Gallery, Projects and General > How to's
Metric Thread On Imperial Lathe
andyf:
:bugeye: Wow, Richard - I didn't know all that BA theory.
I did use "nthreadsp" to help calculate my setups, but because it only allows for two driver and two driven gears, whereas I was using three drivers and three drivens, things got a bit complicated. And most theoretically very accurate combinations proved physically impossible to set up. To avoid frustration I created a spreadsheet with 40T (my spindle gear) as the first driver gear and into which I could enter another two drivers and three drivens. The spreadsheet then tried all possible permutations (using 40T as the first driver) of those driver and driven gears and advised whether any of them were possible in real life.
Andy
BillTodd:
--- Quote ---whereas most of the combinations I worked out...produce much less error.
--- End quote ---
Excellent:)
Given your lathe is only 300mm between centres, and even the longest of thread will only be a few tens of microns out; Why bother with a 127T gear at all?
Bill
Bogstandard:
Thank goodness I got rid of my old lathe when I did. I used to spend hours calculating out gear ratios to give me something close to what I was after. Then overcutiing slghtly to match internal to external (if you were only cutting one).
With the way my brain is addling nowadays, I would have given up on single point threading if my lathe didn't now do it all for me.
I was very dubious when I first swapped over, as with a gear train I could always get somewhere near where I needed to be, then fiddle it afterwards, but it is now just a flick of a lever, and sometimes one or two gear swaps, and it is exactly what is needed.
As long as it is standard imperial TPI and metric pitches.
Bogs
doubleboost:
I think i can finally put this thread :D :D :D to bed
I had a visit from Rob Wilson today naturally the subject of screw cutting came up .
Rob in less than a minute showed me a very simple way of checking the compound slide angle.
The tool was simply placed on the compuund slide at 90 degrees to the lathe bed (as it would be to make a cut)
the compound slide should be at the same angle as the trailing egje of the tool.
this picture has the compound set at 30 deg as you can see the tool trailing edge is not the same as the compound :( :( :(
this picture has the compound set at 60 deg the tool angle and the compound are the same :) :) :) :)
The video will be edited
I have one more chuck to make i will be using the 60 deg mark
Regards
John
Ned Ludd:
Hi John,
When you next cut a thread, will you let us know if you think it cuts better than before, then you can put the issue to bed. If after four pages you don't find it to be better, it would have been better to have kept my mouth shut or at least let my keyboard rest. :D
Ned
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