Bit shifted in collet

[SBaircraft]

I was several hours into a 3D cutting job when my machine suddenly started cutting deeper. I stopped the machine and determined that the bit had slipped down in the collet. It was cutting a very gentle finishing tool path in MDF at the time.

This has happened several times recently and destroyed a bit of work. It has happened with different sized collets and bits; all in nearly new condition. I took extra care to clean the collets and spindle. I made sure the bit extended fully into the collet and I used aggressive torque to secure it. What might I be missing?

[supertigre]

You seem to have covered most of the usual suspects but over-tightening a collet can bend / distort it and cause it to fail.

[Ger21]

If you bottom the bit into the collet, that can prevent it from being tightened securely. If it bottoms out, always pull it back out a little before tightening.

[adrianm]

You shouldn't use anything other than the correct torque to do it up. Excessive torque can damage the collet.

I use collet nuts with bearings in them which gives a much better feel for tightening.

[barrowj]

Adrian,

I like the idea of the collet nuts with bearings, please let me know where you get them.

[adrianm]

I'm in the UK so I get mine from here - http://www.arceurotrade.co.uk/Catalogue/Collets/ER-Collet-Nuts-Wrenches-and-Spanners

I use the type B ones.

[barrowj]

Thanks Adrian, I'll check it out.

[tlempicke]

I have had a number of suppliers send out MM sized bits when I ordered inch sized. They will commonly send out a 3 MM bit for 1/8 inch or 6 MM for 1/4. The difference is that the bit is slightly smaller.
Measure before you chuck it up! Also get MM sized Collet so that when you come across this you can use the proper collet.

[Burkhardt]

I'm in the UK so I get mine from here - http://www.arceurotrade.co.uk/Catalogue/Collets/ER-Collet-Nuts-Wrenches-and-Spanners

I use the type B ones.
Great! Thanks for the link. As it happens I just was looking to buy new collets and nuts to replace the cheap ones I got with the Chinese spindle. I found this company ArcEuroTrade ships to the US and the ball bearing nuts are actually very cheap. I ordered four ER20 Type A and it costs $50 including shipping.

[gundog]

If you bottom the bit into the collet, that can prevent it from being tightened securely. If it bottoms out, always pull it back out a little before tightening.

This is exactly right make sure you are not bottoming out the tool bit in the collet. As the collet is tighten it pulls the bit up inside the spindle if the bit it is bottomed out it can't completely tighten properly because to do so the bit would need to slip inside the collet as it is tightened.

[Bob Eustace]

Thanks Adrian. Got two Er25's and a spare spanner coming to Oz for AU$64.00. Prices are cheaper once you register. Getting a spare wrench because ours went "missing" for 2 days. Stopped the shop!

[Bob Eustace]

Forgot to mention what I think could be the main advantage of these nuts. That is, it should help those with arthritic hands. You have had the gong when you can no longer stick a cutter in your Shopbot! Anyone notice that over on the Camheads forum they are developing a retro fit carousel?