Dies come in several sizes but they are standard. If your dieholder is the wring size it is just that it has been made wrong. Sometimes far eastern manufacturers interpret specs too literally without thinking. So they may strive to make the hole exactly to size +/- a thou thinking they will be criticised if not precise and fail to understand the reason for the hole.

Make a tin or plastic template to align the topslide eg side of it wrt the faceplate and don't be afraid of making a new alignment mark on the machine for future use.

There is an easy but not universally appreciated way and that's to keep the topslide at 90 degrees to the cross-slide (parallel to the lathe bed) and to advance the topslide each time by half the advance on the cross-slide.

That works out as being at tan^-1(0.5) = 26.565 degrees and so works well for both Whitworth and metric thread forms.

It means that the thread depth is the direct reading on the cross-slide and also allows a thread to be widened more easily once full depth is achieved by just advancing the topslide.

Martin Cleave's book **LINK** lists this as METHOD 3 in Section 8 and is the method he said he usually adopted.

HTH

Jon

The difference in an expanded and contracted die is minimal and the small amount of play in the die hoilder allows it to almost self centre. You can get "floating" holders but I've never felt the need for one.

My dieholders are self centering, ie. they are a bit loose on the spindle. It is the die that aligns with the rod to be screwed. The holders are made over size to allow the die to expand, but not much, difficult to be precise because it depends on the O/D and the hole in the die.

Although the ceoss slide parallel to the bed set-up for threading works pretty well its a major PIA getting things set up specially for threading. Especially on a small machine where there isn't room to leave the topslide permanently at 90°. Actually its a bit crowded on pretty much any home shop capable lathe. A technique I only use for ACME and similar feed screw/nut threads which have to be cut for minimal clearance.

I leave my topslide parked at around 25 and bit degrees off perpendicular to the work and use the Zero to Zero screwcutting method described in my post on this **LINK** forum thread, 8 th post down. Any top slide offset angle reasonably close to, but a bit under, the thread half angle will work just fine. No complicated maths, the lathe does all the calculations for you. When you finish, with both dials on zero, you have exaclty what you set-up in the beginning so if all isn't right you have a chance of figuring it out. The usualy offset at half angle method involves maths (Yikes!) which multiplies the chance of error for the inexperienced and when working solely from the cross slide the temptation is to start and finish on funny numbers depending on where things ended up on the previous part of the job.

If you don't have zero setting dials an adequate work around is to set the topslide on zero then move the cross slide past zero to the requisite thread depth and bring the threading tool up to the work before clamping it down. This requires your toolholder have some sort of register to slide the tool along and to be set perpendicular to the work. Both of which I regard as essential preconditions for any attempt at accurate craftsman like work.

Using 25 and a bit degrees offset angle as the normal cross slide position also keeps the cross and top slide handles out of each others way making the machine easier to drive.

Clive.

I can agree with that although on the Myford ML7 there is a pretty annoying design flaw in that the topslide is not free to rotate completely – You have to choose the quadrant by positioning the Tee-nuts to either left or right of the cross slide slots.

So, to save keep mucking about taking the topslide off and on I tend to keep my topslide mostly at 6 degrees from parallel to the lathe bed to give a bit of clearance with the tailstock but also to allow a roughly 10:1 ratio for top-slide versus cross-slide movement. If I find myself wanting to take 0.001" off the diameter, moving the topslide in 0.005" has the effect of advancing the tool in about 0.0005".

This is another trick from Harold Hall – See bottom of this page… **LINK**

It's probably of no help to you, but I HTH someone.

Jon

I have only cut a few threads on the lathe, but used the set-over 29.5deg method when cutting the thread for the ER collet chuck for my tool post mounted spindle. I made a useful little tool to set the top slide to the required angle – it can be seen in my album "top slide angle setter". It also came in handy for setting the angle for grinding the taper of the collet holder – see picture, above. I didn't want to rely on the graduations marked on the cross slide to accurately align the top slide.

John

Edited By John Hinkley on 20/05/2015 13:45:25