[wtwaggoner]

Here is what I am using:
Velox 4x4 CNC
-max speed 100imp
-Bosch EVS 1617 router (2.25HP/ 12 Amp motor 8,000-25, 000 RPM)

I am trying to cut out a shape like this out of 1/2" baltic birch plywood.Attachment 244970

The first time I cut it out I used an amana compression spiral 1/8" bit and it did ok at 100imp 0.125"/pass., the edges were a little rough,. but the next few times I went to cut out pieces I have snapped my bits at slower speeds. Once at 80imp,. another at 40imp,. I slowed it down to see if it would help the finish and under the advise of another cnc operator. I have since tried cutting the same thing out again at 100imp and snapped another 1/8" bit. A total of 5 broken bits and one finished piece. One piece of advice I got was to run tabs,. that maybe a piece would move just a tad and cause the bit the break,. the biggest bit I broke was 1/4".


I am just looking for and optimal feed and speed using that bit that I can run and not break bits. mini-compression-solid-carbide,. and maybe that isn't the bit I should be using. I dunno,. I am trying to figure this all out.


I appreciate you taking the time to read this and would very much so appreciate any help you could lend.

[awerby]

There are a few things you can try. First off, I don't like to cut deeper than half the diameter of the tool at one go, especially in a slot. (Other people will say that's not a problem, but they're not breaking as many bits as you). So if you're using a 1/8" bit, try limiting the depth per pass to 1/16" Alternatively, back off the edges a little and use a 1/4" tool for the roughing passes at 1/8" depth, just to get most of the material out of the way. Then you can go in with your 1/8" tool and clean up the edges in climb mode without having to cut in a slot. I wouldn't advise slowing down too much; wood likes being cut at high feedrates or it starts scorching. Look at the chips you're making - if it looks like fine dust, then you're going too slow.

Tabs are a good idea if you're cutting things loose, since the loose pieces can break bits as they flap around towards the end of a cut. Try to adhere the workpiece to the spoilboard firmly, since the material can break your bits if it rides up a little. Downcut spirals help with this too, but they don't clear chips as well as upcuts and a clogged bit will break. Vacuum works best, but double-stick tape works to some extent. Glues that will release with a little heat are another alternative.

Another issue is the run-out in your router spindle, which can be high in a router designed for hand use. There are aftermarket collet systems available that will help with that: Precision Bosch 1600 Compatible Collets You might also try using HSS or cobalt bits instead of carbide. Carbide is brittle - it stays sharp longer, but it isn't as sharp initially, and it doesn't sound like you're exactly wearing out these bits.

[ger21]

What rpm have you been using? Are chips getting packed into the kerf as you cut deeper?

Baltic Birch is very abrasive, especially on small bits. Running them too slow speeds up the dulling process. Dull bits lead to higher forces, and broken bits.

Are they breaking at different depths of cut, or only when cutting through? Loose pieces when cutting through can get pulled into the bit and break it instantly.

You might want to try downcut bits, as they're a lot cheaper.

Where are the bits breaking? Are they breaking at the transition from upcut to downcut? Or above the flutes?

[wtwaggoner]

One broke at the collett,. another half way down,. but they all seem to be breaking on the final pass 0.07" and 0.01"of side tolerance. So yeah maybe its because there are so many inner pieces that it only takes one of them binding up just right? pisses me off though,. I cut the first one without alot of trouble,. I will look at the latest bit when I get home,. but I didn't seem to see any caking up on it. as far as the other chips,. I was initially running it at 25k rpm,. and on the latest break I ran it at 10-12k. One of the bits I did break was a downcut,.

Another idea,. I could run an initial 'marking' code to locate the centers of the inner pieces,. run screws through to the spoil board,. Maybe that would help. It would just be awesome if I could figure this out. Oh yeah,. and I am using precision colletts. I bought a Onsrud 3/16" downcut,. I should be getting it soon,. and also another 1/8" spiral compression bit from Amana,. I called and complained and they are sending me one on the house.

[ger21]

If they're breaking on the final pass, it's probably from the wood being pulled into the bit.

Try upping the rpm to about 15,000 for 100ipm.

[wtwaggoner]

Yeah I'm gonna def up the RPM,. I was looking at the piece it did finish and the sides were real jagged. So what I am going to do is up the rpm,. and run a drill pattern to place markers on each of the inner pieces so I can run screws through them.,. this will prevent them from getting pulled into the bit on the final pass. I'll post some more pics this weekend,. I just have to get this figured out., my broken bit pile is getting bigger. There just has to be a combination that I can get to work. Anyone live near the Rancho Cucamonga, CA area wanna come check my setup out?

[br1]

How do the fonts look up close, some fonts look good until you really zero in and look, some are best smoothed out with arcs before cutting, as some fonts have really choppy straight lines and can cause issues and produce rough edges. I like your screw down method.

[wtwaggoner]

The fonts look pretty good,. I think another thing I am going to do is make them bold,. give them a little more thickness to them. I'm even considering not using a side tolerance,. you might not be able to 'read' it on the sides of plywood. I only ever really noticed it on MDF. other than that,. upping the bit to 3/16" down cut, higher rpm,. screw down inner cut aways,. and we shall see,. I'll def post a pic next week when the bit comes in,. hopefully the Onsrud rep will come out for the cutting,. at least he said he would once the bit comes in.

[awerby]

If you've already broken bits inside a collet, you need to replace that collet, since the bit breaking in there will damage it and cause subsequent bits to fail.

[wtwaggoner]

I must have spoken wrong,. I have not broke any bits inside the collet.

[wtwaggoner]

So I kept breaking bits,. 5 total,. so I decided to go with Onsrud bits as the Amana brand kept letting me down,. I went with a 3/16" downcut.,. I'm still not paying ultra attention to chip load,. but I know when I did get down with this piece the bit was room temperature. I ran it at 70imp with an RPM of around 18K with a .125" per pass. Everything was going good till the final pass. I should be kicking myself,. so the plywood is 1/2",. but not really 0.50",. I was making it so the second to final put was 0.45" and the piece was pretty much cut free,. so the final cut I was going through to 0.52" and also taking out 0.005" side tolerance and all of a sudden the table started making tons of noise,. lull and behold one of the small fingers was grabbing the bit HARD. It made it around and kept going to finish,. but yeah I think that was my problem,. so I took some advice and placed makers on the pieces that get cut free and used my brad nailer to secure them down,. I was super excited to see the bit make it all the way through without breaking. Total learning experience on my part. Now I think I can refine it even more to be even more successful. Thank you for this forum and thank you for your help. I will be sure to post more as I grow in the industry

-Tom

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