Final profile pass when cutting profiles

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7.62x54r
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Joined: Fri Nov 05, 2010 2:41 pm
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Final profile pass when cutting profiles

Post by 7.62x54r »

I was wondering if there was a simple/automatic way to create a final profile pass when cutting profiles similar to the way it's done when cutting pockets. I've attached a file to illustrate what I'm trying to accomplish. The material is 3/4" baltic birch plywood which I'm cutting in one pass with a 1/4" compression bit at 13,000 rpm and 100 inches/minute (I know you're not supposed to be able to do that, but I do all the time). As you can see I ramp in on a circular lead. The lead is necessary to prevent damage to the surface veneer when the upcut part of the bit is entering across the grain. The problem is when the bit comes back around to finish the hole it wanders into the ramp and leaves a bump on the side of the hole which I have to clean up later. I was thinking I could cut the holes slightly undersized and then make a clean up pass to final size which would probably give me a cleaner finish overall anyway. I know I could create two toolpaths to do this, but thought there might be an easier way to do it in one step.

Any other suggestions on how to accomplish a cleaner cut in this scenario would also be appreciated. Should I just accept that I should be making two passes? I can't go to three as then I'm back to the problem of the upcut above the top veneer.

I'm using an old (circa 2000 or so) ShopBot PRT with a PC 3.25 router. I know the part isn't moving as I bolt it down (the four circles in the corner represent bolt locations) and I'm pretty sure the issue is flex in the machine.

Thanks for any help.
Attachments
ROT009Obase.crv
(180 KiB) Downloaded 120 times

jimwill2
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Re: Final profile pass when cutting profiles

Post by jimwill2 »

Got me thinking a little bit... that can be dangerous! I used your crv but I offset the profile (I used .25" so you could see how it works, I would make it less of a offset.) I then cut both circles and joined them into a spiral with the original profile part of the spiral making a overlap to make sure you get a full circle. It wouldn't work as a profile cut but it will work as a flute toolpath. I ramped the start 3" so the inside spiral would clean up the ramp. You can't tab but you could leave a skin to hold it together if that would work for your application.

Since the flute cuts 'on' the line you would need to enlarge the original profile the radius of the endmill to make it cut the right size and I didn't do that for you. Maybe someone can come up with a better idea but it could work.
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Fluted - Jim WilliamsROT009Obase.crv
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Jim Williams

dond52
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Re: Final profile pass when cutting profiles

Post by dond52 »

In the drop down "LEADS" button there is a place for overcut distance. Make that number large enough to cover the "bump".

7.62x54r
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Joined: Fri Nov 05, 2010 2:41 pm
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Re: Final profile pass when cutting profiles

Post by 7.62x54r »

Thanks for the suggestions. The large circle isn't an issue as I just set the start point on the side that is with the surface veneer grain and let it ramp in. Rather than use the flute toolpath it seems it would be just as easy to set up two toolpaths with an offset. The more I think about it the more I realize that I should probably just make two passes in depth, not offset. I'm not sure that would entirely solve the problem though as the bit might still wander into the ramp on both passes. I tend to get caught up in production and not take the time to just try out different methods to see what really does work best.

The leads overcut extends the path beyond the beginning of the cut (at the bottom of the ramp/lead). The "bump" is before the end of the lead where the bit first encounters the radius of the lead in.

Thanks again.

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