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  1. #1
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    Default Tool post twists !

    No matter how tight I tun down the locking screw , my tool post rotates very slightly when turning between centers! The post is an "A2Z" qr post with an "A2Z" tool holder using a carbide (removable)tool and the work is a steel 3/4 in. dia. bicycle pedal crank. I have tried a short extension on the 3/16 in. locking screw Allen key with no success. The lathe is an EMCO 8 in..X 18 in.

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    Make yourself a solid toolpost mount. After seeing Robin Renzetti's implementation on his HLV-H I did the same with my Emco Super 11. Made a huge difference in rigidity as well as tool repeatability. Been planning the same on my 10ee. Go check out his video on YouTube.

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    On my BXA I had the same problem until i bought a dedicated 16" long box wrench. I really have to pull on it, hard, for hard cuts. I bet over 50 foot pounds or more. The hold down bolt is 16mm so about 5/8.
    3/16 is 7 foot pounds to tighten it. I would say 10-15 foot pounds to prevent rotation. You could even try a clean piece of typing paper sandwiched under the base.
    Bill D

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    Have you checked the bottom of the toolpost is flat without burrs/crud? Is the top of the cross-slide flat also without burrs? Have you tried the old trick of paper between the toolpost and cross slide?

    If all that fails... I bought a Dickson toolpost years ago for my Colchester Chipmaster that had an extra hole at the edge of the block. Don’t know if the factory did that or prev owner, but was useful to spot a hole into my cross slide for a pin. No rotation :-)

    Lucky7

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    Not sure what kind of force your cut is applying, but on a big American lathe at my last shop, the Aloris (DA) regularly rotated on me during heavy roughing cuts (~ ⅜"-½" per side, .030" to .040" feed). I finally got fed up and made a locking plate to go under the toolpost. It was keyed to the slot in the top of the compound and had dowel pins that located in the bottom of the toolpost. That did the trick. If we needed to rotate the toolpost to a weird angle would just remove the plate. Sounds like that is what Bug is talking about too.

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    I don't get it. I have a CXA that I tighten with a normal 1-1/4" wrench (because that's what fits the nut) and it is dead solid with almost no effort. Sometimes...I forget to tighten it much at all and it still does OK.

    I think your T-nut/stud or whatever you have is not being allowed to clamp properly. Maybe the stud is bottoming on the carriage before it can tighten.

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    Quote Originally Posted by Dead Eye View Post
    No matter how tight I tun down the locking screw , my tool post rotates very slightly when turning between centers! The post is an "A2Z" qr post with an "A2Z" tool holder using a carbide (removable)tool and the work is a steel 3/4 in. dia. bicycle pedal crank. I have tried a short extension on the 3/16 in. locking screw Allen key with no success. The lathe is an EMCO 8 in..X 18 in.
    Emco Compact 8 Lathe
    Looks like no "tee" slot.

    As stated above, check that your not bottoming out, running out of threads, etc.

    I would replace the socket head capscrew with a threaded rod, putting a nut on top.

    YouTube

    shows some odd looking plastic wingnut on top....


    EDIT: BTW what are the numbers on the cut your attempting ?

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    Is that one of those hard anodized QC tool posts that A2Z makes?

    If so your best bet is to strip the tool post down, mount the body in a 4-jaw chuck and turn a shallow rebate near the center hole. That will transfer the clamping force to the outer parts where it can more easily resist torque. I had the exact same problem with one of those and rebating the center (maybe 3x the diameter of the central hole) cured it.

    I think the hard anodizing makes them slippery.

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    Here is a link to that video:

    YouTube

    It is a great video about a great mount. He has a very good understanding of what is going on when a tool post is mounted.



    Quote Originally Posted by BugRobotics View Post
    Make yourself a solid toolpost mount. After seeing Robin Renzetti's implementation on his HLV-H I did the same with my Emco Super 11. Made a huge difference in rigidity as well as tool repeatability. Been planning the same on my 10ee. Go check out his video on YouTube.

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    My shop made tool post is not hardened. There is no problem with rotation, even with heavy cuts. Perhaps hardened tool posts are the problem.



    But, for added rigidity, I may make a mount similar to the one in Robin's video to eliminate the compound. That sounds like a capital idea. Capital!

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    Try this first as it is quick and easy. Cut a piece of sandpaper to fit the tool post. Grit doesn't matter. Install between the tool post and the compound.
    Many mini- type lathe instructions mention this when the tool post moves.
    I did this for a youngster who was given a small used lathe and had the same problem. Worked out well for him.

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    Thanks for the tip. R.R.'s creation looks like just what I need but is beyond my abilities. Where do you get a 6 inch cube of cast iron? I will try to work something out but would like to see your version.

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    Thanks Mike. Sounds like an excellent idea. Try the easy stuff first !

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    Quote Originally Posted by Dead Eye View Post
    Thanks for the tip. R.R.'s creation looks like just what I need but is beyond my abilities. Where do you get a 6 inch cube of cast iron? I will try to work something out but would like to see your version.
    Hi, cast iron blanks can be purchased from McMaster Carr. Here is the one I made for my Emco Super 11.

    I couldn't bring myself to modify my Aloris toolpost so I bored the dowel pin hole into a Phase II toolpost. I wouldn't have that hesitation the 2nd time round.
    Attached Thumbnails Attached Thumbnails 2018-02-11-10.39.19.jpg   2018-02-11-10.46.03.jpg  

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    Quote Originally Posted by Dead Eye View Post
    Thanks for the tip. R.R.'s creation looks like just what I need but is beyond my abilities. Where do you get a 6 inch cube of cast iron? I will try to work something out but would like to see your version.
    Your tiny lathe doesn't need a 6" cube. Nor does it need to be cast iron. Even an aluminum block would be FAR stiffer than your compound because it has no moving parts. Expand your search to include "any hunk of metal remotely the right size" Or, stop being such a total cheap skate and BUY a hunk of metal.

    The set screws and pins from the sides, fancy sculpting, etc... are nice but largely unnecessary. You will gain the most from simply not having the moving parts, gibs etc... simply replacing the compound with a flat bar of the same height will drastically stiffen your tool.

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    Quote Originally Posted by digger doug View Post
    Emco Compact 8 Lathe
    Looks like no "tee" slot.

    As stated above, check that your not bottoming out, running out of threads, etc.

    I would replace the socket head capscrew with a threaded rod, putting a nut on top.
    B7 or better, not the cheapy zinc plated shit from the 5 and dime.

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    Quote Originally Posted by Cole2534 View Post
    B7 or better, not the cheapy zinc plated shit from the 5 and dime.
    Naw, got to use TiAn coated "Sooper Billet" all thread.

    No polishing to that turd anyhow.

    What's nice is, when all is said & done with, the Op can simply tuck that LSO under his arm, and carry it to the skip....

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    Quote Originally Posted by eKretz View Post
    Not sure what kind of force your cut is applying, but on a big American lathe at my last shop, the Aloris (DA) regularly rotated on me during heavy roughing cuts (~ ⅜"-½" per side, .030" to .040" feed). I finally got fed up and made a locking plate to go under the toolpost. It was keyed to the slot in the top of the compound and had dowel pins that located in the bottom of the toolpost. That did the trick. If we needed to rotate the toolpost to a weird angle would just remove the plate. Sounds like that is what Bug is talking about too.

    Yep if you spring for a real tool post it comes with at least one free dowel hole in bottom

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    A2Z tool posts are micro-lathe home hobby size toolposts.
    Yyyyaaaawwwwnnnn!!!!

    -Doozer

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    My Dickson QCTP was moving while trying to do some knurling on my Super 11.

    Made a holder from a hunk of 12L14 and pinned the old 4 way to the top, it bolts right to the cross slide in place of the top slide.

    It moves no more...





    Last edited by Terry Keeley; 01-08-2020 at 06:54 PM.

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