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Lapping stainless steel all-thread

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  • Lapping stainless steel all-thread

    Here's an image of the M6x1 stainless steel all-thread rod I'm going to use for a leadscrew in a small project. I'll be making the nut using the technique here. I'm really only concerned with making the threads smooth, not making them more accurate. Plan A is to use a cast polyurethane nut, 60mm long, and valve lapping compound, 120 and 280 grit. The length of the leadscrew is 350mm. I'm not sure if the polyurethane can handle the heat created by the friction from lapping. Has anyone tried this? Is there a better way to do this (inexpensively)?



    Note: Magnification is 7X. The image was created from 156 individual images by focus stacking with Zerene Stacker.

  • #2
    When single pointing threads, I have always used the cratex sticks. I keep four grades on the shelf above the lathe.



    They improve smoothness and appearance significantly.
    Byron Boucher
    Burnet, TX

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    • #3
      Quick and dirty way of trying it out would be to tap an m6 hole in a small scrap of aluminum, or brass. Cut a slit with a bandsaw, or hacksaw inline with the hole to split it. Now just throw some lapping compound in there, and close up the slit with a vice, of c clamp to apply some pressure. Clamp the block in a vice, and run the rod in and out while chucked in a drill. add some tension every pass or so. Should work to clean up the threads.

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      • #4
        Byron, for the unwashed among us, what kind of grit would be sensible for the cratex sticks?

        Elf, that is an impressive picture indeed.....

        Igor

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        • #5
          I have in the past done that, as Dan said, but, I cut one side of a nut, held with vise grip
          and the threaded rod chucked up in lathe using valve grinding compound I simply ran
          the lathe for.&reverse worked well. Then to the buffer. Thats if you have a lathe that
          will reverse. I should say I started with the nut just held in vise grip then a little more
          pressure on the grip until a nice surface. Or a drill.

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          • #6
            Elf,You say it's allthread - is this a length that you bought / acquired? It looks to be far rougher than I'd expect - run that through your fingers, and you'd get them shredded. Would it be worth starting out with a better piece of allthread?Ian
            All of the gear, no idea...

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            • #7
              Damn nice pic, you must have quite the rig to be able to take 150~ photos from the same position. (And to make it pratical to do)
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                x's 2 for what Dan said,you could even use blocks of hardwood or fiberglass for the slip laps.
                I just need one more tool,just one!

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                • #9
                  Igor, I have 120,240,320,400. The 120 and 240 are the most useful.
                  Byron Boucher
                  Burnet, TX

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                  • #10
                    that's horrible looking stuff....I don't know that I'd accept it....but maybe it was free or you've had it forever

                    anyway, to one of your questions, the amount of heat generating by lapping is a result of speed; if you want less heat so you don't melt the plastic lap run it more slowly. imo you won't be able spin it too quickly if its any length anyway as you have to worry about whip

                    the worst areas seem the edges of the crests. I'd try first with a stone held at an angle then finer and finer emery cloth wrapped around wedges of hardwood. protect the bed
                    .

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                    • #11
                      The stainless all-thread was from a local hardware store specializing in screws. It's main redeeming qualities were cheap and available now It's going into a prototype, so if the concept works well, I'll be able to easily replace it with a higher quality screw. Metric trapezoidal screws seem to be way over priced compared to acme screws.

                      Lapping with cast polyurethane seems to be working. I ended up using a drill to turn the screw as it was too long to fit in my lathe and it also had a slower speed. I made several passes with some 240 grit sandpaper attached to a wood block before using the lap with 120 grit. It feels quite a bit smoother now. Here's a shot of it after 4 passes back and forth.



                      I'm making a new lapping nut for the 280 grit valve lapping compound which, unfortunately, will take 36 hours to cure

                      For reference, here's a shot of 1/4-20 plated all-thread:


                      The camera is an Olympus e330 with about 150,000 shutter activations. Just about any current DSLR should be capable of taking these images. Of course having a macro spherical panorama head will help Here's a shot of the setup:

                      http://img.photobucket.com/albums/v6.../AutoFS_02.jpg

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                      • #12
                        Faster than waiting for the PU to cure would be to just use one or more brass nuts and lapping compound. Even better would be two nuts with a spring between them.
                        Amount of experience is in direct proportion to the value of broken equipment.

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                        • #13
                          think of all the great oil retention properties it will have
                          .

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                          • #14
                            Originally posted by Mcgyver View Post
                            think of all the great oil retention properties it will have
                            I'm not sure what oil retention properties have to do with lapping?

                            Here's the result after 15 passes with the 280 grit compound and a few passes with different grits of non-woven abrasive pads:


                            I think it's time to try forming the Acetel nut.

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                            • #15
                              Well that looks better,a few more passes and you'll have 5mm all thread
                              I just need one more tool,just one!

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