Getting Screwed

My plan is to use the one acme threaded rod as long as possible. McMaster-Carr specifies they are 72"+'some'. One came in at 72.5" and the other was 72.375". The longer one had a couple small boogers on the threads, so I decided that one would be the one I cut into two parts, one for the y-axis and the other smaller for the z-axis.

My 0.375" ID bearings came in yesterday from VXB. The acme rod is 1/2" OD so I need to machine the threads off one end down to 0.375" on each of the three rods. Because at 6' the rods sag a bit, when at lathe speeds, it tends to whip some. To support the far end, I used the lathe's steadyrest. Initially I put the rod in the bronze jaws lightly snug, but found it tended to move axially because the threads stilll had a tendency to propel it when turning. I found I had a 1/2" ID wheelbarrow axle bearing, which I chucked up into the jaws of the steadyrest; boom-problem fixed. I left a bit sticking out the end

for counterbalancing and used a quickclamp to the toolbox to hold the steady rest in position. The other end of the acme rod passed thru the lathe bore hole and left as short as possible sticking out the chuck so the jaw marks would only be very close to the end. The bearings are 9/32" thick. I took the end of the shaft down to 0.375" and trimmed the tip off 0.125" and then created a boss by removing threads about 0.282 deep for the bearing to sit on.

I am very happy with how it came out. I used some HFT (Harbor Freight Tools) micro files to clean up the thread ends. I also used the wirewheel on the bench grinder to buff the end and the two places along the span where the threads had shipping(?) damage. The lathe is a very cool tool. You can see the 3/8" diameter did not completely remove the thread groove, but the bearing fits perfect. I am still not a lathe expert, but I can say sharper tools are better and cleaner!

The bearings have an OD of 0.875, so I will be able to use a forstner bit to create the bearing seats in the MDF. Only two more rod ends to go, and I still have to decide how long to cut the one shaft in 'half'. Measure twice, cut once. It's a bit of a nailbiter worrying about taking off too much material. Tonight I will do a nesting evaluation to make sure when I cut parts out of the MDF that I will be able to get all the parts out of the 1.35 remaining sheets I have. I would rather not purchase another sheet if I don't have to.

Anybody out there?








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