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  1. #1
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    Default Clarkson Chuck Collet Problems

    Got a Clarkson NT30 chuck with metric and imperial collets some time ago (auction ?) that I have only recently tried to use.

    The metric collets work fine, a number of various sizes screw in appropriately.
    But, I cannot get any imperial tool to screw into an imperial collet.
    This means the shaft diameter does not slip into the parallel part of the collet, AND, the thread does not screw into a reversed collet.
    The same tools screw easily into a Taiwan made clone.

    Note that this affects all 4 collets in the set.
    Did numerous checks of diameters etc, but no revelations there.

    I initially assumed that is was due to previous operators screwing them down tight on to metric tools.
    But, there is the mystery of the refused thread engagement.

    The set looks absolutely genuine, blue metal box, expanded foam liner, chuck labelling, included spanner etc. Cannot fault it.
    It all looks like a genuine ex-industrial set, same as what I used at TAFE.
    I didn't include a photo because everything looks absolutely normal.

    Any suggestions on what gives ?
    Is there any acceptable resolution ?
    Did the post-machining hardening step shrink them ?

    It is Ok for me to just bin the collets, as I have full sets of ER32 available.

    Don't you just love a mystery,
    John.

  2. #2
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    Default

    Just a WILD guess, but have you checked the thread pitches, it could be different batches have a slightly different thread??
    To grow old is mandatory, growing up is optional.

  3. #3
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    North Yorkshire UK
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    Default

    Hi John,

    It could be that the imperial collets are from a different chuck ! There are/were a couple of Clarkson clones kicking about. Though I would have thought that the shank sizes if not the threads on the tool bits would have been a standard size.

    Anyway I wouldn't throw them out, there must be a reason why they are not to a standard.
    Best Regards:
    Baron J.

  4. #4
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    Default

    I just did some googling and found that both the Thread Pitch on both the metric and imperial cutters for example an End Mill are 20TPI & 55 degree. Here is a couple of links and I'm sure there would be a standards chart somewhere https://www.practicalmachinist.com/v...ne-end-288735/ and https://www.model-engineer.co.uk/for...s.asp?th=35765 . I would be checking both the Cutter Tool thread and the Collet's Thread. It is possible that the unusable Collets have a Burr in them and although they are hard perhaps you can run a thread tap through them to repair them.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  5. #5
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    Default

    Do your Imperial cutters screw into your Metric collet?

  6. #6
    Join Date
    May 2015
    Location
    Richmond
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    183

    Default

    Quote Originally Posted by electrosteam View Post
    Got a Clarkson NT30 chuck with metric and imperial collets some time ago (auction ?) that I have only recently tried to use.

    The metric collets work fine, a number of various sizes screw in appropriately.
    But, I cannot get any imperial tool to screw into an imperial collet.
    This means the shaft diameter does not slip into the parallel part of the collet, AND, the thread does not screw into a reversed collet.
    The same tools screw easily into a Taiwan made clone.

    Note that this affects all 4 collets in the set.
    Did numerous checks of diameters etc, but no revelations there.

    I initially assumed that is was due to previous operators screwing them down tight on to metric tools.
    But, there is the mystery of the refused thread engagement.

    The set looks absolutely genuine, blue metal box, expanded foam liner, chuck labelling, included spanner etc. Cannot fault it.
    It all looks like a genuine ex-industrial set, same as what I used at TAFE.
    I didn't include a photo because everything looks absolutely normal.

    Any suggestions on what gives ?
    Is there any acceptable resolution ?
    Did the post-machining hardening step shrink them ?

    It is Ok for me to just bin the collets, as I have full sets of ER32 available.

    Don't you just love a mystery,
    John.
    John, I have spare 5/8, 1/2, 3/8 collets if you call over. Bring your ones over. Some of the damage to Clarkson collets is caused by spindle "accidently"???? run in reverse which winds the collet back against the centre which can crush the first thread at back of collet. Also a 6mm and 12mm screwed into an Imperial collet (1/4" and 1/2") can close the jaws so the imperial cutters won't go into it. P.s. the ones I have are virus free. 😁. Give me a call.

    D

  7. #7
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    Jul 2010
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    Default

    Quote Originally Posted by steran50 View Post
    I just did some googling and found that both the Thread Pitch on both the metric and imperial cutters for example an End Mill are 20TPI & 55 degree.
    I thought I remembered that also but couldnt find a link to prove it.

    But then I have some Clarkson type collets that have no slits in them so they cant close. There are some strange things out there.

  8. #8
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    Pipeclay makes a good point in his question about do your imperial cutters screw into your metric collets, because they should. I had an experience once in buying a R8 Taper Boring Head off eBay from India that wouldn't accept either of the standard imperial and metric drawbars that I had. I soon worked out that the idiots didn't know about the standards system and that they had put a Metric special pitch in it (12mm from memory) - they got told too. In saying that somethings are getting made to the normal standards that they should be and this could be your problem.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  9. #9
    Join Date
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    Default

    Guys, thanks for the comments.

    Called one of our lunch members, an ex-TAFE teacher, and had a chat about this.
    In addition to operators cranking down onto incorrect tool/collet combinations, he added the problem of operators getting the wrong direction.
    Apparently this can jamb things up.
    He also advised that it was sometimes required to open up the collet segments to enable the tool shaft to enter.

    So, enthused by all the comments, I spent a happy couple of hours systematically attacking the problem with complete success:

    1. Brand new tools can have quite a different feel.
    New Dormer tools had 0.01 difference in the shank, and 0.1 difference in the thread.

    2. Errant collets can be opened up with a screwdriver struck with a hammer.
    I am sure a press operation would be preferable.

    3. Minute imperfections in the thread can prevent entry of metric or imperial tools into the Clarkson collets.
    Wire brushing and fine files can relieve this.
    The same tools enter the Taiwan collets without problems.
    It appears the Clarkson collets are much tighter than Taiwan.

    4. Collets larger than 6 mm and 1/4" do not have any thread entry chamfer on the collet end.
    A tiny burr here can often prevent a tool being tested in the thread.
    A bit of perseverance and teasing fixes this.

    5. Minute bits of dirt can jamb the thread.
    All one can do is to try and clean and persevere.

    6. Tried all the combinations.
    The sizes are: 16, 15.875 (5/8), 12.7 (1/2), 12, 10, 9.525 (3/8), 6.35 (1/4), 6.
    The close sizes are: 16 & 5/8, 12.7 & 12, 10 & 3/8, 1/4 & 6.
    In each case the smaller enters the larger, but not the reverse.
    Some fits are loose, but would be noticed by a careful operator.
    However, the 5/8 fit to 16 is very close, and could easily be missed.

    7. Some tools appear to screw in correctly, but they do not go all the way, without the end engaging the chuck tit.
    One could easily load like this and the tool subsequently be forced further in by the cutting action.
    If the tool moves in, the tip datum is lost.
    If the tool stays put, tool support is lost and the collet could tilt in the chuck.

    This factor is possibly the origin of the TAFE instruction to load with the nut relieved about 1/4 turn and to screw the tool in all the way.
    Loosening of the nut is contrary to both the Clarkson and Taiwan instructions.
    I wonder if the Taiwan answer to this problem is to make everything that little bit looser.

    In future I will follow the TAFE instruction, then repeat per Clarkson.
    A good precaution would be to first screw the tool into the collet at the bench, and confirm that the tool end protrudes a small distance.

    8. Found a couple of new Sutton 1" screwed thread tools.
    Clarkson must have a larger chuck in the range.

    The mystery is solved,
    John

  10. #10
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    Default Clarkson chucks.

    Hello Electrosteam.
    Yes Clarkson did have a large chuck for 1" and 1 1/4" shank cutters. Also an adapter chuck for running small cutters in the large chuck. I remember having trouble trying to use Osborn collets in a Clarkson chuck. The Osborn collets only had a flange on 1 side but looked like they should go. No use at all.
    Regards
    BC

  11. #11
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    Default

    Quote Originally Posted by steamloco1954 View Post
    Hello Electrosteam.
    Yes Clarkson did have a large chuck for 1" and 1 1/4" shank cutters. Also an adapter chuck for running small cutters in the large chuck. I remember having trouble trying to use Osborn collets in a Clarkson chuck. The Osborn collets only had a flange on 1 side but looked like they should go. No use at all.
    Regards
    BC
    I was going to mention an adapter I have, but I couldn't find a ref to it, though I remember someone selling them just a few years ago.
    I had another look and found this picture. The adapter I have is the bottom one, it can be handy at times. I'm guessing the one you are talking about is the second from the bottom? I've not seen one of those before that I recall.
    https://www.model-engineer.co.uk/sit...968/594667.jpg

    https://www.model-engineer.co.uk/for....asp?th=105995

  12. #12
    Join Date
    Nov 2019
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    97

    Default Clarkson chucks

    Another bleat.
    In the first pic both lower items look like FC3 cutter holders.
    The second pic it could be the adaptor but it is hard to make out. The adaptor was a small chuck that screwed into the larger body. Too many years ago and my Clarkson books have gone to the bin worse luck.
    Regards
    BC
    I still have some FC3 cutters I use in an ER11 chuck.

  13. #13
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    Default

    Good to hear that you got it sorted. I meant to say 'aren't getting made to normal standards' in my post.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  14. #14
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    Richmond
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    Default

    Quote Originally Posted by electrosteam View Post
    Guys, thanks for the comments.

    Called one of our lunch members, an ex-TAFE teacher, and had a chat about this.

    This factor is possibly the origin of the TAFE instruction to load with the nut relieved about 1/4 turn and to screw the tool in all the way.
    Loosening of the nut is contrary to both the Clarkson and Taiwan instructions.
    I wonder if the Taiwan answer to this problem is to make everything that little bit looser.

    In future I will follow the TAFE instruction, then repeat per Clarkson.
    A good precaution would be to first screw the tool into the collet at the bench, and confirm that the tool end protrudes a small distance.


    The mystery is solved,
    John
    Nice to chat John. Will be nice to get back to our lunches after this lock down thing!!

    Don't get too tied up with that 1/4 turn thing. A quarter turn with a spanner on a 6mm/1/4" cutter is enough to crack the threaded end rendering the cutter useless for further use in an Autolock Chuck. Yes I've heard about that method by some at TAFE but don't agree and would rather stick with what Mr Clarkson recommends for mounting the cutters.

    D

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