Power cross feed: electric motor or linkage to spindle?

[RainbowsParticipant @rainbows]

Ok well that's a slightly clumsy title

Some of you may remember my lathe identification question

Against all sensibility that lathe got bought and mostly restored so far

However the apron is missing a few part: the worm screw that mounts on the power feed shaft and the assorted gears that transfer that power to either the rack and pinion or cross slide leadscrew.

Option 1: design and build a replacement for the missing gearing to the power feed shaft – the rarity of Wilfins means I can't expect to find someone to give me dimensions as per the original build

Option 2: Slap an electric motor somewhere in or on the saddle and belt it onto the existing gears

To me option 2 sounds much easier but at the same time its rare to see it outside of 1 or 2 modified mini lathes which makes me think there is a catch, A 21W, 60 RPM worm gear motor on ebay is only £15 so why wouldn't more lathes use that instead of all the cost of gear cutting?

[RainbowsParticipant @rainbows]

[JasonBModerator @jasonb]

Posted by Rainbows on 14/09/2019 18:51:28:

…………..so why wouldn't more lathes use that instead of all the cost of gear cutting?

Most people want screwcutting facility so it is only a few extra small gears to add cross feed

[BazyleParticipant @bazyle]

Originally when small motors were expensive it was obvious to use the existing power source as a few gears in production quantities are only a few bob each even today. they were less concerned that the advantage of a geared set-up is the constant feed rate, or at least a constant pitch of the advancing cut if the actual spindle speed varies.
With a non-coupled drive if you have a varying load on the feed due to hard spots, swarf build up, variations in lubrication or tool wear the feed rate fluctuates and this often shows up on the surface even though you can't detect a change in the depth of cut etc.

[old martParticipant @oldmart]

You could do without a powered cross slide, but getting the saddle connected to the leadscrew is important, but usually only needs the leadscrew nut/s to be working. The gears that move the saddle along the rack are important. The gears that power the leadscrew which live at the left hand end of the lathe are frequently missing, but are easier to replace. I have removed all the hard to get change gears on the Smart & Brown Model A with similar size easy to obtain mod 1 metric gears. This is possible because at the left end of the lathe, the gear spacing is adjustable to accommodate different tooth counts.

[Mark RandParticipant @markrand96270]

A few thoughts:-
Do you have another lathe to work with and a dividing head (or access to both)? It would be quite possible to re-make the apron gears and the teeth numbers can be inferred from the shaft (e.g hole) spacing in the apron castings. Worms are just ACME threads of a specific pitch. The Diametral pitch of the apron gears is quite likely to be the same as that used in the change wheels, that's just a way for factories to save money.

I ended up completely re-making the apron gears for my Hardinge HLV, on a Myford ML7:-

Having said that, the shaft feeding the sliding and surfacing feeds was missing in the photos on your earlier thread, so you'd also be in need of that. There's nothing really stopping you from using an electric feed to the apron at this point. You'll still need to design a gearbox, but you'll get the advantage of variable feeds, which I find very nice on the HLV.

[RainbowsParticipant @rainbows]

Throwing in some newer pictures. To the mention of change wheels- one of the gears in the apron is stamped 72T and has been welded onto a hub and fixed to the shaft with a taper pin. Probably a farm repair, or maybe the Wilfin factory ran out of the right gear blank.

I do in fact have the shaft for the power feeds, though I managed to obscure it with the leadscrew in the first pic.

My mini lathe is currently in a half state of repair being mid way through a CNC conversion when I decided to restore the Wilfin. I do have a 3D printer though which would be useful for prototyping (taking bets on how long a PLA wormgear would last in actual use). No dividing head but I could maybe bungle something together on this lathe.

Checking out HLVs they have a 1/10HP (~75w) motor according to the internet (couldn't tell if AC or DC) which is beyond the majority of chinese worm motors on ebay but would be well within a drill motor.

I would trust Hardinge would spec a strong enough motor that the issues Bayzle mentioned wouldn't happen though I'd be interested in a first hand account if it maybe has issues on roughing cuts or the like.

While the leadscrew is fully working there aren't any change gears, so I have been wondering about trying an electronic leadscrew but that's for another day. Buying in metric ones is a neat idea though I'd never thought of that before.

[Mark RandParticipant @markrand96270]

That's about right for the HLV carriage motor. It's a nominally 190v 1700 rpm shunt wound DC motor with two speed ranges produced by halving the field voltage for the high speed one. It is possible to stall the carriage feed, but it's equally likely that it'll be because you stalled the 1hp spindle motor with too ambitious a cut.

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