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Thread: Mini pallet faux pas

  1. #1
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    Default Mini pallet faux pas

    I started building myself an 8in x 8in combination mini-pallet/sine plate, inspired by those I've seen on the web.

    Things were going well but I got some slippage, while drilling, due to inadequate work holding (see below). I drilled through the 3/4in plate and 2-3/4in round stock simultaneously, with successively larger drills, but I should have devised a way to clamp the plate into the crotch in the round stock better, and pinned each hole as I went, but alas. Lesson learned.

    When doing a trial clamp of the plate to the round stock (final fasteners will be countersunk 1/2-13 flat head allen screws) it is apparent that a 0.020" gap has opened up at one end.

    Should I just live with it and try to recover the shambles of my life, or fill the seam with epoxy and a segment of feeler gauge for "rigidity improvement" and to keep swarf and oil out, or can it be somehow repaired?





    Last edited by jmarkwolf; 03-11-2018 at 06:03 PM.

  2. #2
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    You could elongate the holes just enough to tighten the fit on the end and then put the countersink in the proper place. The contact between the countersink and screw head will hold alignment just fine.

  3. #3
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    I would elongate the holes enough to let the plate seat on the roll, recut the countersinks in the proper place.

    Then clamp it in place and put a 1/4" dowel pin at each end to hold location. Make the holes .249 (.001 press fit) in the plate and .251 (.001 slip fit) in the roll.
    Last edited by Toolguy; 03-11-2018 at 06:20 PM.

  4. #4
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    Quote Originally Posted by jmarkwolf View Post
    "a 0.020" gap has opened up at one end."
    Does this mean that the back edge you machined is not parallel with the axis of the cylinder? If so then I would take a skim cut to make it parallel and slot the holes so the plate can sit tight against a good reference surface.

  5. #5
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    Reassemble it with JB weld as a filler. If the dado in the rod is accurately done, you can true up the sides of the plate later.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  6. #6
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    I like your concept here. After living with my homebuilt CNC that has 144 tapped 5/16-18 holes on 40mm centers to match aluminum extrusions, I think I would tap a bunch of holes in that plate as well.

  7. #7
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    I believe that it's bad practice to rely on screws for position holding anyway. At least unless special precision shank screws are used to act as both positioning pins and retention screws all at the same time. So I think a good option for fixing this would be to elongate or enlarge the holes to allow the gap to be closed. Then with the plate held in the intended position drill and ream for proper press fit precision pins or tapered pins to lock the position. With the pins in place then use a bevel end mill to mill the countersink holes for the screw heads so the slotting does not interfere with the proper placement of the countersinking.

  8. #8
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    I'd slot the holes a bit, bring the plate tight to the back edge, and drill and ream for 1/4" dowels out near the ends. I'd also countersink the holes afterwards for flat head screws to provide a completely flat surface. Or there might be enough room to counter bore for the bolts you've got.

    Just my personal opinion, JB weld has a lot of uses, but precision tooling and fixtures just ain't one of them.

  9. #9
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    If I were to add pins to perform the actual locating function I think I'd go for cap screws with counter bores instead of flat head screws. That way there's risk of pulling from the countersinking not being in perfect alignment.

    I'd leave the heads of the cap screws just a skiff proud so that they get skimmed off when the face of the plate is milled. Not so much that it compromises the ability to remove the screws. Just so the bolts add some support area.

  10. #10
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    Update from the OP:

    Thanks for the input everybody.

    I double checked the fit of the plate against the round stock, with the bolts removed, and it's quite good at about 0.003" or less across the entire length. Knocking off the bottom corner of the plate might improve it further.

    I believe the root cause of the problem is that the plate moved as I was drilling, due to inadequate work holding. I actually saw it move. I tightened the work holding at the time but no joy.

    I like the idea of correcting the fit by pinning with new dowel pins, elongating the main holes ever so slightly, and carefully locating the counter sinks. The trick is to clamp the shooting match so there is no relative movement between the plate and round stock while all doing this
    Last edited by jmarkwolf; 03-12-2018 at 08:26 PM.

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