Issue with Z changing depths in Area Clear

[rbarrow]

Trying to figure out why the Z changes depths when it profiles around letters and borders.

I am not changing tools or anything and the rest of the clear is the same depth...just goes deeper around the letters. What am I missing?

AC Pro 2011 is what I am using....and the simulation looks perfect...

http://www.membank.com/portals/3/AC-Issue.JPG

[Brady Watson]

Looks like:

1) The material is warped and is moving (least likely).

2) Your Z axis rack & pinion has a lot of slop in the gear mesh (more a problem on PRT than PRS)

3) Your YZ car bottom v-rollers are loose (PRS only & common problem)

The only way of knowing is to grab the machine and physically move all the axes by hand with the power on (router off of course) and listen and feel for slop.

-B

[rbarrow]

Brady...

Thanks for the quick response!

1> Material and hold-down appear to be flat and stable...
2> No slop in the Z that I can find. Locks in very tight and cannot be moved even a little...
3> I did have some looseness in the hold down bearings on the back of of the car and have readjusted those....what a ROYAL PAIN...whose idea was it to put that lazy S bracket bolt head where normal human appendages and wrenches can't reach....anyway...all tight and tracking...

No slop that I can find on Z or X...the car has just a ***little*** play on the side away from the motor...but think that is more or less normal since there isn't a motor on that side to hold it tight.

I will see if I can reproduce the issue just pocketing a circle or something.

The difference in depth is exactly .02"...seems to be unusual to have it be EXACTLY the same difference in all areas of the entire piece. I have carefully checked the cut file and it is perfect...on every line....so has to be Bot doing something.

Thanks for the suggestions!
Roy

[Brady Watson]

Slipping bit in collet comes to mind...but if it is verifiably @ .2", then it is something consistent. How is your material defined in ArtCAM? When you do a project, there is a material slider and you want to make sure that it is in the right position (aside from Zzeroing top of block or on table...) Check that out - I've run into issues there before. Chances are, you'll want to have that slider ALL THE WAY UP to the top...otherwise, you are telling ArtCAM that you want to shave off however much is at the top AND THEN start machining down from there.

The adjustment on the lower rollers is easy after you have removed the bearing covers/wipers. They give you a flat wrench for holding the shank of the roller axle & a 6mm hex for snugging it up...In case you forgot! Go look in your clear pouch 'toolkit' that had the hex wrenches etc in it.

-B

[rbarrow]

Artcam material setup is correct and I have opened the cut file in notepad to confirm the z moves. All is as it should be.

Bearing covers? Wipers? Toolkit?

This is an 03 PRT. If there are bearing covers and wipers, I forgot to install them and they are not listed in my manual. No tools with this model either that I recall. Nothing on this bot is metric either.

I am not sure what upgrades are out there that will significantly improve this machine. I thought about the new z but not sure it would be $$$ well spent on a machine of this age...

[waynelocke]

The PRT did not have wipers. I would make sure that the Z piñon is tight. It is hard to get to it.

I just upgraded the z axis on my PRT from 4 to 8 rollers . What an amazing difference for about $100. Brady and others have recommended this and it really improves the machine.

[Brady Watson]

Bearing covers? Wipers? Toolkit?

This is an 03 PRT. .

Yeah...sorry - assumed it was a newer tool. Must have been ArtCAM 2011 that threw me off.

Like Wayne said - upgrade to 8 rollers on the Z. It'll give you smoother cutting and the T-rail will last much longer.

You might to check your UV to make sure they are what they are supposed to be & if running the original control box, you might want to consider that you could be losing steps by plunging too quickly, especially with a non-center cutting bit.

How long has it been doing this? Just this project or? Is that dimensional lumber you are carving into? That stuff has a lot of tension in it and moves as you are cutting it - and 9 times out of ten it cups upward...

-B

[rbarrow]

Hard to justify getting a new machine for what I do here...but I wish I had a new Alpha just for grins & giggles!! Mostly artistic 3D work and a little mold making for my wife's glass kiln...

I am running the 4G upgrade so not sure about loosing steps (especially @ .5 ips on Z)

This is the first time I have tried this type of project since upgrading to AC 2011 but I don't think that is the issue (just looking through the toolpath code). And...this was a test run in plywood before cutting in the HDU...so stability should not be a factor.

Weird...is there a post out here about adding rollers to the Z?

[Brady Watson]

How is the material being held down? If with vacuum, how many Hg" are you pulling? If not with vacuum...I'd be very suspicious of the plywood being flat & staying flat, especially after you've cut into it.

I don't think there is a post on adding the v-rollers (meaning a tutorial with pics) - It ain't rocket science as they say...You'll need to precisely drill into the Z towers in line with the other v-rollers...then bolt in the new ones. You'll need 1/4" bolts, eccentric cam bushings and v-roller bearings. All of these are available from ShopBot directly or online if you do your research. The genuine BWC bearings are around $45 ea, the generic ones are somewhere around $12 ea.

-B

[rbarrow]

Brady...

I just want to say how much I appreciate your effort to help...above and beyond is all I can say!

Material is clamped to the table...and it certainly could be plywood warping but in my experience it usually twists...which would make the cuts deeper only one part of the project. The cuts are universally deep across the whole 24" x 18" piece...which leads me to thinking the Z has dropped a step somehow when it transitioned from rastering across (X axis) to following the outline of the "islands".

I will be running this again this evening and see if I can reproduce once again.

Thanks a million for your help!
Roy

[Brady Watson]

Roy - no problem...that's what the SB Forum is all about :D

-B

[rbarrow]

Just to update...I think the issue was (and is) a combination of material and hold down method. I ran several tests on other scrap material and think I have determined that the original issue was caused by the material actually moving and it just happened to move right before the profile pass.

I ran the same file again making sure the material could not move and still got a little of the cut variation but in looking at the material...it was just so slightly cupped...and I set up my Z Zero on one of the high sides instead of the low point....

Just got to pay more attention to the details...but this just happen to be a project where that particular error was very obvious as usually I am rastering over a 3D item with a ball nose...

Brady...I much appreciate your assistance and you were spot on.

Thanks!
Roy