New X-Carve, strange cut pattern at bottom of cut

I’ve had my X-Carve for a week or so, been practicing with my favorite material, Corian. Just cutting pieces to get practice with the machine an procedures.

I’ve got a round piece I’ve been trying to cut and tried the 2-stage carving several times but I simply cannot change the bit without moving the carriage at least a little bit, and the X-Y zero in Easel leaves a lot to be desired in terms of precision. Not owning an X-Y-Z probe, I cannot re-zero it to the new bit size well enough to make the finish cut accurately.

So, in this last attempt I decided to just take the time and make the entire cut with the same bit I would have used for the finishing cut, a 1/16" upcut bit.

This was easily the best I’ve had yet, and it turned out great for the first 12 passes or so. When I got the finished piece out though, this is what I found on the bottom (flashlight to show detail):


So in the middle of the piece it’s higher, in a seemingly random shape, and along the edges a clear curved climb can be seen.

Do any of our more experienced cutters have any ideas on what could have caused this?

Bit: 1/16" upcut
Feed rate: 750mm/min
Plunge rate: 200mm/min
Depth per pass: 0.7mm
Final depth inside design: 6mm
Outer circle through-cut with four .5mm tabs
Stepover: 40%
DeWalt 611 spindle
Material: Corian, 8mm thick

I plan to, believe me, but re-zeroing had nothing to do with this problem. Any ideas on the specific issue of the post?

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Couple of questions-

Did you tram in your machine?

Did you flatten your waste board?

Are your belts tensioned correctly?

Are your v-wheels tightened correctly?

was your Y carriage square to the machine on start-up?

all/ any of these would produce those results, welcome to the club. I second getting Charlie’s plate, great product and Charlie is a great guy.

Thanks for all the replies! The community that’s built up around the X-Carve and Inventables is one of the (many) reasons I ditched the Millright Carve King that I bought initially in favor of the X-Carve.

To the specifics:

@BobJewell: I’ll definitely look it over

@RobertCanning: How do you tell if there are missed steps? I’m not sure how holding torque reduction applies to the problem I have changing bits? I can say that I’ve seen no difference in the situation when locking the motors and not locking them. Is there a setting somewhere that has to be enabled to allow motor locking?

@CharleyThomas: Ok, ok, you got me. Order placed. :slight_smile: Thanks very much!

“Did you tram in your machine?” - Not yet (see below)
“Did you flatten your waste board?” - No (see below)
“Are your belts tensioned correctly?” - As correctly as “similar to a bass string on a guitar” can get me.
“Are your v-wheels tightened correctly?” - Yes
“Was your Y carriage square to the machine on start-up?” - Good question, that’s not something I’ve checked at the beginning of a cut.

These seem like good questions, but I’ve got some questions on your questions.

I’m new to CNC but I’ve been working with machines for 20+ years and a couple of things don’t make sense. Assuming everything is tight, if the tram is off on the machine, it will be off in exactly the same way and to exactly the same extent at all points. That should make any issues it causes consistent, right? The defects here are irregular overall. The shape of the raised area shown in the first picture is very irregular, as are the depths of some of the mis-cuts. This doesn’t seem to fit a regular consistent issue like tram or an out-of-square Y carriage.

It also doesn’t seem consistent with a warped wasteboard. I didn’t include scale, but this piece is only 76mm across. For a wasteboard irregularity to cause this kind of rise in that kind of run it should be VERY visible to the naked eye, let alone felt by touch.

Maybe I’m missing some aspect of CNC that doesn’t apply to other machinery? Do those statements make sense?

I’ll be checking and adjusting square and tram regardless, but I don’t see how they could apply to this issue. Belt tension and play in the Z axis (somehow, how does that happen with a lead screw?) definitely feel like viable possibilities though.

For a little added information, I cut this piece a few days prior. It’s slightly smaller in diameter (48mm) and it has some bottom irregularities, but they are even more random and not as severe as the latest. It seems that whatever the issue is, it’s either getting worse or is more pronounced in the larger area?

If your base isn’t level then your cutouts will not be level which will really shouw up in large bottom cutouts like in the picture

if you are not holding down the material consistently it will cause bows which will show up just like in the picture

if your z Axis belt isn’t tightened just right it will cause the z to slip and show up like the picture

because of the design of the machine and two independent y Axis motors you must “square” the gantry each time BEFORE (don’t mean to shout but it’s important) you power on the machine otherwise your cuts will never be square

if you haven’t trammed yet then your bit is probably not square to the table which could cause it to skip and jump causing what you see in the picture

How’s your dust collection? If your getting chips wedged between the work and the bit it would cause this as well

There are electrical issues that could cause it but check the mechanical first then move to electrical

If you can’t change the bits without moving the the router then your motors are not locked.

Potential progress! The $1 setting was at 0, so my motors were not locking at all. Got that set. Also did find what I would call significant play in the Z axis. Removed the assembly, loosened the pulley set screws and tightened the top lock nut. After reassembly there is no detectable play whatsoever. Hopefully that will solve the raised-in-the-middle issue.

@RobertCanning You may well be seeing ridges on the letters. The entire outside of the outer circle is a series of regular flat planes rather than a smooth curve, almost looks like a 16-bit version of the curve I designed.

I can definitely see it transferring to the base, especially in large bottoms, but wouldn’t it transfer uniformly across the base, mimicking whatever unlevel conditions exist?

The material is held very securely and flat with very thin double-sided tape applied equally to both sides, and the Z-axis belt is tight.

I see your point on squaring the gantry, but I’m not sure how that would cause any of the issues I’m seeing here? There are no square cuts being made, and the few straight lines on the piece are perfectly straight. Or was that just a general tip?

Interesting that you mention dust collection. This particular piece had better dust extraction that the one shown previously as I’ve switched to a bigger vac for my dust shoe. The difference was night and day, there was NO dust visible at any time during the entire cut.

I’m out of cutting time today, but I’ll try this same cut in the same material tonight when I get home from work and see if removing the slop in the Z takes care of the base issues. I can’t see it helping with the faceted sides though, researching that now.

Thanks again to all!

Depending on the bit, you could be getting material lift from the tape.

A bit not square to the table doesn’t cut flat, it cuts at an angle, causing ridges and uneven cuts, especially when doing geometric movements. The bottom of the pocket in the picture looks like an out of square cut. Mine did that originally until I squared it up.