CLARKSON AUTOLOCK CHUCKS

A while back I bought a TOS universal mill, and with it came loads of spindle tooling, all 40 INT taper, including 2 large Clarkson Autolock , and 1 large Osborn Titanic collet chucks. all with 1" and 1 1/4" collets,

The Osborn chuck body runs true, also any cutter I put in runs true,

But the 2 Clarkson chucks both run out of true by about 2 thou on the chuck body, and any cutters I put in run out even more , the longer the cutter the worse it is,

These chucks are a " chunky " lump of steel, but could they have been strained at some point during use ?

There is a centre point inside each chuck body, I have removed one to check for any damage, the point looks "used" but not too bad,

I have a new ish Vertex ER40 collet chuck which runs "spot on " in the TOS mill, so the machine and spindle are OK.

Has anyone got any ideas , or should I scrap the Clarksons and move on ?

Richard.

Hello Richard, How are you tightening the Autolock? There is a common mis-conception that there must be a small gap between the nose piece and the body. This is incorrect.

Steve.

Steve, can you please elaborate on this. I have 2 Autolocks and I am labouring under this misconception,I allways leave a small gap,believing that if the nut 'bottoms' the collet wont close.Everything runs true though..John

Andrew Johnston kindly posted Clarkson's assembly instructions, on this earlier thread.

MichaelG.

The critical point is to understand that if the chuck is assembled tight with a collet but without a tool in it then it will not be tight enough to close down say on a bar of the appropriate size. It takes the thread on the tool interacting with the collet and the centre point to push the collet up into the nose.
This means the nose piece can bed right down on the flange to register truely. The centre point must be the right length/condition to push the right amount.

I've now tightened the chuck as Clarksons suggest and the cutters now run straighter than they did, but the shanks are still running 2 thou out on a dial gauge, I've tried a 1" collet also 3/4" and 32mm, all about the same, am I being too fussy ?

Richard.

Clarkson is old hat nowadays, for a start many cutters are made with the shank size the same as cutting size like 5mm

No collets exist for this size in Clarkson and you will always be paying a premium for the threaded shank, more so if using carbide.

Industry has moved onto ER's you never see Clarksons used in production these days.

One reason is the way they tighten. Yes I know this is going agaist how Clarkson say but they never had the machinery then we have today.

Put a cutter in like Clarson says, put it on a jig to measure the tool length offset and enter this into the tool table.

Now run the chuck and the fact the cutter tightens it's self up then makes any measurements in the tool table useless.

The ONLY way on a CNC to keep the correct length off set is the tighten the cutter into the collet, then tighten the bnut so you have a small gap showing.

Totally against what they say but the only practical way to do this.

John,

I'm struggling to see how the cutter moves out of position when it tightens itself. Isn't this the whole point of the Autolock chuck? i.e. It can't go any further in than the centre point will let it?

Steve.

I gave away my clarkson autolock, it came with my mill and I had never used it.

As the other JohnS says, metric and clarkson are difficult, and the ER collet holder is what is on my mill 99% of the time.

I know, not very helpful...

The across the pond JohnS.

For info:

Here is how they explained the locking action, in 1942

MichaelG.

I've been playing with these chucks this afternoon, and have come to the conclusion that the tightening procedure is quite inportant to maintain any sort of accuracy,

I now screw the nut up by hand , until it touches the main chuck body, then screw the cutter in until it contacts the centre, then gently tighten with the spanner,

They seem to run quite nicely using this method, perhaps Clarksons knew what they were talking about,

I always used to leave the nut uncsrewed about 1/4 turn and then tighten, but when you think about it all you are doing is squeezing the hardened cutter even harder against the centre, doing it as Clarksons suggest is less damaging to the centre,

Richard.

Hello Richard

This was my point exactly. I was taught the "incorrect way" in the mid 70's at an engineering training centre where all the local companies sent their first year apprentices. Despite breaking out the centre of a 1/4" dia end mill, I carried on in this manner until there was an exchange of letters in the Model Engineer magazine in the 90's (I think) and only then did the penny drop. I have discussed this point with many people and the general concensus is that most of us were taught incorrectly. At the risk of incurring John's wrath, I would still say that if the cutter was inserted correctly i.e. hard up against the centre, then it shouldn't be able to move "a few thou" when it is used for a heavy cut. All that should happen when the cutter rotates under cutting torque, is that the collet will be pushed down into the taper within the nose piece and grip the cutter more tightly, therefore preventing further rotation. This is surely the ideal situation - the cutter will only be (self) tightened as much as it needs to be. Despite being in the Autolock wilderness for too many years, I now firmly believe the Clarkson people had it right all the time.

Steve.

I was taught the Clarkson recommended method. It now becomes clear how the small 1/4" 6mm cutters get their centre ends broken, following the Clarkson procedure this has never happened to me.

Mike

For anyone who cares ...

Here is the Patent

MichaelG.

Steve,

I fully agree.

Richard.

Edited By Steamer1915 on 19/10/2015 12:16:05

Edited By Steamer1915 on 19/10/2015 12:24:19