Making a small profile tool.

This topic has 11 replies, 10 voices, and was last updated 2 May 2017 at 10:04 by Martin Connelly.

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29 April 2017 at 23:36 #295558
Robin Graham
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@robingraham42208
I have a job which involves making semicircular grooves in round brass stock.So I need something like a parting tool, but with a round nose. The groove needs to be about 2.5mm wide at the surface.

I have 2,5mm silver steel, so my first thought was that if I could round off the end to a hemisphere, harden and grind down to D/2 I'd have a toolbit.

The trouble is that my manual skills at the moment aren't up to making anything much like a hemisphere on such a skinny piece. Probably I just need to plod on with file and eye, but maybe someone knows a better way?

Rob

Edited By Robin Graham on 29/04/2017 23:43:44
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29 April 2017 at 23:36 #8686
Robin Graham
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@robingraham42208
29 April 2017 at 23:59 #295562
duncan webster 1
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@duncanwebster1
What diameter is the bar stock? If it's quite small you might succeed by arranging a holder to support the silver steel at 5 degrees off vertical, and just grind the top off at 5 degrees. Bit like a tangential turning tool. However if the stock is big, you'd have a lot of overhang of the 2.5mm stuff to clear the holder. Draw it out and see what it looks like

Otherwise it's a tool like a parting tool but with a half round end. You can profile the end with a diamond file, slow but sure

Edited By duncan webster on 30/04/2017 00:01:06
30 April 2017 at 08:05 #295573
Hopper
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@hopper
You can buy pieces of round HSS that could be held like a tangential tool bit to turn a half-round groove.

Or make a ball turning tool to turn a proper half-sphere on the end of a piece of silver steel. But a bit of time with a file in the lathe and a profile gauge made from drilling a 2.5mm hole in a piece of sheet metal and then cutting it in half and you should get something close enough. The only way to develop those manual skills is to do it.
30 April 2017 at 08:09 #295575
GoCreate
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@gocreate
Hi Robin

You could make a steel shank and silver solder a piece of 2.5mm HSS or carbide drill shank to it. If your going deeper than 1.25mm then grind some side clearance.

Some HSS drills do have a soft shank though, so a good quality drill will be needed. The temperature of silver soldering HSS won't effect the HSS hardness much.

As illustrated below.

Nigel
30 April 2017 at 08:12 #295577
Nick_G
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@nick_g
.

When making the Hoglet engine I had to do similar. I reground the tip of a small HSS parting tool and all went well.

Nick
30 April 2017 at 09:53 #295600
Chris Evans 6
Participant
@chrisevans6
Hands on is the only way to learn, grind and check with a radius gauge. At that size it will not be easy, I resort to magnifying glasses a good light and white paper under what I am attempting to grind. A final rub with a diamond file should see you done. No one will notice if the radius produced is a couple of thou wonky.
30 April 2017 at 10:03 #295605
Gary Wooding
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@garywooding25363
What a coincidence. I've just done exactly that. I got a bit of HSS drill rod and made the tool holder, shown in the following picture, from a piece of scrap. (That's why the thickness is a bit odd.)

The drill-rod is held at 12 degrees and ground off to be horizontal.

EDIT – I've just noticed that the TurboCAD imp has struck again. The dimension shown as 15.00mm should be 10.00mm. I used the Drafting Pallet and scaled it up by 1.5, for some reason the 10.00 was scaled to 15.00, but the 15.40 was left alone. Don't you just love bugs!

Edited By Gary Wooding on 30/04/2017 10:26:34
30 April 2017 at 10:36 #295608
Brian Wood
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@brianwood45127
Hello Robin,

Would it be sacrilegious to suggest finishing the bottoms of the grooves with a round file which the lathe turns the job. You don't indicate how important that finish is and for a few off it is what I would be tempted to do. You say they are grooves which implies shallow features with little risk of the file fouling the sides of a trench.

Something like a chain saw file which is parallel sided all the way might be ideal.

Regards
Brian
30 April 2017 at 10:56 #295613
Anonymous
If the radius is non-critical I'd hand grind the radius on the end of a piece of HSS, using a radius gauge as a sanity check. If the radius is critical I'd look for an insert that might do the job. Failing that I'd mill the radius on the end of a piece of HSS. Personally I'd mill with CNC, but equally as good would be a manual mill and rotary table..

Andrew
1 May 2017 at 23:09 #295932
Robin Graham
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@robingraham42208
Thanks for your suggestions – all good stuff, Perhaps I should have said that this is more rolletry – the aim is to make brass discs to emboss a pattern (in this case a continuous bead) in clay. The rollets or roulettes are about 1.25 inch diameter and a quarter inch thick or so thick at the axle. The bead needs to be about 2.5mm at the base and about 1.15(ish) high..Anything over D/2 pulls the clay into the tool.

I hadn't thought about the tangential tool approach – I'll experiment with that. If it doesn't work out, plenty of other suggestions to follow up.Thanks again.

Robin
2 May 2017 at 10:04 #295979
Martin Connelly
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@martinconnelly55370
About 18 months ago there was a thread where pre-insert threading tools were discussed. This is an alternative to the tangential tool design above that may be worth consideration. The tools discussed look like this.

It should be quite easy to produce a disk in gauge plate with the required profile, harden and temper it then sharpen the cutting edge. You can make a profile tool to create the disk by drilling a piece of gauge plate near an edge then cutting half of the hole away followed by hardening, tempering and sharpening. The advantage of this is only one tool body is required and a selection of discs could be made over time as the need arose. Larger radius disks may need a half profile tool to cut each side separately.

Martin C
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