Form Tools (A Lathey thing).

[Richard T]

After a lot of web searching yesterday I seem to be no closer to finding info on either the grinding of concave forms or any firm that make standard forms.

I tried, moderately successfully, the other day to grind a tool with a central point curving back on both sides(Concave curves in 3/8 HSS). . The tool turned out to work pretty well but the wheel on my grinder has no edges left.

Do I need something like a Dremmel with many wheels of varying widths/shapes? Or do people use made - for - purpose bench grinder wheels?

 

[AndyT]

I can't claim any experience of these but as chance would have it I was reading the chapter on Form Tools in "Using the Small Lathe" last night. Mr Mason refers to 'careful filing'' followed by 'normal hardening and tempering' so I suspect the answer may be a different sort of steel.

 

[chipmunk]

Hi Richard,
MrPete222 has a recent upload talking about form tools and this supports Andy's idea of HCS rather than HSS.

http://www.youtube.com/watch?v=XR49xRCi59k

On the other hand I think that a die grinder or Dremel with a small grinding wheel or point can be used to save your grinding wheel edges. These will also make it easier to create something round. I've done the same for Sorby-style woodturning beading tool inserts from HSS.

HTH
Jon

 

[Harbo]

My Unimat came with lots of assorted grind wheels with arbors attached which I use, though I have also used my normal grinder at times - it does wear the edges away though.

I've seen lots of Quorn Tool Sharpening set ups at various MEX shows but they are very expensive. You can also buy various grinder shapes including tapered cones.

Rod

 

[woodfarmer]

get a grinding wheel and construct the radius you need on its surface with a grind stone facing tool. Then use this to grind the form in the tool. re do the wheel after, then you can use it for sharpening the tool. To form a polished surface you will need a very slow speed eg 10-30rpm and take the thinnest of shavings off. Just nudge the tool little by little thou or less at a time. There is an alternative way which is much harder on the tool and leaves not such a shiny surface. Use high (ish) speed ( say 500 rpm) and go in fast and out. It can easily chatter though. Note the top surface should be at near 90 degrees to the work and you do not need much clearance below the cutting edge as the tool advances very slowly through the work. Done this way the cut surface is left polished and work hardened.

 

[Richard T]

Thanks Andy and Jon - It had crossed my mind that it would be easier to shape tool steel and harden it but thought it must be done with HSS these days ....

I had been looking at Mr.Pete's videos but had not got that far. He has made a lot of videos.

I must dig out some bumf I got from Coventry Grinders. Maybe they carry something likely. If not, they also sell 01.

 

[Richard T]

Thanks folks.

I think I only need two form tools for a while so a big investment is not justified.

As I suspected there is a picture of a wheel that looks spot on in the Cov. Grinders paperwork. I'll bother them later on.

 

[Cheshirechappie]

Probably a bit late to be useful, but - the industrial approach to forming is either a) programme the CNC and use a fairly pointy tool with a small tip radius, or b) form a grinding wheel to profile and shape lathe tools with that.

For the chap doing a one-off, or a few-off, I think Andy's file-and-then-harden approach is probably as good as any. Subsequent sharpening of tool, if needed, by grinding on the top (flat) face.

When using a form tool in a lathe, keep everything as rigid as possible - absolute minimum overhangs. Slow speed, gentle feeds, lots and lots of cutting oil. Free-machining grades of stock material really help, too.

 

[chipmunk]

Keith Fenner is also worth watching on YouTube, for hints and tips.

Towards the end of this video he's using a more crude form tool to machine the outside radius on small stainless rings...

http://www.youtube.com/watch?v=TNe3F1VAwrk

It's interesting to see less of a plunging cut and more an intuitive touchy-feely cut which is all the more impressive on his small lathe :wink:

Jon

 

[user 5024]

If the curved shape that you want to make is in brass then gauge plate shaped by any means, even just files and then hardened is the easiest way
to make the form tool.

When making brass ball handles many years ago I made one tool to cope with all the different ball sizes.
I drilled several holes in the tool to be and taper bored them to give clearance on the cutting edge.
Then I hacksawed across the holes and filed and polished all the cutting edges before hardening.

You might get away with this technique for machining free cutting mild steel but I have never tried it.

 

[Richard T]

Thanks Dave.

It is brass that I will be turning. I've had another go with grinding a hss tool but not tried it yet.

I will let you know how I am getting on when we have got this bonfire night stuff out of the way.

 

[nicguthrie]

I may be a bit late to say anything, but there's a lot of interesting stuff on YouTube about working in steel for making knives. The techniques would be very similar for your form tool.

You'd want a tool steel blank that you could work while unhardened. That way plain fully hardened metal work files will cut it nicely and grinders won't wear excessively. A Dremel would be great for fine tuning.

The knife videos hold a lot of info about hardening, and I guess all you'd have to do would be to cut down on tempering, to leave your profile tool as hard edged as you like.

I'm no specialist and am probably trying to preach to the choir, but I thought I'd pop my tuppence worth in. I'm bored while the missus is shopping

Nic.

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