Losing router bit from collet

[SteveS]

I am having an issue with the router bit screwing into the material during a cut, basically coming out of the collet quite a bit and into the spoil board. This has happened twice, first time it went out far enough to touch a metal screw below the surface damaging the bit and I thought it was the setup, so bought another bit. Same thing happened. Machine is set to stop z travel prior to the spoil board with the initial tool length.

Cutting is in two passes, 10 mm first pass and 13 mm the second pass. Problem has been happening on the second step. Wood is sassafrass which isn't that hard.

Router motor is a Kress FM6990 running at 26,000 rpm. Bit is an Onsrud 40-111 HSS, 3" long, 1/4" shank and cutting diameter with 1" cutting length. Collet is four segment with one slot the entire length, tapered with snap ring to secure in the nut.

No evidence of cracks or spinning on the collet. No witness marks on the router bit of it spinning and and all of the information on the shank is still very visible. There are nicks in both flutes for the first 1/4" from the end where it looks like they touched something harder than it. Bit did not contact anything metal during the cut. No material found in the collet slots. Collet does look polished on the inside diameter, but I never looked at it before to know if that is different. Collet doesn't have any circular spinning pattern.

Second time that the same thing happened, I made sure it was very tight.

I had been using all whiteside up to this point, but woodcraft was out of the particular size and I bought the onsrud. This has only happened with the onsrud, but haven't cut this particular design with a whiteside yet.

I don't have a backup 1/4" collet and Kress collets aren't available in the US that I can find. Other posts say it is not ER compatible.

So the question is; What can make a bit walk out of the collet into the material?

Loosness doesn't seem right as the screwing into the material shouldn't happen in that case.

Do I need carbide tip cutter?

Steve.

[ger21]

Either it's not tight enough, or, the bit was bottomed out when you tightened it, which usually prohibits it from being tightened correctly. Never seen a Kress, so don't have much else to offer.

[SteveS]

Gerry - double checked and the bit cannot bottom and be at the length I was using it. That made some sense to me.

I took the motor out and really did some cleaning on the collet and the contact points of the motor. There were some almost film marks at the contact points where the collet mates with the motor. Took 600 grit wet/dry and polished the surfaces. Won't run the same configuration for a couple days.

I'm guessing that I was getting too aggresive on speed and depth of feed coupled with the non pristine surfaces. The bit must have decided to thread into the material being cut and not held securely in the collet. This was an upcut bit. My tightening was false due to the surfaces being contaminated.

Will post back if it goes away during the same run later in the week.

Steve.

[jweinhold]

Steve,

Check your Collets, there are some collets out there that say they can be used for imperial or metric, don't do it, if your using metric use a metric collet. Also are you using a spiral tool? An upward spiral is more likely to pull out of the collet.

Jeff

[SteveS]

Jeff - I know what you are saying about metric to imperial, but I have been using imperial in the metric collet for couple years.

As I pointed out, after the issue, I did some maintenance and found a film and residue on the collet to bit mating surfaces.

Your comment on upward spiral is probably right on. With the less than perfect clamping the bit screwed itself out of the collet and into the material. I had been using downward spiral up to then without an issue.

Steve.

[Big-tex]

If it has happened with only one bit, check bit diameters with caliper.
There is slim chance you got bad batch bit.
Onsrud has nice tooling but I have came across some issues w/ them, not same as you.

[Boots]

I might add that HSS will heat up very quickly @26,000 rpm and heat destroys tooling. I would and do only use Carbide. It can take the heat and is more ridgid than HSS.

[Stewey]

I had 12mm chinese ebay tungsten-tipped cutters walk right out of a 12mm collet, just the same way you mentioned. It was an accident getting the 12mm cutters.

I have a stack of high quality 1/2" ones, and bought an 1/2" collet, and they've been terrific. Every time I use the chinese cutters in the correct collet, it's as good as grease for holding capacity.

Lesson well learned- don't buy cheap woodwork router bits on ebay.

I have bought great cnc endmills on ebay though!

[zool]

there are brass brushes made to clean collets .. wonderful devices

also, use old scotch bright pad on shank of bits with a bit of alcohol or brake cleaner fluid [get it at NAPA .. cleans and leaves no residual .. smells horrid, use with lots of ventilation!!!]

[yosemitesam]

I use oertli hsk tool holders and collets, they double lock and the tools never come out.OERTLI