Suddenly breaking bits like crazy

[gordonh]

I have broken four bits today - and I never break bits! I'm cutting hard maple with a 1/4" Onsrud DC (57-910). Cut depth is 0.1" at 16K RPM and 0.5in/s. Chip load calculates to be about 1/5 of what is in the Onsrud catalog. I've been using the 57-910 at the higher feed rates for over a year. I am getting chips (small ones), not dust. The bit is cool to the touch (after it breaks). The bit breaks almost immediately - within 30 seconds of starting to cut. I replaced the collet with a new one. No change. Ran a different cutting file. No change. All the bits snap right at the collet. There is a solid inch of bit in the collet. The 1/4in bits have always been extremely loud, but the sound is different on all of them now - may actually be a little quieter. I always blow out collets with air at every tool change. Still using the original collet nut, but it looks OK to me.

I am running one of the first PRSalpha BT's with a nice spindle. The bot is lightly used as a prototype machine.

This is starting to spook me. Something has changed, but for the life of me, can't think of what it is. Any suggestions? I keep this up and we should all buy Onsrud stock. BTW - I ordered a couple replacement bits from Whiteside and Centurion Tools, but I have I feeling I'll break those too.

I appreciate any ideas anyone may have.

[Gary Campbell]

Gordon...
Make sure that the .5 ips speed is showing on the console speed panel, type in a 20" move in the x and then the y direction. Time the move to make sure you are actualy moving at that speed.

Unless you have defective bits, or an eccentric condition in your collet/nut, there is no reasonable explanation other than the speed is off. (but I have been wrong before)
Gary

[ron_moorehead]

Make sure your spindle is up to full speed. The only time I have broken a bit was the spindle was running to slow and check your ramp settings in the control software.

[coach]

Gordon, From Onsrud. Hope it helps.


TROUBLE SHOOTING TOOL BREAKAGE PROBLEMS
In the unlikely event that you encounter a breakage problem, here are some
things that may help you identify the problem. The tool is the weakest part of the routing
system. When it breaks, it is the first thing that is suspect, which not always true. 80%
of all router breakage can be attributed to three factors; improper tool selection, poorly
maintained or worn equipment, and or poor fixturing.
Poorly maintained equipment includes, collets, collet nuts, spindle bearings,
spindles, spindle housings, slides and head control items.
The first thing that should be done is to change the batch of the tool if you have a
different batch number on hand. Onsrud Cutter batch numbers every tool we make. If
your tooling doesn’t have this information on it, you have no way of isolating a bad
batch of tools. If the problem goes away then the tool is suspect. Return a sample of
these, preferably a broken one, and a new one from that batch via your distributor. If
the problem still exists after changing the batch, then something else is suspect.
Examine the shank of the tools for poor collet contact or “collet burn”. This will
show as brownish, burned marks on HSS and Carbide tipped tools. The same will
appear to be shiny marks on Solid Carbide tools.
The weakest part of the tool is where the primary clearance angle stops. If a tool
is a smaller diameter cutting edge than the shank diameter, i.e., 5/16” on a 1/2” shank,
and the shank is broken, then the collet is definitely the main suspect. Try a tool with a
straight through shank I.E. 3/8” on a 3/8” shank.
The following items require that the machine be off and the operating items
shutdown for safety reasons. Please be careful of all machinery.
A quick check of the slides, bearings and head mountings for play or for
looseness can be made by grabbing the spindle by hand and pushing and pulling it.
This will show most unacceptable conditions. The full procedure for spindle runout is in
the back of the Onsrud Cutter catalog. This will reduce the variables in trouble shooting
the problems.

[knight_toolworks]

your rpms though are pretty high. I cut solid wood at 1ips at 1/2" depth of cut with a 1/4" bit in tropical hardwoods and I cut at 8k rpms

[srwtlc]

Ramp speeds too high and it's taking off too abruptly? Bearings starting to go bad and causing excessive vibration when the cutter gets in the wood? Try a deeper cut and load the bit higher up on the CEL. Is that 0.1 section of the bit dull?

I used to use the up and down of that series bit and I know that it doesn't seem right, but I always found the "Extreme Heavy Duty" bits to be noisy and brittle. I had better results with the 57-200 and 52-200 "Wood Rout" series. I now use Centurion instead.

[gordonh]

Hello Everyone,

I want to thank everyone for all the suggestions and sharing their experience. Here is what I've done so far.

Went back and checked the bots alignment and found a little play in the Y carriage, tighten it up. Checked alignment on the spindle and added a thin shim it improve it a little (it was a little). I should be doing this every six months or so.. so shame on me.

Ran another onsurd 57-910 and broke it.

Thanks to your advice, I also ordered some whiteside (RD2100) bits and also some onsrud 57-200's. The whiteside bits came in today and they worked just fine. I think the cut is a little cleaner, but I get a little chatter in places that was not there before. I also replaced the nut as it was the last part that could have any effect. (I checked runout with the nut and it was non-existent.)

So here is the score - I broke five 57-910 with about 30 seconds of cut time each on the same file and the same wood. The whiteside cut as you would expect.

My current theory (I've had so many!) is that I have created a harmonic in the bit - a strange combination of material, speed, depth and light load that really makes the 57-910 vibrate. The RD2100 being a different design doesn't share the frequency.

If there is a moral to the story, maybe it is to have a few different brands of any important bit and don't be afraid to experiment to see which work best in a particular situation.

Many thanks to all of you for taking the time to help me out, you really did.

Best regards,

Gordon