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It's the little things that catch you !

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awemawson:
There you go see, wikipedia doesn't know of this HUGELY important use of sodium thiosulphate  :lol:

vtsteam:
(oops, hit edit on your post instead of reply -- sorry -- restored).

Well add it then! Wikipedia is yours to update.  :thumbup:

Just thought you'd be interested in:

It's effect on your person.
It is used in food.
The yellow of the old solution is sulfur, after decomposition to sulphite.
Under another entry Thiosulphite it talks about its corrosive effect on stainless steel. Also carbon steel is mentioned
Its use in patinating copper.

Manxmodder:

--- Quote from: awemawson on October 25, 2013, 05:02:49 PM ---I >think< I've sussed it.

If you look at the chart in the Sandvik link I posted above, the vast majority of threads fall in the 'needing 1 degree' category so the 1 degree supplied shim is right in virtually all 'normal' threads, so  this is why most dealers only supply that shim. Sets of other inclination shims are available at significant cost  but rarely needed.
--- End quote ---

Andrew,
 the shims are primarily for setting the helix angle and as you say it isn't a problem with the standard 1 degree shim until you start cutting coarser pitches with steeper helix angles.

Then you do need to consider fitting one of the optional shims with a corresponding helix angle to suit the thread being cut.

A significant problem can be encountered when cutting a left hand thread running the leadscrew feed from left to right to cut a left hand thread.

 Rather than using a standard shim of +1 degree which is designed for flank clearance on a right hand thread you need to fit a -2 degree shim to compensate for the opposite helix angle now being generated.(The manufacturers seem to classify a minus 1 degree shim as a minus 2 deg so must be classing +1 deg shims as their datum)

A very inexpensive solution to all of this is to simply fit a thin packing shim under one edge of the tool holder and tilt it to give the required helix angle and flank clearance.

Trick that I use: if you ain't sure about the pending result then cut a dummy run in a soft material like acetal rod and look closely at the results before proceeding with the job for real......OZ.

rotorhead:
Hi All,

Regarding the left and right threading issue, I had a similar problem cutting a LH Acme 10 tpi thread with a right hand tip and tool, completely shagged the work and tip (including the shim).

So I bought some Internal tips and found a Left hand threading tool for said 16Ex tips, the threading tools I ended up with have shim adjusting screws, to alter the helix angle (Didn't use that feature though).

Anyway the job went fairly well after that, as the pic below will show, the top screw is my incarnation of the original lower one(original is 9/16" Acme 5 tpi x 2start, new one 5/8" Acme 10 tpi x 1start).

Manxmodder:
Hi Chris,I meant to ask you where did you purchase the left handed threading tool from or at least could you tell me what brand is it?.......OZ.

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