Why can you reverse the direction of rotation of metal lathes?

**Billy Bignutz** · 17th November 2006, 05:30 AM

I have not touched a metal lathe since high school and have just acquired a restorable old lathe 9"x36" that was certainly built to last. The 3 phase control panel allows the motor to be reversed and I have noticed that all the Hare and Forbes lathes also have a switch to reverse the motor. Before I bother wiring up a single phase motor for the lathe to be reversible I ask the question why bother??. The guy at Hare and Forbes said so that you can reverse cut threads or cut left/right hand threads but you can do this by simply reversing the rotation of the lead screw (hence saddle travel direction) at the flick of a lever. I can think of no other valid reason - any ideas?.

The lathe I am restoring I guess to be about 50+ years old with no ID apart from the number 34 on the front apron (and stamped on many of the lathe parts for ID during maintenance) which tends to indicate it came from a large industrial situation with many machines of the same type. All aluminium designation plates etc have gone through wear and tear and an apparent fire. It does have some SK brand thrust ball bearings made in UK as the only hint. When restored I will post a pic if there are any old hands out there who may be able to help ID the type or if any one has a suggestion as to how best to ID an old lathe.

Thanks
Bill

**Article99** · 17th November 2006, 05:44 AM

Internal / External cutting requires opposing directions of rotation.

**Billy Bignutz** · 17th November 2006, 05:48 AM

How many left hand drills have you found as an apprentice? Have never found one myself!!
Bill

**Article99** · 17th November 2006, 05:52 AM

I'm learning to make them from carbide for a living. If it's ordered, we make it. That simple. Sometimes the flutes travel LH rather than RH. Not really a big deal, mate.

But hey, just so you don't have to use your head too much, I'll edit it for a slightly easier answer to understand, ay?

**Billy Bignutz** · 17th November 2006, 05:57 AM

Originally Posted by Article99

Internal / External cutting requires opposing directions of rotation.

Eureka - I think you have it.

When cutting internal threads (or any internal work) it would be a definite advantage to see easily what you are doing by cutting on the opposite side of the internal surface. Otherwise you have to be screwing your neck around to see what you are doing particularly on small jobs - yep I will go to the effort of having a reversing switch.

Good one

Bill

**Article99** · 17th November 2006, 05:59 AM

Hehehe. Thought you'd like that one.

**TassieKiwi** · 17th November 2006, 07:16 AM

Originally Posted by Billy Bignutz

Eureka - I think you have it.

When cutting internal threads (or any internal work) it would be a definite advantage to see easily what you are doing by cutting on the opposite side of the internal surface. Otherwise you have to be screwing your neck around to see what you are doing particularly on small jobs - yep I will go to the effort of having a reversing switch.

Good one

Bill

Won't the thread cutting gears go backwards too?

**Wood Butcher** · 17th November 2006, 08:21 AM

Originally Posted by TassieKiwi

Won't the thread cutting gears go backwards too?

On some lathes the lead screw that guides the thread cutting can be reversed for cutting LH or RH threads

**Andy Mac** · 17th November 2006, 09:14 AM

There are probably many regulation tasks involving reverse direction, but I just discovered another use for the reverse switch, when re-winding MIG wire.

I knocked together a plywood carrier for the empty 5kg spool, driven by the chuck, and its much easier to have the wire feeding over the top of the driven spool than under, guiding feed by hand...
WB, I think an idler can sometimes be fitted in the back gear train to reverse the lead screw direction too.

Cheers.

**acton** · 17th November 2006, 12:21 PM

I use reverse all the time. It is handy for cutting a chanfer on the back of a piece without swinging the cross slide right around (tool set up the same just cutting at the back of the work-piece instead of the front), can be handy for parting off if you turn the tool upside down (acts the same as rear toolpost) which I often use for silver steel to reduce that awful screeching, and I often use it because I'm lazy when threading, and so without disengaging the leadscrew, you use the lathe to back the saddle up to the same starting position without mucking around with the little leadscrew indicator.

Some of these method may be a bit bodgy but work for me. Careful with threading because I regularly knock the tip off the tool because I didn't retract it enough. I must make a retractable toolpost one day.

My lathe has a tumbler reverse for left hand thread cutting. It also has a bolt on chuck. You would have to be careful with screw on spindles I'd imagine.

**acton** · 17th November 2006, 12:27 PM

On the topic of reverse turning, does anyone have the H&F AL300 (not the 330A)? I like the idea of backgeared belt drive, and the wide range of speeds, as well as the general look of the machine, but with my tendency to use reverse a lot, will the screwed spindle make backwards turning impossible? Can you lock the chucks on? Is there even a reverse switch?

And what do you think of the lathe in general?

**Big Shed** · 17th November 2006, 06:37 PM

Maybe so that you can undo your mistakes?

**Grahame Collins** · 17th November 2006, 09:54 PM

A good site to scratch around in to Id an old lathe is here

http://www.lathes.co.uk/latheparts/index.html

It may have have info on what you may want.

Grahame

**Metal Head** · 17th November 2006, 09:59 PM

I learnt a great "trick of the trade" off someone for when facing off round plates with a wall thickness of more than 6mm thick. Tighten the chuck (3 Jaw) lightly on the edges of the round plate and put it in reverse spin (@ no more than 300 revs) and bring the cutting edge of the toolbit preferably with a radius (do not use tipped tools) and lightly press on the face of the work piece (near the edge of it) and the piece will straighten up to run nearly true.

I wish I had a lathe to explain (via pictures) but I haven't

. This is not a trick for the faint hearted.

**Ashore** · 18th November 2006, 12:25 AM

Billy Bignutz
Because you can,

as well as all the other reasons given.

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