First broken bit!

[coryatjohn]

Ok, lots of people have posted a thread like this over the years. I didn't see the same issue I had so I'm asking for advice...

I was at the end of cutting a 1" thick piece of MDF (about 10' total cut length) done in 6 passes. The last pass was about 1/10" and it was on the last leg, about 12" to go and the bit broke. I touched the bit moments after it broke and it was cool to the touch. The chips looked good and it sounded like it was cutting normally before it broke. I'm ashamed to say that I finished the cut with (of all things) a hand saw.



I used the default settings for speed and RPM.

I've read that bits are broken in three's so I'm asking for advice before I break the other two. I am unfamiliar with MDF. Did I do something fundamentally wrong? Should I adjust RPM, speed or cutting depth when using MDF?

Thanks.

[steve_g]

Good morning John...
Can you tell me the IPS and the RPM . Did you calculate the chipload when you created the tool path?
SG

[MogulTx]

And tell us if it snapped inside the collet or AT the collet. It is broken very high up. It should be seated farther than that into the collet. If it broke inside the collet, two potential problems are: it may be the wrong size collet or the collet may be bad. ( Is it an ER25 collet on a spindle or a PC Router ?)

MGM

[jhedlund58]

Did that break inside collet? Perhaps not in collet far enuff... and i broke one early on using default settings was told i was going too slow. two things i do... one- i cut half depth of bit not the recommended full ... so .25 bit i go .125 per pass... second... i trust the chip load calculator and my tool db settings which have been tailored to my machine. I have a standard and spindle... many have more powerfull machines etc. my approach may not be correct. Works for me

hope this helps

[coryatjohn]

The bit broke right at the collet.

RPM: 14,000
Feed rate: 6 IPS

Spindle: HSD 4hp.
Collet: ER 25 1/4" (from SB)
Bit: Onsrud 52-901 (from SB)

Chip load calculator? Haven't gotten that far... Maybe I need some edukaton.

Should I just toss this in the trash or can I use it as a short bit? I've done that with the hand router without any trouble.

[steve_g]

Well that's what I thought... much to fast IPS back off to around 2-3.

Chip load calculator is found under tools in SB3

SG

[bleeth]

You should be able to cut through MDF much deeper per pass with that bit. Although Steve is right when asking for more info (feed and rotation speeds), assuming that the break happened below the collet, I would say you didn't have enough of the bit in the collet.
You should always have the bit inserted the full depth of the collet, but never so deep that the bottom of the collet is over any cutting area of the bit.

Assuming your machine is an Alpha feed and speed are not unrealistic, although I would spin somewhat slower. You can also cut deeper. That bit will handle a 3/8 plus pass in MDF. If you have a standard, you are going too fast at 6ips.

[steve_g]

http://www.onsrud.com/files/pdf/2012%20LMT%20Onsrud%20Production%20Cutting%20Tools %20MDF.pdf

Will give you the manufactures poop sheet for your particular bit... the recommendations for that bit in MDF are .006-.008 per tooth at one diameter deep, reduce by 25% for 2XD and 50% for 3XD deep. I routinely cut at 2 X the bit diameter without issues.

SG

[jhedlund58]

I would be affraid to re-use it.

[MogulTx]

Yes. This bit is trash. And some would tell you that you should replace a collet after a bit break. I don't buy into that. If it CRASHED the bit into something, then maybe I would-

but in this case, just replace the bit, modify your speeds and rock on.