Imperial screwcutting on Metric lathe

[chillybilly]

Hi ,

Need to cut a Imperial thread on my metric lathe ,is it as simple as finding the pitch of the imperial thred and setting the machine to that ??? I have a Harrison 11" with the 3 lever gearbox ,and also a pile of changewheels ,i still dont fully understand how to read the chart of pitch rates yet but i am on the case !!!Any help greatly appreciated .

 

[John S]

Picture of the thread chart please ?

.

 

[chillybilly]

Will go and get one and suss out how to get it on here .........

I am in Nottingham too ...Small world..........

 

[chillybilly]

Attached pic best as poss ...

On the left is the posn of levers A and B on the bottom is position of lever c .

Each square of the chart has two numbers ,one at the top of the square and one at the bottom ,i belive these to be the pitch.....on some of the squares there is a 3rd number in bold in the centre ,i believe this to be the feed rate .the plate is double sided ,one for fine and one for course ,and the necessary changewheel arrangenment to get this ....sorry about the crap pic

View attachment Image002[1]

View attachment Image002[1]_thumb

 

[John S]

Yes you are right it's a crap picture

Looks like it has a Norton type screwcutting box.

http://www.lathes.co.uk/harrison/page19.html

Is this it ?

 

[chillybilly]

Thats the one ,mine is the 11 inch with the rounded head ,all the same as a 140 failing that ..........My nipper has had hold of the camera and killed it so it seems so was reduced to a mobile phone ................grim

 

[John S]

In the pile of gears do you have one with 127 teeth?

 

[chillybilly]

Yep pretty sure that one is there,will check.......is that a key player????

Just looked up about the Jones 250 engine ,what a fella ,didnt realise the jet ski came from these parts either .Have you ever seen the film of john Britten and his bike ???

 

[chillybilly]

Wrong again ,biggest i have is a 120 tooth next down is 100 tooth then all the rest must be smaller ,there is a good few however !!!!!!!!!! hey ho

 

[John S]

Look inside the end cover, there maybe an imperial conversion chart there.
If not I have a friend with a Metric 140 that i can scrounge a copy of the chart off.

 

[chillybilly]

Does not appear to be any charts in the end cover ,it is all a little dirty in there to be fair ,will have a look in the dayshine tomorrow .What is the general objective with this problem ,to identify the pitch of the imp thread ad convert to metric ? or set the gearing to cut a specific TPI using gears to compensate? its a little confusing ..... :-X

 

[John S]

First thing is to determine it is a metric lathe, that is metric on the leadscrew, probably is with it having the 3 lever gearbox.
Then you need to change the drive train on the end to suit Imperial threads and also select which gearbox ratio [ the table should give you all this information ]

Then it's just a case of screwcutting your thread but you MUST NOT disengage the 1/2 nuts at any time.
You will have to reverse to go back for another pass.

What part of Nottingham are you in ? I'm in Long Eaton.