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Setover Topslide Screw Cutting

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Will_D:
Tried searching for the answers but as some of you know the search engine on SMF is not the greatest. Its what we use for the national homebrew club and sometimes I can't even find my own posts:

Any way back on thread:

I am in the process of making an ER32 collet chuck for my ML 7 based on John's (the Twastard) videos.

So I am cutting a 1.125" by 12 tpi Whit thread.

I will use the offset topslide method.

So I set the top slide to 27.5 degrees (using the correct 27.5 degress!!). Infeed is via the top slide, Retracting the tool in and out is controlled by the cross slide.

So if I put on a 10 thou cut on the top slide I reckon that the actuall depth of cut will be:

Cos(27.5) * 10, which is 8.870 thou

Is this correct?

Also depth of cut for 12 tpi is 0.053"
So total topslide infeed is 0.060"


Can someone confirm please?

doubleboost:
Sounds good to me
Just keep trying your dummy spindle in the hole
John

velocette:
Hi Will
Here is the way I was taught in the dark ages. Set the Top slide to half the thread angle less 1/2 degree this will allow a good finish to the working face of the thread.
Set Top slide to Zero.
Touch the work with the tool using Cross slide and set dial to Zero.
Back out tool using Top slide.
Move carriage to right to clear work.
Advance Cross slide to the root diameter of thread.
Back out Cross slide move carriage to work area
Touch tool on work and set Cross slide dial to Zero.
Advance Top slide to touch the work.
Start cutting thread
Back out using the Cross slide
Reverse
Advance depth with top slide
Cross side back to Zero
Repeat until Top slide reads Zero

Looks a bit complicated to simplify you back out the top slide to the thread depth and use Zeros as the finished Datum

Eric

doubleboost:

      

BillTodd:
er collet chucks are usually metric so thread angle is 60° ( bsf, bsw and some odd microscope threads use 55° . BA is 47.5°)

set the top-slide to match the V of the thread (i.e. 30 ish)

Bill

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