Taper turning

Different component lengths , assuming turning between centres will require a different tail stock offset for a given angle.

tony

It would be quite hard to work out what the actual offset needed for a given angle should be due to the fact as soon as the tailstock barrel is tightened into the work the long edge of the triangle would alter so your carfully worked out trig would be wrong.

For the same reason they can't be graduated in anglular measure as that will alter as the tailstock is moved along the bed

George, If you have a boring head, have a look at the two photos below before you disturb your tailstock setting.

The idea is that you can easily dial in a chosen offset using the sliding part of the boring head.

In my case I made the boring head centre using a broken solid carbide centre drill.

I had a need to make a taper pin for a newly acquired shaper, so clocked in the correct offset using the actual taper pin reamer that I was planning on utilising to re-ream the clapper toolpost.
Note Imperial reamers are 1:48 taper, whereas Metric are 1:50

The one thing you must remember, in a case like this, is that the workpiece must be exactly the same length as the taper you are trying to reproduce; centre to centre. In my case that was way too long for the pin required, so I just turned the workpiece round and made a spare.

The photos below are a quick lash-up I've just done to illustrate the principles for this post. At the time, I had a clock set up more rigidly in the front toolpost.

There are ready made devices available for this type of offset turning, but why shell out if you already own a boring head.

Grinding the carbide centre (ex-drill) was a bit of a lash-up too.
No photos for that one as it was in a previous workshop, where the Clarkson Tool and Cutter grinder was (too) near the lathe. A flexible shaft held in the lathe chuck bent through 90° to the T+C grinder and spun the centre whilst the grinder shaped the cone on the end.

Bill

Edited By peak4 on 29/10/2018 19:58:48

That's true, but an accurate vernier scale could provide a capability to set the offset either from calculation or records of previous operations.

My Warco WM250V has a straightforward scale with no vernier. So far as I can see, it's totally NBG though - it's well off the marked centre when head- and tailstock centres are accurately point-to-point.

After a few very time-consuming and fiddly experiences on a number of lathes getting the tailstock back to centre, I generally avoid the offset centres method if I can.

No scale is going to be good enough if the taper you're cutting has to fit into any other taper. For that, you need a sine bar or an indicator and some trig. Or a lot of trial and error.

+1 for the boring head to set the offset , i had to turn the taper on a conrod a few weeks back and i though no hassle just offset the tailstock and have at it . The issue was that the cheese grade grub screws that locate the tailstock on its base stripped the hex out so i end up getting it as close as i could then finished off with a file , the grub screws are about an inch long or so and i didn’t have replacements at hand . I now have a boring head set up specifically for this and the bonus is I don’t have to fiddle around resetting the tailstock afterwards.

Yes, I found that out in the 1970s - but a decent scale could get you close enough to cut out a lot of the faffing about.

Maybe the manufacturer of the lathe recognises the faffing about you need to do to offset the tailstock or use an offset centre etc, and just expects you to buy their taper-turning attachment which bolts to the back of the bed (usually) and controls the cross-slide movement as the carriage moves to the left. Its an expensive way of doing it, but it gives good results and usually allows easier adjustments to create a 'matching' taper.

Ah, it was more of a response to George. He asked why no scale - it would be of very limited use.

The maker of commercial lathes will just sell you a taper turning attachment, it's only some of the hobby lathes that don't have TT attachments.

Not that rare, George. Just look at the classified ads. A n LJ with more precious extras than the lathe!

Regarding the scale and actual angle, think of using tangent tables to calculate the angle with two work lengths, one double the other with the same tailstock displacement.  The distended angles would not be the same, and for small displacements the angles will almost be doubled/halved.

Edited By not done it yet on 30/10/2018 08:48:16

Oops, edited while the next post arrived and covering the same ground!

Edited By not done it yet on 30/10/2018 08:50:04

It is easier for manufacturers to make the tailstock adjustable as any maching faults can be adjusted out easily .

The reason that the scale is no good is it cannot give a true indication of taper or angle , think of a right angle triangle where the base is say 4 inches long and the opposite say 1 inch high , using trigonometry you can work out the angle of the hypotenuse from the base but if you make the base longer the angle will be less . Easy way to visualise this is to draw it out on some paper .

I seem to recall a toolmaker telling me a taper was 0.0175 inch in diameter per inch of length per degree of taper or something like that - it was a long tome ago and I don’t think i was really listening to him at the time anyhow !

If your lucky the drawing will give you a diameter at each end of the taper and a length so it is just a matter of subtracting the minor from the major then divide by 2 and this gives a figure that can be used to set the offset with a dti over the required length , not precice i know but plenty good enough for thing like conrods or anything that doesn’t lock into another taper .

Resetting the tailstock is made easier with a dti mounted in the chuck or a coaxial indicator if you have one .

Re-setting the tailstock is a simple matter just put a piece of scrap in the chuck and turn it to the diameter of the tailstock barrel. Now bring the tailstock barrel up to it, mount an indicator on the carriage somewhere and sweep across from the barrel to the part you turned. Adjust until they read the same.

If you must set your tailstock over why not use a plunger type DTI mounted in the toolpost and bearing on the tailstock barrel. Either adjust the tailstock to the correct indicator reading or maybe a safer method would be. Set to zero. Wind the cross slide out to show the required setover , clamp the cross slide and the saddle to prevent any accidental movement. Adjust the tailstock to read zero once more.

regards Martin

Pete,

Even easier is to grip the tailstock barrel in the chuck directly and interate in with the final adjustments from that

Brian

Oh yeah there are a dozen ways to do it. Just use whichever suits you best.

I think it's quite difficult to make any taper that fits another without a test-fit and some blue. I use a tenth-reading dial to make small top-slide adjustments and I've even seen a setup that someone made that used a pair of jacking screws to set and then hold a taper angle for very fine work.

Pete Rimmer:

Was it this kind of thing you had in mind?

The adjuster screws can be seen bearing on the "topslide" base (it is actually a cross slide adopted for its extra length in boring a taper in work supported by bush-type steady).

Yes that's exactly the idea. It was a one-off setup for cutting one particular internal taper angle in a hardened shaft using PCD tooling.

Love that cross-slide idea.