Conventional LH versus RH threads for cross slides

[morrisman]

Hi

The normal convention re top and cross slides is for a clockwise rotation of the lead screw for a inwards movement ( LH thread ) . But looking at the old Visby lathe, the top slide has the opposite setup e.g., a 5/8 " - 8 acme RH thread , which means a anti clockwise rotation for inward travel of the slide .

Is there any reason why a main carriage cross slide ( I don't mean the top slide ) should not be anti clockwise for inward travel ?

Mike

[Ueee]

Hi Mike,
It would be OK if you were used to it and only used the one lathe and never ever used another. Getting used to it that way could lead to a big crash on another machine. I'd say the screw has been replaced at some stage with a RH one cause some slack owner decided it was too hard to turn it LH, or did not have or want to make a LH tap for the nut.

Ew

[morrisman]

Hi Mike,
It would be OK if you were used to it and only used the one lathe and never ever used another. Getting used to it that way could lead to a big crash on another machine. I'd say the screw has been replaced at some stage with a RH one cause some slack owner decided it was too hard to turn it LH, or did not have or want to make a LH tap for the nut.

Ew

hi Ewan

yes I follow your reasoning > I think the modern RH thread leadscrews advertised by vendors on EABY are for CNC applications , but I'm not sure . The LH ACME stuff is very hard to find nowadays , but RH stuff in the metric trap. form is far easier to buy .

If you are used to the normal convention, then rotating clockwise with a RH leadsrew would pull the tool outwards , not towards the work , thus negating a crash ... thats the theory

[Ueee]

If you are used to the normal convention, then rotating clockwise with a RH leadsrew would pull the tool outwards , not towards the work , thus negating a crash ... thats the theory

Yes but if you instinctively go to wind the tool out quickly (say when threading or machining to a shoulder) and you turn the handle anti clockwise the tool goes in....

[Stustoys]

Are there graduations on the dail? which way do they go?

Stuart

[morrisman]

Are there graduations on the dail? which way do they go?

Stuart

Yes Stuart

the graduations are 0 to 125 , beginning at 0 if you rotate the dial clockwise you go upwards to 10-20 etc

the top slide lead screw is pictured

[Stustoys]

Surely that would mean Ewan was on the money then?

Stuart

[pipeclay]

I don't think it's unusual to have the compound or as you call it top slide right hand.

There are quite a few lathes that have a right hand thread in their compounds, and these handles are turned clockwise.

I think it depends on how the nut is retained,whether in the fixed or moving part of the slides.

[bollie7]

I used to have an old flatbed Purcell lathe (Purcell went on to make Visby and New Visby lathes I think) and it had the cacky handed thread in the compound. I got used to it but it was pia when switching between the "normal" lathes at work and the Purcell at home.
bollie7

[PDW]

Hi Mike,
It would be OK if you were used to it and only used the one lathe and never ever used another. Getting used to it that way could lead to a big crash on another machine. I'd say the screw has been replaced at some stage with a RH one cause some slack owner decided it was too hard to turn it LH, or did not have or want to make a LH tap for the nut.

Ew

Amen. This has been done to my slotter by a previous owner and I *HATE* it. I have to double-think every single move. If I used it more frequently or speed of movement was more critical I'd have tossed the screws & made new ones by now. As it is, that is on the list of jobs I may never get to.

As for the comment re CNC machinery not caring, I'd say that's correct. It would be a dead simple programming switch to indicate direction of rotation.

PDW

[franco]

Some time ago I did some restoration work on a friend's small nameless English(?) lathe which had a right hand thread on the cross slide screw - it's very disconcerting at first, but you do quickly get used to it. It's a bit like getting into my 1927 Chevrolet after a long break, and again having to get used to having the accellerator pedal in between the clutch and brake pedals.

I would guess this lathe was from somewhere between 1880 and 1910. It had several other unusual features, including a 7TPI leadscrew. Oddly enough, this works out quite well for cutting all the common smaller imperial threads.

Frank.