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Thread: Clarkson autolock - I like it
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19th Jul 2019, 10:42 AM #16Most Valued Member
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Having had a 3/4" cutter grow about 1/4" longer, I'm in the "prefer Clarkson when I can camp". I still use ER but I keep a much closer eye on them.
There are two types of people in this world, those that have had a ER holder slip and.... yeah yeah I know, in a perfect world they wouldn't slip.
Hi Bobs,
Can I ask the leading question of "what is the draw bar thread?"?
Thats how it is on all the ones I've seen(granted that about 5). Its the cutting forces that tightens things(its right there in your instructions). Wouldn't that be where the "auto" in autolock comes from?
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19th Jul 2019, 05:54 PM #17
Hi Guys,
Its a long time since I had anything to do with a Clarkson Autolock chuck ! From memory the cutter is screwed into the collet and the collet inserted into the body, then the cutter is screwed in until it hits the point inside, after which the nut is tightened. This locks the cutter against the threads on it and the back of the chuck. If you can unscrew the cutter then its not fitted properly.Best Regards:
Baron J.
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19th Jul 2019, 07:57 PM #18.
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A Problem.
I feel a bit like I'm white anting Greq's thread but this is Autolock usage related....
After Lex's observation regarding the incorrect position of the nut on my small chuck, I conducted some tests using the small and intermediate chucks on the 1/2 horsepowered Hercus and the intemediate chuck on the 2 horsed 13. I installed the cutter in each chuck as per Clarkson's instruction i.e. with the nut screwed down onto the chuck face after installing the collet before screwing the cutter into the collet.
I marked the position of the cutter in relation to the chuck before cutting into some 1045 using the little Hercus. The cutter in the small chuck rotated a distance of roughly 3mm. The 1 1/16" cutter in the intermediate rotated no more than about 1.5mm.
Here is the intermediate with the marks at about 7 o'clock cutting roughly 6 x 6 mm.
IMG_20190719_105915779.jpg IMG_20190719_110714783.jpg
The same 1" collet and cutter mounted in the 30 taper chuck with the same depth and width of cut but a faster feed given the 13's additional horsepower.
IMG_20190719_131643496.jpg IMG_20190719_131848851.jpg
The cutter rotated about 12mm. Clarkson use a 20TPI thread on all their screw shanked cutters so that rotation equates to approximately 0.0075" or 0.1905mm of axial movement.
So here is my problem. If the cutter is touched off the workpiece to set a zero point for a cut of a certain depth, the rotation accompanying the automatic tightening will mean that touched off zero point is not accurate.
How do other Autolock users deal with this?
I previously used the same method of tightening as John Baron.
BT
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19th Jul 2019, 09:16 PM #19Golden Member
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Hey Bob, no troubles. I'm learning here and am happy for the input.
Greg.
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19th Jul 2019, 10:03 PM #20Most Valued Member
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20th Jul 2019, 06:09 AM #21
Hi Guys,
Since the collet cannot rotate, any movement of the cutter will cause it to climb up the threads and rise.
I no longer have access to the original Clarkson Autolock manuals so I am unable to post scans of them, unless maybe they are on line.Best Regards:
Baron J.
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20th Jul 2019, 10:41 AM #22Golden Member
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Hi Baron,
Bob has posted the instructions for the "Modern" Autolock (see post 15).
The original Autolock used a 2 piece collet system but still relied on the cutter rotating slightly to lock positively.
Clarkson Autolock.jpg
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20th Jul 2019, 10:44 AM #23Most Valued Member
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Yes, the collet can't rotate, its either "pined" to the nut or "pined" to the chuck body, but it is free to move axially until the the length of the cutter and collect is longer than the space available.
As Karl says, once the cutter is screwed back against the center its not going to move(well not far lol) so the collet is forced down into the nut instead.
I'm happy to report that both ways in fact work. But there are a couple of possible problems using the "leave a gap" technique.
If you are to heavy handed with tightening I believe* you can break the center on the back of the smaller cutters.
*I haven't done it but I have seen cutters with the center broken and assume this is how it happened as I assume if the cutting forces where high enough to break it the cutter would have broken before hand, but of course I could be wrong).
The nut/ body on the Clarkson has(from memory) a ground taper and face, surely you aren't going to do that if you are meant to "leave a gape". Leaving said gape means the nut(which remember is holding the collet and therefore cutting forces) is supported only on the thread(at the back of the nut). Not the most rigid setup. No gape, the taper and flat faces meet(at the front of the nut), Would have to be far more rigid.
IT many depend on exactly which chuck you are using. One of my other chucks doesn't have the taper. Though still ground surfaces. Sadly no instructions either. Maybe they thought Clarkson was going over the top?
Hi Bob, How do you feel about the repeat of your tests using the "leave a gape" technique?
I hypothesis that with the leave a gape technique the chuck is still auto tightening(at least with the larger cutters). Surely if you are doing all the work* you would have tighten the Clarkson with the same force as you use to tighten an ER chuck of about the same size? Given that the Clarksons come with a super short spanner that would be tricky.
*subject to the Clarkson having a finer thread but a steeper taper........
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20th Jul 2019, 11:30 AM #24.
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Thanks for the replies Karl, John, Lex and Stu. And Greg for being okay with me posting this stuff in your thread.
Stu, I take your point about the ground finish on both the nut and body. My larger chucks are so precisely finished that assembly can sometimes be difficult if the nut is slightly cocked in the body's bore. They are beautifully made bits of gear.
You mentioned drawbar threads. My small chucks are both threaded 1/2" BSW. The much heavier intermediates have, strangely, 3/8" threads, BSW in the 30 taper and UNC in the 3 Morse arbored chuck.
IMG_20190719_130347261.jpg
I will undertake more testing this morning.
Bob.
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25th Jul 2019, 06:03 PM #25.
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Obviously foot dragging has occured but here is the result of installing the cutter incorrectly. The cutter was screwed snugly by hand up against the centre and then the nut was tightened with the stumpy Clarkson spanner. Not centre fracturing tight but what I felt was tight enough.
IMG_20190725_141830690.jpg IMG_20190725_140704763.jpg
The same cutter taking a 6 x 10mm cut in some Hercus EN6 (1030) keysteel.
IMG_20190725_141504379.jpg
The cutter has not rotated.
IMG_20190725_141744672.jpg
BT
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25th Jul 2019, 11:14 PM #26Golden Member
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A late reply to your original question Greg - I still use them and I do like them although I probably use ER style chucks more now that they have become more affordable.
The chuck that I use at home is one that I made close to 30 years ago, to suit my German Vertical Milling Machine, see pictures below. It is hardened and ground but only the working surfaces of the Chuck and Nut are ground.
I always run this type of chuck with the collet nut in contact with the chuck body for maximum rigidity and concenticity.
Autolock.JPGAutolock 2.JPGAutolock Collet Nut.JPG
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