B&S No. 20M Toolholder - What is it?
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    Question B&S No. 20M Toolholder - What is it?

    I recently purchased a lot of toolholders on ebay for my small turret lathe. One of the toolholders is a Brown & Sharpe No. 20M. I have not been able to find any information about it, and don't know what it does.

    When the middle plate is moved, the block on the end pivots back and forth. Does anyone know what it's for, or have any ideas?







    Scott

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    That's a "bump recess" tool.

    http://cgi.ebay.com/BROWN-SHARPE-20M...ayphotohosting

    It is used to machine an internal chamfer, annular groove or the like into the ID of a turned part at any place along its length. If, for example, you were making a threaded standoff, you would want an ID chamfer on the back end of the standoff before you ran a tap into the drilled hole. Without the ID chamfer, you would get a nasty burr when parting through the threads and would need to do a secondary chamfering operation.


    A modified boring bar is held in the center hole of the tool holder which is mounted to the turret. It slides into the drilled hole of the part as the turret moves forward.

    The rod shown in the picture above hits a stop very close to the end of the turret's forward travel (either on the machine headstock, cross slide or vertical slide) rigged by the setup man.

    As the turret continues forward, this causes the grooving tool to then go in a sideways direction, machining the internal groove or chamfer in the part - stopping when the turret ceases its forward movement. As the turret retracts backwards, the boring bar in the tool swings back into the drilled hole before being retracted from the part - hence the reason for the die spring .

    These bump recess tools should be set completely into the turret so not much pressure needs to be exerted by the turret clamps to hold them in position. If the turret clamps are tightened too much, the piston within the tool holder shaft can be put in a bind, and the tool itself will not retract when the turret backs out of the work.

    That is a very handy toolholder if you have a turret lathe or screw machine.

    Incidentally, for you B&S guys out there, there is a "secret" page in the MSC catalog which is not anywhere in their index and which has solid carbide, left handed, mini boring bars with a great variety of shaft diameters, shank diameters and depths of cut.

    They are made by circle tool I think and are very reasonably priced. They have such a variety that, for even very small parts, you can easily turn offset collets in a 4 jaw chuck to fit a bump recess tool holder to eliminate virtually all grinding of the tool shaft. All you have to do is modify the cutting end of the boring bar to whatever you're after.

    Cheers,
    Jim
    Last edited by clampman; 09-09-2008 at 03:35 PM. Reason: clarifying some confusing wording

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    Jim,

    Thank you for the excellent explanation. My search for 20m (without the a) didn't show that listing.

    I'm not sure I fully understand the movement of the tool, but I'll take a look at the toolholder tonight and see if I can understand it then.

    Thanks!

    Scott

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    Scott,

    I am stuck at home at the moment, but I have a little camera that takes short videos. When I get to the shop, I'll take a short video of how it works - since I will be running a job on a B&S which is using one.

    The reason I mentioned the left hand boring bars is because B&S's involved in tapping operations generally do the tapping in slow forward and the other machining operations in fast reverse. It may also be of benefit for turret lathes depending on the setup.

    Cheers,
    Jim

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    Jim,

    If you're able to shoot video of it, that would be great! I imagine it's one of those things that easy to understand when you see it, but hard to describe in words.

    Scott

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    Jim,

    I completely reread your first reply, and see that you edited the part I was confused about. I was trying to visualize two stops. So, I think I understand it now. However, I would still love to see some video of it in action if you have the chance.

    Thanks again!

    Scott

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    Scott,

    I hope you have a fast connection, because I couldn't edit this camera with my regular software. For some reason, when I cut the resolution down to less than half, instead of the picture getting smaller, the software cut off half the picture - the part with the turret in it.
    So the file size is 14.5 MB. It took me 8 minutes to download with DSL connection at 28KB/Sec.

    Well, at least it's clear.

    http://www.miterclamp.com/videos/recesstool768.wmv




    The one on the left was done by the bump tool.



    Cheers,
    Jim

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    Thumbs up

    Jim,

    Thank you very much for going to the trouble to show how it works. It's quite clear now.

    I really enjoyed seeing the machine run. For awhile, I entertained thoughts of buying a small screw machine, but finally realized that it probably didn't make sense for a home shop guy like myself. So, I'll try to be happy with my little turret lathe.

    There doesn't seem to be a whole lot of info out there about these types of tools, so information and videos from people who know how to use them is invaluable. Thanks again!

    Scott

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    Scott,

    You're very welcome. It's a rare occassion when I can help someone on this forum because I don't know very much myself, and it's really good to be able to give something back for a change. I was lucky that I met two very capable B&S men who sold me the machines and gave me a crash course on how to set them up and run them.

    Both were patient enough to put up with an endless barrage of questions from me which continued all the way out of my shop and into the parking lot as they were heading home.

    I used to make those standoffs on a little Weiler turret lathe which was set up for 5C collets. I made an air stock feeder for it, but it took a light touch on the collet closer while shoving the turret stop towards the headstock to maintain consistent lengths, and I wound up running them all myself - thousands of them. I finally got my own screw machines to save my left wrist and to practice JAIT manufacturing (Just almost in time) to cut down on inventory costs.

    So thank you, Scott, as well.

    Cheers,
    Jim


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