So the issue below has been driving me nuts, and I’ve checked many of the obvious things on my machine (a 3XL with HDZ) already… but the issue is one of those things where you think it got less, and then it doesn’t.
Instead of being a nice smooth flat pocket, it almost seems like the cuts go progressively deeper.
I’m cutting with a 0.078" bit at a DOC of 0.015" at 20ipm, not aggressive by any measure.
Belt tension — the Z-axis should be guitar string tight (but careful not to bend the motor shaft): http://docs.carbide3d.com/assembly/shapeoko/xxl/step-5-belting/ on deep cuts it may help to remove one spring from the Z-axis temporarily (which side doesn’t matter), esp. if one hasn’t added a spoilboard on top of the wasteboard — it also helps to install the router as low as possible (installing the Makita adapter upside down will help). Some folks have found it helps to remove bolts which won’t stay tensioned (M4 Z-axis tension bolt, various V wheels with eccentric nuts), apply a thin bead of threadlock along the length of the threads, then reinstalling. See the video at: https://www.youtube.com/watch?v=_lIIb_PdziA Note that the X-axis motor is held in place on standoffs and if those bolts are loose this can cause belt tension issues.
How thick is the piece? Are you using doublesided tape to hold down the center?
It looks like certain passes were deeper than others, maybe because the workpiece got lighter and lifted up a little? Or maybe the opposite, early on the endmill caught a too much (with more stock engagement) and pulled the carriage down/workpiece up…
As @WillAdams suggested, definitely check the rigidity of the Z-plate carriage.
And maybe less of a stepover helps…
EDIT: Just saw you are using the HDZ, still check if it is rigid enough (does anything flex when you try to pull by hand, etc). The uneven pattern of your problem still leads me to suspect the workpiece isn’t staying level for some reason…
0.25" tick wood, total depth is 0.06" (first pass is 0.045" second pass 0.015")… yes on double sided tape…
it’s a down cut mill so it would be pushing the work down I think.
with HDZ it’s pretty darn rigid but I’ll check if something is lose.
(I’d love to tweak stepover but you can’t tweak that it seems with CC 460 and advanced vcarve toolpaths… the edit field isn’t editable)
everything is very rigid, with the exception of the collet in the dewalt router… it almost feels like there’s a bit of play on that… both forward/backwards and up/down, there seems to be a tiny “wobble” in that… hrmpf. I wonder if that’s normal or if that means it’s time for a new router …
It looks like there are a couple “starter” spots for your pocketing operation, and the lowest depth cut seems to be on a pass just after hopping away from one of those “starter” spots. Since it doesnt seem to be a consistent misstep of any kind, my vote is for stock movement from the double sided tape. Any hold down method that is less than “completely” rigid will show more and more defects the thinner the stock gets in my experience. I think thats why a lot of guys ditch the double sided (read gooey) tape for painters tape and ca glue. Seems to be much more rigid. I ditched the double sided tape (because of problems like this) for 18 gauge brads with heads set deeper than I was going to cut at the corners and every few inches around the edges before finally setting my table up for proper clamping and hold downs. The gator clamps grub screws work great for securing stock from the side with some downward pressure leaving the face completely open for cutting.
Is your wasteboard just the stock mdf? Push down on it in the centre and see if you can detect any movement. The wasteboard flexing gave me a similar issue, as when the endmill was pushing down the wasteboard flexed and didn’t cut full depth.
I ended up removing the feet and replacing the stock mdf with 1" ply with sacrificial mdf strips on top
I’ll go do a test with the tape+glue method… I have one of those aluminum base boards so I doubt it will flex much on that end, but if it looks like flex then I need to start using tape+glue and maybe clamps as well
New to the cnc thing but wood work by trade…with it only being .25 stock I’m going to question moisture content of the wood. As you machine the wood the water will expand and cause the wood to bow. I would suggest trying it on a thicker piece. Maybe MDF to do a flatten pass and see if it’s the machine, material or hold down.
I would tend to conclude that, from your description and the looks of the cut, and the fact that you know what you are doing, and a couple of similar threads like this one
Time for a spindle upgrade ?
Did another cut today from a piece of wood from the same set, but this time double paying attention to the double sided tape and adding a clamp on the inactive side.
(I was out of painters tape and Amazon will only deliver the new roll tomorrow)
@Swartw1 may have a point since I could see the wood warp on a little bit during the cut and on one side it managed to pull itself loose from the double sided tape.
Anyway the results are much closer to acceptable, and I’m willing to blame the workholding for the issue at this point, I’ll do another cut tomorrow once the tape arrives.
(and yes you can see my machine is very slightly out of tram as well, next on my list)
I’m still not happy about the dewalt wobble so will start investigating what it takes to go to a spindle… too bad the carbide3d folks don’t just sell a kit for that.
Just leaving this here, to give you an overview. There are many interesting posts in the forum, you may want to check @wb9tpg’s thread where he documents his ongoing upgrade to a 800W spindle
definitely a worthy upgrade in my opinion. quieter, less runout (depending on the quality of spindle), ability to turn on and off, and set speed via Gcode
I was cutting some 0.03in aluminum (admittedly way thinner than your piece) and went with my pretty standard application of tape and super glue, maybe 1in spacing. It didn’t dawn on me until I ruined a piece how much the flex was in between the tape and at the edges (unsupported by maybe 1/8-1/4in). I switched to complete tape coverage and even did some spot application of machinable wax + torch to get it to wick under in some of the places. I got vastly improved results.
With double sided tape you wouldn’t have my problem (gaps in super glue), but my point was not to underestimate things wanting\to move due to forces on the bit! I think the recent cut indeed looks way better.
