Reverting An ML7 To Change-Wheels: Any Thoughts??

[Nigel Graham 2Participant @nigelgraham2]

I wonderedif anyone else has done this and whether they found it worthwhile…

 

Some years ago I treated my Myford ML7 to a second-hand, older-version gearbox; keeping all the original components including the leadscrew. I bought a length of stock ACME “studding” and made the appropriate, shorter leadscrew this pattern of gearbox needs.

This has suited my needs very well until I wanted to make several M6 studs recently, with screw-cut threads for more certain concentricity.

Unfortunately, the machine cannot now cut common metric threads, which even the standard change-wheel set will allow to close limits. (The cumulative errors even without a 127T wheel are not significant over many tasks’ thread lengths, such as studs.)

So I am pondering reverting to normal change-wheel operation for greater flexibility despite slower setting-up.

Has anyone else done this? Did you find it worth doing?

Or might I be better using dies with perhaps rather better die-holders than I have? (I have one of those commercial sets with a Morse Taper shank, but it really needs a tailstock that can accommodate tanged shanks, and is almost unuseable on an ML7.)

 

[DC31kParticipant @dc31k]

Would there be any possibility of changing the connection between spindle and gearbox input to facilitate metric?

A synchronous pulley and belt setup might offer possiblities that gears do not.

An option could be to change the leadscrew to metric, but the halfnuts require some deep thinking (Martin Cleeve talked about changing leadscrews in his book).

How interchangeable are the gearbox internals? On competition motorbikes, they use drop-in clusters to tweak the ratios to suit the circuit.

With 3D printing today, gear production has become a lot easier and you are not limited to standard DP or MOD sizes. Drawing software can also understand pitch shifting so fixed meshing distances are not a problem.

A second hand Super 7 tailstock could be a possiblity.

[JasonBModerator @jasonb]

I thought the usual practice was to swap the mandrel gear, 34T in the case of M6. As this chart shows you can get a pitch of 0.999mm which should be OK for a few turns on a stud.

https://www.model-engineer.co.uk/wp-content/uploads/sites/4/documents/gear%20errata%20tables.pdf

Why do you need a tanged shank? My tailstock die holders don’t have shanks

[bernard towersParticipant @bernardtowers37738]

If you are cutting long lengths of thread would an ELS be the way to go?

[Dave WoottonParticipant @davewootton]

Have you had a look at the late Brian Woods book on screwcutting? There are very clear explanations of cutting metric threads on an S7B. I use them regularly with no problems, the extra two changewheels are available from Myford/RDG. I believe the method was originated by the late and much missed John Stevenson.

Book is still in print and available published by Crowood.

[Trevor Drabble 1Participant @trevordrabble1]

• Why not buy a pair of 33 and 34 tooth gears from Myford / RDG ?

[noel shelleyParticipant @noelshelley55608]

Is there not a change wheel conversion set for the quick change box to give metric threads ?  Noel.

[JAParticipant @ja]

I bought John Stevenson’s two gear wheel set up about 10 years ago but they did not fit my S7. The structure of the lathe got in the way. For a lot of money Myford will, or would, sell you a nice conversion kit. However all this comes with a warning: These conversions take some time to set up and then dismantle.

The easy option is to find someone with a metric lathe or use a die holder as you suggest. Both are cheaper and quicker that the gear wheel option.

JA

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