metric threads with Harrison 11″ imperial gearbox

[Gareth Jones 9Participant @garethjones9]

I'm new to machining. I've been looking at a Harrison 11" lathe which has an imperial screw cutting gearbox. The metric conversion gears are not available for sale. Is there any way of using the imperial box to cut metric threads, or is the only fix is to get the conversion gears? If so, are these available, alternatively can they be machined easily?

Many thanks,

Gareth

[Gareth Jones 9Participant @garethjones9]

[not done it yetParticipant @notdoneityet]

I'm surprised there are no replies, so here goes from someoe who knows nowt about Harrisons.

The most usual perfect requirement is a 127 tooth gear, but there are alternatives, depending on lathe and your reqirements.

The Harold Hall musings on the topic may be of use or just muddy the waters.

http://www.homews.co.uk/page339.html

Doubleboost on u-toob has a Harrison, but I know not the model, and he has some vids on cutting threads, including changing gears.

If the conversion was listed as an option at one time, then the gears are relatively easy to make. But not cheap if you have one made.

Virtually anything can be achieved at a cost. Heres hoping someone more knowledgable than me will comment.

[Chris HembryParticipant @chrishembry84309]

Join the Harrison Lathe Yahoo group where you will find several other owners, some of whom will have exactly the answer. All Harrison gears are available in some form, maybe someone there will have the ones you need.

Regards, Chris, a slightly more recent Harrison owner

[Phil PParticipant @philp]

I have a Harrison manual with my L5A that has a metric screwcutting chart, I could scan it for you if you like.

The 127 gear is the one you will need along with 40, 50, 60 and possibly a 63 to get most of what you might need.

Phil

[Ady1Participant @ady1]

And don't forget, it's all just TPI at the end of the day whether it's imperial, metric, or a threaded bar from the planet Zog.

[BazyleParticipant @bazyle]

The most useful approximation is 13/11 or multiples ie 65 and 55 changewheels with 13 as driver ie on the spindle. So incorporate them and then work out what else is needed which is normally a simple ratio. Doesn't fit 1.75 which needs 11/12 but that is still your 55 wheel. Not scientific, just luck that it works
I know that sounds like gibberish but just remember it and when you start playing with spreadsheets you will find it works.

Making changewheels. The multiple key slots looks complicated if the 11" takes that type but you can cheat and have it ride on the crests of the spline and provide one key.

[Gareth Jones 9Participant @garethjones9]

All who replied, thanks for the advice.

Not done it yet, thanks for the link. I've read the Harold Hall information which answers my question.

Also thanks to Phil for the offer to scan the chart. As I am still considering whether to buy the lathe, no chart required at the moment.

Thanks,

Gareth

[JonParticipant @jon]

I scrapped a Harrison 140 6 years ago took me 10 years to kill, same as Double boost now has. Change wheels near on impossible to get the last 15 years and command a high price. Changewheels alone would have got over £200 plus coolant, 4 jaw 11", 6 1/4" 3 jaw, original C spanners, etc all for £200.
Not as bad as the Chinese machines to change change wheels but still a pain and easy to decipher with the Norton gearbox.

The L5 and L5A are very early, substantial mods it became the 11" then the last of them was the 140 metric only up t around 1965. 140 main difference is the square ish head stock rather than previous rounded styles, superb machines lost without mine much better than M300 apart from screwcutting.

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