Taper turning

I indicate the bore not the outside diameter as that is where action is at ! You have no guarantee that the bore is concentric and another reason to indicate is the tailstock barrel can be high or low and coaxial indiction will show that up .

You can cut a long taper just by offsetting the topslide.

The one I recently did in stainless below was 300mm long, involved resetting the top slide five times.

Get your initial taper calculations spot on, and take your time, one perfect taper.

I had to do four matching ones too!

My neighbour builds and repairs oak framed buildings where the mortice and tenon joints and braces are joined with oak pegs, he asked me to make him some framing pins, so he can rough assemble frames prior to installation on site.

Christ, they were a lot of work, but they turned out well

Put accurate centres in HS & TS. Bring TS up to HS until the points nearly touch. Place a thin bit of shim between points and nip up TS to grip. If TS is aligned shim will be at right angles to lathe axis - if not then adjust 'til it is. Simples.

Reading yet again about taper turning woes makes me ever more sure that CNC is the way to go. Not need to offset anything, just dial in the dimensions to the appropriate wizard and set the machine going.

. . . . and if the shim is at an angle to the vertical break out into cold sweat and swear copiously (

Yes have seen many home made units but unless you are going to turn a lot of tapers the expense and hassle is not worh it and many think you just look at the scale and set it to what you want and bobs your uncle mother but it doesn’t work like that , there are other factors at play especially if your machine has some wear and tear .

A boring head is probably the easiest out of the lot and has othe uses on a lathe and mill so one tool can cover a few jobs , a taper attachment is only good for the lathe it is fitted to ..

I forgot to say that the adjuster was subsequently modified to work also with the standard top slide.

The PCD tooling sounds very useful.

No one has mentioned the fact that when you offset the tailstock or use a boring head to simulate this the centres do not sit correctly in the centre holes. This adds to the difficulty of calculating the tailstock offset. The ideal centres for taper turning like this is are ball ended. No doubt someone makes them but they are probably costly. I have seen some on the Practical Machinist web site but you have to do a lot of tapers to make them a worthwhile investment of either time or money.

Martin C

That's exactly why I don't offset the tailstock to cut tapers.

The engineering principle (or lack of) behind it really grates with me.

Make/buy a couple of MT blanks; reduce the parallel bit to a truncated cone and centre drill; put a ball bearing in each one between it and the blank.

I've never needed to offset the tailstock to cut a long taper, as I have other means of producing them. But if I were to do so I'd use a radius centre drill, in conjunction with a standard centre, which are readily available at reasonable cost.

Andrew

Edited By Andrew Johnston on 30/10/2018 16:05:07

Like many others,I tend to leave the tailstock alone[too much messing to get it right again ],so now I use a boring head when cutting tapers. I use something with the taper I require in order to set the boring head,unless it,s an odd ball taper,then it just has to be worked out. The good news is that does not happen very often.

In theory the offset centre does not seat properly in the centre hole and a radiused centre drill should be used etc. But in practice, if you use a revolving tailstock centre nipped up just firmly it works ok with a conventional centre drilled hole each end.

Yes the theoretical geometry is going to be off by a few thou due to the exact point of contact etc but you are never going to get a taper set just right on first go anyway, whether you use a taper turning attachment or offset tailstock method. It seems you always have to do a few test cuts then measure carefully or preferably test with a matching taper sleeve etc with lead pencil marks and observe the rubbing pattern. Very much a "try and fit" job.

I've never had a problem with offsetting the tailstock using conventional centres and centre drills. It works for me. (Although it's not something I do every day or even close to it.)

Edited By Hopper on 31/10/2018 07:37:06