Clarkson Autolock vs ER collets

[Steamer1915Participant @steamer1915]

Posted by Steamer1915 on 01/07/2013 18:42:45:

"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."

It would appear that we sing from the same hymn sheet Martin.

Best regards,

Steve.

[John Stevenson 1Participant @johnstevenson1]

Well I am obviously in a minority which for once may work in my favour.

As part of the Grand Down Size [ trade mark ] I have a big tin of chucks and collets of various sizes and taper that are never used now and never will. So later this week I'll sort them out and bung these either on Ebay or the homeworkshop site, probably the homeworkshop site as there are no fees and use the cash to buy a few more ER collets.

 

I have an upcoming project that may appear in the mag and this relies on ER25 collets and could not work with any other system without a vast outlay in workholding.

Edited By John Stevenson on 19/10/2015 12:27:05

[AjohnwParticipant @ajohnw51620]

Posted by Martin Kyte on 19/10/2015 11:59:52:

The way I see it working, the cutting forces tend to rotate the cutter on the centre which draws the COLLET further into the chuck not the CUTTER. If anything Clarksons are easier to undo because only get as tight at they need to.

Also if I could quote what is possibly the most accurate statement on Wikipedia

"The tightening sequence of Autolock collets is widely misunderstood."

;0)

note the old fashioned emoticon

 

It pushed the nose of the collet more firmly into the mating part of the nut so self tightens if the cutter slips at all. They aren't designed to accept a loose spinning tool bit and totally self tighen – just to limit slippage to a very small fraction of a turn of the cutter.

Some of the problems mentioned here are a bit weird. It was one of the most used methods of holding a cutter. Clearly people were mad continuing to use them.

They have one weakness as far as I am concerned. The actual collet is driven as well. They have a pair of ears on them. This means that if too much screw thread is allowed to stick out of the back of the collet the engagement distance is reduced, might even be zero . I have seen collets that have been broken due to that – usually far east ones. I've also seen 3 & 4 morse ones that have been bent to. I'd guess on large machines that have been fitted with an adapter rather than buying the correct chuck.

John

 

Edited By John W1 on 19/10/2015 13:05:41

[Martin KyteParticipant @martinkyte99762]

I don't think you are in the minority John, I agree with a,b,c,d.

I always nip up with the spanner after leaving a gap so I don't quite agree on the loss of offset particularly as I cut for fun not for a living like you so don't push the cut to the limit.

and lastly

Wikipedia for once are right, there is a lot of misunderstanding probably including wikipedia. so I think I agree with you on that too.

I would reiterate the Clarkson system does rely on having good cutters which includes accurate threads and centres properly concentric with the shank.

regards Martin

[VicParticipant @vic]

Tell us more about this "upcoming project" John!

[John McNamaraParticipant @johnmcnamara74883]

Older Clarkson chucks can be quite worn

I have a 2mt version I purchased new and it is accurate. well within about .001"

Also have int40 chucks that came with a machine, they are not accurate the closing nose thread which continues onto the aligning surface that aligns with the chuck body bore is worn, this allows the closing nose to move laterally. In my new chuck the joint is tight.

Also have a second hand but better int40 1'' – 1.25" size collet chuck. this bigger chuck runs out about .002"

Clearly condition is important If there is play between the collet closer and the body alignment will be compromised. There is no taper to bring it back into alignment. The threads help a bit, but not so if they are worn.

My ER40 collet chuck also purchased new is more accurate better than .001" radial at the cutter shank. Being taper to taper wear is compensated.

Regards
John

[Michael GilliganParticipant @michaelgilligan61133]

Cross reference to the other thread … where I posted a couple of explanatory links about Autolock.

MichaelG.

[AjohnwParticipant @ajohnw51620]

I haven't always used them like that – simple reason. I didn't want to cut my fingers on the flutes on the cutter. Most of the ones I have used have been resharpened and they were like razors. If there is enough shank sticking out fine.

John

–

[David Clark 13Participant @davidclark13]

We had imperial and metric collets for Clarksons. The metric has a ring around the upper part outer diameter. The shank sizes of cutters were either imperial or metric but the thread was the same pitch but different diameter.

Edited By David Clark 1 on 19/10/2015 13:53:51

[John Stevenson 1Participant @johnstevenson1]

David is correct, they are all 20 tpi across the imperial and metric ranges.

[AjohnwParticipant @ajohnw51620]

Posted by John Stevenson on 19/10/2015 15:45:44:

David is correct, they are all 20 tpi across the imperial and metric ranges.

Which caused a number of people problems who wanted to make a collet or tool and use a tap or die to do it.

Personally I feel they have had their day now.

 

John

–

Edited By John W1 on 19/10/2015 17:23:25

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John W1 on 19/10/2015 17:22:30:

Posted by John Stevenson on 19/10/2015 15:45:44:

David is correct, they are all 20 tpi across the imperial and metric ranges.

Which caused a number of people problems who wanted to make a collet or tool and use a tap or die to do it.

.

Perhaps they did it specifically to prevent people using taps & dies … I believe all the original threads are ground.

MichaelG.

[John Stevenson 1Participant @johnstevenson1]

Can't see it.

All the imperial sizes are of a standard of some form or other, 1/4" is 1/4 Whit etc

The spurious ons are the metrics with the 20 tpi. Seeing as they wrote the book and made the tooling then 6,10,12 and 16mm x 1.5 would have made more sense.

It's not like the metric cutters could share an imperial collet.

Possibly the truth is like Wadkin who mixed imperial with metric a lot is that they never had a metric lathe.

About right for British investment in engineering at the time.

[Nigel McBurney 1Participant @nigelmcburney1]

In the 1950/60s when industry was going great guns Claksons system was widely used,and the only persons who wanted to cut a thread on special cutter would have been toolmakers who would have not worried about taps and dies,the tool would have been screwcut or in larger poolrooms thread ground after hardening, during my time in the drawing office ,if a special milling cutter was drawn up with Clarkson thread and the work put out to a cutting tool company, the invoice would include a charge of a shilling which went to Clarkson as they held the patent rights.I was also taught that the cutter was screwed into the collet so that the when the cutters centre hole engaged the point ,the cutter was given a further half turn,and then the collet nut only tightened by hand ,the spanner was only used to release the tool, though If I remember correctly after all it was 55 years ago the Clarkson system we used was earlier than the Autolock, the collets had two small ears which engaged in holes in the body of the holder and there was also a thin sleeve surrounding the collet. Since then I have always tightened the auto locks by hand and left a small gap,I now have two Clarksons each for my mills and tend to use them for the larger cutters ,with my double angle system of collets if there is a risk of a cutter drawing forward then the clarksons are used with the smaller cutters, a customer would not be happy if i had an accident with some part of a vintage machine,which is not easily replaced.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 19/10/2015 19:41:58:

Can't see it.

.

Sorry, John … I should have included the winky smiley thing

Didn't really expect the first bit to be taken seriously.

MichaelG.

Edited By Michael Gilligan on 19/10/2015 19:54:04

[Martin KyteParticipant @martinkyte99762]

Regarding the 20 TPI discussion. Maybe I could suggest the reason for having the same TPI accross all the cutters is that it keeps all the movements the same for each cutter size. 1 degree twist on the cutter is going to move the collet by the same amount for the whole set the tapers being the same for all. Certainly make it easier to grind a thread on a cutter.

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Eminently logical, Martin

MichaelG.

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