Modifying Bolts

[Nigel Graham 2Participant @nigelgraham2]

This was prompted by a task I have just completed, and not very long after someone asked for advice on holding bolts in the lathe for turning their shanks.

I give the recipe I found effective.

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Needed: three pivot shoulder-screws thus:

… 2-off 10mm dia X 6.5mm long + M8 thread.

… 1-off 8mm dia X 25mm + 6mm dia X 13mm + M6 threaded tail. (i.e. two plain diameters then the thread).

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Ingredients: Suitable bolts (not machine-screws) of shank to the required bearing diameter. These were not super-critical for the application, and at least one bolt was second-hand.

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Method:

1) Hold the bolt by its shank, with the hexagon head nestled behind the 3-jaw chuck jaws.

2) Centre-drill the tips – I completed these two steps on all three bolts in one sequence.

3) Hold the bolt by its head and a half-centre.

4) Face the underside of the head to form the end bearing surface, and to give the measurement datum.

5) Machine the diameters, leaving the shank generously over–length. Turn the excess length down to give the die something of a lead, and the intended thread part down to a little under nominal diameter.

6) Die-cut the new thread.

7) Trim to length. I used a hacksaw and file, as the end lengths and finishes were not critical. If they had been, I would have repeated Step 1) and faced the end.

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NB: When turning the shank, unless the bolt head is backed by a mandrel stop (mine weren't), use only light cuts and gentle feed to avoid pushing the bolt back off the tailstock centre.

[Nigel Graham 2Participant @nigelgraham2]

[Howard LewisParticipant @howardlewis46836]

A larger version of John Ashton's Screw Modification fixture, (He got the John Stevenson memorial Trophy ) to take a M10 bolt would allow the job to be done without the need to centre drill, and the risk of the work moving whilst cutting the thread.

Howard

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