Gallery, Projects and General > How to's

Single point threading on the lathe

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Bernd:

--- Quote from: miken on August 03, 2009, 05:26:22 PM ---Id like to add that sometimes people are reluctant to try screw-cutting on their lathe ,especially if their machine is not fitted with a clutch or perhaps does not have a  low enough speed because they are concerned that they not be able to stop in time at the end of the cut.
  There is no need for concern if you make a mandrel handle a bit like an old fashioned car starting crank that fits up the hollow head stock mandrel and allows you to carry out the entire operation by hand and under complete control.
  It might make your arm ache on a long thread though.
Mike

--- End quote ---

And your knukles hurt when you turn on the machine and forgot to take out the crank.  :doh: :bang: :bang: :bang:

Bernd

John Hill:

--- Quote from: Bernd on August 03, 2009, 07:39:16 PM ---

And your knukles hurt when you turn on the machine and forgot to take out the crank.  :doh: :bang: :bang: :bang:

Bernd

--- End quote ---

Make a spindle handwheel if you want to do something like that, I think you can buy them for the small lathes but I assume they would be useful on any size lathe especially when jogging the gears when selecting ratios in the head.

DavesWimshurst:
For short threading jobs or up to a shoulder I made a balanced crank.  If I forget to remove it at least it isn't trying to shake the lathe apart. :doh:
This is it in use when cutting a metric approximation using change gears.



I couldn't close the gear cover because of the extra gears.
Dave

NickG:
The hand crank is a good idea as a lot of modern lathes can't attain low enough speeds.

The lat bit of threading I tried went OK, however, my depth of thread calculations just didn't work, I just had to keep taking more off until it fit. Not sure why. Maybe my internal tool and external tool weren't close enough in angles?

I also used the thread dial indicator so I could withdraw the tool from the work piece and disengage the half nuts.

Jonny:
Nice write up Tim, there will be variations of how its done by others and method may differ with the lathe used.

Incidently i did it the same way when using Colchester machines. Certain Harrison lathes you can disengage half nuts, wind back carriage and engage half nuts again any where on 1, 1.25, 1.5 & 1.75mm pitches. Cant do it on imperial it must remain engaged as it was built as a metric lathe in 1965.

Always use back gear 45 rpm loads of torque with one hand on the clutch. I have a variable speed mini lathe as well, threading on that powered would scare me plus its got no torque.

The reason for winding cross slide out to clear cut thread is when spindle is reversed any backlash in gears and lead screw will effectively reposition cutter or spindle.

One thing worth mentioning is the tooling of which i have always liked the HSS Cobalt ground to shape and give a reasonable finish. Indexable types theres a lot of junk out there mainly from China that flex, no substitute lash out for known brands such as Kennametal, Sandvik etc with the correct inserts.

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