Wednesday, October 14, 2020

Auto Parts Lathe

I wanted to start building my own machine shop.  Again, I'm cheap, so I don't like to spend money on things I'd only use once in a great while, and I still wanted the full capability.  I looked at Harbor Freight lathes (seriously, don't even bother with them - they are tiny, and not as accurate - if you need accuracy, buy a big one).  My father had a book series by David Gingery about building your shop from scrap.  I could easily start that, but I had a need for a lathe in pretty short order.  I didn't need one I could put stock through the headstock for cutting things off (I could easily use a saw to cut and then surface if needed).  That gave me more options, and, since I had access to a few left over auto parts, I thought I'd put something together.

First, I grabbed the two rear hubs that had been sitting around waiting for my father to build a trailer.  (He donated them to the cause.)  Additionally, I had some pulleys left over from a small block rebuild I had finished up a few years earlier.  This gave way to the auto parts lathe.  I threw down some ideas on paper :

I toyed with the lay out a few times until I had something I thought worked, then started over when I realized the rear hubs I had were not driven (they were from a rear wheel drive), so I couldn't be turning the hubs on top of the spindle.  I needed to anchor the hubs down because they can take some serious lash (this is why I went with them - the bearings are perfect for a headstock).  I revisited until I had the above design (there were three different designs before I settled).

Next up, was to dismantle the assemblies.  It took a blow torch and a hammer to break the drums from the hubs, but once freed, I could remove the spindle nuts and bearings and separate the hubs from the spindles.  This is IMPORTANT, because the bolt holes on the back of the spindles are NOT SYMMETRICAL!  (To illustrate why that's important, think about the vibrations in a washing machine that is unbalanced - it is NOISY, and that is also after the vibration cushions have removed the bulk of the unbalanced load - imagine spinning it even faster with some serious weight - it gets dangerous).

So, once I had the parts apart, I could mark where the symmetrical holes needed to be bored.  I put the two spindles back-to-back, and by identifying the larger-spaced holes on opposite sides and getting as close to centered as possible, I sprayed some spray paint into the holes and let it sit for a minute.  When I pulled the spindles apart, I had BOTH sets of holes marked.  If you only get one spindles holes marked, then you have some amazingly tight spindles.  Odds are not in that favor (which is good for lazy people like me), because of rust, time, and the fact that the spindles didn't need a perfect balance because they weren't the parts spinning while you drove down the road.

Once the holes were identified, I had to transfer those marks to the OTHER side of the spindle flange, because my drill press wouldn't work from the back side using a caliper and a scratch awl (it's a cheap, harbor freight, 8", bench top drill press).  With the marks on the upside, I could then drill them out.  I found the drill bit that matched the already-existing holes, clamped the parts down, and began to drill them out.

You will note that, once the holes are drilled, you will end up with four sets of close holes.  Before starting to assemble anything, grab a spare, used, Chevrolet small block pulley.  I had some aluminum pulleys left over from a previous engine build, so I had something light to work with.  Mine had a lip on them, and before I thought about it, I had started to grind off the lip on it.  You don't need to do this, because that lip will be machined and well balanced.  What you really need to do is center one spindle on the pulley (on a side that is flush, preferably), and mark four symmetrical holes from the spindle to the pulley.  Separate them, and drill the holes out.

Once drilled, you can assemble the bulk of your headstock.  First, obtain some bolts that are just long enough to go through both spindle flanges, the pulley, and have just enough room for the nut.  Any longer, and you can run into interference from the hubs that are going to be put back on.

Lock those bolts down solidly - your life depends on it.  Then, reinstall the hubs onto the spindles:

Once complete, you have the basics of a headstock.  The pulley should turn independently of each hub.      The only things left to do on the head stock are :

  • Build an assembly that will attach to the spindle and allow a faceplate with clamps.
  • Build braces for the hubs to bolt to the "bed".  These can use standard angle iron, or you can use a length of a cars frame.
  • On that note, don't forget to build the bed.
  • And you will need a tail stock.
The braces can be built from angle iron welded together.  I have yet to do this part, and likely never will (I bought a lathe).  Sure, the theories are good, and I'm leaving this post here because someone could use this in an emergency.

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