# Mini Lathe Caution



## Ken I (Sep 7, 2011)

Whilst dismantling my mini-lathe's headstock (no name Chinese brand) in order to replace the bearings, I broke the locknut - its made of cast iron - not steel - and I see my minimill is exactly the same.







I was driving out the shaft using a copper hammer against the nut (to protect the thread) - now I'm going to have to make a (steel) replacement on a friend's lathe - left hand thread to boot.

Why was I doing this ? I'm trying to locate the source of "banding" in my surface finish - see thread.
http://www.homemodelenginemachinist.com/index.php?topic=15645.30
Ken


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## Omnimill (Sep 7, 2011)

Thats looks nasty, and it's such a slim piece of material. What thread is it, metric or imperial?

Vic.


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## Ken I (Sep 7, 2011)

Vic, Its Metric M28x1.0 Left Hand.

BTW the material is "Black" cast iron - Damn Chinese.

I'll be making its replacement from mild steel.

Ken


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## Herbiev (Sep 7, 2011)

Can you get a replacement lathe from where you bought it from if it is still under warranty?


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## websterz (Sep 7, 2011)

It looks like a fairly clean break. If you have the room I would suggest cutting a steel sleeve to shrink fit on the outside, pressing the two halves back together. Chill the cast parts in the freezer, heat the sleeve with a torch and press them together.


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## winklmj (Sep 7, 2011)

I would go the hose-clamp route if you have room to work with. That should get you up and running long enuf to make a new nut.


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## Ken I (Sep 8, 2011)

That's what I love about this site.

Two useful suggestions right off the bat thanks Websterz & Winklmj.

Thanks,
      Ken


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## steamer (Sep 8, 2011)

Hey Ken,

If your making a new one anyway, change that ()#*& design while your at it!

Make the nut a split clamp with a clamp screw like a SB nut and get rid of that set screw...man I hate set screws.....

Like this






Dave


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## Ken I (Sep 8, 2011)

Dave, Don't use them professionally - normally use that design.

If I make it - I draw it.

Thanks,
      Ken


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## steamer (Sep 8, 2011)

Ah........A man after me own heart! :bow:

Righteous!

Dave


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## Ken I (Sep 13, 2011)

Just an update on my mini lathe teardown / rebuild.

The broken locknut is in fact steam treated sintered iron - go figure - steam treating is to reduce it porosity ???
I'm guessing the Chinese used minimal or nil copper content (cost) which is normally included in SI to improve the impact resistance / ductility.

The backgear selector arm - also SI is cracked (again minimal material possible used - only 0.5mm thicker than grub screw - I made a replacement from gauge plate.

The bearings have been replaced but the "harmonic" vibration is still there - seems to be the Gates Powergrip drivebelt - can't see anything wrong with it but it must be stretched as the motor is at the extemes of its adjustment.
Adjusting the motor to get the belt tensioned and running true is a right PITB.
New belt on order.

As regards the half nuts - what an unmitigated abortion - the fixed side of the dovetail slide is incomplete and badly weld-repaired and cleaned up with a file (like that from the factory) and is so far out of whack that the worthy oriental gentlement that assembled it has wedged in a strip of metal to make up the difference (this fell out some time ago and I couldn't at the time figure out where it came from - thought it was a piece of stray scrap - that's what it looked like anyway.)

Remachined the dovetail and made a more permanent insert/spacer to make up the difference.

Putting it all back together - hope this cures all its ills.

Ken


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