Maximum chuck weight Myford Super 7

Gents,

I was looking for a slightly larger chuck for my Super 7. We have a P&B 3 jaw (100mm) on it at the moment. On the Myford website they have a 125mm chuck (also P&B brand) but that comes with a warning about it being to heavy. We have the normal spindle on our lathe.

What is the general consensus regarding chuck weights? Our lathe doesn't run for great periods of time and is not used professionally.

Thanks in advance,

Mark

The other factor in your equation should be speed. Your real concern might be rotational momentum?

E=MV^2

Mark,

I think you will find it worth looking at this previous thread: **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=111162&p=1

It's inconclusive I'm afraid ... but an interesting discussion.

MichaelG.

I usually leave my 4" chuck mounted on my Myford but I have a 5" for when it is useful. I made the backplate as slim as I could to minimise overhang but it is still quite a bit more than the 4". Myfords have survived doing jobs that are well outside their comfort zone so just take things gently. It is good to think about overhang as measured from the bearing and not just from the chuck, if possible use a centre in the tailstock to avoid pushing your luck too much.

Mike

My old Drummond M-type has had a honking great 5" (125mm) chuck on it since 1937 and is still going strong. The Drummond's headstock bearings are smaller than the ML7's yet have stood up well, so far.

Michael, Mike and Hopper,

Thanks for that link. I should have searched beforehand as my question is almost a carbon copy!

The common wisdom appears to be that it’s of no consequence.

Thanks again gents,

Mark

Edited By Mark Gould 1 on 06/05/2018 12:21:00

Consider a thin four jaw, less weight than a standard three jaw. I bought a Zither from ARC and fitted to my SC3 no problems of twelve months use. Consider not only the chuck weight but also the weight and overhang.

Also don't forget the all up weight as a bigger chuck will mean you are also likely to hold bigger items too

I ran a five-inch 4-jaw on my Super 7 for years without problems. But it was a shallow, threaded-body chuck, and therefore light in weight and with not much overhang.

It really depends what you are going to put in the chuck...

Myford will have calculated the stresses and strains involved and then sized everything up by a safety factor, probably at least x5. You have headroom.

With moderation you can use a heavier chuck. Bear in mind Jason's point about keeping an eye on the total weight - resist the temptation to put extra large, heavy, or unbalanced work in the chuck just because it fits.

Personally I wouldn't overrate anything I care about by more than 1.5x normal for long. Slight overloading will likely take decades to harm a lightly used machine. Routinely overloading a busy lathe will cause early problems. In other words, go for it within reason - just don't take the piss. If you break the lathe it's your own fault.

Dave

I think we’ll go for a direct mount chuck. Saves weight and reduces overhang. You are if course correct about having certain leeway but after spending a small fortune on our Super 7 I have become like an overconcerned mother and tend to clean it more than I run it!

Thanks again for all the suggestions, they are much appreciated.

I have got a 6" 4 jaw which I use on my ML S7, often intermittent cuts on a chunk of Cast Iron or black mild steel, 2"/3" square x 3" or 4" long, but only at very low speeds. The chuck alone is mighty heavy but I think it's more a test of my weight lifting ability these days. Lathe appears to be able to cope with it OK, no swash - plate effect so far.

John