John Stevenson Blocks Internal collet clamping. #ESI #RELS
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The late John Stevenson developed the ER 32 collet holders and was an overnight success.
His original design still manufactured commercially was based around the ER 32. The problem being when buying commercial blocks the ER 32 locking collar has a larger diameter than the 4 or 6 sided body. this means when clamping the blocks horizontally in a standard mill vice the locking collar touches the jaws before clamping onto the 4 or 6 sides.not really an issue but means using packing pieces between the block flats? and the vise jaws. i wanted to find a solution, the easiest being, make the blocks larger across the flats than the diameter of the locking collar. I also wanted to use my ER 25 collets in a small 2" toolmakers vise. Solution, make a set of blocks with an internal locking ring that pushes the collets down the taper of the body. Set about doing this and instead of 4 flats I developed 8 flats and a traditional 6 flat holder. So the body was a standard lathe op, internal taper and screw-cut with the ELS. The internal locking ring, screw-cut and a 30 degree cone that pushes onto the collet. The block flats were milled and finish cuts were done using the Electronic Step Indexer. Using a ER 32 holder in the indexer spindle and a 16 mm ground bar stock, the internal block was clamped onto this. All worked out well, TIR of the flat variance from c/line within 0.0025". I hope the photos can explain better. -- John |
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Well, that addresses some problems I had finding a set of blocks I liked for my ER32 collet sets. Could you provide a little more detail on the internal locking collars? A photo or two should do it. :) I considered something like that, was looking to see if anyone made them, and not finding any. Not at all sure I could make the blocks for the standard external locking rings. Nice work! Bill in OKC On Saturday, September 7, 2019, 4:45:30 AM CDT, John Lindo <bechetboat@...> wrote: The late John Stevenson developed the ER 32 collet holders and was an overnight success. His original design still manufactured commercially was based around the ER 32. The problem being when buying commercial blocks the ER 32 locking collar has a larger diameter than the 4 or 6 sided body. this means when clamping the blocks horizontally in a standard mill vice the locking collar touches the jaws before clamping onto the 4 or 6 sides.not really an issue but means using packing pieces between the block flats? and the vise jaws. i wanted to find a solution, the easiest being, make the blocks larger across the flats than the diameter of the locking collar. I also wanted to use my ER 25 collets in a small 2" toolmakers vise. Solution, make a set of blocks with an internal locking ring that pushes the collets down the taper of the body. Set about doing this and instead of 4 flats I developed 8 flats and a traditional 6 flat holder. So the body was a standard lathe op, internal taper and screw-cut with the ELS. The internal locking ring, screw-cut and a 30 degree cone that pushes onto the collet. The block flats were milled and finish cuts were done using the Electronic Step Indexer. Using a ER 32 holder in the indexer spindle and a 16 mm ground bar stock, the internal block was clamped onto this. All worked out well, TIR of the flat variance from c/line within 0.0025". I hope the photos can explain better. -- John |
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Bill Will do, but basically the locking ring pushes on the front face chamfer of the collets, this ring has a matching?angle to the collet. 2 wrench flats to turn the locking ring pressure on or off the the collets. Surprisingly it works.? Fresh photos in a couple of days. For your interest (photos) I have attached a 3D printed 20 mm square ER 32 collet for a good friend who had a need?in Australia. He is a serious wood worker and this collet did what he required. Run out/ eccentricity well within metal workers tolerances. You can buy square hole ER collets, special orders but you would need to take a second job to pay for them. I am retired. LOL I don?t have a first?job, well I do, it?s called a hobby, and of course there?s the normal wife honey does. just hate them. interferes with chips flying. John On Sat, 7 Sep 2019 at 11:55, Bill in OKC too via Groups.Io <wmrmeyers=[email protected]> wrote:
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John |
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Exactly. in the photo it was just showing a few turns in. and total length of the ring will also depend on the distance the ring screws in and pushes down onto the front of the collet to clamp the part being gripped. You can make the ring as long as you like, the object being the front threaded part of the ring does not bottom out into the body threaded undercut before you have reached the full clamping potential. To check this, for example use a 5-6 mm collet, keep screwing the ring down onto the collet till it bottoms out, if you cannot then pass a 5 mm dia bar through the collet hole then you are OK , back the ring out 1 turn, the 5 mm bar should pass through the collet. It?s also possible to radially slot the front of the ring so as you can get a cutter almost to the front face of the collet. You would need to "sync" the ring first?by clamping down on a part so you will cut the radial slot vertical. Not done this yet, I have never needed to but an option if required. This alternate J Stevenson block is ideal for ER 16 - thru ER 25 with the smallest collets dia collets gripping less than 1 mm. I am not claiming a "new wheel invented", possibly this method has been tried before, but I do not know, but this internal type suits my needs,? if the forum members or anybody wants to make these different type of different angular blocks, consider 6 flats as standard,? always nice for making 6 sides, and the second block, 8 flats, why a square 4 sides ?, it?s nice to have the option to machine surfaces at 45 degrees to each other as well as 90 degrees. ?John On Sun, 8 Sep 2019 at 16:02, CLevinski <clevinski@...> wrote: On Sat, Sep 7, 2019 at 08:39 AM, John Lindo wrote: --
John |
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As an add on, whilst still fresh in my mind, the internal J S blocks. The internal locking ring diameter can be any size provided your largest collet diameter is smaller. The "cone" taper or pressure point against the collets need not match the collet front angle. provided the angle is less than, IE an acute angle less, more pressure can be applied by the ring by reducing the surface area between the two. Again I matched the locking ring angle to the collet angle, and works OK, collets are meant to grip equally around it?s diameter , nothing else. Cheers. On Sun, 8 Sep 2019 at 17:24, John Lindo via Groups.Io <bechetboat=[email protected]> wrote:
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John Lindo
Bill in OKC too
