Spindle Nut

Vegemitesandwich

Vegemitesandwich

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Jul 3, 2016
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I am trying to make a spindle nut for an old Jet Drill/Mill. The shaft thread OD is 1.153". The nut ID is 1.119". 1.25mm left-hand thread. I made an aluminum prototype. The threads were good but the fit was much too loose. My original bore was 1.115". I know it has to be less but how much less than the nut @ 1.119"?
 
I read the specs wrong, so I deleted this post.
 
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Thought I would post this also, a trick for metric tap drill sizes; subtract the thread pitch from the thread size - the result is the tap drill size. (a 3mm thread x .5 pitch would be 3-.5=2.5. A 3-0.5mm thread uses a 2.5mm tap drill).
 
The standard thread charts don't really apply (I don't think) as this is not a standard fastener. But a wacky bastard nut. Seems I have about .035 between major and minor. My previous bore was under by .005 and still produced a sloppy fitting nut. My first experiment was in aluminum, and it doesn't thread well anyway. Been looking in Machinery's but all that math makes my eyes glaze over. Perhaps it was the material, or most likely the operator. Does the actual threading operation enlarge the original bore and if so by how much?
 
Mixing units can be confusing. Your measured OD of 1.153" converts to 29.29mm. If there are significant flats on the thread, it's probably a nominal 30mm thread. How did you arrive at the 1.25mm pitch? If those figures are accurate, then:
 

Attachments

  • M30-1.25.bmp
    1.2 MB · Views: 5
I think I discovered the problem. There is a loose nut in front of the lathe. I established the thread pitch using a thread gauge. The threads seem to be pretty accurate. Gauge fits shaft, existing nut and attempted replacement equally. I bought several similar undersized nuts to bore and re thread. My latest attempt which I managed to over bore by .020 still albeit sloppy, fits better than the first attempt. Slow down, pay attention, focus.
 
Yeah, definitely tighten up the nut in front of the lathe. And no lube for it until after the job is done!
 
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