Cut Parameter Recommendations

I normally cut plastic with my PRS standard (2.2hp spindle) but I'm looking to cut some parts for a vanity out of 3/4" hardwood plywood. I'm hoping some folks with more plywood experience can provide recommendations for good spindle speed, feed rate, and cut depth. I'm planning to use an Onsrud 1/4" compression bit (PN 60-111). The quality of the cut is more important to me than speed. I'll be using a somewhat weak vacuum hold down but the parts will have a good amount of surface area. I may include a few tabs just to be safe. Any recommendations would be appreciated - thanks!

There is a lot of info on this forum about this...
Don't be lazy! do some research about cutting ply with your compression bit...

On a PRS Standard I'd do this:

First find out how deep you need to cut to get past the upspiral portion of your compression bit so you don't tear up the top veneer. My guess would be .35".

Do .35" per pass make your part about .005 larger than it needs to be (you can use offsets in VCarve/Aspire).

Cut almost all of the way through (about .04 shy of being all the way through)

On the final pass reverse the direction of the cut and eliminate the offset.

Your parts should come out barely needing any sanding.

Don't go much faster than 2.5 to 3 IPS at 12-14k RPM.

https://forum.vectric.com/viewtopic.php?t=25333

Very helpful info. I appreciate it!

Quote:

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Originally Posted by EricSchimel

On a PRS Standard I'd do this:

First find out how deep you need to cut to get past the upspiral portion of your compression bit so you don't tear up the top veneer. My guess would be .35".

Do .35" per pass make your part about .005 larger than it needs to be (you can use offsets in VCarve/Aspire).

Cut almost all of the way through (about .04 shy of being all the way through)

On the final pass reverse the direction of the cut and eliminate the offset.

Your parts should come out barely needing any sanding.

Don't go much faster than 2.5 to 3 IPS at 12-14k RPM.

https://forum.vectric.com/viewtopic.php?t=25333

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I'm not lazy. I run my own business and I'm fixing up a house almost entirely on my own. This is a small project and so yes, I was hoping someone would lend their expertise to help save me some time. You could have just passed up the post rather than stopping by to make assumptions.

The quality of the plywood will make a big difference in the final result. I cut ply all the time and multi ply cabinet grade from a wood store is best not cabinet grade from HD. If you have some scrap to test with make a few test cuts and LISTEN to your machine, it will give you instructions on feed and speed! ;) Russ

Thanks for the advice - I'll keep it in mind!

Quote:

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Originally Posted by chiloquinruss

The quality of the plywood will make a big difference in the final result. I cut ply all the time and multi ply cabinet grade from a wood store is best not cabinet grade from HD. If you have some scrap to test with make a few test cuts and LISTEN to your machine, it will give you instructions on feed and speed! ;) Russ

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Totally agree, I would also add that if you dial in your toolpaths/bits well you can get great edge quality even on bad plywood!

I cut over a thousand sheets of plywood a year for cabinet jobs. What I found works for me with MY machine is:

FIRST pass is a climb cut
With a compression bit, plunge down the depth of the upspiral portion of the bit
Ramp down to half the thickness of the plywood (plywood over 1/2" thick). Run two climb passes leaving 1/32" skin
The climb pass is going to push the bit AWAY from your cut line
Now do a last pass in conventional direction, cutting 1/32" thru your material in ONE pass
This last conventional pass cut will pull the bit to the line and create a super clean cut exactly on the line

Been using this method for 11 years on my 2009 PRSAlpha with 2.2hp spindle and it's worked perfect. I recently upgraded to an ATC with 5hp spindle and still use the same cutting method.

I cut with a 1/4" compression bit running 13,500RPM at 7ips cutting speed. My limit is NOT HP, it's the fact that I'm at an altitude of 2500' and my vacuum system doesn't have the hold-down capability that a lot of folks at lower altitude have. If I had the hold down capability, I'd probably use a 3/8" compression bit cutting around 9-10IPS in one climb pass and one conventional pass. ShopBots have to much flex to cut in one conventional pass and have a good clean cut exactly on the line. Just a fact after 11 years of tuning and tuning the machine.