Shimming between the saddle and apron on a Myford ML7.

The short question - has anyone shimmed between their saddle and apron? And do you see any problems with it?

From what I’ve been reading it seems to usually be the opposite problem – apron too low.

The background to this question...

I got a Myford ML7 back recently from a bed regrind and saddle/slides regrind and scrape in. Part of the condition of the reasonable price for this work was that everything was stripped back and only the parts applicable were sent away (i.e. no headstock/apron/leadscrew/rack etc.). Before regrind apart from the tightness near the tailstock was that the leadscrew used to lift up when engaged (never really thought about it till now).

My problem now is that after refitting the apron is that the apron is too high, which means the carriage won’t move when trying to turn the handwheel and the leadscrew still lifts (perhaps always was always too high based on my comment on the previous leadscrew alignment). The other thing I have done was replace the worn rack pinon assembly with a new one.

So the combination of the bed regrind/saddle regrind and scrape in/new rack pinon/how it was previous, means I need to do something to align the apron with the rack and leadscrew. It’s 0.030” from assessing using feeler gauges, this means smooth movement of the carriage and no leadscrew lift.

1) Take 0.030” off the saddle.

2) Raise the rack and leadscrew – doesn’t sound good…

3) Shim between the saddle/apron.

My preference is 3) does this sound like an okay solution? Shimming also looks like the easiest option.

PS Have also tried the standard Myford procedure to set up the alignment of the apron off the leadscrew but this didn’t solve any problems.

Edited By mrbuilder on 28/12/2017 06:54:43

Yes, I have once shimmed between the saddle and apron. My son and I did a wide guide conversion on an ML7. We found there were three red fibre washers between the saddle and apron, one on each mounting screw, apparently there from the factory, but no way to be sure. Tried reassembly without them but the apron was too high and the rack and pinion jammed. Put them back in and all was good. Probably would be better to cut a gasket the same thickness. One day...

The way we set it up was to leave the apron mounting screws in place but loose, close the half nuts tightly on the leadscrew, then measure the gap between apron and saddle. Insert shim (or in this case washers) of correct thickness and nip up mounting screws while holding halfnuts firmly engaged. This gets lateral alignment of nuts and leadscrew in line too. The rack to pinion clearance was then a tad on the loose side but was fixed by moving the rack down a bit, using the clearance in the mounting screw holes for movement. Those holes could be drilled out if more movement were needed.

Likewise, leadscrew can be moved up and down a small amount due to clearance on the mounting screw holes on the bracket at each end, so it can be a matter of juggling both until "just right".

So far it's all working well. Zero taper on a turned test piece and no chatter on heavy cuts.

I would assume (and we all know about assumption!) that many left the factory with such shimming between apron and saddle. Being a mass produced machine it seems unlikely that every single bed and every single saddle and every single apron was machined to exact dimensions so close that it all fit together perfectly every time without shims. The smart way to do it would be to machine them on the high side so any misfits were rectified with shims and none had to go back to have further metal machined off (ie aprons sitting too low). That's the way a production engineer would look at it.

Edited By Hopper on 28/12/2017 07:57:32

Edited By Hopper on 28/12/2017 08:00:54

Thanks Hopper. Sounds like the same problem I've got here. That all makes sense to me, going to make a shim up tomorrow.

I can only think when the last person rebuilt this machine they didn't replace whatever "shim" was there or just didn't bother to fix.

Good to know this is working for you - I couldn't find any documentation on this being done...

No, I haven't seen any specific mention of it anywhere either.

Quite possible if your lathe had been apart before the fibre washer "shims" were left out, or simply fell apart with age.

Be sure if you make a shim to put suitable holes in it so the oil can dribble down from the saddle into the cavity in the apron where the traverse gears live.

Edited By Hopper on 28/12/2017 10:17:08