Burning bit, need advice

[team08]

So I finally finished my custom CAD/CAM software and now need some help cutting! I am bascially pocketing a snowboard core out of a blank of wood 1cm thick. I cut anywhere from 0-8mm deep. I need to clear as MUCH wood as possible, this cut took 30 min.! I am using my MDF bit that came with the bot and tried running it from 13000-21000 RPM on the PC. I ran it at 2IPS roughly for the whole time, overlapping by half the bit width. I am doing a climb cut since I dont want to blow out the laminates (its vertially laminated finger joints). Any suggestions?

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[patricktoomey]

Greg, it looks like your RPM's are WAY high. For a bit that size in soft wood I would usually try to go for a chipload around .010 which works out to 6,000 RPM at 2 inches per second. I would try 3 inches per second at 9,000 RPM as a starting point. I run a spindle which typically should not be run below 9,000 RPM so sometimes I have to kick up my feedrate to compensate. What is happening is that your bit is producing wood chips so fine that they are too small to effectively carry away all the heat being generated. To worsen the effect, the extra RPM's are generating way more heat. By slowing the bitspeed down or dramatically increasing the feedrate, the chips will be big enough to effectively carry the heat away from the bit and you and the bit will be happier.

[team08]

Okay, I will give it a shot. It does sound like at the lowest speeds that the bit is really bogging down and might stall though. Guess I have to try though.

[patricktoomey]

Greg, I forgot that you're using a router, that does tend to complicate matters since it won't hold its RPM's, what about leaving your RPM's up but increasing your feedrates? Are you running a PRT or an Alpha machine?

[richards]

Before I switched from a router to a spindle, I mostly used 1-flute cutters. Since the chipload is proportional to the number of flutes, a 1-flute cutter can be spun at twice the RPM of a 2-flute cutter or the feed speed can be 1/2 the rate of a 2-flute cutter. I found the lowest two speeds on the PC-7518 to be useless for the kind of work that I do. The second to the highest was what I used most of the time. I adjusted the feed speed to get the desired chipload and then adjusted the cut depth to keep the PC-7518 from bogging down. Although the system was limited compared to using a spindle, it worked better than I expected it to.

[team08]

I am running a PRT (and would LOVE to but a spindle but not for another year or more). Mike, any sources for 1-flute cutters 1-inch+ in diameter? Should I possibly cut the diameter in half and increase speed x2 if there are no bits?

[richards]

Greg,
I can't help you with large cutters. Except for a 1-1/4-inch Freud cutter that I use to level the spoil board, the largest cutters that I use are 1/2-inch, and then only rarely. My prefered cutter is 3/8-inch. Eric Lamoray suggested that size when I first got my Alpha. His suggestion has proven to be exactly the perfect choice for what I cut.

Chipload is basically independent of the diameter of the cutter. That was a hard concept for me to understand, but it seems to be true. At one time, Gerald Dorington posted a graphic that showed the cutter 'peeling' the chips off of the material, much like we would peel an apple. At that point, the concept of how a cutter works became clear to me.

As far as sources go, contact your Onsrud supplier and get their recommendations. Better yet, do a search on 'Eric Lamoray' and see what he has suggested. His recommendations have always worked for me.

[David Iannone]

Greg,
I use Southern Saw for all my router bits. They are located in Maryland, and ship anywhere. 410-327-0050. Ask for Craig. He is very knowledgable about bits and even sugests feeds and speeds to start at. I just tell him the material I'm cutting and diameter bit I want, he will know the best one to use. They have probalbly anything you need. In the past they have even taken custom ogee bits, taken the bearing off, and ground the top makeing it plungeable if you ramp into the material.

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