thread cutting

On or around 30 Oct 2006 14:04:32 -0800, "Robin" enlightened us thusly:

you need the 127 to get accurate metric threads; you can apparently get away with 63 if you're not doing precision work...

it's 'cos there are 12.7mm to half an inch, and you have an imperial leadscrew.

in my case, I move the lever on the gearbox from "Imperial" to "Metric"

although why it doesn't list 1.75mm pitch on the gear selector chart eludes me, bearing in mind it lists a load of others.

Reply to
Austin Shackles
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"Metric"

Austin,

Your Student was probably made in the mid to late 1960's - possibly

1.75mm wasn't a standard metric thread then?

AWEM

Reply to
Andrew Mawson

from "Andrew Mawson"

My 1923 'Machinery's Handbook' lists 1.75mm pitch as 'International Standard' on 12mm dia but 1.5mm as 'French Standard'.

I certainly remember 12 x 1.75 being a standard during my appenticship (1957 - 1962)

JG

Reply to
JG

I have a simple die holder I use on the lath it is a hand held job, quite large handled thing. But it has several holding points for split dies so in effect has three screw points.

I screw in to the split firt then the other two screws are used to lock the die.

I put the bar stock in the normal three jaw chuck and rest the die holder against the tail stock barrel. I have one of the handles resting on the top saddle with some scrap steel between.

I set the lathe turning at relitivly slow revs say 150 the use pressure by wining in the tail stock barrel to start the thread. I always keep pressure on from the tail stock to keep the die square.

Basically once the thread is started it pulls it self in. No it can not be done with keep dies and holders but reasonable quality.

The maximum size I have used this on is 16 mm x 2 mm pitch something like

20 pieces for a small job with lentgh of thread around 30 mm. 10 tie bars for someone elses project.

If I had to do larger quantity and had more time then i would go to using a coventry die holder and the dies, but that can get costly.

It can be very gratifying cutting threads on the lathe using point cutters and doing multiple cuts. So it can be worth doing, but I used to find it took to long and many times needed finishing off with a hand chaser to look better.

Adrian

Reply to
Adrian Hodgson

On or around Tue, 31 Oct 2006 12:10:23 -0000, "Andrew Mawson" enlightened us thusly:

not sure how old it is TBH. it's been around a bit, judging from various repairs... possibly 1.75 wasn't standard, but it is a standard metric pitch for various sizes.

BTW, any of you lot know of a likely source of the parts to rebuild the brake? The internal parts are missing...

Reply to
Austin Shackles

I was disappointed with the limited metric range of my imperial/metric student (MkII). I've swapped (for other reasons) from having one imperial/ metric & one metric/imperial (which had a very good range of both) lathe to two Imperial only. Luckily I don't do a lot of metric threading, though. Anyone got spare metric changewheels for a 17" DSG? Thought not, I expect I'll have to make them.

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

Reply to
Tim Leech

On or around Wed, 01 Nov 2006 08:49:53 +0000, Tim Leech enlightened us thusly:

Mind, on the Mk1, notwithstanding the missing 1.75 on the chart, you can get

1.75 by using one of the other positions, but the metric gearset. In principle, I reckon, using the metric output gear you can get almost any pitch; although it's not in the chart; just needs a bit of work to translate the numbers. For example, to get 1.75 I was using DA18 I think, which is not labelled as a metric pitch but works nonetheless.
Reply to
Austin Shackles

I didn't have any extra gears for mine, but it wasn't really a problem as I could do metric threads easily on the TOS, even if it was a bit big for some jobs. Bit of a bugger though when you forget, & are halfway through the job & realise that thread isn't in the box....

Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

Reply to
Tim Leech

On or around Wed, 01 Nov 2006 16:26:26 +0000, Tim Leech enlightened us thusly:

Mine has the typical norton type box with about 9 or so positions along it,

2 levers on the left with ABCD, and on the top a lever which engages the leadscrew (as distinct from the power shaft) which is labelled imperial-neutral-metric.

I assume the leadscrew is imperial, and the "metric" position applies suitable gearing to make it behave like a metric one. For every position of the ABCD levers and the gearbox you can have either "metric" or "imperial" - but I assume that some of the "metric" answers wouldn't make sense.

I'll have to have a think about it and try and translate the TPI figures on the chart to make sense when in metric mode.

Reply to
Austin Shackles

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