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PostPosted: Mon Jun 13, 2016 7:27 am 
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Cocobolo
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Location: Southwick,MA
City: Southwick, MA
I'm having a terrible time getting dialed in on shell cutting using these bits from precise bits:

MS3I8-0100-006F 0.0100 in. (0.254 mm) 3-flute optimized natural shell cutter, 0.020 in EFL, 0.060 in. max reach

I have followed the recommended feeds and speeds they posted on their site - depth of pass .005, RPM 24000, Feed Rate 1.5 IPM (they recommended 4) and still I'm breaking the bit after a very short time. I'm wondering if I should invest in a higher speed spindle rather than the router for this, or is there something fundamental I'm missing? I've already RTFM over and over to see if I missed something, but I'm stacking up bits like cord wood now and need to resolve this....

Suggestions? thoughts?

Thanks in advance....

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PostPosted: Mon Jun 13, 2016 10:16 am 
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Have you tried the 4 ipm @ .005?
If you go too slow you can pack the cut full of shell dust and overload the cutter as it cant clear the dust fast enough.

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PostPosted: Mon Jun 13, 2016 10:27 am 
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Cocobolo
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I tried 3 ipm and it snapped halfway through the first letter, that's when I backed it off to 1.5 - Seems like it cuts ok until it gets deep into the cut (shell is right at .60) and then it gives up its ghost. I may try some thinner shell to see if that makes a difference....

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PostPosted: Mon Jun 13, 2016 1:14 pm 
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What spindle or router. Run out might be the culprit.


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PostPosted: Mon Jun 13, 2016 1:25 pm 
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Hitachi MV12 Router

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PostPosted: Mon Jun 13, 2016 4:33 pm 
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Cocobolo
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I use their .025 shell cutting bit, and have never had a problem with their recommended speeds and feeds. I'm actually kind of impressed with how much I've cut and not dulled the bit!

I was warned by someone on this forum (Don Williams if I recall correctly) to be careful of tir so I measured my router and wound up switching it out for a dewalt which has very low TIR runout. (I do use the precision bits collets as well).

I also use an air chuck or canned air to blow out the paths as it cuts,
Mike


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PostPosted: Sat Jun 18, 2016 11:30 am 
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Cocobolo
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Definitely run out. This could be a problem right from the factory, a worn out collet or spindle taper, dust or dirt in the taper, the grooves of the collet or up inside the nut.


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PostPosted: Mon Jul 18, 2016 4:50 pm 
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If you want cutters at that scale to survive, you're either going to run so slowly that there's virtually no load on the cutter...really, really, really slowly. And it's going to get chewed up by abrasion and wear really quickly doing this. Or you need to decrease your run-out to tiny, tiny numbers.

Ten thou at a sixty thou depth of cut is a very high profile cutter combined with being insanely tiny. If you've got more than a tenth of run-out then you're absolutely battering it, and you're not going to get less than a tenth of run-out with a router. It's hard to make those cutters survive long even with the right equipment (very high RPMs, 40-60-90K, and very low runout). They also take forever to cut anything, so I always charged accordingly when customers wanted that level of detail.

That 0.01" cutter is 1/40th as stiff as the 0.025" cutter. It's even only 1/5 as stiff as a 0.0156" cutter. Those ratios also more or less correspond to your margin of error with any operating parameters. I'd say try the 0.0156" cutters first and get your bearings and then go to the tiny ones.

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These users thanked the author Bob Garrish for the post: Durero (Mon Jul 18, 2016 6:34 pm)
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