Can I cut at 600 ipm? Video added!

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Yes, definitely!!  Did I mean to do that?  Absolutely NOT!!

I have made several changes to the toolpath profile for cutting the Longworth chucks and all for the better.  When I started cutting them 100 chucks and almost a year ago the feed was 125 ipm, 18k rpm, 0.125" depth of cut, with a 1/4" downcut spiral bit.  These chucks are 1/2" Baltic Birch and I knew this was conservative but I tend to stay on that side.  I have slowly crept the speed up to where I am now cutting chucks at 250 ipm and all the other specs are the same except depth of cut is now 0.2".

When I opened the file for the 16" chuck I realized it was still at 200 ipm for the outer profile, with tabs, so I changed it to 250 ipm.  Or so I thought...  What I actually did was replace the '2' with '250' and didn't delete the extra '00'.  My new feed rate was now 25000 but since I thought I had overwritten the 200 all I did was hit Ok and went out to the shop.

Everything cut just fine until it got to the outer profile.  The ramp was at 250 ipm but when the cut reached the 0.2" depth it jumped up to 600 ipm, which is the max setting I have on the X & Y steppers.  I was in a mild state of shock for a second trying to figure out what had happened but it cut around that 16" circumference so quickly that all I basically did was watch it cut.  And it cut perfectly!  The 3kW (4HP) spindle didn't blink at what I had inadvertently thrown at it, the bit was cool when it finished, and the edge was just as clean as it could be.

I don't plan to move any future cuts to 600 ipm but I have to say, now that it's over and nothing broke, it was fascinating watching it cut that fast! :D  This Saturn frame is one stout and rigid CNC setup!



I have a camera in the shop but the output is proprietary and requires its own player.  If I can figure out how to export that to something I can upload to YouTube I'll show y'all.


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I might need to pick one of these up I made one with a router jig but its off just enough to be a real pain in the butt. Perfect job for a CNC

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5 hours ago, Mark J said:

@difalkner how accurate is a CNC with regard to dimensions?  To what level of precision are you able to set yours up?  .1 inch?  .01, .001?

Closer to the 0.001" to 0.002", Mark, when I'm doing smaller things like guitar bridges out of East Indian Rosewood or Ebony.  On larger items, like Baltic Birch Longworth chucks, it's probably in the 0.005" to 0.010" range although I can only check accurately out to 6" with my dial calipers. 

The last time I checked at 6" it was within 0.003" to no more than 0.004", depending on what I'm cutting.  Harder woods like Walnut hold to tighter tolerances where the softer woods tend to spring back after the bit passes making it harder not only to hold tolerance but to check measurements.


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