Setover Topslide Screw Cutting

[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

[lordedmond]

Use the method Eric describes

It's in GHT books it works fine no maths involved when both dials read zero it done


Stuart

[Will_D]

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

Agreed but the body screws onto the lathe mandrel's nose (ML-7 Imperial like Johns Boxford). The Collet Closer is the metric bit!

[Will_D]

Cheers Eric for this but I think something is missing?

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.

Something for the top slide here?

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

[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°)

Agreed but the body screws onto the lathe mandrel's nose (ML-7 Imperial like Johns Boxford). The Collet Closer is the metric bit!

Ah yes. must learn to read these before replying ;-)

So, you're  cutting an internal thread.  The topslide needs to be angled like this  /   and you should realy make a male thread measured with wires or mic to ensure you get it right (infeed is +0.0597 @ 26.5° but ...)



bill

[Fergus OMore]

As  follow up to Eric's dissertation, I would also add reading up Martin Cleeves Screwcutting in the Lathe.

Two reasons really! The first is that George Thomas and Martin Cleeve( actually Kenneth Cleeve Hart) both had Myford ML7 at one time and the words and the music  require no re-design to achieve these results.

Actually 'Cleeve' was made redundant many years ago and used his highly modified ML7 to make 'special' nuts and bolts( and a very good living) from his machine.

Over the years, I made a lot of GHT and Cleeves additions to their designs which appeared in Model Engineer and some of Cleeve's in Engineering in Miniature.

Regards

Norman

[Will_D]

OK, Just spent a few hours on the lathe and also google!

I am still not understanding the process as outlined:

The goal is to set the tool tip at its end postion (for depth of thread) with the Cross & Topslide dials at Zero

So reading the guidelines:

1. Set Top slide to Zero.   OK
2. Touch the work with the tool using Cross slide and set dial to Zero. OK
3. Back out tool using Top slide. OK
4. Move carriage to right to clear work.OK
5. Advance Cross slide to the root diameter of thread.OK
6. Back out Cross slide move carriage to work area

Surely step 6 has just negated step 5?

7. Touch tool on work and set Cross slide dial to Zero.
8. Advance Top slide to touch the work.
9. Start cutting thread
10. Back out using the Cross slide
11. Reverse
12. Advance depth with top slide
13. Cross side back to Zero
14. Repeat until Top slide reads Zero

I have neither of the reference books by GHT and Martin Cleeve.

Can someone look up this technique please?

[lordedmond]

Ok

Set the tool to touch the work
Set both dials to zero
Move the carriage to the right
Wind in the cross slide to the corect thread ( half or full depending on jour dials) set the dial to zero
Wind out to clear work and move to the left

Move cross slide to read zero
Wind out the compound to clear work
Now when both are at zero you have the correct depth

Stuart

[Will_D]

Thanks Stuart for the Info.

When I've finished cooking the late Sunday lunch I will be off to try it!

[Will_D]

Two noses are better than one!

Have just made my dummy lathe nose on a blank 2 MT mandrel. It will act as a gauge for the ER Collect nose I will make and also when I make a bit more stuff a handy thing to mount my 3 jaw elsewhere.

Used this a a test of the offset top slide screw cutting technique.

So here goes:

After a lot of help from the group I think I have nailed this! I am using exactly half the angle – I know some people like 25 degrees for Whitworth and less than 30 for Metric/American

1.   Prepare work as normal for thread cutting.
2.   Set over top slide to 27.5 degrees for Whitworth. Set tool tip square to work.
3.   Infeed the top slide a bit and set to zero.
4.    Using Cross slide wind in tool until it just touches the work and set to zero
5.   Move carriage to right to clear work.
6.    Advance Cross slide to the root diameter of thread.
7.     Set Cross slide back to zero
8.   Wind back the top slide to clear the work and move carriage left to where the cut will start.
9.   Apply marking blue to threaded area.
10.    Advance Top slide to touch the work. Move right and set first cut with top slide - say 2 thou.
11.   Check: Cross slide on Zero, Top slide is whatever (Zero minus approx depth of thread root minus cut ), Carriage moving to the left (for normal thread)
12.   Start cutting thread.
13.   At end of cut disengage half-nuts and wind back cross slide.
14.   Check the blue that its correct pitch
15.   If all OK, move carriage to the right, Set cross slide to zero, and put on a bit more cut (say 5 thou). As you go deeper use smaller cuts and towards end workout the spring of the tool.
16.   Repeat step 15 until within say 10% of the depth
17.   Start to check the thread, apply fine cuts as required. Note some people like to cut the last 1 or 2% on the crossslide.

Before trying this, set up a piece of bar and a dial gauge on the top slide. So Step 4 is wind in cross slide and put say 5 thou on the clock. Zero the clock and cross slide, Then proceed as normal. When topslide reads zero, the clock should show depth of cut.

Attached 2 picture of the finished piece! Its a nice smooth fit and runout with the 3 jaw fitted is less than 1 thou! Not bad for a 2 mt mandrel

[lordedmond]

Glad you have it sorted

It's a good method because it sorts out the depth without maths

Stuart

[Will_D]

So external thread cut with no problems.

Found the internal cutting a bit confusing on Johns ER32 video as his protractor was not set to 27.5 degress!

Any way pictures are worth 1000 words so here is a picture:

Click on the picture to make it bigger!