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Lathe spider - how to match threads to spindle?

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  • Lathe spider - how to match threads to spindle?

    The recent thread by Dave C reminded me of a project I've been needing to get to, but haven't sat down and figured out how yet. Maybe you guys can help.

    I've been wanting to make a lathe spider for the back of the spindle on my Grizzly 12x39 lathe/mill. The spindle has external threads for the two bearing preload nuts; my thought was to make the lathe spider to fit those threads. My problem is how to precisely match the spinde threads to the lathe spider.

    Normally I cut the threads and test fit until the part fits just right, but of course can't do that in this case, without removing the spider from the chuck. I haven't learned to use thread wires yet, but that might be the most correct solution.

    I thought of maybe trying to cast a female image of the spindle threads with epoxy, or something like that, but haven't gone too far down that train of thought.

    Ideas?

  • #2
    Why not get a spare preload nut and use that to turn a match to the spindle thread. Then use the sample male thread to test the spider?
    Kinda over the hill and through the woods type of plan, but that's how I turned the spider to fit my 7x14.

    Chuck

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    • #3
      When I did this I removed the chuck with the work piece still chucked up and test fit. I have a d1-4 spindle and just marked the clocking position.

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      • #4
        Is there a shoulder or other feature near the threads you want the spider to fit on? If so, use it for aligning the spider. A perfect fit to the threads then becomes much less important.
        Any products mentioned in my posts have been endorsed by their manufacturer.

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        • #5
          Both answers will work well, I turned the threads of a chuck faceplate attached to the 4 jaw chuck and had to unscrew the assembly to check it against the spindle. I got away with it as the threads were 1 3/4 X 8, big enough to see the tip in the thread.

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          • #6
            Originally posted by chucketn View Post
            Why not get a spare preload nut and use that to turn a match to the spindle thread. Then use the sample male thread to test the spider?
            Kinda over the hill and through the woods type of plan, but that's how I turned the spider to fit my 7x14.

            Chuck
            Good idea, that probably makes the most sense, if I can still get an extra nut from Grizzly. It's a discontinued lathe, so some parts are unavailable.

            I'll do intend to leave the threads a little loose, and shoulder against the end of the spindle. Alignment doesn't have to be perfect for a lathe spider anyway, since it's basically a crude 4-jaw chuck.

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            • #7
              It's routine to check sample and part over thread wires. This doesn't require special thread wires for external threads made to match a sample. Drill shanks work just fine for comparison measurements. They don't even have to be the same size drills; sequential drills from the index will do provided they are close to the best wire size.

              Get access to the thread on the index end of the spindle. Check over wires, note reading and where each wire went. Make a male gage to match the thread. Use the gage to make the female thread.

              Fool proof.

              Yes, old time machinists of vast experience and keen awareness of the bottom line will make rough and ready one-use gages. 5 minutes to make a gage (an efficient lathe hand can cut a 1 3/4 - 18 UNEF thread or its metric equivalent in about 5 minutes on a handy remnant) Vs cut and hope is time well spent. Certain success is, in the end, far more economical than cut and hope.

              Adding, it would make sense for the owner of a new lathe to make a complete set of spindle nose and taper gages and a set of replacement lead screws and nuts while his machine is fresh and accurate. Keep the gages handy for when new or oddball spindle tooling is required. Heavily preserve the lead screws and nuts and store them against the day 20 years hence when enough wear accumulates to justify replacement. It would make sense but I know of only one who actually did it.
              Last edited by Forrest Addy; 07-06-2015, 05:42 PM.

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              • #8
                All you have to do is set the spider to a repeatable depth in the chuck and make a sharpie marker line from a chuck jaw to the body of the spider. Turn the ID of the threaded part, then thread a little under size. Take the part out, try the fit on the spindle, put it back in to depth and line up the marks, thread some more, rinse, repeat. The sharpie marker is plenty good enough to index by. You have to make sure you don't rub off the mark during handling. You can also use a marker on the chuck jaw and a center punch mark on the part.

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                • #9
                  It is the old and frequent problem seen here in a new light.

                  Use the bore as the root diameter of the thread and using standard formulae proceed to workout the (probable?) outside diameter.

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                  • #10
                    Or you can make a Go gage to fit your preload nut, then use the gage to make your spider.

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                    • #11
                      Originally posted by Forrest Addy View Post
                      It's routine to check sample and part over thread wires. This doesn't require special thread wires for external threads made to match a sample. Drill shanks work just fine for comparison measurements. They don't even have to be the same size drills; sequential drills from the index will do provided they are close to the best wire size.

                      Get access to the thread on the index end of the spindle. Check over wires, note reading and where each wire went. Make a male gage to match the thread. Use the gage to make the female thread.
                      Would agree and also thats the way i made mine (and obviously check the pitch before hand).

                      Only thing i would add, if you do use drill bit shanks (a cheap set of wires is only like 10 bucks) you want to make sure you pick "the right size", you dont want them too big that they do not set in the valley of the thread and also do not want them too small that they rest on the minor (very bottom) of the thread, you want to "see light" between the bottom of the thread and bottom of the wire.

                      _
                      ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
                      http://site.thisisjusthowidoit.com
                      https://www.youtube.com/user/thisisjusthowidoit

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                      • #12
                        Simple solution. Don't turn it in a chuck.

                        Turn it between centers. Leave the dog attached to the work and you can always reseat the work at the exact rotation and position as you took it out. No fussing about getting it centered either.

                        Tip: An elastic band between the lathe dog and faceplate can prevent annoy chatter and make sure it stays in sync with the lathe at the start of the cut. Also if your using studs in your faceplate to drive the dog, put a stud 180 degrees from the 1st stud, but mark it with an extra nut on top, or similar so you don't accidentally put the work back engaged with the wrong stud. This will balance out the lathe. (Yes, just a single bolt sticking out of the faceplate will unbalance the lathe some and make it shake, depends on lathe size it might be enough to make turning slightly annoying, or maybe affect surface finish)

                        Making a thread that fit my lathe headstock was the only time I have turned between centers. Worked great. Just make sure you turn the thread crest to the correct size, slightly less(more?) then the measured root on the other side because your thread crests are square but you are measuring a rounded root.
                        Last edited by Black_Moons; 07-06-2015, 10:01 PM.
                        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                        • #13
                          Assumptions:
                          1) It really is a true bearing nut
                          2) You own Machinery's Handbook

                          Simply look up the standard (both inch and metric available) and make it to spec'. All the dimensions are in the book: OD, pitch, pitch diameter, tolerances, etc. Most bearing nuts have their official size marked on them, but you may not realize it. For example, the size could read "N09;" it will not be the diameter/pitch combo.

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                          • #14
                            Originally posted by Black_Moons View Post
                            Simple solution. Don't turn it in a chuck. Turn it between centers.
                            Wow. I'd like to see that. How does a guy turn internal threads between centers? And simply at that? Interesting.

                            I've done similar projects like this a few times and the only reliable way I've come up with is to make a mandrel (go-gage) using thread wires to carefully match the PD to your spindle's threads, then use that mandrel to measure/make your internal threads. At first think it seems like a bit of a hassle, but threading the go-gage only takes about a half hour if you take your time. If it takes longer than that, you needed the practice anyway and you will also find it kind of fun anyway as well. Once you have it made, then you can use it to make future attachments to fit that same thread as well.

                            I prefer to do this than to use a nut or something that just "fits" the threads already. it is difficult to get an accurate quantifiable measurement of an internal thread. Thus making your own gage to match the existing thread DP as perfectly as you can measuring with thread wires will give you an actual thing to fit rather than the relatively wide tolerance of the DP any generic existing nut can span. You can try to match the same feel of the fit of a generic nut, but trust me that I speak from experience when you think you've got it matching just right, it SUCKS when you are "done" and it's still just a tad too tight (even though there are ways to fix that).

                            edit to add: using thread wires is tricky dry but it can be done. They have a tendency to drop into your chip pan about every 15 seconds while you're trying to use them. Usually though I just put a bit of grease on the threads so the wires just stick where you put them. This trick works well.
                            Last edited by tyrone shewlaces; 07-07-2015, 01:47 AM.

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                            • #15
                              Quote: Wow. I'd like to see that. How does a guy turn internal threads between centers? And simply at that? Interesting. :Endquote

                              That was the first thought that I had when I read his response. Come on BM read the OP's problem. :-)
                              ...lew...

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