Surface quality issues on x-axis

CNC Machines Shapeoko
1

I’ve been machining some polycarbonate and some cast acrylic and note that the surface I get on the X-axis is a little rougher than what I’m getting on Y, and sometimes I can see deviation from a straight line by .003" or .004", a sort of wavy instead of straight line (the Y is pretty darn straight).

I’ve tried climb vs. conventional cutting, final passes of .01 and .005", different bits (including new), etc.

I’m using .125" bits (1/4" shank) and DOC of .004" to .006" and I’ve tried feed speeds as low as 40-IPM and as high as 65-IPM.

The thing is, it only happens on the X-axis, and I’ve tried everything I can on the X-axis, checking and replacing wheels, etc. It is snug, I cannot find any play there.

Ideas for debugging this?

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Doing more research on this, it turns out the problem I am experiencing is called (in the CNC Cookbook and by some others) “waviness” or “wave.”

Apparently happens due to resonances which makes sense because my x-axis finish is rougher, too.

Here is a link to the relative page:
http://www.cnccookbook.com/CCCNCMillFeedsSpeedsSurfaceFinish.htm

I think I will play with my speed settings on the router, and also feed speeds.

FWIW I did watch a video on youtube of an industrial machine cutting polycarbonate. Video here:

They’re using a 1/2" bit spinning at 20k-RPM, 45-IPM, .270 DOC. I haven’t done the math but that is a very small chip load.

And if you watch the video, you will see they slow down to I’d say about 20-IPM for a finish pass.

So I will concentrate my research on adjusting my router speed first.

Depending on how that goes, I might add a finish pass that slows down to 20 or 25-IPM.

I’m using Cut2D, which works fine but doesn’t allow me to easily reduce feed speed for the finish pass. I’d have to add a 2nd profile and create a new tool. All doable.

If anyone is still reading this (I can’t believe I’m still typing it), does the Shapeoko CAM software allow a slower finish pass?

Also, is there are free CAM software for the Shapeoko? I downloaded MESHCAM but it wanted a license code and I got my machine used and don’t have any codes or anything, so I just stuck to Cut2D.

Anyway, thanks!

3

The Shapeoko Carbide Motion board includes a license for Carbide Create as well as Carbide Motion (for the latter, you may need an activation code if using a Stepoko board, contact support@carbide3d.com w/ the purchasing details):

In order to do finishing passes it seems one has to create extra geometry or tools.

MeshCAM, while bundled w/ the Nomad is an extra purchase for a Shapeoko.

The community maintains a list of free / opensource software at: https://www.shapeoko.com/wiki/index.php/CAM

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You did not mention the bit you were using. Some people have had acceptable results with many feeds/speed and tools, but commercially “O” flutes produce very fine cuts at high feeds and rpms when cutting acrylic and polycarbonate sheets. Looking at the edge finish in the video, I would wager it was an O flute bit. They work great on aluminum, as well.

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5

Thanks for chiming-in, Ed.

I’ve tried a few different bits, and had the greatest success w/ a 2-flute .125" spiral bit intended for wood.

I did source a single-flute Onsrud bit for hard and soft plastics on Amazon and I tried that yesterday, and was surprised that it was actually a little worse finish-wise. Also, .5" holes were coming out undersized (I didn’t measure them but I’d approximate .005 to .010").

I think one advantage of a 2-flute bit is that deflection is reduced because there are opposing cutting surfaces. As the bit deflects, the other cutting surface is forced into material (provided there is any). All just my crazy opinions, of course.

So I should have ordered a 2-flute version, but didn’t. I will rectify that.

FWIW, for some crazy reason, I’ve never had any Onsrud love. I know they get awesome reviews and are dominate in industry, I just haven’t been impressed. But that is likely because I’ve been using 1-flute bits and need to try 2-flutes.

Or I could be completely wrong.

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There are so many different profiles available for various materials that it can be difficult to match the tool, material, feeds/speeds sometimes. As you know, a 2 flute for steel is not the same as a 2 flute for wood, or a 2 flute for plastic. They are ground differently. I don’t cut a lot of acrylic, but I tried the O flute from Toolstoday at their their recommended feeds (at least as fast as my courage would allow) and had good results.

I recently had to create many very large pockets (in wood) for a item I designed. I dreaded using conventional upcut, or downcut bits, because of the time involved. I called and got a tool recommendation for plunge bit that looked somewhat like a conventional router bit with fishtails for the plunge. Gosh it hogs out those pockets like a champ. I would never have thought to use that tool. There is just so much to learn.

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7

Yep a heckuva learning curve no doubt about it. Makes things simultaneously interesting and frustrating.

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I would check your X axis wheels again. I had to replace my X axis wheels after around 9 months, one was egg shaped. This caused the X axis plate to move back and forth swinging the router bit like a pendulum. I make 2"x 12" plastic nameplates and noticed this when I had them all lined up next to each other. I noticed oval shaped gaps where the long edges met. Sliding them back and forth along side themselves I saw where they would close the gap then open. the center of the wave happened to be the circumference of the wheel.

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9

Okay for it, I will look into the wheel possibility, thanks for the feedback!

10

Over the last few days I’ve been examining the machine, trying to maximize accuracy, and figured I’d post an interesting if not that helpful follow-up to this post.

The original Dewalt router had a tiny bit of bearing knock. It was used (abused) and I had a hardly used one on-hand from my woodworking hobby so I swapped them out.

Finish quality didn’t improve, though, and I really thought it would.

Knowing I was going to be swapping and selling the older/troubled Dewalt on eBay (with full discloser of its problems, of course), I had ordered the Makita. So yesterday I got around to installing said Makita and make a couple of test cuts and got a similarly rough finish.

I was using a CMT 1/8" bit upcut spiral, which is the bit with which I achieved the best finish to this point. But for some reason I decided to swap to a Whiteside bit (not new) and make another test. Wow, a substantial improvement in finish quality. I’m using the same RPM’s as I had been on the Dewalt.

So my theory is that I settled on that CMT bit with the original (bad bearing) Dewalt because it achieve the most accurate results with that router. However, the CMT bit with the good Dewalt router was now the weak link. Unfortunately, I never tried the Whiteside bit with the newer/better Dewalt (I will eventually get around to this).

So, to summarize, swapping parts out has led me to a finish that I find very acceptable. I will likely try an O-flute bit again (was getting poor results in that original Dewalt).

I’m only posting this as inspiration for those that don’t get great results first-time around. I can’t work on this full-time and it does take time to become familiar with the machine. My first CNC router (the K2 prototype) was a tremendous learning curve which has helped in figuring out how to approach this used Shapeoko unit.

I do like the Makita for CNC use quite a bit because it offers both a spindle lock or two-wrench method for tightening the collet. I prefer the two wrenches, just personal preference I guess.

Thankfully my dust shoe design can work with either the Dewalt or the Makita, it was as simple as swapping-out the motors.

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