125mm HBM Chuck too heavy for Myford ML7???

I still have the original Pratt Burnerd 4" 3-jaw (completely worn out) and 6" 4-jaw chucks that must have been supplied with the lathe. Interestingly they weight almost exactly the same at just a shade over 4 kg. I also have a very old 5" Taylor tapered scroll 3-jaw chuck that came with the lathe and that weighs just over 5kg, however i've never used this chuck in anger.

I purchased the larger 125mm HBM chuck (there is a 100mm version) to replace the worn out 4" original. I decided to go with this particular manufacturer based on its cost and quality both being acceptable and also becasue it has a larger hole through the middle meaning I wouldn't be left with so many stubs of material.

I only use my lathe for small jobs as I have access to a Colchester student and a Boxford Industrial lathe at work.

Just to confirm - on the ML7 the distance accross the shears is 4.5" and the max swing radius is 3.5".

I'm still a bit concerned that the HBM chuck weighs 1.5kg more than the original chucks, but I guess the maximum speed i'll be using is ~600 rpm and as long as I don't load the chuck up with anything too heavy it should be okay.

Whilst I would concur with much of the comments on shear dimension etc

The Myford site says

THIS 125mm CHUCK IS TOO HEAVY TO MOUNT ON ANY MYFORD WITHOUT THE M42.5 x 2mm 4MT SPINDLE

As far as I am aware the shears on the big bore Connoisseur lathe are no bigger than the small bore Super7. (I am happy to hear if someone knows different). The warning seems more concerned with the slenderness of the spindle. The big bore is going to be a lot stiffer than the much lighter small bore spindle.

I too purchased a 125mm 3 jaw and a 125mm self centering 4 jaw from Myford about 4 years back so I am intrigued to know just what the thinking behind the warning is. I have to admit to removing the 125 from the lathe when not really required and using the 100mm or ER collets for general use until I know more.

It really could be anything, even that maybe the risk of damage to the spindle nose is that much greater when attaching or removing the chuck from the small bore spindle to bearing overload to twist or whip of the spindle itself when running up.

What we really need is to ask Myford why they issued the notice. They will be at the Midlands show so a direct question seems to be in order.

regards Martin

As they supply a bigger 4 jaw the comment doesn't make much sense really. I only mentioned Boxford because it's right by me so I could measure it. I just don't believe an extra kilo or so would make any difference. I could understand why people wont do what I am about to do fit a 200mm 3 jaw. The weight difference in that case is very large. I'm doing it to obtain a bigger hole in the chuck not to hold bigger work,

Noticing another comment, chucks shouldn't be used with the jaws sticking out really and I'd guess some people do take a bit more care if they have to use them like that. To far out and the scroll and teeth on the back of the jaws wont all be meshed and there is far more chance of striping the scroll.

I can't weight to hear the answer.

John

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I totally agree, I did send Myford an e-mail about this but never got a response.

I also contacted RDG who did get back to me and they stated that the 125mm HBM chuck is lighter than the Pratt Burnerd chuck sold by Myford and is therefore suitable for use on the ML7. However, we have a 125mm Pratt Burnerd chuck at work so i've weighed both chucks and the HBM chuck is actually slightly heavier - so even more reason to be concerned about the warning from Myford!

I also remove the chuck when its not in use as it just feels to heavy for the size of the spindle.

Could not agree more...............................

No one yet seems to have asked the obvious, and pertinent, question:

Does anyone have a Lathe Handbook produced by the current Myford company ? ... and does it include any reference to a maximum 'nose weight' ?

... It is just plausible that there is a 'Type Approval' issue.

MichaelG.

As I mentioned earlier I usually have a 4" threaded body PB mounted and the distance from the register face to front of jaw is about 73mm, the 5" TOS is 105mm, this is quite a lot of overhang on a small spindle and is the factor that concerns me more than weight. As a significant amount of work done in a homeworkshop is too big for the machines it is a tribute to all makes that it takes it in its stride, of course material removal rates usually match the precariousness of the setup but with care and sympathy for the abuse no harm is usually done. Some chucks I have are marked on the jaws to indicate the maximum allowed extension from the body but jaws sticking out are another danger as I often use my hand on the chuck as a brake (probably bad practice) and doing this with jaws sticking out will propably result in the red stuff leaking out.

Mike

I cant weight to hear the answer.

John you have had it already, in big red letters, the post above yours.

At the end of the day i dont see it matters much 4" or 5" there are folk reading this using either

As for jaw projection if you take a look at Brians pics with his on going saga with the little TU one shows a chucked fly wheel and the jaws are sticking out past chuck dia, it"s the one with the threading tool being used on the rim........Nuff said at least by me on this topic. it"s getting to be a bit like how longs a piece of string

bodge.

Apologies if my original posting has generated such a drawn out debate.

Just to re-focus this thread - my concern was specifically about using a 125mm chuck that is ~25% heavier than what was supplied with the lathe, and that concern was reinforced by what I found on the Myford website:

THIS 125mm CHUCK IS TOO HEAVY TO MOUNT ON ANY MYFORD WITHOUT THE M42.5 x 2mm 4MT SPINDLE

This statement is specifically referring to the weight of the chuck and the size of the spindle, I’m not sure where the "bullshit baffles brains" mentality comes in here, the engineers at Myford must have carried out the relevant spindle/bearing load calculations and identified a potential problem.

In reality I don't suppose there are any safety concerns to worry about and nothing is going to break if you use the bigger chuck. If the lathe is worked hard with the bigger chuck I guess you may suffer accelerated spindle bearing wear and perhaps the rigidity of the lathe is not quite up to the size of the work you could potentially clamp with the bigger chuck. Who knows, let’s wait to see what Myford have to say about it.

The fact that the 125mm chuck is physically bigger is not really of concern because as practical, mechanically minded engineers, I’m sure we would all use our common sense and machining skills not to try and hold something too heavy or too big for the chuck (and that goes for any size of chuck!!).

Ross, Hi & welcome

No apologies required, thats just the way it goes on here at times, and like your self, im not too sure just as to how the " bullshit baffles brains " got into it either ! seemed a simple enough question to ask, and as others have rightly pointed out a 6" four jaw is usually a stock item to go with a ML7 as far as that goes, if one wants to hold some thing lumpy and chunky ones probably going to need a bit bigger chuck, so as a general rule the 4 jaw is usually 2" bigger, the idea being the work piece most likely wont clear the cross slide anyway, plus if it"s lumpy ones going to have the revs down a bit, and then one gets to the face plate usually bigger again , 9" ,so i figured these two items were out side the scope of the original question. If you were to load the 5" up with as big a bit of bar as will clear the cross slide and 14" or so length then you would also be using a fixed steady or a rolling centre or both, so i dont think it"s going to matter to much.

bodge.

Do the "big bore" Myfords have roller or ball bearings rather than plain bearings, maybe that's the answer.

Ian S C

Thank you Bodge, yes I completely agree with what you said - I'm not going to worry about it too much, although I will be interested to know what Myford have to say about it.

Regards,

Ross

Edited By ross748 on 10/10/2015 11:25:32

Perhaps you should ask them how big a piece of depleted uranium you can machine on the lathe.

John

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So I asked Myford at the Show. The essential facts are that there were a little concerned regarding bearing wear on the small bore lathe when running with the bigger 3 Jaw. They freely admit that you can do it, they recognize that you probably will do it but they suggest you should not do it all the time.

I think that's basically where we all go to on this thread too. I Use the 125mm when I need to but use my other chucks or collets when I don't.

regards Martin

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Thanks, Martin ... Nice to hear that they responded !

Perhaps they will now see fit to 'soften' the bright red upper-case 'shouting' on the web page.

I did try contacting them about this discussion, via the 'Myford' website form, but have received no response or acknowledgement.

MichaelG.

The weight of the chuck would help compensate for the upward pull of the belt drive which will and does cause bearing wear. Cutting forces push up and back too - hence the popularity of under drive and it's variants.

John

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UPDATE

I have received a reply from 'Myford'

[quote]

[/quote]

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Quite frankly, I don't think I have the enthusiasm to pursue this any further.

MichaelG. 

Edited By Michael Gilligan on 21/10/2015 16:42:54

Thank you to everyone who contributed to this thread.

I checked the spindle bearings on my lathe the other night and I can confirm that the large 125mm HBM chuck I've been using (and that's not a lot of use in reality) has significantly worn the front bearing shells on my lathe! I last checked the bearings when I bought the lathe a few years ago and the bearings were in fine condition. That was just before fitting the HBM chuck!!!!

In my opinion the 125mm HBM chuck is too heavy, too bulky and most importantly, it protrudes too far from the end of the spindle for use on the ML7, particularly when compared to the original Pratt Burnerd 4" chucks that were specially made for the ML7.

The 125mm HBM chuck and its backplate literally dwarfs the Pratt Burnerd chuck, and the difference in weight is massive. Further evidence comes form the fact that the specially made Pratt Burnerd chucks have a threaded body rather than a backplate to improve the rigidity on the ML7. So having a chuck that is much heavier and which has its business end much further away from the spindle bearings is not going to help with rigidity one bit!

Just to reiterate - my machine has the original white metal bearings, perhaps the later machines (or upgraded machines) fitted with bronze bearings and hardened spindle may cope better with the bigger chuck.

I've brought one of the Pratt Burnerd 4" chucks that were specially made for the ML7 now (a good second hand item), but part of me feels that RDG owe me a replacement spindle and bearings because they were selling these larger chucks as "take out if the box and screw directly onto the spindle of your ML7 or Super 7" without really considering its suitability for the older machines.

Oh well, you live and learn!

Cheers,

Ross

I'm surprised you could even open the jaws far enough (without them hitting the bed) to make the use of this chuck advantageous.

One of my "tooling" luxuries is to have 2 four jaw chucks for my ML7. One is permanently fitted with internal jaws & the other with external jaws. Both of these chucks are Pratt Burnerd.

One is marked "Specially made for the ML7" & is "Badged" as a Model 34M it weighs 4447gms or 9Lbs 12.9ozs in old money.

The other has Pratt Burnerd Int Stamped on the edge and no other markings. It weighs 4383gms or 9Lbs 10.6 ozs.

Don`t know how old my lathe is but there is no wear in the white metal bearings & it is in pretty regular use and well kept. Personally speaking if I had been in the market for a 4 jaw & seen the warning label as originally stated I wouldn`t have touched it with a bargepole ! You pays your money & takes what you get. At the risk of being hounded off the forum I would say only buy British, U.S. or German tools but they are getting scarcer than hens teeth.

Alan