Deep Cut
- gkas
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Deep Cut
I need some help with the theory and implementation of doing deep profile cuts. The last time I made this box (Oval Sculptured Box, by SPalm), I cut the base from two 0.75 thicknesses, then glued up the two pieces.
This time I wanted to mill a glue up as a single 1.5" piece. Piece of cake... I used a 0.5 inch Down spiral mill to mill the center. No problem. It came out nicely. The problem comes with the profile cut-out. I figured I'd use a 0.5 upcut 2-flute spiral to do the profile.
All tries include a 0.005 finish pass.
First try: Ramping and spiral lead. Bit jammed on the 3rd pass of about 0.25/pass.
Second try: Dropped pass to about 0.15/pass. Ripped side off bowl and scattered pieces.
Third try: Bought a 0.25 bit with a 1.75" DOC. Cut completed, but cut so rough, especially on end grain, that piece was unusable. Very rough profile. Most likely bit flex.
Threw up hands in frustration.
Should I make a wide pocket (wider than bit) cut, then cut the final profile? Is this doable?
I'm running a Axiom AR8 Pro+ with water cooled 2.2KW spindle.
thanks...
This time I wanted to mill a glue up as a single 1.5" piece. Piece of cake... I used a 0.5 inch Down spiral mill to mill the center. No problem. It came out nicely. The problem comes with the profile cut-out. I figured I'd use a 0.5 upcut 2-flute spiral to do the profile.
All tries include a 0.005 finish pass.
First try: Ramping and spiral lead. Bit jammed on the 3rd pass of about 0.25/pass.
Second try: Dropped pass to about 0.15/pass. Ripped side off bowl and scattered pieces.
Third try: Bought a 0.25 bit with a 1.75" DOC. Cut completed, but cut so rough, especially on end grain, that piece was unusable. Very rough profile. Most likely bit flex.
Threw up hands in frustration.
Should I make a wide pocket (wider than bit) cut, then cut the final profile? Is this doable?
I'm running a Axiom AR8 Pro+ with water cooled 2.2KW spindle.
thanks...
- scottp55
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Re: Deep Cut
Can you show a pic of the holdown method you used?
scott
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Re: Deep Cut
Can you clarify what you mean by "bit jammed"?
I would not use an upcut, as they are more likely to grab the wood and cause tearout than a downcut.
Also, maker sure that you are conventional cutting, and it's preferable to have material on both sides of the bit. If you are removing less than the tool diameter from the edge of a board, the chances are very high that you'll get tearout.
I would not use an upcut, as they are more likely to grab the wood and cause tearout than a downcut.
Also, maker sure that you are conventional cutting, and it's preferable to have material on both sides of the bit. If you are removing less than the tool diameter from the edge of a board, the chances are very high that you'll get tearout.
Gerry - http://www.thecncwoodworker.com
- gkas
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Re: Deep Cut
I used a flat bar on one side with the opposing side using side clamps. Pretty close to this picture. I also used 4 corner clamps. The block did not move.
- gkas
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Re: Deep Cut
The bit actually jammed. I got a controller error and had to reset the machine. I think I had it set for a 0.3" or 0.4" @ 18,000 RPM cut in 1.5" Birch.ger21 wrote:Can you clarify what you mean by "bit jammed"?
I would not use an upcut, as they are more likely to grab the wood and cause tearout than a downcut.
Also, maker sure that you are conventional cutting, and it's preferable to have material on both sides of the bit. If you are removing less than the tool diameter from the edge of a board, the chances are very high that you'll get tearout.
I used an upcut to make sure the chips cleared. The cut looked fine, and the chips looked good, as far as it got. It was a conventional cut with a couple of inches of wood around the profile.
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Re: Deep Cut
So, you're saying the spindle actually stalled? what was the feedrate?
Is that plywood? If so, then the upcut should be fine. Try doing a finishing pass to clean up the edge, maybe .01-.02".
Is that plywood? If so, then the upcut should be fine. Try doing a finishing pass to clean up the edge, maybe .01-.02".
Gerry - http://www.thecncwoodworker.com
- gkas
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Re: Deep Cut
The spindle actually stalled. I've never had that happen if I didn't accidentally bury the bit. I keep my cuts to 100 ipm or less. This was probably 80 or 100, maybe less. I usually don't push the cutter with an unknown carve. That was in a Birch board. Tight grain and fairly dense.
Re: Deep Cut
One reason why the mill will jam, is it will go into a tight area, such as an angle or against a tab and the travel speed is faster than then the mill can retract or make the turn. To help out on that, make the roughing pass a little wider by giving the boundary offset wider than 1/2 the diameter of the mill. In fact, I started using the full diameter of the mill as an offset. Also, that will give a better allowance for the finish pass, to avoid the jamming. It increases the time of the job, but you avoid the problems you're having.
Gary
Gary
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Re: Deep Cut
What kind of spindle does that machine have? You should never be able to stall a spindle.
Gerry - http://www.thecncwoodworker.com
- IslaWW
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Re: Deep Cut
Were you using an air blower to remove swarf from the cut path between passes?
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- gkas
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Re: Deep Cut
That was my final guess. I'll try that next time. I just gave up and made another type of box, because I had to knock out a small gift and I wasted a few days on this. ....not actually a waste, because I learned a lot from this. It was definitely out of my comfort zone.garylmast wrote:One reason why the mill will jam, is it will go into a tight area, such as an angle or against a tab and the travel speed is faster than then the mill can retract or make the turn. To help out on that, make the roughing pass a little wider by giving the boundary offset wider than 1/2 the diameter of the mill. In fact, I started using the full diameter of the mill as an offset. Also, that will give a better allowance for the finish pass, to avoid the jamming. It increases the time of the job, but you avoid the problems you're having.
Gary
- gkas
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Re: Deep Cut
It's a Axiom AR8 Pro+ with a 2.2KW (7.5A) spindle.ger21 wrote:What kind of spindle does that machine have? You should never be able to stall a spindle.
- gkas
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Re: Deep Cut
IslaWW wrote:Were you using an air blower to remove swarf from the cut path between passes?
I have a 4" dust collector hooked up to it. It didn't look packed. That's why I used an upcut bit, to help with the chip clearance.
Re: Deep Cut
A spindle may not stall, but it definitely will snap your mills. It also throws out of kilter where the g-code vs. where the spindle actually is. What happened with what I described in the post below was caused by exactly this problem.What kind of spindle does that machine have? You should never be able to stall a spindle.
viewtopic.php?f=27&t=29131&hilit=something+definitely