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My first threads

So who else has used muscle power to form threads on a lathe besides me? I used power feed for backing out after the cut some times but I turned the chuck by hand after engaging the feed and setting the start depth with .005” cuts, the material was brass and aluminum the thread was fine and the size about 3/4”. Best thread I think I’ve made yet. No chance of cat ass trophie
 
[mention]Bofobo [/mention] yes I’ve done it that way. It works well especially when threading up to a shoulder.


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I got up the nerve for another attempt at a back plate. It turned out not to bad. Those are chatter marks but they look worse than they are. I used a 16IR insert on 4140 and I doubt my lathe could do any better.
Right now the collet chuck is frozen onto the backplate. While I was sneaking up on the central boss I decided I should warm up the chuck first. As soon as it started to slip onto the cold backplate it shrunk on.
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I didn’t intend for a shrink fit but I did want it as close as I could get. Warming up the chuck ensured that I wouldn’t cut the backplate too small. Tomorrow I will see how hard it is to get off.
 
Looks great! In the future if you have an assembly like that where removing light interference parts is required, consider pre-drill some threaded holes in one of the plates. Then you can put some bolts or set screws in from behind & kind of jack screw the plates apart. Need even & equal pressure obviously. But it beats trying to wedge things in from the side which immediately causes mis-alignment & can make parting ways worse.
 
Peter, the chuck has threaded holes so I should be good. There probably was less than 40 deg temp difference so it shouldn’t be too tight.


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According to some online calculators there might be as much as 0.002 interference. It might be tighter than I thought.


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I have a whole new appreciation for thermal interference fits from my radial engine cylinders. Coincidentally also 0.002" diametric. Doesn't sound like much but that can make for a lot of gription between parts unless you have a means to heat one part rapidly before the other conducts the heat & just grows at the same rate (assuming steel + steel). And even if you have different thermal expansion materials like aluminum + steel, any surface imperfections like typical machining marks act like engaged threads so the thermal gap has to clear those engaged hills & valleys.

It kind of clicked with me when you see vids of those big hydraulic presses installing or removing bearings. When its the same temp & minor interference fit, the amount of axial force can be considerable. And typical bearings & bushings are relatively small surface contact area.
 
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