I'm hiding under the rug, ready for the barrage.

Steve.

YOu could do a Burt Munro and cut a section out of your bed with a hacksaw. I suppose in today's world an angle grinder would be more appropriate. ( )

Edited By Hopper on 15/11/2020 23:41:53

Sorry rik. There was a thread the other day with the same question nearly. Many said a 125mm chuck on the Myford would not do the bearings much good. I have a 125mm 4 jaw & use it often. On the Super 7B. But that has a bronze front bearing & twin races at the rear. . I think you may have white metal bearings which are considered to be fine with a 100mm but not with a 125mm. Only a reply from others. I do not know the answer.

Steve.

Bearing load and other stresses increase more than common sense might suggest because the weight of a chuck is proportional to the square of it's radius. A 50mm x 125mm chuck is roughly twice the weight of a 40mm x 100mm chuck, not 25% heavier. And because bigger chucks will used to support heftier work as well, the total stresses could be out of specification.

As even grossly overloaded machines are unlikely to fail immediately, such 'upgrades' often seem harmless. It takes time for damage to become apparent, thus a bearing that would have lasted 20 years, now only lasts 2.

Bodgers rarely think about long term consequences, so in their world this isn't a problem. Think twice about buying a second-hand machine the owner has 'improved' with this sort of modification. Self confidence is not valid engineering, ask to see his sums and references!

But hobby lathes generally have an easy life. They aren't worked flat out round the clock like production kit. So while I wouldn't fit an oversized chuck to a lathe as a permanent feature, I'd happily risk it to get the odd job done. Point is it's a mistake to overload machines all the time, but thay have a safety margin that can be exploited occasionally. Don't take the p*ss though, best get a bigger machine when lots of heavy work is to be done.

Easy test. Put the big chuck on and use it to grip a suitably heavy lump of metal. Then put 360 hours of work on the bearings, gears, belt and motor by leaving the lathe running continuously for 15 days. Would it be a surprise if this caused a problem?

Dave

The thought of cutting a bigger gap into a lathe bed with a hacksaw, or angle grinder, appalls me. It will weaken the bed, and so may well affect accuracy, by making the bed more flexible.

Granted, there ARE times when needs must, and the devil drives!

Risking the wrath of Myford owners, in my book, the ML7, and it's offspring, is too flexible anyway.

Confessing some of my many prejudices, I learned on industrial machines, and so am a graduate of the "Brick mausoleum" school of engineering.

Which is not much good for aeronautical work, but does explain why so many Victorian machine still survive!

Howard

Horses for courses springs to mind, would you use a watchmaker's lathe to machine a 8" flywheel?

No, then there are reasonable uses for Myfords as well as industrial size machines in the right environment. History of ME proves the case.

For the occasional job you might look at faceplate dogs which with a little thought you could design yourself to give greater capacity than a chuck.