Uneven Depth of Cut issue

(Brian Hunter) #26

@DanoInTx - Dallas (Allen specifically). I was just in FW at the Lumber Co of FW.

I did turn it on, tried moving along X, Y and Z. None move in that regard. However, the whole z-axis tower moves slightly, rocking up and back, or down and back. The pivot point seems to be the v-wheels on top and bottom of the x-axis beam. Right now, I’m tightening bolts, but not sure how any of them will stop the movement. I’ll see if the v-wheels tighten. They are engaged with the gantry, but still rock slightly forward/backward. I suspect that the uncut portions occur due to pressure occurring upon the z-tower when moving forward/backward along y-axis. It does not really happen when machine moves only along x-axis.


(William Adams) #27

Adjusted V wheels? http://docs.carbide3d.com/support/tensioning-eccentrics/


(Brian Hunter) #28

@WillAdams - I did on the z-axis, but I just went through and did the others as well. I followed the recommendation on your link. Found that the y-axis bottom v-wheels were all loose. And it is while moving along y-axis that the fully cut and not fully cut portions occur.

I’ve made many adjustments to the machine now so it seems time for a test. Thanks!


(Dan Nelson) #29

Coolness, sounds like you may have found your issue. Be sure and report your findings here so others can follow your path.

Lumber Co of Fort Worth? I’ve never been there or even knew it existed. Will have to check it out!

I’m actually in Haslet, right at the edge of Tarrant and Denton county. I actually pay property taxes to both. If you go about 10 miles straight West from Texas Motor Speedway then you’re in my garage, haha! Good to have another ShapeOKO user close by.


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(Brian Hunter) #30

Dan, no solution yet.

Lumber Co of FW is neat. Only been once. You actually get to go into the clean warehouse and see everything. They do have some hardwood as well, long and thin pieces mostly. but some are rough cut. Good prices. Really nice staff.

I’ve only been as far West as the Speedway, but I get the general area you’re in. Not crazy far away. Contact me whenever at brian@woodengenuity.com


(Brian Hunter) #31

UPDATE: Many changes have been made to machine and program settings on my cuts.No change in outcome. See photo.

Okay team, what else have I overlooked? My z-axis tower rocks up/down slightly, but the “play” seems to come from the v-wheels and that appears unavoidable. They all engage and have been tightened. Hey must have some freedom otherwise they won’t turn. Nothing else seems to move or be loose.


(Brian Hunter) #32

@WillAdams - I know I’ve not tried your pocketing option, but it’s because it would double all my cuts. Meaning more time and more wear on bits. What I could do is try it on one or two shapes instead of the entire file.

The example in your link you recommend the offset distance to be:

I’m not using aluminum, rather a special plywood. I use GWizard so I do have a chipload number shown, is that what I’d use? My bit diameter is .24-ish.

Could I simply make a pocket cut that is .2 or so inside the desired cut path? Then run the cut for the full depth at desired cut path?


(Neil Ferreri) #33

Still trying to take .25" per pass?


(William Adams) #34

Agree w/ @neilferreri that if you’re taking a heavy cut you should lighten up, at least for the final pass.

I still think that the slotting is part of the problem, the other consideration is could your vacuum be pulling at the carriage as it circles around?

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(Brian Hunter) #35

If you mean the depth of cut per pass, yes that’s roughly what my setting has been. If that is too deep per pass, then I’m getting the wrong data from GWizard. Or using it wrong.

@WillAdams - I’ll run a test here with lighter depth per pass. See what happens.

Per your vacuum question, my hose has plenty of slack. Mounted from above. It may get a little snug in one corner, but my ‘problem’ occurs equally across the job. Good thought though.


(Neil Ferreri) #36

I haven’t used gwizard, but I don’t think it takes machine rigidity into account. You don’t have a heavy duty mill, so you will most likely need to back off some numbers.
On a profile cut like that, I’d try 3mm depth at 1500mm/minute (or less to figure this out)
Get a video yet?

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(Brian Hunter) #37

@neilferreri - Here’s a screenshot of my results in gwizard after entering my details. It actually has Shapeoko3 with my router as an option. As for rigidity there is a dropdown on the right - select Normal or Rigid. Not very specific, but I always pick Normal. But agreed, mine is far less than commercial/industrial machine.

But the results in the picture show an even more aggressive recommendation than what I’m using.


(Neil Ferreri) #38

I’m surprised by those numbers. Maybe someone that uses gWizard can chime in. Based on my experience, try the values I gave in my last reply. If nothing else, it’ll help rule being “too aggressive” it as a cause.


(Brian Hunter) #39

@neilferreri - Agreed. I’ve reduced DOC. We’ll see how it goes here. Thanks man!


(Dan Nelson) #40

Those wheels really shouldn’t turn freely super easily. I adjust my eccentric nuts while turning those with my finger until they stop moving. If they are still super freewheeling then your eccentrics are still not adjusted properly, and/or the top V-wheels are loose.



(Charles Van Noland) #41

This looks a classic case of machine flex, with the dead-giveaway being that the cut-side swaps when you switch climb/conventional cutting direction. EDIT: Or something loose (V-wheels) that’s causing excessive slack. At the end of the day the spindle is deviating from its path mechanically.


(Brian Hunter) #42

@radioteeth - I don’t doubt the flex. My cut preview always shows a full depth of cut throughout the job. I have and will continue to check the v-wheels. What still confuses me is how any of this causes one side of a shape to not cut all the way and the other to cut through beyond the set 100%. The bit spins the same directions and cuts against the shape just the same on both sides… no matter how large the object is. Looks like the bit digs in (down) when moving South toward the front, but pushes itself up against the material when moving North away from front. What would consistently cause this reaction?

UPDATE: I’ve run 4 jobs since my last update. The first two (the same file) had no cut/uncut issues. The next file, that I ran when I first shared this issue, DID have the issue as shown above. The fourth job (new file) had the issue, but it was 50% less severe.

For all four runs I reduced my depth of cut per a few of yall’s suggestions. I believe this has been the primary reason for any/all improvement in the cut/uncut problem. I may need to reduce further and/or reduce feed rate. If that continues to resolve the issue until perfect, I’ll conclude my feeds/speeds were too aggressive. That does not eliminate that existence of flexing/loose wheels/etc., but updating all of those elements had no immediate or noticeable change to my issue. Maybe due to less aggressive feeds/speeds those flexing/loose components are not being aggravated. Either way, I’ll keep my eye on those mechanical elements going forward.

I hope anyone in the future can see that reduced feeds/speeds did positively impact my efforts to resolve the cut/uncut issue. But, at this second, I’m not 100% sure that’s the only problem or if those changes are all someone else may need to implement.

Anything I’ve missed?


(John Waldo) #43

I had a similar problem and it took me a while to figure out my problem. Seemed like I had too much play or flex in my spindle, but when I would raise the z axis and try to move it it was pretty solid. Finally removed the spindle and Z axis plate (I guess that is what it is called…the plate that the spindle attaches to) and everything looked normal. I removed the wheels at the bottom and found that one was broken on one side.

As long as the wheel was engaged everything was fine, but when it got to certain levels where the broken piece was exposed, that wheel lost contact with the plate which led to crazy cutting patterns.

Here is a picture of my broken wheel. Replacement coming today, so hopefully I will be back up and running soon. Many thanks to the Shapeoko team for the quick replacement.


(Brian Hunter) #44

Hi @rvs0002, I just realized I never responded to your comment. Nice photo too. I need to go over my wheels more closely it seems. It may account for some of my cutting issues, though likely not issues that occur only when X & Y are engaged and Z is static. But who knows, I could be wrong.

UPDATE: I’m beginning to suspect my hold-down method. Or at least my individual use of the method. I drill holes through my stock and put bolts through that screw into threaded inserts that sit inside my wasteboard (made of MDF). That is not a bad method from all that I’ve read. However, I may be using too large of a drilled hole in my stock and thus it’s creating some play for the bolt. Plus, the MDF wasteboard is probably soft enough to allow for movement of the insert due to pressure from the bit against the wood mid cut.

Regarding z-axis, I’ve had several recent instances where the bit made a large jump off track. I’ve looked over the wood afterward each time and the most likely cause is the bit is not making it out of the cut (pass the top of the stock) before moving in the next X/Y direction. So, it gets hung up, then skips and continues cutting in the wrong place. Very annoying and costly. Oddly, a couple times the jump happened while on the second of 4 passes required to complete that shapes cut depth. A knot in the wood is what I’ve blamed in those cases.

I have more investigating to do. Thanks all


(system) closed #45

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