best bits for 3/4 birch plywood

[lapoza]

Hello all,

I'm new here, my dad has a shop bot with the router type cutter, not the spindle. Im making finger joint speaker enclosures using his machine and am wondering what the best bits/speed settings to use for cutting 3/4 birch plywood. I currently have and upcut 1/4 inch bit, and a downcut 1/4 bit that i bought from centurion tools. I run both bits at 12k rpm using the downcut for the first pass at .2 depth to cut clean lines in the plywood, then i come back in in three passes with the upcut bit at .25 a pass with the last pass cutting all the way through the wood leaving tabs.

I am running this at 1.5 ips. I have gotten the cut time down to around an hour for what I am trying to do. But my dad seems to think if I buy the right bits at the right RPM and speed I can do this in one or two passes in half the time. I'm wondering it a 3/8 bit in one pass and then coming back and using a 1/4 to clean up.

The reason I use the downcut on first pass currently is the up cut bit was not cutting sharp edges and actually was pulling the veneer up on the first pass. This was creating a lot of sanding to get rid of the burrs after. The downcut took care of this.

Anyhow any help is appreciatted, plan on building a lot of these so I appreciatte any help from the experts out there.

J

[Gary Campbell]

Jeremy...
You should be able to use a 3/8 Compression bit. Centurion sells them, a good number of us use them.

You dont say what model machine you have, as they vary in speed and power, but I would cut them at 3-4 ips, 12K rpm, 1 or 2 passes down to a .035 onionskin in CLIMB direction, and then follow that with a conventional pass with tabs in the conventional direction.

The compression is a combo of up and down spiral and the pass depth must be greater than the upspiral portion on the end of the bit to keep the top veneer from chipping.

[dlcw]

Jeremy,

Like Gary said a compression bit is great for veneered products. It also works well on laminate products along with melamine.

I use a 3/8" compression on 3/4" material (1/4" compression on 5/8" or thinner material) at 4 or 5 ips and cut in two passes. I do a climb cut first and leave a 1/32" skin on the material. I then do a conventional cut to cut all the way through.

When climb cutting the bit is pushed away from the cut line. A conventional cut pulls the bit into the line. If you take deep cuts in a conventional direction there is a chance you will undersize your part. However, with climb cutting forcing the bit away from the line and then a final conventional cut removing very little material, you will end up right on the line and have a crisp, clean cut.

As you mentioned in your post, you are using a router. So as Gary indicates, make your climb cuts in two passes instead of 1 pass. Take about .32" on each pass and leave that 1/32" skin to remove using the conventional cut. This should give you a very crisp cut right where you want it. And with a compression bit, you can do it all with one cut file instead of having to change bits and do a second cut. Saves a lot of time.

I hope you will post some of your projects when you get done.

[lapoza]

Thanks, Ill order some of those bits.

All I am doing is making simple boxes for speakers to go into, and cutting 1.5" finger joints to contstruct them, nothing too fancy.

Really appreciatte the info, im sure this will be much faster than 1.5 IPS with 4 passes!

Jeremy

[Gary Campbell]

Jeremy...
Depending on the thickness of your plywood, you may need to order mortise compression bits. They have a shorter upspiral section on the cutting end and may do a better job if your plywoods actual thickness is under .725

[lapoza]

yeah the plywood i have been buying is actually .6875 thick, right at 11/16 thick, dont really get what you pay for anymore.

Do i still use the same speeds, passes, and direction on that same bit as was mentioned with the normal compressions?

[Gary Campbell]

Jeremy...
You bet, the bit will be slightly less loaded, will be easier on the router.

[lapoza]

Since I dont know anything about bits, is this the correct one? it says up cut only in the description:

http://centuriontools.com/router_bits_toolcase/centurion_tools_showcase.html?page=full&cart=13111288883648662&__max=6&--eqskudatarq=38CR21.1253FEM200&id1=374&id2=6&id3=734

[Gary Campbell]

Jeremy...
Look at this one: http://centuriontools.com/router_bits_toolcase/centurion_tools_showcase.html?page=full&cart=13111288883648662&__max=20&--eqskudatarq=38CR21.03FEM200&id1=374&id2=6&id3=734

It has the mortise end, and a 1" cut length, which should be good for your application

[lapoza]

Thank you Gary,
Im going to order a couple of these.

J

[rej]

just noticed this post.
my machine is a 2001 prt with the old board.
robert jones