Which is the best diameter for an ML7 Leadscrew.

Hello,

I will be putting a new lead screw on my ML7 as part of its long drawn out rebuild. I will be buying the item direct from the manufacturers in Hull.

It did dawn on me that I could put either the early or later (thicker)lead screw onto the lathe. I shall have to turn the ends of either lead screw on my friends larger lathe.

Is there any advantage in going for the thicker (later) lead screw or conversely what are the downsides of such a move. I have certainly got the bearings for the older lead screw and I probably have them for the thicker lead screw amongst my pile of Myford spares.

Andrew.

Primary advantage of the larger screw is that it will be somewhat stiffer. Probably noticeably so on a change wheel machine with the extra length between bearings where the gearbox goes. Whether that makes any real world difference, stiff enough is stiff enough after all, is a whole n'other thing.

Most likely disadvantage is discovering the hard way that there were small changes in component size, shape and position made to accommodate the larger screw. Big changes are easily seen but essentially invisible changes like that often involve components being shifted by a few tens of thou with accompanying changes in size to turn a shoehorn job into something with proper fitment room and engineering clearances. If you have both sizes og bearing maybe a bit of careful measurement, maybe a mock up too, might be in order. Half nut operating co-axila and central on the leadscrew would be my big worry. Small adjustments there look like being a complete PIA.

Clive.

Thanks Clive,

I was aware of the likely problems with the half nuts, which need renewing anyway. If there is no real advantage with the thicker lead screw, then discretion is the better part of valour!

Thanks,

Andrew.

Which is the best diameter for an ML7 Leadscrew.

It does rather beg the question of why they changed in the first place?

Could it be that the size was increased to be the same as that on the S7 so as not to have to manufacture 2 different diameters and therefore save on production costs?

Gordon.

With a bigger diameter the load on the thread surface will be over a larger area. Perhaps this reduces wear.

Martin C

The long bed ML7 always had a 3/4" dia lead screw as opposed to the 5/8" standard lenght bed.