Supporting > Tooling & Machines

How to make a form tool?

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Sanjay F:
I have asked this question before and have tried searching for both the question & the answer, but can't find the thread  :wallbang:

I need to make a form tool as I'm thinking of taking on the Stuart Williamson engine as the next project and the column machining requires one. I would like to make one similar to the picture below from one of Jason's builds. As can be seen from the drawing I need 1/8" radius. I vaguely remember I could use mild steel, use an 1/4" end mill to get a 1/8" radius, then angle in a slope (wrong terminology, I know) and then somehow harden and temper. I guess the distance of the sticky out bits of the tool are important as the will be cutting either side of the curved section?

As you can tell I need to fill the large gaps in my knowledge before attempting this, all assistance gratefully received

Jasonb:
Mild steel is not really going to cut the mustard. You either want gauge plate (ground flat stock) or Silver steel ( Drill Rod)

To make the cutter you have a couple of options, you can drill a 1/4" hole and then remove half of it. Or just mill a half round into the end/edge. Both can be done with the material tilted a few degrees which will give some front clearance that applies to teh half round and the edge either side.

Due to the higher carbon content of gauge plate and silver steel they can be hardened by heating to cherry red and then quenching. I don't bother with any further tempering. You only need get the business end to that heat so the shank does not become hard or brittle.

If using silver steel that is round mill it to half thickness first, then tilt and mill the end and finally do the half round with a few plunge cuts stepping over say 1/32" for 4No plunge cuts to get your 1/8"

Jasonb:
Just check that bead is a full half round it may be a bit shallower in which case less stepovers.

Edit, looking at the bottom bead it is indeed only 3/32" high so your form tool only need be cut that deep with the 1/4" milling cutter or if using a drill machine back beyond the ctr of the hole.

Jo:
Before going any further: I seem to recall the column on the later Williamsons was made of aluminium. What's yours made of?

It would be lovely for all of us to make ourselves a set of form tools for every possible diameter but there are other ways.

Jo

Jasonb:
I thought they were all produced in alloy except the pre production prototypes.

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