When pocket cutting walls are tearing out

[joelintzenich]

I just cant figure out why my pocket walls are tearing out, we have increased speed and decreased speed, changed stepover and wood species, nothing seems to help also tried new bits we are trying to carve dice boxes, we have increased the wall thickness as well, just pulling my hair out in Indianapolis

[Bob]

First step: Stop pulling out your hair!
It sounds like you have tried some good problem identifying methods so far.
Second: Try a different direction of cut. Try less depth of cut per pass. Post your settings. Or, Post your crv file. Or, Post a picture of the defective project. Sometimes it's easier to diagnose problems if we can see what you're doing.
Bob

[joelintzenich]

Update: played with the settings some more and made the most problematic walls just a tiny bit wider, and finally got a cut without any blowout on the practice board (poplar, which we'd had issues with blowout on that file a lot). Bit the bullet and put in a brand new bit and ran the file on the purpleheart and snapped the bit in half...and then in a fit of brilliance (or not, hah) I thought maybe there was a glitch or a bit problem so I put the other bit I'd been using back in and ran it again...broke that one too. Both during the final profile cut passes.

The first time I cut the file on maple, because it we had it and it was more similar in hardness to the purpleheart which we hadn't cut before. Everything went fine.

Proceeded to the purpleheart, had a huge problem with a whole inner wall collapsing. I only had two pieces, so I got nervous at this point.

[joelintzenich]

Switched to poplar to try some different settings, because we had trouble with poplar doing the same thing on a previous iteration so hoped solving it on the poplar would be a good step and it's cheaper. The first one was awful, with a lot of issues on that top wall.

Made some more adjustments, only had blowout in one spot where it was the narrowest.

[joelintzenich]

Another picture of the above box. Determined that maybe some of the walls were simply too thin, so I reworked my file to make them just slightly thicker and more even all around.

Had success with this one, felt good about how it ran and what it looked like...so I went back to the purpleheart...

Broke two bits on this one. Both cutting the profile. One brand new, and the other that had just cut that last box well. Both just snapped in the shank while running the top profile pass cut out.

We're running a 1/4" endmill with two flutes. File parameters for the last two were pass depth of 0.18", stepover 20% (0.05"), spindle speed 23000 RPM, 30 in/min feed rate, 10 in/min plunge rate. Climb, not conventional. Added ramps to the profile cut out at 20 degrees with the last two...just to see if it helped.

[Kayvon]

That's a beautiful design. Sorry to hear about the problems you've been having.

From what you're saying, wider walls and slower feed rate?

[joelintzenich]

Thank you! I am excited about the design if only I can make it work consistently.

We eliminated the tear out with faster feed rate and wider walls, which felt like progress, but now I am having bits break in the final profile cut-out stage. I'm a little worried about tearing out those sidewalls again by slowing down the feed rate for that portion...is there a way to make the profile cut wider/two passes wide maybe so it isn't as narrow and maybe the bit won't get hot?

[Bob]

Usually heat is caused if you're not making chips...The feed rate is too slow. If the feed is too slow you're making dust, which does not remove heat.
Or, the bit speed is too fast...same result, dust instead of chips.
Your boxes don't seem to show burning, so I'm not sure what is causing the bits to get hot.
Are you using up cut bits? These will help to pull chips out of the cut.
Is the cutting edge long enough to cut the entire depth, and carry chips out of the cut.
Does the bit have straight cutting edges? This would also make it hard to eject the chips.
Are you doing a final pass full depth cut? This engages the full length of the bit and cause more pressure.
Would you be willing to post your crv file? Sometimes it's easy to see the cause of the problem.
Bob

[joelintzenich]

We are definitely getting chips, not dust, and no burning on the boxes that I can see either.

We have been using 1/4" x 1" CEL x 1/4" SK x 2 1/2" OL (75-102 by freud) solid carbide 2 flute upcut finishing bit. The one exception was the few cuts I ran yesterday with the 75-025 solide carbide 1 polished flute upcut bit that I bought on accident on my last trip, which was cutting beautifully on three cuts and then also broke - 1 box with the wrong file that was messed up, 1 box that went well out of a scrap board, and then went to run my curly cherry and my bit broke on the profile pass again.

I am not sure what you mean by running the final pass full depth cut - yes I think so, but it is breaking before that final pass. I am going to attach my file, but I did not think to come check here before making another round of changes last night but I didn't change any of my cutting parameters just adjusted the file itself because the fit was a little tight top to bottom.

hex box dice v2 purpleheart calculations.crv

(1.24 MiB) Downloaded 317 times

[Bob]

I was just thinking...If a collet is damaged internally, it can cause higher pressure on one side of the bit. Causes of damage: a broken bit, normal wear, improperly cleaned collet, improperly cleaned bit, dropped collet, and the list goes on. Also sawdust in the collet can cause uneven clamping pressure. Bit clamped with too much sticking out. Bit clamped with cutting edges clamped up inside the collet.
A collet and collet nut are both considered consumable, and should be replaced regularly.
The collet is becoming the prime suspect... Even a visual inspection will probably not show the problem, but the problem with a collet can still be there. Also, clean up inside the collet shaft on the spindle.
Bob