[Kevin067]

I just built a 4x8 wood cnc machine. Armed with a set of 1/4 diameter flat end 4 flutedbits, happily went ahead and started cutting some parts out. Half way through I started smoking the bit. Realized I had already dulled the bit. Went through 5 bits before I was done. I was not going fast at all.I tried to slow it down to a crawl. But it still can smoke the bit. I tried reducing the cut level. But it just wearing out the tip of the bit as it ends up milling 10 times more material at the tip. And extend my cut times drastically.I realized I needed to keep bit cool with a direct air nozzle right into the channel it is cutting. But still wearing out bits before I am finished.So I guess I have a lot to learn about the bit type and levels I can handle, and the feed/spindle speed.I am cutting 5/8" mdf profile cuts. So what bits should I be using? Can I get away with cutting the profile cut on the first pass? And just slow it down? I can handle having a rough edge. Seems I will wear out the bit evenly this way.My router is capable of 16k to 24k speed.What feed speed is typical for this type of cut?Would a 1/8? diameter bit be a better choice for just cutting out parts?Basically what is optimal for cutting mdf wood straight through?

[awerby]

Be careful about blowing air into a situation that's smoky already; you can start a fire that way. Wood (and MDF) needs to be cut fast, not slow. But you don't want to cut the whole depth in one go. Try using a 1/4" 2-flute (not a 4-flute) center-cutting bit, 18k RPM, a depth of cut of 1/4" per pass, and a feedrate of 200 inches per minute (or more, if your machine can do it without missing steps). The reason your bits are burning is because they're rubbing more than they're cutting. Going slower makes this worse, not better.

[Kevin067]

Thanks awerby, I was going as fast as the router could, and going a snails pace. How many sheets of 4x8 you think I can cut before I have to change the bit? All profile cuts. Just estimating how many bits I need to buy in advance. Anybody have a resource for buying these at a good price?

[minicncuser]

I cut 3/4 plywood one pass 18000 rpm 150 imp with a single o flute Onsrud bit 61-082. One used bit will last 4-5 hours of cutting before I change it out

[ger21]

Basically what is optimal for cutting mdf wood straight through?

A 1/2" 3 flute compression spiral, 15,000 rpm and 1200ipm.
But your machine won't be able to do that.

Realistically, you're going to be limited by your spindle power and machine rigidity.

When you are burning bits, it's because you are going too slow.
Don't use 4 flute bits, as they are not designed for cutting wood.
Try a good 2 flute 1/4" spiral bit, and around 200-250ipm at 16,000 rpm, if your machine and spindle can handle it. Try doing it in 3 passes.

[aarggh]

Thanks awerby, I was going as fast as the router could, and going a snails pace. How many sheets of 4x8 you think I can cut before I have to change the bit? All profile cuts. Just estimating how many bits I need to buy in advance. Anybody have a resource for buying these at a good price?

I use 4 flute cutters routinely as they produce nice small swarf that sucks up easily (and they're quieter when running!), but I run them as fast as I can without losing steps or whatever I'm happy with, and take a conservative depth of cut. For example on 18mm MDF which is almost the most abrasive thing you can machine, I run rapids of about 4m/min, and feed of around 2.5m/min, at around 16k rpm with a DOC around 3-5mm. I'm yet to blunt a cutter, and have used the same few cutters to cut hundreds of metres of MDF, and hardwoods. I bought a few dozen thinking I'd chew through them, but I think I'm on my third one after breaking a couple on side clamps. The current cutter use probably translates to around 60 or so hours machining time roughly.

Slow the feed down though, and it will smoke and char like mad, and burn the cutter fairly instantly.

The other trick though is to clear the swarf as much as possible, as the worst thing, especially for MDF, is to re-cut swarf and clog up the paths.

cheers, Ian