Hirth Couplings

My current project is the engine for a pre-war Mercedes GP car. The crankshaft has a Hirth coupling at either end to drive the flywheel and supercharger.The shaft diameters are 20mm and 15mm respectively.

Has anyone out there any practical knowledge regarding the design and manufacture of these tapered spline couplings. Any advise would be appreciated

Mike

Interesting.

**LINK**

Looks like there are no standards... "Hirth joints are designed as mating pairs and, unlike splines, there is no standardised off-the-shelf sizing system for them."

Neil

I made some fairly basic ones, to extend the reach of a set of adjustable motorcycle handlebars.

It turned out that all I needed was a Carbide vee-groove cutter [intended for a woodworking router] ... The alloy spacers were indexed on the rotary table, and cuts ran straight through, on the diameter.

However; I suspect that "the engine for a pre-war Mercedes GP car" will be rather more demanding!

MichaelG.

MACHINERYS handbook show tooth angles etc for 'clutches' of a similar design.

There is a very interesting write up in the book by Wayne R Moore "Foundations of mechanical accuracy" on how his company makes a dividing head using this coupling. They lap the joint wearing it in by indexing the coupling a tooth at a time then pressing the two halves together. This process slowly averages the errors made in machining the joint.

Moore Jig borers, grinders and measuring machines, are still highly prized.

If you have not read it this book is one of the best available on precision manufacture. It is well up my top 10 engineering books list.

Regards
John

Some very good reference material here

MichaelG.

... and a Voith Universal Joint Shaft here!

This book by Wayne R Moore "Foundations of mechanical accuracy" is it still available I've searched and can't find it, sometimes these books become available as pdf's on google books but not this one as yet.

Shaun

Apparently 150 USD here. http://mooretool.com/publications.html

For information rather than encouragement:

... There is a copy on Scribd

MichaelG.

Thanks everybody for all your help and advice. The information on the Voith website was most useful. I have now been able to draw my proposed Hirth couplings.

To summarise, the Hirth coupling is a compact, highly accurate, highly repeatable, self centering, high torque coupling between two shafts. Auto Union used Hirth couplings to assemble the built-up crankshaft on their 600HP V12 engines, That required more than 12 couplings per crankshaft. Fortunately I only need to create two couplings for my Mercedes model.

When the Hirth coupling is drawn out, the top and bottom lines of the teeth all project to a single point on the centre line of the shaft. The teeth are therefore tapered in all axes.

The Hirth coupling is machined in a similar manner to a bevel gear, except a 60 degree cutter is used instead of an involute cutter. The teeth are cut at a shallow angle (6 to 7 degrees) to the axis and both halves of the coupling are identical.

I think a few practice pieces will be required before I commit to the real crankshaft.

Thanks again

Mike

Moore table.

There is a table for sale on ebay

**LINK**

Regards
john

.

That's nice !

Shame that neither the Lottery, nor my Premium Bonds will cover it

MichaelG.