Thread: Turning Tapers without adjusting Tailstock

Originally Posted by pipeclay

Apart from the method that Bruce used to turn the tapers,you do realize that this system of arbors has been in use for over 100 yrs.

Peter
Thanks for that mention.
Today I went through my old Tech book notes & they were written 60 plus years ago.
There is an outline of how to mount a spur gear for milling on a tapered mandrel.
Its a method I have used many times, & its simple accurate & effective.
I have always used an Arbor Press to squeeze the gear blank or the part to be machined onto the mandrel, & the same way to remove it. A hardwood block & hammer could also be used with care.
To answer Andres question about which steel is used, I just made mine out of 1020 steel & left soft, they will be fine for occasional hobby use.
A little better is to case harden each end of the mandrel so as to protect the centres. This means there is vitually no distortion & accuracy is maintained.
The ultimate is complete hardened & cylindrical ground.
regards
Bruce

OK, I understand the principle and that it works and that better people than me have done it succesfully ............. however am puzzled .............

when you crank the tail end centre across to turn the taper, surely this means that the T/E pointy bit is no longer sitting central in the centre drilled workpiece - does this end up deforming the workpiece or scratching the tailpiece.

In one book I saw a sketch of a spherical blob on the tailstock to overcome this issue but not many people seem to bother with this.

When you have a workpiece sitting on a tapered mandrel isnt there the possibility of it getting knocked or misaligned whilst machining see exaggerated sketch - essentially its a washer sitting on a cone - doesnt have to sit square ............. or are these tapers so tiny that it doesnt really matter ?

Bill

Originally Posted by steamingbill

or are these tapers so tiny that it doesnt really matter ?

Bill

Thats exactly how it works. I also wouldn't put somethin on an arbor that was contacting for less than half the dia of the bore. No doubt there are age old rules on this?

I have seen somewhere the use of a ball bearing in a center hole and a cup center. You only really need to do this for big tapers though-big enough that i would think the compound or a TTA would be a better option.

Ew

Bruce,
Great job as usual, I have been going to make a couple myself, but what put me of before was when reading how to use a lathe etc etc somewhere in the text it would say something like, harden and then finish grind to size.
What grade of steel,also would you still use an assembly lube.
Regards
Ted

Originally Posted by TED C

Bruce,
Great job as usual, I have been going to make a couple myself, but what put me of before was when reading how to use a lathe etc etc somewhere in the text it would say something like, harden and then finish grind to size.
What grade of steel,also would you still use an assembly lube.
Regards
Ted

Ted
Thanks for the follow up.
I have machined these mandrels out of 1020 Bright Mild Steel. This is a relatively soft, easy to machine grade of steel.
Some few years back I had hundreds of 5/8" bore idler pulleys to machine using a plunge cut technique on the OD (fairly high cutting pressure).... lathe in back gear at slow speed using HSS Formed Toolbit.
I have still got that mandrel & its in good condition & accurate.
The main point to remember is to have an accurate bored & reamed hole in the workpiece (nice finish) & use a lube when pressing the mandrel into the workpiece.
Have always used a mixture of white lead & oil but that is a taboo substance in this day & age. (The same mixture works well on lathe centres.)
Any lube on the mandrel, rather than dry, would assist in reducing any galling or metal pickup & ensure longevity & accuracy.
Hardened & ground mandrels, are the ultimate but not essential, for hobby & small run production.
Hope this answers your question.
regards
Bruce

Originally Posted by steamingbill

when you crank the tail end centre across to turn the taper, surely this means that the T/E pointy bit is no longer sitting central in the centre drilled workpiece - does this end up deforming the workpiece or scratching the tailpiece.

Yes, I believe the sockets will wallow out slightly to form a curved surface - which kind of solves the problem. But because of this change you need to monitor pressure and lubrication. Normally the male centres are harder than the work so they should be damaged less.

In one book I saw a sketch of a spherical blob on the tailstock to overcome this issue but not many people seem to bother with this.

I made a set of ball centres once, but haven't needed to use them. The principle is better but in practice, as you say, people seem to get by ok with 60 degree centres.

Post script: I had a dim memory of reading about a special curved centre drill for this purpose, so I went hunting.
This short thread on taper turning is worth a read:

http://www.practicalmachinist.com/vb...d-task-278663/

An easy way to make ball centres - use tappet adjusting screws from an old engine. These ones are 3/8" diameter from a 1927 Chevrolet (because I happened to have them available).

Frank.