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Cleaning up an LOO ID taper?

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  • Cleaning up an LOO ID taper?

    My lathe came with a rather worn Buck 6.25 3 jaw chuck. It's got some wiggle in the hard jaws, but turns out that the master jaws actually fit reasonably well. Not sure, maybe the hard jaws don't belong with this chuck? Whatever... My only real problem with using it for low precision work now is that the L00 taper is in pretty sad shape. Looks like it was installed on top of swarf on several occasions, and you can even see the “Câ€‌s and curley-q shapes in the taper. The body is 3 piece, but I don’t think this is actually a plain back chuck with backing plate. The L00 taper part extends into the chuck, and I’ve not seen an L00 backing plate look like that. On this chuck, there is only enough protruding on the back for the threads plus maybe another 1/4â€‌ clearance between them and back.

    So, what to do?

    1) Set compound using DTI on spindle ID taper, careful of exact center line height. Chuck up the back piece with the taper (backing plate or not, it’s not worth the cost of a backing plate based on the wear). Use my 8â€‌ P&B 4 jaw and carefully center as concentric as possible. Very carefully and slow clean up the inner taper with a very sharp HSS boring bar, stopping before I start actually removing any metal other than the high spots, and hope it doesn’t start trying to come off one side. A tool post grinder would likely be best for this, but after the responses on my last lathe grinding question, I’m trying to avoid this.

    2) Turn a mandrel to match my L00 spindle exactly (within my ability). Use D/A tac (used to hold non-adhesive abrasive paper on D/A pad) to secure some sand paper (220 followed by 400 maybe) and run it in light oil inside the taper. Taper may be mounted in the 4 jaw as in #1, turning at low speed, with the mandrel mounted on a sort of “wigglerâ€‌ shaft so that it can float but stay aligned. It could be fed in using the turret. Or I could just make a handle and “hand lapâ€‌ like doing a giant valve seat. This would be similar to flat stoning in that it would work first (and fastest) only on high spots. Up side of this is that when done, I have an L00 taper that I can use to make a mount for my Hartford Spacer and Troyke Rotab to use my chucks interchangeably.

    I’m leaning toward #2, but I’ll have to pick up some suitable stock...
    Master Floor Sweeper

  • #2
    There's nothing wrong with the techniqu you propose but it might be premature. Before you start machining, try a little TLC on the internal taper.

    Remove the backing plate from the chuck if possible because you'll have to handle it extensively before you're done. Anytime you reduce the weight of anything that has to be hand fitted you increase the chances of success and painless toes.

    Using a sharp scribe, remove any imbedded chips and debris. Using a round or half round india stone held in an axial plane stone the tops off the bruises. Do not stone below the conical surface representing the L-00 taper - just take it flush.

    Once that is done remove the key from the lathe's spindle and do a careful-clean up on it removing all bruises to the taper cone - no deeper. Apply a thin coat of blue - thick enough to be vivid but thin enough for the underlying finish to be visible.

    Apply the backing plate to the spindle and draw it up with the clamping ring firmly without banging on the spanner. Remove the backing plate carefully and inspect the indications. If you have speckles all over you're in good shape. If not hand scrape to correct.

    It's a little tedious but it's the minimum possible material correction technique. Boring the taper would be a last resort without making and fitting a gage first. There's many a slip possible between setting the taper and actually acheiving an accurate fit by boring.
    Last edited by Forrest Addy; 09-17-2006, 04:50 AM.


    • #3
      Thanks for the suggestions.

      For one thing, there are a LOT of scars inside the taper. There is still a lot of seemingly virgin taper between the scars, but it’s like looking at nice grass lawn after a heavy rain when scattered weeds have sprung up all over the place. I’ll try to take a pic that shows them tomorrow, though that sort of thing is notoriously hard to get clear in a pic (at least for me).

      To do as you propose I would need to buy a stone as I don’t have one suitably shaped other than a very course “rodâ€‌ shaped stone. The rest are flats and triangles. Probably a good investment, options are always good, but I haven’t really seen much use for such a stone in everyday shop work.

      Embedded debris is already cleared, there wasn’t much and I suspect much of the damage is old just based on the matching patina in the scars. This shop didn’t do much chuck work at all (almost exclusively collet work on my lathe) and I guess they didn’t care for whatever work they were doing using the chuck? No idea...

      There is no damage what so ever visible on either the spindle cone or key. They appear very hard surfaced.

      I don’t have what I believe is called Prussian Blue used in surface matching. But this brings up a question that has occurred to me before. I do have layout blue, how effective will that be for this?

      As for scraping, I have no tools or skill/training for doing this on flat surfaces, much less a taper which seems to be considerably more difficult. Also, wouldn’t it be important to use the keyway so that it is scraped in the proper and consistent phase?

      You mention the risks of boring, and those are the things that make me nervous about that approach. However, you don’t comment on the lapping. How would that fit into you suggested plan of attack? I would guess after attempting some simple (and limited by ignorance) scraping, but before boring?
      Master Floor Sweeper


      • #4
        Forrest is damn close to being right, but wouldn't work for every case. This is one of those things where we can all spout off our fixes, but we can't see it. Drop it off at the shop, if I can't fix it....I know how to get rid of it!


        • #5
          [[ don’t have what I believe is called Prussian Blue used in surface matching. But this brings up a question that has occurred to me before. I do have layout blue, how effective will that be for this?]] Contrary to popular opinion, layout die works just fine. It's all in the eye and the ability to determine a surface using instruments that defines the exact surface in relation to any other surface. It's not rocket's finesse.


          • #6
            Prussian blue is as near as your local auto parts store. Layout blue will work but to a limited degree. The indications may brush off. Scrapers you make from old triangle files. Grind the teeth off and stone the resulting flats to a keen edge.

            A small triangle stone will work if you don't have a round or half round.

            As I pointed out it's tedious work but it leads to success. What I proposed to you is what I've done myself probably once a year since 1961 whenever I've run across a beat-up spindle tooling tapers.

            Not every road to success is straight across the wilderness. The machinist's trade is a collection of skills, methods, equipment, and culture to achieve success in a general class of work. Just as framing carpenters have to work in the weather, and plumbers have to bail turds out of the bowl; machinists have to buckle down to accomplish tedious work. What I propose takes only an hour of time.

            Millman is right: it IS finesse. Finesse is tedium made to look simple through practice.

            Man on a fully crewed firetruck yells to an old man on the sidewalk: "How do we get to Carnegie Hall!" "Practice, my boy, practice."


            • #7
              The backplate you describe is for a Buck Adjust Tru chuck. There should be four allen screws on the side of the chuck that bear against the part that extends into the chuck to permit dialing the chuck in.

              I believe the 6" chuck uses proprietary outer jaws, and if other jaws have been fitted, that would account for their being loose. Jaws are available from Buck, but might not be cheap. Soft jaws are easily made if you have a milling machine.

              Prussian blue or High Spot are better for close work than layout blue or magic marker as the layout dies have a thickness, and application may not be even giving a false reading. The non-drying hi spot compounds made for the purpose will "squish", and can be applied in a very thin coat that will not affect the mating surfaces and give a truer reading.

              Stoning and scraping the offending taper to get a good fit up should be followed by mounting the backplate on the spindle and taking a light truing cut on the flange and raised portion to ensure they are true to the lathe spindle. Once all this is accomplished, you should have a very accurate chuck.

              The Buck is worth spending some time on to bring it back into it's original accuracy.
              Jim H.


              • #8
                Here is a pic, if that makes any difference. Looks like I missed some of the chips too. Or at least it looks like a few remaining chips that are showing up in that lighting. <sigh>

                Also, it's not an Adjust True, at least there are no adjustment set screws, though your description does make sense. Hmmm...

                I'll see about getting some Prussian Blue if it's available at the local auto parts stores. And I've got a couple of old files I could make a scraper out of I suppose, though I had planned on trying some of the resharp techniques I've seen people talk about. Though I don't have a sacrificial triangle file, and never realized they were used for scrapers. Aren't those usually made from flat files? I guess I need to do some more reading... I seem to remember finding a web site with novice scraping info somewhere, anyone know of such or have a link?

                Master Floor Sweeper


                • #9
                  Loo back plate

                  I have one you can have looks better than one you got e-mail me with shipping add will send it to you.
                  Every Mans Work Is A Portrait of Him Self


                  • #10
                    Damn, looks like somebody was too lazy to wipe it off before mounting. Always hated cleaning up someone else' s mistakes. That can be fixed, though. Done much worse.