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Thread: leadscrew

  1. #21
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    Jan 2003
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    Chilliwack, B.C.
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    Here's a crude sketch of the cable path. The dark lines represent the steel tubing, the rest should be evident.


  2. #22
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    Mar 2010
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    switzerland
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    what did you pour the nut with?

  3. #23
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    Jan 2003
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    The nuts are poured with table top epoxy. I cleaned up a section of lead screw, then polished it up with something- don't recall what, but I think it was carnuba wax. I made a fixture to hold the lead screw aligned where I wanted it, then I used silly putty to seal the threads in the ends of the mold pieces. It was not trivial to get a good enough seal everywhere so epoxy wouldn't leak all over the place.

    When it was cured, I found it difficult to remove the lead screw from the nut, but by clamping the lead screw in the vise and using a crescent wrench on the aluminum case of the nut, it came loose. I ended up making a tap out of a section of lead screw and running that through several times until I could get a fairly easy threading action going on.

    I didn't want to compromise the strength of the epoxy, so I didn't include any anti-friction additives in it. That is something I'll experiment with in the future.

    I chose table top epoxy because it has some slight permanent flexibility to it. Some of the other formulations cure very hard and crisp, and some early experiments showed them to be not really suitable.

    Long after I made these nuts, I experimented with that low melting temperature plastic- don't recall the name of it- but it actually does form quite well and has lower friction. I would think it would wear less as well, but as I suggested earlier, these nuts haven't worn either. They do have some use on them, but not much, so I don't really know how well they'll last.

    Have been busy doing other things (not the cordless drill project ) so haven't had any time on this project until today. I hope to make some headway on getting the best Y axis alignment I can.

  4. #24
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    Jan 2003
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    Here's a quick drawing of the method I'm using to find square on my layout table. The circles represent a pair of sockets that I'm temporarily using as locating points. They are bolted upright onto the table. I'm using one square, but my drawing shows two to show how I am positioning it to see if I can get both sockets to touch the square for each position of the square. The main guide rail has been selected to be about as straight as it gets. It's damn close according to my best straightedges, so consider it to be perfectly straight. I'm setting the square up on spacers so there's no angle errors to creep in while testing.



    Both sockets have been checked and are the same diameter within half a thou. With the bottom one secure in place, and the square firmly against the guide rail and that socket, I set the other socket to touch against the square as well. Checking with the square from the other side, the square doesn't touch the upper socket. I measured the gap, then cut that dimension in half and moved the socket over by that amount. The end result is that gap a is equal to gap b.

    What this tells me is that my square is not square. I expected that- they seldom are that good. I did have to sand the short edge so it would sit perfectly flat against the guide and therefore give a repeatable performance against the sockets, but you could see the curve on that edge. I could (and will) sand it more to make it more accurate, but I believe that what I've done has found the point where the vertical axis is exactly 90 degrees to the horizontal axis. The sockets will remain in place as points to align the main vertical guide rail to. I plan to epoxy that guide rail to the slider on the horizontal guide rail, then carefully lift it off to transfer bolt holes and place the bolts. When that's done and re-checked, I'll finish assembling the vertical axis guide assembly. At that point, the cable attachment can be made to the upper end of that assembly.

    Anybody see any flaws or pitfalls in this?
    Last edited by darryl; 05-04-2012 at 04:08 AM.

  5. #25
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    Apr 2009
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    Ashburton, near Christchurch New Zealand
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    Darryl, I was shown long ago that hammering a metal square near the inside of the corner opened the square, hammering near the outer closes the square.

  6. #26
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    Artful, I'm aware of that square-adjusting idea. It does work- I've done that several times. I don't really want to be hammering on this one since there's a lot of engraved info on it.

    What this procedure is giving me, besides a true square layout for the machine, is a way of measuring the square as I trim it by sanding the short edge. When the edge contacts my adjustment points (the sockets) such that the gaps are gone when checked with the square on either side of them, then the square is also true.

    The bed on my belt sander is cast iron and there's no graphite slipper pad between the belt and the bed. If the belt is good I should be able to keep the edge of the square very straight as I creep up on the 90 degree goal. I will of course be checking it on the surface plate as I go.

    At this point I wish my s/p was larger so I could have checked the entire length of the main guide rail in one shot. No matter- I think I'm within my design criteria for this project. Now I just have to see how I could go about making the footprint smaller when I'm not using it- lean it against some other junk leaning against some other junk leaning against a wall, I suppose

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