threading metric on an imperial lathe

[mike mcdermidParticipant @mikemcdermid41977]

I have an imperial lathe

Its an emco with an imperial box it now transpires, How would i cut metric threads on the lathe?

[mike mcdermidParticipant @mikemcdermid41977]

How to cut metric threads

[John HaineParticipant @johnhaine32865]

What do you want the threads to do? Short metric threads for fasteners can be approximated on an imperial lathe by the right choice of change wheel often to within the accuracy of the lathe. There are details in other threads here. If you want to make exact threads you will need 127 and 50 tooth wheels to give an exact metric lead fro your imperial leadscrew.

[Harold Hall 1Participant @haroldhall1]

Mike

As John says you will need to use a 127 tooth gear to achieve precise metric pitches, that is of course dependent on the accuracy of the leadscrew on your lathe. However, very close values can be achieved for most metric pitches using the standard gears.

For example, take a required pitch of 3mm. 25.4 divided by 3 gives a value of 8.4667TPI. Not surprisingly, an exact match is not available but there are 11 combinations using standard gears that provide a value of 8.4656 TPI. This is an error of just under two one hundredths of one thou between adjacent threads.

See here for a listing showing the results for every possible combination of gear sizes, **LINK**

The list explains how to achieve metric pitches, such as above, on a lathe having an imperial leadscrew.

Harold

[mike mcdermidParticipant @mikemcdermid41977]

Good evening all.

John

The threads are indeed just for fasteners and the like ,Say for example a long shaft with 10-15mm of thread on the end

Graham

it is an Emco V10 i have read the user manual and it mentions either metric or imperial gearboxes

Harold

Unfortunately I do not have any change gears other than those that came with the machine,there is very little wear in the machine however, so i would say the leadscrew is pretty accurate?

Many thanks for the replies, Where would i get metric change gears?

Mike

[Harold Hall 1Participant @haroldhall1]

Mike

The lists I refer to are using the standard gears supplied with an imperial Myford lathe, nothing special. If you could list for me the gear sizes you have then almost certainly I can provide you with an example of just how close we can get. Of course, I do not know what gears you have so there may be some problem that I am not visualising, but I doubt it.

Harold

[Thor 🇳🇴Participant @thor]

Hi Mike,

have you asked the EmcoV10lathe Yahoo group? They may be able to help.

Thor

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

In case 127 is too large, use 21 instead 127 to make imperial to metric treads. Up to 1% wrong in pitch is acceptable. Download the program to calculate the change gear to your lathe when the treads is in metric or imperial here: **LINK**

Edited By Jens Eirik Skogstad on 02/08/2013 07:08:57

[Roderick JenkinsParticipant @roderickjenkins93242]

My understanding from the OP is that his lathe has a gearbox, so most of the suggestions may not be relevant. I don't know the Emco lathe but it may be that some variant of the John Stevenson method of changing the output gear from the spindle may produce acceptable metric approximations.

Rod

[Michael GilliganParticipant @michaelgilligan61133]

Mike,

I don't know if this will help

Sears have exploded diagrams for the V10 spares

MichaelG.

[Harold Hall 1Participant @haroldhall1]

Mike

Like others I did not read your original post carefully enough, sorry, As you have a lathe with a gear box my comments are less relevant.

However, I do know of some who, typically, set their gear box to 8TPI on a lathe with an 8TPI leadscrew, and then use the normal set of changewheels, if they have them, when my listing can be used. Of course, it does require a quadrant to place them on and at least some changewheels, not necessarily all. The wheels can be purchased as required.

Regarding the accuracy of the leadscrew, What I was attempting to say was that, using the normal changewheels, values that are extremely close to the required pitch can be achieved.

Therefore, even using a 127 tooth wheel cannot be guaranteed to achieve better due to manufacturing errors (permitted) in the pitch of the leadscrew. Even a precision toolroom lathe will have permitted errors in the pitch of its leadscrew, albeit, very small.

Harold

[Anonymous]

Presumably, whichever gear train is used, exact or approximate, the half nuts will need to be kept engaged throughout the whole process. So no disengaging the nuts at the end of a cut, and re-engaging at the start of the next cut.

Regards,

Andrew

[jacques maurelParticipant @jacquesmaurel42310]

For cutting short threads, with no new gear, go to: **LINK**

regards.

J Maurel

[Paul FallertParticipant @paulfallert28101]

For some of the EMCO lathes (7, 10, 11) with a gearbox you can just change what is termed the "stud" gear and shift the banjo/aka quadrant to meet it. [btw, it is called a "stud" gear because it is mounted on a fixed stud screwed into the headstock casting (as opposed to being mounted on the movable quadrant) and the "stud" gear is also pinned to another gear with which it turns on the "stud"].

For example, if I replace the 45T stud gear with either a 32T or 64T gear, I can cut a 1.0mm metric thread with my 8tpi leadscrew by shifting the gearbox to the appropriate position.

There is an Excel spreadsheet for download in the files of the above referenced Yahoo Emco forum that gives the many possibilities and the degree of error in the metric lead. There is also a file which provides the same information to cut inch threads with a metric leadscrew.

Paul

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