Bolt heads

Hi Folks.

A friend of mine has several vintage motorcycles and has a need to machine a large crown or radius into replacement bolts he is attempting to make . His ball turning attachment cannot reproduce the large curves he needs and he wonders if anyone can describe a possible solution for him. Many thanks

Can just plunge straight in with a form tool.
Presume its the heads.

Thought all ball turners you could pull the cutting edge out to give a much larger rad?

Turn the curve on the head as a series of flat (tangent) faces and then smooth with a file.

Paul.

If it is a very large radius try and find someone with a CNC lathe or a copy lathe and make a template to correct radius.

David

What's the radius?

I've been turning some 4.25" radii this last couple of weeks with my ball turning attachment.

Grind up a curved form tool. That's how the originals were most likely made.

I'd go for a form tool and a "sprung holder".

I've done some big rads on a few stainless jobs that way. The head is about 1 1/2"

Jim

Calculate the simple maths and smooth with a file as suggested by Paul. Once you have calculated this you then have all the info needed to work out an angle between points to get closer before blending. I have done petrol and oil filler caps this way.

Definitely a form tool, easy to make and efficient in use, but is it just one radius he needs for all his bolts, what’s the radius, what machine does he have ? (Lathe)

Make up a rod of 1/4 - 3/8" diameter and the length of the required radius, with 30 degree included points both ends.

Centredot the chuck-facing side of the crosslide and the carriage-facing end of the headstock at the same level. You may have to interpose a a fixed distance piece.

Generate the radius by holding the carriage manually against the radius rod and operating the crosslide, so that it moves out in a curve as it approaches centre.

I've seen the steam-tight ballnoses of locomotive superheater tubes machined in this way.

Mick B1:

I, too, can vouch for your suggested method.

It is perhaps worth mentioning that concave surfaces can be generated by putting the rod between carriage and tailstock base. If accuracy is necessary in either case attention must be paid to the position of the tooltip in relation to the rod.

jimmy b:

Beautiful work which I would hesitate to touch with a screwdriver!