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40G 1/8" thread ?

Hi Folks I need to cut a filter thread into a 1.25" telescope eyepiece barrel with 1" I.D. and from my thread gauge its Whitworth 40G 1/8". I have one of the little Warco mini lathes but its metric with various change gear wheels from 20 to 80 teeth. The thread needs to be an internal one but I`m a wee bit confused as to what 40G 1/8" means. Its certainly not 1/8" pitch and would that be 40 tpi? which obviously rules out 1/8" pitch anyway. The filter is only 5mm thick so a long thread is not needed so not sure how much lea way I have with a metric lathe.No doubt most folks on here are more knowledgable than me so any advice most welcome please. Cheers Steve

Reply to
Steve
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The gauge is calibrated in terms of TPI ie 40TPI and the 1/8" refers to the diameter of a standard whitworth screw that has a 40tpi thread You can cut a 40TPI thread on any diameter you wish.

On a metric machine you will have to juggle changewheels to get the nearest to 40tpi which is a pitch of 0.635mm. Your lathe manual should help here. It is likely that once you have started the thread, you will not be able to disengage the half nuts but instead, retract the tool and reverse the lathe ready to start the next cut. Practice on some scrap first!!

Good Luck

Bob

Reply to
Bob Minchin

Cheers for that Bob. Steve

Reply to
Steve

If you let us know the pitch of the leadscrew on the lathe and the change gears you have (i.e 20 to 80 'by fours' or 'by fives'), we can work out the nearest you can do.

Are you aware that for less than £20 Warco sell a set of gears for imperial thread cutting on this lathe?

Reply to
John Montrose

Ta for that John, no I wasn`t. Steve

Reply to
Steve

This was interesting (I have one of the metric Sieg 7x10's) so I went to Warco's site.

They list an imperial threading kit but don't say what's in it. Best would be a pair of gears, 127 and 50 or 127 and 100, but they don't say.

So I emailed them.

Got a reply - they won't tell me what's in the kit, and they won't sell it to me anyway as I didn't buy their version of the the lathe. This translates pretty much to "piss off".

Does anyone know what is in this kit?

If it is a 127 and whatever pair of gears, would there be an owner of a Warco willing to finess the transaction for me?

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