Cutting 3/8" Baltic Birch

[jim_vv]

Greetings, All

I just finished cutting some parts from .375" Baltic Birch and thought that I would share some information that may benefit others in the future.

The odd shaped parts did not offer much surface area so I used vacuum (two Feins on four zones pulling 7hg) and tabs to hold them.

I only had exactly the amount of material that I needed so testing was limited. The following settings may be conservative, but they worked nicely for me and I had plenty of time figured into the job.

To cut the parts out I used a profile strategy (conventional direction) with a final pass thickness of .06" and a final pass allowance of .005"

Tabs were .060" thick. I cut the parts loose with a knife and then cleaned them up with a flush trim bit on the router table

Cutter Onsrud 60-113 .25" Compression

Step Down .25"

Feed Rate 4 ips at 15,000 rpm

Plunge Rate .5 ips

The cutter made no squealing noises while cutting and was a little above room temperature when complete.

Kind regards,

JIM

[bleeth]

Some very interesting looking parts. Are you doing the whole assembly as well?
Like to see the final object.

[jim_vv]

The parts are finished and assembled by my customer. He is working on a few versions of spring driven rotating Wall Arts. I will ask him if I may share a picture on the forum.

[knight_toolworks]

cool parts for sure. But I would go to 10 on the rpms if you can. if you use a 5/32" downcut you don't need tabs at all. I never use a compression bit and I use the sawdust to hold the parts in place. I have just cut 20 sheets of bb 3/4" with another 30 to go. I used a 1/4" downcut for the most part only lost a couple parts that were 3" wide along the edge. I cut a bunch of purse ovals that were close together used a 5/32" and I have to knock the pieces out of the sheet. never any tearout on the underside.

[jim_vv]

I have a 2.2hp HSD spindle and am not sure at what rpm I loose torque. I don't usually let it below 14k rpm for cutting. I have not been able to find a torque/rpm curve. Does anyone know if there is such a thing?

[knight_toolworks]

8k is about the max I use most of the time. you won't be loosing power. it is in the lower 2 to 3 I think on power loss.

[bob_s]

Jim
With a spindle running at 14k your forward speed has to be far higher than you want to use, to have correct chip load. The higher rpm will cause your bit to heat up and it's life will be somewhat shorter than if you cut that down to 8 to 10k. Search a little for feed speed here on the forum. It may be counter intuitive, but making dust instead of chips is not right
Nice cutting though

[brian]

Those parts resemble the kinetic art that David C Roy makes.
Goggle Him to see the many variations he has come up with.

Brian

[dlcw]

I cut 3/4" prefinished maple at 10K rpm and 4ips. 3/4" melamine at 9K rpm and 3ips.

I use compression bits on plywood and cut the first pass climb cut leaving a 1/32" skin. Then a conventional cut to cut the skin.

With my new vacuum hold down system (thank you Gary for your incredible design - Black Box Vacuum), I've done away with tabs completely.

I've never used 14K rpm since I purchased my PRSAlpha with 2.2 hp spindle almost 3 years ago.

The fastest spindle speed I've used is 12K rpm at 1ips when doing v-carving soft woods like cedar. Gives me a really clean cut.

I use line boring bits for drilling holes (1/4", 5mm, 8mm, etc.) at 6K rpm at 1ips plunge and the holes are clean with no chip out on the backside. Still using the boring bits I purchased 2 years ago and the holes are as clean today as they were when the bits were new.