Metric threading with inch based leadscrew

[olderdan]

Noticing recent posts mentioning 127 tooth conversion gears I thought it may be useful to show a different method using standard gears, namely a
54T pegged with a 44T giving a very close conversion for most thread lengths.
This is not my idea but taken from a site called Workshop Protects which seems to no longer exist, fortunately I took screenshots of it.



Hope someone finds this useful.

[ncollar]

Olderdan
Do you have any idea what the foot notes are for the three astrichs? ***

[hemmjo]

Looks like the *** line got cut off on the screen shot.

I have this link tucked away for when I need to cut a metric thread on my old Logan lathe.

Metric Threading

[olderdan]

Looks like the *** line got cut off on the screen shot.

I have this link tucked away for when I need to cut a metric thread on my old Logan lathe.

Metric Threading

Thanks Hemmjo, that is a very comprehensive article, thanks for the link.

[olderdan]

I think the three asterisks indicate a slightly increased error for those pitches but I have not done the maths.

[ncollar]

No, three *** mean there is more info for it.

[rebuilder1954]

I would second Nelson's recommendation: the 37/44 tooth combination shown there yields a 1.2703:1 ratio: very close to the ideal 1.2700:1 ratio. according to Logan's web site, it's only 2/100s of 1% error. the 54/44 combo yields 1:2273:1.

Kudos to OlderDan for bringing this to the surface: an easy way for inch-based lathes to cut metric threads!

[mklotz]

Noticing recent posts mentioning 127 tooth conversion gears I thought it may be useful to show a different method using standard gears, namely a
54T pegged with a 44T giving a very close conversion for most thread lengths.
This is not my idea but taken from a site called Workshop Protects which seems to no longer exist, fortunately I took screenshots of it.

Your text in your writeup says 54:44 gear pair

54/44 = 1.2273

but the text in the picture you included seems to indicate 56/44

56/44 = 1.2727

which is, indeed, closer to the desired 1.2700000....

Was the "54" a typo or am I missing something here?

Of course, 47:37 is still a lot closer...

47/37 = 1.27027027

[olderdan]

It was indeed a typo, thanks for pointing it out, probably would have been better to let the chart speak for itself.
I am sure there are better combinations but the chart is for standard SB change gears which are all of an even number.

[mklotz]

I would second Nelson's recommendation: the 37/44 tooth combination shown there yields a 1.2703:1 ratio: very close to the ideal 1.2700:1 ratio. according to Logan's web site, it's only 2/100s of 1% error. the 54/44 combo yields 1:2273:1.

Kudos to OlderDan for bringing this to the surface: an easy way for inch-based lathes to cut metric threads!

Another typo I think...

44/37 = 1.11892

The correct form is...

47/37 = 1.27027027...