The Shop > Tools

Setover Topslide Screw Cutting

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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

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