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Unimat 3 top slide (part #150190) damage

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  • Unimat 3 top slide (part #150190) damage

    Hello:

    My recently acquired ca. 1980 Unimat 3 (1st./2nd./3rd. hand?) came with quite a few accesories, among them a very hard to find milling table.

    One of the accesories was the top slide attachment (part #150190) which these days commands prices of over US$100.
    I must confess, would not have purchased had it been offered separately, much less for that silly money.
    It looks flimsy and frail from wherever you look at it, but as it was part of the relatively convenient deal, I now own it.

    Unfortunately, it came with a couple of issues.

    The first one I detected was with the gib (not the original but an odd shaped stainless steel one) and stripped threads in the adjusting screw holes.
    I have been able to solve threads issue, albeit not without much grief and am in the process of making a new gib.

    The second issue seems to be a bit of a sticky wicket.

    As a picture is worth 1,000 words, here it is:

    Click image for larger version

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    What you are seeing are photos of the mounting hole for the top slide's body, seen from above and below.

    No need of a loupe to realise that the well that receives the M5 allen head bolt that screws into the 'T' nut in the carrier's slot to secure the slide in the desired position is cracked, no idea how this got this way.

    I had only put the slide in place once or twice to see how it would fit/work and as I found the problems and the adjustment screws, put it aside till I could fix it properly.

    Could this possibly be my own doing or is it part of this U3's history?

    After all, at serial #80070243 it has just turned 42 - ie: 80 => 1980 07 => July
    And just like health issues for us, stress/strain in metals is a fact of life.
    But I digress ...

    If I set the slide in its place on the carrier (without the bolt/'T' nut), I find that the deformation you can see in the photos does not allow it to turn freely or sit flat against the surface of the carrier, so this problem needs to be addressed, lest I put it in use and get this damn thingy flown into my face in the midst of a job.

    Evaluation:

    The top slide has a thickness of 8.00 mm:

    Click image for larger version

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    The recess in the carrier ie: where the top slide should sit and turn ~ 40° CW or ACW, is a cylinder 2.80 mm x 12.00 mm:

    Click image for larger version

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    But the recess in the top slide's aluminium body ie: where the M5 bolt sits measures 7.50/8.00 x 11.00 mm.
    The 8.00 mm is where it has cracked open.

    It would seem that there is very little material (between the recess in the carrier and the recess in the top slide) to take the stress of the bolt securing the top slide in position.
    But I have to get it fixed somehow , otherwise my U3 attachment will only serve as an expensive (US$80.00/US$125) paperweight.

    I have made a rough sketch to try to grasp the problem:

    Click image for larger version

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    Sorry for the freehand, don't have a drawing board nowdays and never cared for CAD.

    As you can see, the weak spot of the top slide is a tiny cylinder measuring ID 11.0 mm x OD 12.0 mm x 1.0 mm.
    This 1.0 mm x 1.0 mm cylindrical section of aluminium takes all loads applied to the slide.

    The protruding section is 12.00 mm x 2.0 mm and goes into the 12.0 mm x 2.8 mm recess seen the photo above.
    So when the mounting bolt is tightened, the bolt's head exerts downwards pressure on the surface at the bottom of the mounting hole.

    The 0.8 mm gap (2.8 mm - 2.0 mm) allows for the aluminium to deform and crack and that is how/why things got as they are.

    To make things even worse yet, the width of the narrow part of the dovetail is only 14.0 mm, which means that the ID of the hole for the mounting bolt is only 1.0 mm away from the dovetail at that point, so the mounting hole cannot be drilled any larger to add more metal.

    It has been suggested to me that the solution is to fit a plug (aluminium/zamak/brass) with loctite to replace the damaged section and then drill as needed.

    Unfortunately, the slide is too long for the U3's available swing (need at least ~55 mm swing to mount it on the 4-jaw) so I won't be able to bore out the hole or make a recess from below to register the plug accurately on the slide.

    Not having a mill to do it, I'd have to carefully drill on the press and fit a pre-drilled plug with a permanent loctite type anaerobic.

    The plug would have to pre-drilled to use a smaller/custom mounting bolt ie: not the standard U3 M5 allen head bolt.
    Maybe flat head? This would allow the plug to be just a wee bit heftier, brass being my choice of metal to use.

    I confess I'm rather annoyed as I really did not expect to find this type of issues in the U3.
    Problems due to wear and tear in a 42 year old mini-lathe are unavoidable and to be expected.
    Headstock/tailstock spindles and ways have been toroughly cleaned and oiled, headstock bearings have been replaced, ways, nooks and crannys have been thoroughly cleaned, etc.

    But all the problems I am encountering are (in my opinion) caused by bad design/manufacturing practises on behalf of Emco.
    Makes me wonder what else I'll find further on.

    I'd appreciate some advise with respect to solving this (very annoying) problem.

    Thanks in advance.

    Best regards,

    G.

  • #2
    Yea you need a mill to make that ring thicker and bore the Al. plate for press fit. Or even better make the "washer" a big part and screw in in the plate with the appropriate hole for the screw. Any near by helpful buddys with a mill? :-)
    ...lew...

    Comment


    • #3
      Hello:

      Originally posted by Lew Hartswick View Post
      ... need a mill to make that ring thicker ...
      ... buddys with a mill?
      Unfortunately not.
      The milling table is awaiting a new motor and tooling (collets, bits, vice, etc.)
      There's a bit of cash to be put in there.
      Eventually.

      Took a while and it was not without a few hitches but it's finally done.
      But as the proof is in the pudding, I'll know when the loctite is cured and I get to use it the top slide on the U3.
      I still have to make a new gib for it.

      The bad light make the photos look awfull and still needs some cleaning up:

      Click image for larger version

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      I drilled out most of the 11mm hole to 12mm but left ~1.0 mm at the top.
      I was able to do that by making a jig to chuck the piece on the tailstock and work with the headstock chuck to drill.

      Unfortunately the 11.0 hole in the original piece turned out to be slightly conical.

      So to get a proper register I had to leave a 16mm diameter piece of material between the 8.0 and 11.0 mm parts of the jig.
      ie: the jig is/was a piece of 16 mm aluminium stock, one end turned to 8.0mm for the drill chuck and the other end turned to 11.0 mm to glue into the slide's existing hole.

      Glued it into the hole on the slide and was then able to chuck it on the tailstock and drill it out from below using the headstock chuck.

      Click image for larger version

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      Trial an error allowed me to progressively get a suitable fit between the brass and the aluminium.
      When that was done, I cleaned up, dowsed it with loctite and sent it in.

      The brass protudes into the carrier base just 0.1 mm less than the holes' depth, just enough to tighten it in place.
      And the base where the bolt sits is now ~ 4.5 mm of hard brass instead of 3.0 mm of aluminium.

      I expect that there is enough surface contact and interference between the brass and the aluminium to keep it all in place with the loctite.
      We'll see how that goes.

      Thanks for your input.

      Best,

      G.

      Comment

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