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Cutting pearl with a CNC
http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=9293		 Page 1 of 1
Author:  Mark Tripp [ Mon Nov 13, 2006 12:26 pm ]
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So...

I have a new logo, it will be a PAIN to cut by hand, and frankly, I suck at cutting MOP. I'm probably going to have someone do it for me to start out. But I am wondering; would a small CNC like a Sherline milling machine be able to do this task? I figure it would be a good intro to the way the technology works, without spending the big $$.

Anybody know?

Thanks.

-Mark
Author:  Bob Garrish [ Mon Nov 13, 2006 3:49 pm ]
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The main things you need to cut pearl are extremely low runout and very high spindle speeds. If your spindle has any runout, it's liable to put a lot of stress on the tiny bits one would use to cut pearl. And, even spinning at 60000 RPM, pearl is pretty slow to cut (just barely out of the single digits in IPM=inches per minute) so if you're planning on using a mill with a spindle speed below 20000 RPM I don't know that you could move it slow enough to cut.
Author:  Jim Watts [ Mon Nov 13, 2006 4:22 pm ]
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I've cut it on a Fadal before with a 10K spindle. 1/32 cutter and went slow, like 5-6 ipm. When you get down to it there's not that many linear inches in an inlay. That said, a 60K would just be excellent.
Author:  Mark Tripp [ Tue Nov 14, 2006 12:37 am ]
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Ok, thanks guys - the spindle speed on the little Sherline mills is WAY too slow then - less than 3000 rpm...

-Mark
Author:  Pwoolson [ Tue Nov 14, 2006 1:01 am ]
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Mark, I obviously don't have any first hand experience with CNC like Bob and Jim, but I would be careful with a "small" CNC machine. If you look at it like many other woodworking machines, the smaller they go, the cheaper they go. They aim more toward Hobbyists rather than professionals. I know it's quite hard to find small woodworking machines that have the same tollorances as the larger ones.
That said, I think a small machine would have way too much runout on both the spindle and the bearings to do an accurate job on inlay. And you already answered you spindle speed question. WAY too slow to cut pearl. I'd even say 3000 is to slow to cut many woods. I'd think you'd be breaking cutters left and right.
Just my $.02 worth.
Author:  npalen [ Thu Nov 16, 2006 9:47 am ]
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Maxnc
I've cut pearl and wood on this machine for several years at about 8K RPM max. Probably average about 3-5 IPM on the feedrate. I have broken a few 1/32" endmills along the way as well as a couple of 1/64".
I have upgraded the steppers to servo drives and increased the X axis travel by a couple inches but did a lot of cutting prior to that with the stock stepper drive system.
We run a couple Fadals, Haas and other CNC machines at my day job so I appreciate what the big machines can do.
Author:  Steve Spodaryk [ Sun Dec 03, 2006 4:49 am ]
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I built a benchtop CNC machine recently. This is a very rigid aluminum frame, THK SR15 rigid rails, rolled ballscrews, preloaded (no backlash) ballnuts, etc - so probably considered a "mid-range" DIY unit.

I'm running a PC890, with exactly .001" of total runout 1" from the end of the chuck (dial indicator on 1/4" precision ground rod). So, the amount of runout on a 1/32" cutter, .300" from the bottom of the chuck is pretty minimal. Less than .0001". Over time this will only get worse, but a great starting point. I just cut some pearl and the results were outstanding.

Paul, there are some amazingly high tolerance small CNC machines available. Your observation may apply to general purpose woodworking machines, but with CNC, often the smaller the machine, the more important the accuracy. It all depends on what they are designed to do. If the machine is well designed, your spindle is fast & solid, and you choose correct tooling and feedrates you will see good results - just like everyone has commented.



This was cut yesterday. My 8 month old daughters name, in letters .5" tall. 1/32" carbide upcut. .060" gold MOP. (4) .015" passes at 5/3 ipm (faster in ebony). I undersized the MOP by .001" on the perimeter and got a *perfect* slip fit. This is just pressed in, unglued and unsanded.

Steve
Author:  Don Williams [ Sun Dec 03, 2006 5:02 am ]
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SWEEEEEEEEEET !

Got any spare parts you want to sell???
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