How to make a form tool?

[Sanjay F]

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

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.

[Sanjay F]

Mine is most definitley Ali, it looks like the set is still in its original packaging; unnecessarily huge box with parts sealed in the top, bottom and side.

@Jason - just checking, from the drawing, is the bead a full half round, or am I missing something?

Also:
How many degrees is a 'few' degrees for the tilt? 
Is the quenching in oil?

[Jo]

Have a look at router bits I suspect you will be able to find the profile you need for not a lot.

Making a tool out of hardened silver steel or case hardening steel is easy enough if need be.

Jo

[Jo]

Water cools quicker than oil. So I normally use oil for tempering and water for hardening.

Have you got any square HSS? And a 1/4" grinding bit? If so you can use your dremel to make a good tool that will last a life time.

Hand turning a one off small diameter is also an option 

Jo

[Jasonb]

See my edit. up a couple of posts

The bottom diameters are only 3/16" different so the bead is only 3/32" high I would say the top is the same.

Due to this difference you are unlikely to find a suitable router bit and much like rounding over milling cutters they tend to have a length of straight cut at the end so even less suitable.

5degrees at the most. I always Quench in water.

Also rough it out first much like you can see on those beads I'm cutting around that cylinder. So face the plain round bands ot overall diameter, reduce each side by 3/32" deep and then you can just form the curve with the form tool, run slowly to avoid chatter and lubricate with paraffin or WD40

As there are two beads to produce a form tool makes more sense once you have more than one item to form so they match unless you have a cNC lathe..

[Jasonb]

I just had a look at the drawing for my Big Willy (amson) and you can see that the ctr of the bead is inset from the flat areas each side

[john mills]

the ground stock and silver steel if it has its original wrapping it will have the heat treatment it has if it is water
or oil hardening   some is water hardening and some is oil  hardening 

[Sanjay F]

Thanks Jo, Jason & John

I haven't got any square HSS, but have a 1/4" grinding bit.

I think I've got it, from my understanding -  I only need the curved slot in the tool to be 3/32" deep;  I cut above and below the bead first, bringing them to size, then use the form tool to create the curve in the bead. I think this calls for an experimental piece before diving into the casting!

[Jo]

I think this calls for an experimental piece before diving into the casting!

It is always better to practise on a bit of scrap first   

Jo

[Charles Lamont]

If I remember correctly, gauge plate is mostly oil hardening, while siiver steel is water hardening. If you quench an oil hardening steel part in water the thermal shock can crack the material, as I know from experience.

[Jasonb]

Yes generally what is supplied as gauge plate here in the UK is O1 oil hardening. I must have been lucky as all the bits made from it and quenched in water have been OK. If it were a part like an expansion link with a lot of time invested then I'd probably go with oil but for simple form tools and small engine parts water has worked fine for me.

[pgp001]

I will need to make some form tools for the Pollit trip gear on Agnes.
A friend of mine gave me a good tip, that is when making a form tool for a radius from flat gauge plate, to use a taper reamer to finish the hole with some cutting clearance prior to heat treatment.

Phil P

[Jasonb]

Here you go. piece of 8mm Silver steel first milled to half thickness.

Then held at an angle to mill across the end and cut the half round.

Heated to cherry red at the business end and dunked in water. Held with minimal overhang in the tool post.

Not easy to take a photo as it was so smooth and shiny.

<a href="https://www.youtube.com/watch?v=yDTWT7ZBo5I" target="_blank">http://www.youtube.com/watch?v=yDTWT7ZBo5I</a>

[Sanjay F]

Fantastic, thanks - I love the way the tool creates the strand like chips and the finish is superb.

I think I'm sold on making the Williamson as my next project - I just need to finish up the current one 

I'll still make the tool and try a piece of scrap first

[crueby]

That worked really well Jason!  Never tried one myself, not sure if my little lathe has the rigidity to take that wide a cut - need to try it and see!

[Jasonb]

If the lathe is not upto it you can make a pair of handed tools or a single 1/4 circle and move the tools position so you are removing less material.

I would suggest Sanjay cuts the beads close to the chuck which will be more solid, it will mean swapping the casting end for end. Luckily, he is aiming to represent a cast feature that will be painted so if it does not come out as shiny as mine which is doubtful from a casting then a bit of work with file & emery on the rotating work will smooth and blend it all together.

[Sanjay F]

I was looking at this picture on MEM from a previous build and it looks like both ends have been supported with wooden plugs; looks a good way of holding and machining the beads.

I'm not sure how they are physical attached to column or what is happening at the tailstock end? Is it a live centre?

[Jasonb]

It may be possible to simply expand the chuck jaws inside the base of the casting (might need the 4-jaw to true it)

Rough shaped (turned) hardwood bung with a bit of taper can be driven into the casting and won't move

Looks like a revolving ctr that can take different "points"

[Sanjay F]

Do you mean one of these?

https://amzn.eu/d/egAcW7h

[Jasonb]

That is the sort of thing shown but a normal rotating one would do, it's all I use

[Sanjay F]

Silver steel arrived and I've made a the tool to 3/32" dimensions and hopefully it was hot enough before dunking! Now let's see if it works......

[Sanjay F]

and here it is, my first attempt, I think it looks ok, but I may have gone a bit too deep as you can see the grooves either side of the bead?

[Grateful Ted]

I just learned something again, after machining for 50 odd years.
Thank you.

[Jasonb]

One thing you might want to do is after hardening give the top of thetool a couple of licks with a diamond slip or oil stone. The close up before hardening looks like you don't have a really crisp edge possibly when you cleaned off a burr.

[Sanjay F]

thanks will do, I have an oil stone which should do the trick! 

[delta88ragtop@yahoo.com]

New Member here from the US. I'm attaching a YouTube link to MrPete222's video. He's a retired shop teacher, or Industrial Arts teacher as it used to be called when I was in high school. <a href="https://www.youtube.com/watch?v=XR49xRCi59k" target="_blank">http://www.youtube.com/watch?v=XR49xRCi59k</a>  . I enjoyed the industrial arts curriculum but was guided away from it to college prep by my parents. Retired now, I have built up a home machine shop and am starting my 1st major project of the Quorn T&C grinder. Hope the video helps some.
Nick

[Sanjay F]

Hi Nick,welcome to the forum, thanks for video and you have taken on a major project, good luck. As for tool grinding I'm not yet at novice level, but working up to it!   

[delta88ragtop@yahoo.com]

Thank You. In the video I liked the use of a tapered end mill in the production of the form tool. With the one tapered cutter several different radii form tools can be manufactured. As for the Quorn, the major delay was getting a steady rest for my 14" Logan lathe to finish the spindle. And as always A tool is needed to make another tool to make the tool. Once the Quorn Motor head is finished I think I would find it VERY useful as a tool post grinder on the lathe...

Best to you Sanjay!

Nick