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  • Home built lathe

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    I thought some might be interested in a lathe build project of mine from 36 years ago. It has a 7" swing and 12" between centers. I call it the 7E the E is for Elbridge, the town I was living in when it was designed and built.


    This lathe was inspired from reading the lathe book by Dave Gingery. The design of the 7E is similar to the Gingery lathe in capacity and some lathe features. It differs greatly in that Gingery built his around Aluminum castings and this one is built from steel weldments. Dave Gingery thought that it would be difficult/very hard to build one from steel weldments. I thought it could be done in steel and decided to give it a try. The 7E is all steel weldments with only a few odd pieces made from aluminum.


    It was built it in 1983-4 while I was working at a steel fab shop, so had ready access to various steel stock and tools to weld, cut, mill and bend parts. The limitation on using shop tools for the lathe parts, was that I could only use them on my own time during the workday, 30 min lunch and two 10 min breaks. It felt like I was living in that Johnny Cash song about building his Cadillac.

    The 7E lathe uses the Gingery belt drive transmission design. The fabricated steel (HRS) headstock, carriage assy. and tail stock are made approximately to his lathe's dimensions. The box ways are built up from separate pieces (CRS), alignment is maintained with 1/8" roll pins. The headstock is welded with SMAW (stick), the carriage parts and tailstock with TIG. They were not stress relieved and residual stress was not an issue during machining. The headstock has minor welding warpage that is cosmetic.

    The lathe bed is made from a 24" length of 3/16" wall 2"x2" tube with the 1/4"x3" CRS flat bar ways bolted to the top with four 5/16" screws. Machining techniques followed those outlined in Gingery's book, but machining steel is slow going. The headstock and tailstock bores were finish honed with an automotive wheel cylinder hone. A few years later I made friends with a machinist who remade my spindle, bearings and tail stock ram. The tool holder is inspired from one I saw in HSM magazine built in the 90's.

    The machine cuts fairly well and does not chatter as long as the gibs are snug and a moderate cut made. Remarkably heavy cuts can be taken, but three design shortcomings became apparent when doing so.

    Spindle diameter is too small and/or too soft (1144 stress proof) and have worn loose (.002 clearance) fairly quick. The spindle bushings are not split so can't be taken up for wear, my machinist friend omitted the split feature. I have thought about slitting them with a jeweler's saw, but have not yet done so.

    While the square tube is quite rigid, the 1/4"x3" "bar ways" are too limber on heavy cuts, and tends to twist along the long axis. Maybe more screws should have been used or use 1/2" x 3" flat bar.

    Lastly, the first time the lathe was used, the smooth CRS steel ways wrung together with the HRS carriage like gage blocks. This lead to some light scoring of the ways. After some careful stoning and cleaning of the sliding surfaces and plenty of oil, the ways and carriage work well. The carriage should have been scraped for flatness and oil retention, but I was ignorant of the process at the time. The underside of the carriage and compound was lapped flat with 220 wet or dry using a table saw as reference flat.

    The light scoring didn't effect the accuracy. The score marks retain sufficient oil such that the scoring has not got any worse. I consider the lathe a semi-precision machine, +-0.002" or better with care.

    The project was a good learning experience. Would I build one again, today? Probably not, too much time and effort invested for little gain. In the early 80's inexpensive hobby grade lathes from china were not commonly available, so construction made some sense. However, the HF 7x12 mini lathe, which I have had a chance to use, is equal to or better than my 7E in all areas. I have a 9"x48" model B South Bend now, far more capacity and rigidity than the my little steel 7E lathe.

    Dave
    Attached Files

  • #2
    that's really neat, thanks for sharing. I've heard similar issues with the thinner bed Atlas lathes - the 1/2" thick bed ones are alot stouter for their size than the 3/8" bed ones. Makes sense really. I don't think it'd be too hard to slit the bushings and take a skim cut off the headstock caps to create clearance. Then you can add shims back to get the right clearance. As for the carriage, I bet a few minutes with a dremel and a cut off disk will get you perfectly functional "flaking" to prevent stick slip. that's a lot of surface area to keep oiled! Some oil grooves and a Gits oil cup to feed them might be a worthwhile investment, it certainly was on my Atlas 618

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    • #3
      That's a great story and a great looking machine. And it shows just how much thought goes into any such machine. Shortcomings? Sounds like yes. But you learned a lot.

      Years ago I got a small book from the local library that detailed making up a small table top lathe similar in size to a Sherline or Taig. So a little smaller than your lathe. But it used much the same methods and a flat bed from, I believe, the same 1/4 x 3 flat stock as you used. And I believe that the carriage, cross slide and compound used stacked layers of the same stock much like I see on your lathe. And I'm guessing a shim layer of some sort for the small but important clearance?

      Anyway it was an interesting book to read. But even then I felt a rather intensive project all told. So I doff my hat to you for having the chutzpah to wade in and make your own lathe like this. And subsequent lessons on this or that choice and results aside a fantastic bit of work.

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      • #4
        Yes! Thanks for sharing that with us!
        Am I correct in thinking I'm seeing power longitudinal feed? Is that bent handle on the apron actuating half nuts?

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        • #5
          Thanks for the kind words about the lathe. It has sat in pieces in limbo collecting dust for about 25 years. Last spring I decided to put it back together and work on it again.

          The spindle bearings will be split with a slitting saw so that the bearing clearance can be adjusted. Better oil distribution grooves need to be added to the bearings as well. Better oilers are needed also, either drip type or wick type, uncertain which would be best for this application.

          Lynnl, yes the lead screw is powered from the spindle with a double reduction belt drive. The lever does actuate the half nut but it lacks a detent and must be held engaged for longitudinal feed. It does work, but needs improvement. If there is interest, I would be happy to update this thread from time to time with progress made on the lathe improvements.

          The photo shows the disassembled headstock. Before I slit the bushings, I need to slow down the spindle speed on my mill so that I can run a slitting saw at a proper speed.
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          • #6
            That looks like a mini but incredible machine! Nice

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            • #7
              Wow thanks , very interesting

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              • #8


                The spindle bearings will be split with a slitting saw so that the bearing clearance can be adjusted. Better oil distribution grooves need to be added to the bearings as well. Better oilers are needed also, either drip type or wick type, uncertain which would be best for this application.

                I think drip oilers would much better than the grease cups.Glad to see you will improve the lubeing of the headstock bearings.

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                • #9
                  Whenever I click on a picture link, I get "invalid file specified"!

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                  • #10
                    very neat. I think with time and care you could slit those bushings with a hacksaw. Especially if you bored a hole in a piece of square alu stock to hold the bushing and provide some guiding material to start the cut.

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                    • #11
                      I would first try just one saw cut using a hacksaw, rather than two, and replace the SHCS with studs done up tight with locknuts for fine adjustment. The cut would need to be horizontal and you might have to prevent the bearing from rotating. Most wear will be in the front bearing, so do that one first. Moly grease might be better than oil for slowing the wear.

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                      • #12
                        Originally posted by Corbettprime View Post
                        Whenever I click on a picture link, I get "invalid file specified"!
                        I was having that & it went away when I logged in. (I hadn't clicked the "Stay logged in" box.)

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                        • #13
                          Slitting with a hacksaw would be just fine. Lay the shell in the saddle and mark then cut. It may not be picture perfect but it would certainly do what you're planning on doing.

                          There's also a lot to be said for the single cut to just split the bearing rather than cut it into two. If you only split it then the anti rotation pin you have now will be enough to stop the whole bearing from rotating. But if you cut it into two the upper half should have its own locating pin. At least that's how I've seen it done on all manner of split bearings be they automotive or in machine tools like this.

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                          • #14
                            I appreciate your comments and suggestions. The lathe build was started a year before I went back to school for a mechanical engineering degree. I took a few short cuts and made some mistakes because of limitations in time and money, and sometimes I didn't know better. My goal now is to take what I've learned over the years and fix the shortcomings in the design and workmanship to the best of my knowledge and machining skills (self taught).

                            My machinist friend that made the spindle bearings didn't understand the purpose of the slit on the spindle bearings, so omitted them. He did the work as a favor for me so I wasn't going to be too critical of his effort, and he did do a nice job on them. The lathe cut well for couple of years after.

                            As the spindle clearance became larger, I compensated by using higher viscosity oil, when chatter returned I installed the grease cups which didn't improve things for long. That was 25 years ago, life got busy so it sat untouched. A few years later I traded a motorcycle for a South Bend 9B, so there was no pressing need to repair my little 7E lathe.

                            I would prefer drip oilers but have had no luck finding one that has 1/8 NPT threads and 1 inch in diameter. Anything bigger interferes with changing belt position. There are some Chinese oilers that are almost right, but have 1/8"-28 BSPT threads, so I would need to get a BSPT tap and make an adapter. On the other hand I have some Gits oil cups in on hand and they will accept a felt wick.

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                            • #15
                              I see that you lived in a town called Elbridge?
                              Was that the one near Syracuse?

                              Sid

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