Thread: Clarkson Autolock and Vertex Posi-Lock Chucks - Installing the Cutter

Originally Posted by Anorak Bob

My thinking is that if a cutter rotates (tightens) under load then the position of the cutter alters height wise. Probably such an insignificant amount that it doesn't matter but the idea of an 1 1/2" end mill finger tightened has always made me a bit nervous.

As I see it.
1.This it what is meant to tighten the collet. The nut has nothing to do with it(other than supplying the female taper, but the chuck and the nut are "one piece" if that makes sense?).
2.As the cutter rotates*. The cutter can only move up. If it was srewed in against the centre I cant see it moving "far", its the collet being forced down that tighens things.

Although
3. As I said before it doesnt seem to matter much. Maybe big cutters pushed hard would show up some issues but I've had almost nothing to do with production milling(well I did mill a lot of PVC pipe but that hardly counts )

Stuart

*I'm assuming it always rotates if the chuck was tighten as per instructions, not as I was instructed and how I did it for a long time until I purchased my own mill.


Am I repeating myself................

You have to forget about the cutter moving upwards. Because the cutter has a helix, the forces involved want to pull the cutter down, not up. This is of course why collets relying on friction can result in the cutter coming down unless really tight under heavy load. The screwed collets if correctly applied as per manufactures instructions will never result in a cutter "walking down" with the consequent ruination of the work. The PosiLock is a direct copy of the Osborne Titanic chuck and uses the same type of collets. I have an Osborne with a 40 Int arbor on one of my mills plus an ER 40 and a Clarkson, both with 40 arbors. For my other mill there is a PosiLock with 30Int arbor, a Clarkson, a Dormer, a Qualcut, and a ER40. When confronted with heavy cuts/big cutters, screwed shank tooling is the way to go but unfortunately these days straight shanked carbide cutters and ER chucks have taken over industrially due to the proliferation of very high speed -light cut machining on CNC's for which friction held cutters are successful. I have yet to see a screwed shank carbide cutter though no doubt they could be made somewhere albeit at great expense. the other type of non pull down cutter is the Weldon type where a grub screw locks the shank but this type requires a chuck for every size of shank used.

When you analyse the logic in both the Osborne and Posilock instructions the nut is tightened first then the cutter is screwed by hand (I use a rag to prevent cuts!) till the centre snugs up at the same time pulling the collet down to seat on the nut taper which is broad enough to accommodate both the chuck taper and the collet taper. Because the collet nose taper is tight in the chuck nut and the cutter is held by the thread in the collet it simply cannot pull down when the cutting forces come into play. I have had a few "pull downs" with the ER holders but none whatsoever with the screwed shank holders.