Another “what lathe”

[MWParticipant @mw27036]

Posted by Ady1 on 21/10/2016 02:46:08:

Personally speaking I wouldn't get a lathe if it didn't have any backgear but that's just me

May i ask why? Many a new lathes, you wouldn't even get one anyway.

Michael W

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Joe Heath on 20/10/2016 23:45:45:

So tell me, do I have to choose sides on the whole new vs old thing? p

.

I think that might be a useful first branch on your 'decision tree'

It's not a simple choice though … You may need to refurbish an old lathe; but equally [unless you have unlimited funds at your disposal] you may need to work on a new one.

MichaelG.

[Ady1Participant @ady1]

May i ask why? Many a new lathes, you wouldn't even get one anyway.

Michael W

I know, and it's a pity.

I've done a few 6-8 hour almost non-stop tuff jobs, like in a production environment, and I doubt that any electronics would have stood up to it, especially hobby level electronics. It was very very Hot work. Also, I find Backgear turns a basic hobby machine into quite a serious bit of kit for heavier jobs and tough jobs.

I also notice that many electronics based machines are pretty much redundant after 20 odd years while backgeared units go on and on until they are truly finished and have no useful life left

(My own lathe is 70-80 years old and runs great)

[MWParticipant @mw27036]

Posted by Ady1 on 21/10/2016 10:35:04:

May i ask why? Many a new lathes, you wouldn't even get one anyway.

Michael W

I know, and it's a pity…

I'd agree with that, in the sense that i'm not fond of the DC + electronic setup. I'm slightly more keen on AC with Inverter but even that has it's useful limit when reducing speed, I usually use either pulleys or gear setup to reduce speed and it delivers far greater torque once you have the full power of the motor behind it.

A good question i have for you though is, aside from the backgear convenience of having a low gear power immediately to hand, what does this give you that a replica pulley arrangement couldn't? you'd still have roughly the same torque delivered surely?

Controversial point i guess but it would explain why they just don't do it anymore? I know it's obviously far cheaper to not have to hob all these gears and make an idler spindle for them to rest on, but i'd like to optimistically think that the designers were basing their decisions in reason. 

Maybe i misunderstood the whole concept of it but i'd like to know what else it gives you that a simpler mechanical reduction arrangement would not. 

Michael W

Edited By Michael Walters on 21/10/2016 11:25:59

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Walters on 21/10/2016 11:18:14:

Maybe i misunderstood the whole concept of it but i'd like to know what else it gives you that a simpler mechanical reduction arrangement would not.

.

It's very compact.

MichaelG.

[Ian S CParticipant @iansc]

The trouble as I see it of electronic speed control without back gear is that as you reduce motor speed you lose torque, and the cooling effect of the built in fan in the motor reduces to effectively zero. With back gear, as the speed drops, the torque increases, and as the motor keeps it's speed, the fan is fully effective.

Ian S C

[AjohnwParticipant @ajohnw51620]

Posted by Joe Heath on 20/10/2016 23:45:45:

So tell me, do I have to choose sides on the whole new vs old thing? p

You need to remember that wanting a lathe isn't new, In fact it was more popular than it is now. A Myford of any type was a budget lathe of it's day. Something to lust after as they were probably relatively more expensive relating to what people earned at the time. You might say the ultimate budget lathe of it's time in some respects.

The other thing to realise is that there are several design aspects that aren't used any more. Oil lubricated plain bearings in the headstock and the plain flat saddle guides on the bed. There are good reasons for this especially the bed. Neither of these wear well. It doesn't take much to spoil them. Very little in fact.

Toolroom people can also be fascinated by super 7's in particular. Part of that will be all of the operations that can be carried out on a lathe with a T slotted cross slide and a vertical slide. The other aspect is that given an excellent example they can produce excellent results. There are 2 aspects to that. Lathes will vary as they come out of the factory and they wont stay like that for long. The beds can be lapped up by hand to take out wear but it's not an easy thing to do. The dovetails on the cross slide can be too. The worst aspect though is the headstock bearings. It's not just a case of adjusting them. They need scraping back into alignment otherwise the lathe will turn a taper and it wont be possible to set it to get the best out of the lathe. The thing to appreciate is the amount of taper in a turning test on a new lathe. It might be a few 10s of um or less. I'd expect under 20 on a lathe with a test certificate. That's not much in terms of wear. 3/4 of a thou in old money over 4".

I wish you luck if you want to find one in very good condition. You'd probably need to find a one owner well looked after one that hasn't done a lot of work. My Boxford is one of those but it could do with new headstock bearings really. There isn't any appreciable bed wear as far as I can tell. That isn't that common on Boxfords. They get used for all sorts of things as do Myfords. I have seen Super 7's next to production lines probably for remedial work or batch work where it isn't worth setting a machine up. You can get some ideas of what might be called real lathes cost from lathes.co.uk. I understand a modern boxford would cost about £15k. Some other well known makes a fair bit more. These days if some company want a cheap lathe they probably buy chinese. At one time they might have bought a Super 7. They wont expect much out of it performance wise so are likely to work it to death. Toolrooms etc often do that with all lathes they buy. Sell it when it can't even do what they regard as rough work. How bad will vary.

John

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Edited By Ajohnw on 21/10/2016 13:15:57

[Roderick JenkinsParticipant @roderickjenkins93242]

As MichaelG says: my S7 back gear gives a 7.75:1 reduction. Also, there is a lot of torque available – belts might slip.

Back to MichaelW's point: Hobby lathes are clearly designed to a price point so electronic speed control is cheaper than additional belts, pulleys and gears. However, modern lathes don't tend to have gap beds so the ability to turn large diameters (for the size of lathe) is redundant and, anyway, TC tools can cope with a faster surface speed. I don't think I've used my back gear since I've had a VFD and TC tooling. Longevity is a different matter but if I had a speed control board go west I'd be comfortable fitting a 3phase motor and VFD in its place.

Rod

[Ian S CParticipant @iansc]

Up until 20yrs ago Russian lathes were popular in NZ, When I bought my Taiwanese lathe it was a toss up between it and a similar sized Russian lathe, the initial price was pretty much the same at first, but over a few weeks I bargained the Taiwanese one down $NZ 1500, and then someone drove the fork of a fork lift truck into the switch gear on the lathe in the show room, so they knocked another $NZ 250 off, so I bought it, and when it arrived there was no damage to the switch, they'd given me a different lathe but I still got the full discount.

The lathe can take 17" in the gap, I think it's been out twice in the time I;v had the lathe. There is less chance of belt slip with back gear than direct drive as the major reduction is after the belts.  Don't worry about the chuck, it's hanging on my hoist.

Ian S C

Edited By Ian S C on 22/10/2016 10:38:44

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