Imperial Thread Cutting on Metric 140

[Pete.]

If the graph is to be believed, that has come off the L5 with a two lever norton box. Then I can go 50, 40-60, 127 and get the majority of pitches.

You can't Brad. That chart is for a imperial lathe to convert to metric threads. You have a metric lathe you wnt to cut imperial threads. the conversion is not reversible. Metric to imperial is less straightforward.

 

[Tinbasherdan]

I use a 63 on my 11” , basically a rounded headstock 140 and it works fine with minimal error

 

[Pete.]

This was on the HarrisonLathe .io group

And so was this:

 

[Brad93]

The reason I wanted to use a 127 gear is the fact I don’t have to buy any other gears. To get a 40 and a 63 is gonna cost a fair bit.

 

[Tinbasherdan]

The reason I wanted to use a 127 gear is the fact I don’t have to buy any other gears. To get a 40 and a 63 is gonna cost a fair bit.

I offered you a 63t some time ago and you didn’t reply beyond the first message. Unfortunately that gear is now gone

 

[Brad93]

I offered you a 63t some time ago and you didn’t reply beyond the first message. Unfortunately that gear is now gone

Did you? Sorry mate I don’t even remember.

 

[Fastdruid]

The reason I wanted to use a 127 gear is the fact I don’t have to buy any other gears. To get a 40 and a 63 is gonna cost a fair bit.

Ignoring for a second that everyone says it doesn't fit. You need to get the "same" ratio at the Norton box as you would have with the 50-63/40-120 combo and I just can't see you can achieve it with the gears you have.

If we assume a 1:2 ratio in the Norton box on the first setting (4TPI with fig 1 and 16tp with fig 2) then 1 turn (of the spindle) results in either 6.349206mm or 3.174603mm movement of the carriage with a 6mm pitch leadscrew which is 4.0005TPI or 8.001TPI.

50-63/40-120 is 1:0.26455
60-63/80-120 is 1:0.529101

To be exact you need to be 1:0.264583 or 1:0.529167

I can't seem to get anywhere close to the first, the nearest I can manage doesn't even involve a 127t!

40-55/20-55 or 20-55/40-55 results in 8.003636 TPI but you don't have a 40t, 20t or two 55t's.

The coarser ones however are achievable. The following should work.

127-120/60-120 or 60-120/127-120 results in 4TPI but you don't have a second 120t (and I don't believe that combo would fit anyway).

Now of course you _might_ be able to better that if you ignore the settings on the Norton box, work out the exact ratios in it and plug them into a screwcutting calculator. That _may_ still be possible. I would start by working out where you can fit the 127t because odds are you can only fit it in a limited number of places which will eliminate potential combinations.

IMO your best bet really is to get the 63t and 40t gears you're missing. You can get delrin ones pretty cheaply https://ebay.us/kDXhmQ and https://ebay.us/En31id

 

[Agroshield]

IMO your best bet really is to get the 63t and 40t gears you're missing. You can get delrin ones pretty cheaply https://ebay.us/kDXhmQ and https://ebay.us/En31id

I have bought off that seller and his gears are good value and well made.

I believe the gear spec. for a 140 is the same as a Drummond (14DP, 14 1/2PA) so a 40t from one of those is a possibility, but you would need to make the centre fit and unlikely to find one cheaper than the delrin one.