Inconsistent Z heights

[john_r]

I've got scrap piles of hundreds of dollars of material, from dow blue foam, sign foam to highly figured bubinga, cherry etc. Ohand lots of sheet goods...I think it's more annoying having to get rid of the wasted scrap. There seems to be no consistency in my Z-heights, one day I cut a file and all is good and the next it's either to shallow or too deep. Right now I'm working on a job that has gone from 50.00 per hour to 25.00 per hour because of re-purchase of materials twice...FUN Working so hard for so little.

PRT Standard bought Used.
Recent purchase (Last Year) of new PRT control box from SB.

Things I've looked at.
1. The cutting file.
2. SB control Software
3. The collet, new one used
4. Grounding grounded the router, dust collector and table.
5. Brushes replaced in Milwaukee router.
6. The bits, don't know but why but running out of ideas.
7. Material thickness.

Any Ideas before I sell this thing and buy a Techno or shop sabre? I can't even market anything and have to tell people were too backed up with work right now...there goes those customers.

[Brady Watson]

John,
You've failed to list the condition of your spoilboard. This is where the rubber meets the road on your CNC & if it is all gashed up and hasn't been maintained/flattened/surfaced regularly, then I can gaurantee that you are going to have inconsistencies in your cutting.

How the spoilboard is fastened to the support board is also critical and simply screwing the top sheet to the support board is completely inadequate if you want a consistent machine & Z heights. The spoilboard should be glued to the support board. Screws = bad. I went to a customer's shop who was complaining about the same issue you are and I immediately saw that there was all kind of debris between the spoilboard and support board...plus the top of the spoilboard was criss-crossed with all kinds of marks. After assisting with replacing the spoilboard with a fresh one and gluing it down, the customer could not believe how well the Bot cut. Give it a whirl...and keep that table clean and flat.


-B

[john_r]

Hey Brady,
Yeah forgot to mention that one. Just surfaced it. 3/4 MDF lag bolted every foot across each beam on a 60X120 table shopbot spec with another sheet glued and screwed and freshly surfaced at checked with a Straight edge...no light peeking through or rocking motion. I cut some 3/4 baltic birch cabinets, no problem in fact these were the best edge cuts I've seen off my bot since I've owned it. Went to cut some V-carved plaques today and not so great. Just cut the same file yesterday and it was fine, the differences today are almost an 1/8in depth difference. OK so a question. When I ZZero out my Z it sometimes acts jerky, erratic movements. Sometimes it sounds like it's grinding stepper motor and sometimes it sounds like the sweet whirring of a servomotor and the movements seem to follow suit during this. Since this unit was used what should I look at in the Z axis? It was used heavily in a cabinet shop.

[harryball]

Something similar occured with me, I had problems with the Z height changing during a cut file, noticed it mostly in 3D and plunge actions like drilling holes, some didn't go all the way through. It turned out the Z pinion was not secured to the shaft. It appeared to be... I couldn't move the Z by hand... but at the prompting of SBot I finally removed the Z axis and grabbed the pinion with plyers giving it a good twist and POP it moved. I replaced the pinion and made sure it was tight... alls been well since.

Might be worth a quick check.

Robert

[fleinbach]

J.

I was about to ask if you had checked your pinion gear when I noticed robert beat me to it. I would put a wrench on it and make sure it is tight. You need to apply a fair amount of pressure so much so that you will feel something is going to break. Some allen wrenches don't fit as well as others. I just did an upgrade and all 3 wrenches Shopbot sent with the motors slipped when turning the allen screw. Luckely I had one in my collection that fit well.

[srwtlc]

J.

After you check the above, since you mention the difference in sound, check the wires to make sure there's a good connection at both ends of the cable and you could also try swapping the Z axis over to the accessory channel to eliminate the possibility of a bad driver.

[john_r]

Thanks guys,
I wouldn't be so stressed out if I didn't have customers material sitting in the shop.
I'm in the process of checking this all out. I did realize after closer inspection. I can move the z-axis 1/32in while the motors are engaged or not engaged. The ends of the pinion teeth aren't sharp and the edges of where the BW roller bearings ride is rounded over in comparison of to the rest of the Z rail. Although the bearings touch all the way around.

[john_r]

Ok I'm retarded...(I did get dain bramage from a 80lb piece of teak hitting me in the head last year, what a fun trip that was.) My Inconsistent Z heights were because I raised my Z 2" extra by using 8" C Channel to build my table, and I had recently resurfaced my table down about 1/2". I didn't see it until last week my Z was bottoming out and popping back up ever so slightly. Sometimes it would stay and other times it would pop back up. So I put a 3/4" piece of MDF and presto perfect cuts. Dang self inflicted problems. Thanks again for all the help.

[gene]

Hey
I have a problem simular to this . I drew 4 squares and did an area clear on each one at a different depth, After doing the cuts the bit had lost .5 inch . I checked the bit and no slippage there Good spoilboard tight pinion gear . Any help would be helpful

[Brady Watson]

Gene,
Did you by chance just do a 7.2 upgrade? If so, make sure that the multiplier for your Z axis is correct. If using a 1:1 on the Z, then the multiplier should be 4. X&Y should be 5. Check Unit Values as well.

-B

[gene]

Brady,
CONGRATULATIONS YOU WIN !!!!
Thanks That did the trick , I entered the rest of the values correct , i just had that one wrong..
Thanks again, Gene