Coventry EASY-CHANGE chuck.

[MAX THE MILLER]

What's the correct way to fit a cutter to the holders used which this chuck? My holders have a fixed (ie not adjustable) internal centre and I'm using threaded cutters and collets. (The Triac manual refers to adjustable centres and makes no mention of screwed collets or screwed cutters).

What I've been doing is to fit the collet in the holder, hand tighten the nut on the holder and unscrew it half a turn. I then screw the cutter into the collet until it contacts the centre and "nip up" the nut. However I've succeeded in splitting the 8mm shank of a cutter. Should I be using the "Clarkson" method of fully tightening the nut, screwing in the cutter and then letting the machine do the rest?

Is the lock screw meant to contact the collet, prevent the collet rotating by sitting in the cutaway portion of the collet, or fit the flat of the cutter?

Thanks.

[John Panter]

Ive recently aquired my triac and had trouble with my easychange chucks. The only way I've been able to have the collar screw down correctly onto the 'C' type collets is to grind a 1/8" relief on the high portion of the collet back. I then screw in the grub screw fully, and rest the relief onto the screw. The collar then tightens to the collet correctly and centres and grips the cutter.
I was finding that with the collet in as far as possible, the collet was not being fully clamped up before the collar thread bottomed out. As a result the cutter ran wobbly.Therefore I had to raise the collet toward the collar slightly. I suspect that these chucks may have originally had a spacer at the base.
The previous owner had never used the easychanges and always used a single three jaw drill chuck!!

[MAX THE MILLER]

Interesting to receive a reply after so long. I thought perhaps I was the only person having a problem with these chucks.

However I thought the 'C' type collets were an externally threaded draw in type. My chuck uses Posi-lock collets and I expect yours uses something similar. I can see that resting the collet on the radial grubscrew would enable the nut to be tightened, but wouldn't it also prevent the female centre in the end of the cutter contacting the male centre inside the tool holder?

These chucks would work fine if the centre inside the tool holder could be adjusted axially as described in the manual. However the centres in my holders are fixed.

[angel-tech]

It maybe that you have an osbourne holder not a clarkson. They work the same but the osbourne holder has a different shape back to the collet.

https://www.ebay.co.uk/itm/NEW-POZI-LOCK ... 19d244c8c4

[angel-tech]

there you go, the same answer.

[MAX THE MILLER]

Coventry, Clarkson, Osbourne. This is getting confusing.

The CHUCK definitely has EASY-CHANGE written on it, leading me to think it's a Coventry EASY-CHANGE chuck as described in the Triac manual.

However the HOLDERS appear to be Osbourne types with posi-lock collets.

I have an Osbourne chuck somewhere so I'll see if the collets fit that.

[angel-tech]

Coventry is the manufacturer/designer of the taper lock holder/spindle adapter, and clarkson/osbourne is the design of the collet. The common clarkson type holders that come with the Denford mills are osbourne holders that take the posilock collets, and have a coventry taper on the back to fit the easychange spindle adapter.

[MAX THE MILLER]

Thanks for the clarification. Yes, Coventry EASY-CHANGE chuck with Osbourne cutter holders and posi-lock collets. (The Triac Manual shows taper collets which I believe are Coventry types).

The posi-lock collets are identical to those in my Osbourne Titanic chuck, but the centre in the Osbourne chuck is longer than that in the Osbourne holders. This means the cutter doesn't have to be screwed in so far in order to prevent the screw collar bottoming.

My problems with cutter shafts splitting must be down to over tightening.

With the increasing use of threadless cutters without a female centre, I guess I'll have to switch to a taper collet system?