us only get to assemble one of these and it is usually at three in the morning when you get to this stage and a freind to hold things has either passed out from too much beer or left long before you get to this part of the assembly.

I lived with my Z being slightly off for the first few months, then I decided to try and do something to make it more easily adjusted.

[Brady Watson]

Dave,
You put the level across the steel crossmembers and AL extrusions...Level it all around, adjust feet when necessary. If you get the steel level, then the wood on top doesn't matter...the rails are connected to the AL extrusion bone, and the X-car is connected to the rail bone...and then Y-car is connected to the X-car bone and the Z axis is connected to the Y-car bone...Level is level is level...

I guess it depends on whether you ate your wheaties or not...but the Z axis isn't all that heavy.

-B

[blaz_in_az]

Dave,

Even if your Z is not perfectly vertical, run a tabletop surfacing routine anyway. At least now you have a level surface, but with ridges, and a place to start from, to get your table dead level and your Z vertical.

You can construct a simple leveling device with a 1/2" by 2" nut and bolt and a 1/8"T x 1"W x 10"L of aluminum or steel. Drill a hole in one end about 1" from the end. Mount the bolt and nut and insert the bolt into your collet.

Bend the strip of metal downward so that the far end is below the level of the bolt head and then lower the router so the metal strip just touches the table surface. Rotate the strip in a full circle and find the direction of the tilt in the Z axis.

I used shims to square my Z, but I like some of the ideas in this thread for simple and fine adjustment. It takes a while, using shims, to get it level.

After your Z is adjusted, run a table surface routine again. On my table, you can see the machine marks left by a 1 1/4" bit, but you cannot feel them. That is good enough for me and it has held up for over 2 years now.

Hope this helps.

[beacon14]

or REALLY make a big boo-boo and crash into something

Bingo. My biggest concern with adding outriggers and stiffeners to the z tower is that in the event of a near-catastrophe, i.e. running the spindle sideways into the edge of the table or board or a clamp (NOT that I've ever done that or known anyone who has, ahem) then something has to give. I'd rather have to stop and tweak the z axis than replace a cracked spindle housing or mount or a bent shaft.

[drodda]

Once you get it perfectly aligned you can easily remove the outriggers with two screws each and then your Z is free to move in case Skylab falls on your shop I guess. I guess after working in the engineering field for twenty plus years I want something that I can precisely adjust so this is what I came up with. Just sharing with the forum not preaching to the chior?

-D

[paco]

I personally think that the PRT Z can use some stiffening, hence a brace system. While at it, why not make it so that it can be easy to adjust?! My sketches are based on the yellow model above... The last couples of times I hit clamps and fool with toolpaths, I both break the bits and got the Z completely off.

Either I am the kind of guy that adjust something with a hammer of mallet... unless it's the only way.

I made my router mounting modification because I found that it wasn't parallel with the Z T-rail. This setup easy half of the adjustment hassle. Can one be 100% sure that it's spindle axle and body are perfectly parallel?... I'm pointing this because I notice that my machine was leaving stepdown mark on two sides of the parts while none on the other sides. Finish allowance solve this problem but it actually told me that even if my Z T-rail was square, the bit wasn't. I could get a perfectly flat spoilboard but still got stepdown tool marks on two sides of my parts. Fine tuning allowed me to tweak this to a point where both are dead on (or almost).

In that last year, I had to adjust my Z for several reasons; collision, stupid toolpaths, maintenance and very special projects which have required to raise to whole thing up.

[waynelocke]

Brady is right, you don't have to adjust the Z often, however, when you do, an adjuster like I and others have installed makes the process a breeze. Before yesterday I always had small ridges which I never liked but was never able to completely eliminate. Since I used a 2" cutter to surface the table the adjustment error wasn't that great and, In reality, it didn't really affect normal cutting that much. I have no ridges on my spoilboard now. The ease and accuracy of the adjustment is just amazing...even if I don't do it again for another couple of years.

David, I had already decided to take the adjustment screws out after the adjustment.

[jay_p]

The point that Brady was making above was that if you are going to use a level to plumb the z-axis, the entire table system must be "dead" level. The spoilboard might be flat, but that does not mean that it is level.
The other means of adjusting that are being discussed adjust the z-axis so that it is perpendicular to the spoilboard.
If your entire table system was level when intitially set up (as it should be) and hasn't changed, then plumb and perpendicular to the spoilboard would be the same. If not...

Jay