screw-cutting basics

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Fergus OMore:
The 24TPI is simply because the number factorises with 8TPI on a Myford( and several English Lathes)

On the T and C postings, I make some comment about my GHT VDH. Mine has a solid Myford spindle but really shouuld be changed to accept Myford and ER Collets.

This is for MY way but others must find their own developments. The design allows for such changes.

minerva:
Norman ,
I suspected as much but thus far I haven't given the latter stages of the build much thought, however having so said I use my ER32 collets in both the lathe and the mill so an adapter to fit the VDH would fit the bill a treat.
Regards
Terry T

Fergus OMore:
Terry,
You are using a 'Metric' lathe although you maybe working in 'Imperial' for dials etc.
GHT used 24 TPI because many Myford etc users couldn't afford the gearbox and made do with change wheels. Having said that, most of his writings apply equally to the 920- if you watch what you are doing. There is no real reason to stick with Imperial- if you are happier going metric/metric. If you are working from a 'non kit', you will find metric kit/metal far cheaper and more available.
There is no reason that I can think of not to metric thread on an imperial diameter shaft. After all, 24TPI is a 'Bastard' thread and so is the Myford which is Whitworth thread but should be UNF 60 degrees. Don't ask- but I fell for that one :wack:

As for this lot of nuts, please realise that all that you are doing is allowing the spindle to turn and another holding the gear wheel against the spindle-- and both have pegs and - grubs screws. I have pegs galore- dropped somewhere and I know the problem-- but can't find the things.

I have no idea where you are at but I would seriously look at several GHT 'goodies' to help.
I would have( and did have) a steel sub table with a GHT rear parting tool on it. I had a vertical slide/vice from a ? that had also been on a Myford. I have a boring head( and an aching one sometimes) but I made up a pair of inline boring bars again GHT and did the Quorn.
Finally( yea I've got more GHT) but I'd make up a mandrel handle to sort out the speed which at 130 rpm, I can't cope. You may, I can't. I fitted and inverter/now on my Myford.

Concluding, you will enjoy the re-learning experience

Cheers

Norman

minerva:
Norman,
The kit from Hemingways is unashamedly Imperial as are most of GHT's designs, and as a 70 odd year old having grown up with old numbers they hold no particular terrors for me . I do however take on board the comment as to the availability of Imperial sized stock it is certainly becoming as rare as rocking horse dung!
I do have as part of my kit a good quality boring head with which I have had good results, but I will be making one of GHT's in line designs as his comments as to the direct measurement of dimension achieved appeals .
I have manufactured an adapter to facilitate the use of my vertical slide on the 920 , which only leaves the rear mounted tool post , Although I must say parting off is one skill that I have retained and thus far have had no real problems from the QCTP in the normal position.
I re-iterate how much I value your (and all other contributors) input . and the thought processes thus provoked makes membership of this forum so worthwhile.
Kindest Regards
Terry T

udimet:
Terry,
Go to the VARGUS website and download the free programme VARDEX TT, it will give you all the info you could want and will also calculate the DOC for a given number of passes. Fantastic programme. Just make sure you download TT [Thread turning] and NOT the programme TM [Thread milling].
Best wishes.
UDIMET.

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