Lathe Spindle sizes

[Glenn at Raven]

My analysis is that with this shaft configuration the lathe will perform like a lathe with a shaft of uniform 1!/4 inch diameter, since the reduced section will not influence it's capability. So I don't subscribe to the misleading advertising accusation.

Glenn

[Leo Van Der Loo]

My analysis is that with this shaft configuration the lathe will perform like a lathe with a shaft of uniform 1!/4 inch diameter, since the reduced section will not influence it's capability. So I don't subscribe to the misleading advertising accusation.

Glenn

Maybe they could make that head on that 1" shaft 3" instead of just 1¼", and then could call it a 3" spindle, should be OK in your analysis right ??

I disagree with your analysis, but it is non of my concerns here, that kind of lathe will not get inside my shop, I've seen enough of the Quality of these Chiwanese products, made so they can undercut prices of good quality products and increase their bottom line.

[Murray in Brights Grove]

I think at a normal load for this size lathe Glenn is correct the spindle should be ok. I also think that at a maximum load or overload condition the shaft will flex in the middle and maybe continue to oscillate until something has a catastrophic failure. So, is the lathe engineered poorly or is the lathe being used over its capacity? If huge loads are wanted maybe a second dedicated huge sized bowl lathe is needed. I understand pushing things to the limit. It is our nature but hanging a tree off of a lathe that is meant for a twig? Maybe some have gone a little far.

Murray

[Leo Van Der Loo]

Murray yes if one goes past the capacities of something, it will break.

However the thought here was that the lathe had a heavier spindle than it does have, and of course this is what was questioned.

Is it right to call a spindle the size of the head that is on there, like I said could you now add a 3" head on that 1" spindle and call it a 3" spindle, and in my view that is just not right.

I am not justifying the size that was hung on there, I just think (in my view) it is dishonest advertising, and it is also my opinion that a full size shaft/spindle would be stronger and stiffer than a spindle that is thinner right behind the treaded head, and yes that spindle could of course be overloaded, but that was not the question.

Anyway this is my view on it, you might look at it from an another angle

[Rod Sheridan]

[QUOTE=Leo Van Der Loo;409095]Quote

So you think that a 1" shaft with a 1¼" head outside the main bearing is just as strong as a 1¼" shaft/spindle ???

QUOTE]

No Leo, it wouldn't be as strong, however that has nothing to do with proper engineering.

The correct question from an engineering aspect is whether it is strong enough to withstand design loads. If it is, it's good engineering.

Regards, Rod.

[Leo Van Der Loo]

QUOTE]

No Leo, it wouldn't be as strong, however that has nothing to do with proper engineering.

The correct question from an engineering aspect is whether it is strong enough to withstand design loads. If it is, it's good engineering.

Regards, Rod.[/QUOTE]

I know that and you know that Rod, but it was implied that it was.

Of course the loads being put on there could be what one thought what a full size spindle would be able to handle, as in this case it was probably much more than even a full size spindle should be expected to handle, and then when the spindle was flexing the question arose of is it right to call the stepped down spindle the same as the outside treaded end.

And that is where I do disagree with

What is the design load on a 12"X24", 16"X30" lathe or 18"X 36" wood lathe ??

I suppose it is a good question, but a hard answer with all the variables that can be brought on, and I don't think stepping and machining down that spindle and calling it the size of the thicker treaded end on there is a good idea, or honest advertising, just IMO

[gwilki]

I agree with Leo and the OP on this one - belatedly. This thread has gone off subject and seems now to be more about whether a given diameter of shaft will put up with certain loads. That's not what the OP raised. The issue is whether, as purchasers of lathes, we accept that a manufacturer can claim that the spindle size is 1.25" when, in fact, only the threaded part is that diameter. Those who are arguing that this is acceptable seem to be basing that on the fact that the 1" shaft will be fine for the purpose to which the lathe will be put. That was not the original point of the thread. I am not an engineer, but I'm assuming all those on here who have stated categorically that the 1" shaft will not flex are engineers. Good on them. However, to repeat, that was not the question put to us. If the engineers believe that it is acceptable to mislead or lie about the specs of a machine, I can only hope that I never need to use a machine that they designed.

[billh]

It seems that the spindle size, ie the actual size of the spindle throughout, is not specified. Oneway, Nova DVR, and General specify the thread size, not the spindle size on their sites.

billh

[Glenn at Raven]

My problem with this thread is that some are accusing the manufacturer of unethical advertising, without an adequate analysis of the operation of the lathe. The shaft inside and outboard of the outer bearing is apparently 1.25". As advertised. This is the critical , load carrying portion of the spindle. The reduced diameter of the spindle inboard of the outer bearing will not compromise the load carrying capability of the lathe unless we were looking at much greater torque loading than we would ever encounter.
So I think the thing which is unethical is this accusation leveled at the manufacturer by some who appear to lack understanding of the mechanics of the lathe.
And throwing in comments on the countries of origin does nothing to contribute to the analysis.

Glenn

[Roudhead]

Glen if you read the manufacturer's literature it clearly states spindle size as 1 1/4". Not just the bit at the inner bearing. If I go and buy 3/4" dowels I expect them to be 3/4" the whole length, not for just a short piece near the end. Also I wouldn't want my dowel drilled through to accommodate 3 screws. Of course that has been sort of pushed aside as the focus has been on the spindle diameters. So considering there is a morse taper and a through hole the length of the spindle there are also 3 holes drilled radially opposing one another right where any flexing would occur if the spindle was overloaded. Not exactly confidence inspiring. But that's OK as we really don't expect too much in quality or honesty in advertising when the product is made off shore. If Oneway was doing it there would be an uproar. Anyone checked their Oneway yet?

[Leo Van Der Loo]

You thought they would be like these ??, yes me to

Lathe spindle.jpg Spindle Vicmark.jpg
Oneway spindle.jpg

[Glenn at Raven]

Thanks for the diagram Leo. You will notice that the shaft size in the outboard bearing in the coloured cut-away is larger than the inboard remainder of the shaft. I think that that is what we have been discussing as a design fault ...? I am not sure which model lathe this diagram represents. The Oneway shaft also shows a reduction in shaft diameter at the inboard end.
The screws tapped into the inboard end of the shaft on the International would have no effect on the load capability of the shaft. That is not a section which is subject to any flexing unless there is a pulley or other load applying device attached to that end..

Glenn ..... (a Mechanical Engineer.)

[stevem]

the odd thing is that it costs money to machine that spindle down to one inch from the blank which was somewhat bigger than 1 1/4, in fact the blank was bigger than the largest diameter on the spindle. so the center section was turned down to accomadate the pulley set. the smallest pulley size is chosen by the required max speed of the machine and the spindle has to accomadate that

the spindle in a beaver 3400, is 7/8 od from the threaded end to the shoulder for the outboard bearing where it drops to 3/4 but there also a shoulder for threaded stuff to stop against, im guessing 1 1/8 in diameter, so of course the billet blank had to be at least 1 1/8 od

the spindle diameter inside the headstock has to be small enough to accomadate the smallest drive pulley which has to be big enough to house a set screw and the woodruff key

[Leo Van Der Loo]

Do we look at the same pictures here, or do we see what we want to see ??

The threaded end is the same size as the spindle, not larger, only the bearing land is larger on the inboard end of the spindle.
spindle enlarged.jpg

On the Oneway the treaded inboard end is not larger than the spindle as can be seen quite well in the pictures.
Oneway spindle and housing.jpg

Oneway spindle.jpg

The Vicmark spindle is also not thinner than the treaded inboard end, these are the way I would prefer my lathe spindle to be.

And calling a spindle the size a fat head in on the end is not very ethical IMO, and this is all I'm going to say on this matter

[Roudhead]

Thanks for the diagram Leo. You will notice that the shaft size in the outboard bearing in the coloured cut-away is larger than the inboard remainder of the shaft. I think that that is what we have been discussing as a design fault ...? I am not sure which model lathe this diagram represents. The Oneway shaft also shows a reduction in shaft diameter at the inboard end.
The screws tapped into the inboard end of the shaft on the International would have no effect on the load capability of the shaft. That is not a section which is subject to any flexing unless there is a pulley or other load applying device attached to that end..

Glenn ..... (a Mechanical Engineer.)

The 3 screws are in between the pulley and the inboard bearing so going by your statement that's exactly where flexing would occur from the drive system or by a sudden stop of a large spinning chunk of wood
(not a mechanical anything, just a turner)

[Glenn at Raven]

the 3 screws are in between the pulley and the inboard bearing so going by your statement that's exactly where flexing would occur from the drive system or by a sudden stop of a large spinning chunk of wood

There is very little bending moment between the two bearings. The critical diameter of the shaft is at the outboard bearing. Quoting that diameter, form an engineering viewpoint, tells you the load capability of the lathe, and is a perfectly ethical approach.
If you don't want to accept that - so be it!

Glenn

[Roudhead]

So we've now gone from "not a section which is subject to any flexing" to "very little bending moment" I guess that's engineeringspeak for I don't know. If the critical diameter for the shaft is at the outboard bearing why is that bearing usually smaller and the spindle diameter smaller than the inboard end. Methinks your ethical approach is a little bit off somewhere. Plus the usual spindle size reference is the threaded section on the inboard end, at least it is in my world

[Glenn at Raven]

Sorry if there is confusion with which end is which. I describe the end to which the chuck, faceplate etc is mounted as the outboard end - away from the drive mechanism. Steve makes a good point when he points out that the reduced diameter between the bearings permits the use of a pulley with a reasonably substantial inner hub, yet a small diameter. As has been pointed out the shaft reduction adds to the cost of manufacturing the spindle, and this pulley accommodation is probably the justification.
So Roundhead please just continue to feel cheated, but from an engineering viewpoint it is good design, and the listing of the critical shaft diameter is sound practice.
Amen!!

Glenn

[gwilki]

Glenn: I believe that it's fair to say that, other than you, everyone in this discussion is calling the inboard end the end that is closest to the tailstock end of the lathe. The outboard end is the other end. :-) :-) I'm not criticizing your take on it. I'm simply trying to explain why there may be some degree of disagreement here. Any lathe literature that I've seen, which talks about "outboard turning", is always referring to turning from the end of the lathe headstock that points away from the tailstock, not towards it. That's why you can invariably turn bigger when outboard turning. The ways don't get in the way, so to speak.

[Glenn at Raven]

Hi Grant,
Thanks for straightening out the nomenclature. I was simply considering outboard from the drive , but this is clearly confusing. Mea Culpa!

Glenn