Myford S7 Bronze backgear

Helping a newcomer to our hobby here in Johannesburg, I have just inspected an old S7 (serial number 78745) which overall is in reasonable condition except the teeth on the bronze backgear. Compared to my own more modern S7, the bronze teeth are both worn and chipped in places. (The other backgear teeth, the 17T/53T cluster and the 60 T are in good shape)

It is not clear from the Myford manual how the vee cone pulley / bronze backgear assembly is put together.

What options does he have should he want to retain the use of the backgear to get low speeds? The backgear works at present, but I would think that failure is not far off!

I did point out that he could avoid using the backgear by fitting a VFD as one solution.

Thanks for any help.

Dennis

His first project should be a mandrel handle so he has something to fall back on when it does fail. It shuld be anyway as it is the best way to learn screwcutting.

Lots of lathes don't have backgear so not a disaster.

If there are no gear suppliers in SA or money is a problem he can measure the gears and start looking in scrap yards for something similar to the larger one. The exact ratio isn't necessary and nor is the material just the distance between centers. Having found the larger one the smaller one can be filed if he doesn't want to get into machine cutting yet.

Thanks Bazyle.

I'll pass on the mandrel handle idea. As we still have an active engineering industry here, there would be no problem in having a replacement gear made, or even sourcing a near-fit as you suggest. However from what I can make out from the Myford pages on www.lathes.co.uk, (thanks Tony!) the gear as manufactured includes a sleeve:

On both ML7 and Super 7 that part of the (bronze) backgear carried on the headstock spindle was in the form of a "sleeve pinion" - that is, the small gear was extended to form a long bush on which the pulley was pressed, the whole assembly rotating on the spindle when backgear is engaged - a design that did much to enhance the lathe's ability to run reliably at slow speeds for long periods.

This would indicate that when repairing these one might have to buy a complete pulley assembly! New or 2^nd hand that could be very expensive.

New Myford have the pulley/gear assembly for sale, Old Myford would sell them separately (yes I did)

Get the backgear sorted.

Backgear turns a bog standard lathe into a proper machine tool which a VFD couldn't hope to compete with

Still not a big problem. You want to keep the bronze bit there as a bearing but it doesn't mean the whole gear has to be bronze. When the replacement is found you can turn down the old gear to leave a residual tube at least 2mm thick and soft solder the new one on top provided the new gear when bored still has say 3mm of meat under the teeth.

If the bored gear would end up a bit thin I would try to get the original gear out (heating up the pulley and pressing out with a drift provided you can see teh inner end of the bronze inside teh pulley block) so that the new gear can be silver soldered on to the turned down stub for a bit more strength.

I'm not a Myford owner so perhpas Kwill can give a view on this proposition.

Another thought. For preference the large gear is steel so not broken in a crash and the small gear is 'sacrificial' in something weak like cast iron or aluminium. Fewer teeth to cut for the repair.

Thanks KWIL - I see the assembly A1994 in http://www.myford.co.uk/acatalog/Myford_Super_7_Headstock_Assembly.html

Did I understand you correctly that Old Myford would sell the bronze gear / sleeve separately, which the rebuilder would have to press fit to the pulley?

ADY1 - I will pass on your sentiments to the gentleman who asked my help to inspect his proposed purchase.

Dennis