Problem- Cutting 0.5mm wide slot in stainless bolt head

[greybeard]

I need to find a way of cutting a 0.5mm wide slot in the head of M4 x 20mm stainless button cap bolts.
I've done this manually with a small hacksaw, crudely, but it was a proof of concept trial.
Now I need to do it in batches of 100, and with a consistent finish.

The dimensions are not critical, but consistency is, and doing a batch in under an hour would be economically desirable !
The slot is parallel to the axis of the bolt, but offset from the center.

Should I be looking at small diamond wheels, or HSS slitting saws, or what ?

John

[RICHARD ZASTROW]

Do you have a freindly EDM shop in the area?

Dick Z

[Geof]

What kind of machine do you have available? It is possible to buy small slitting saws made for screw slotting. Here is an example:

Screw Slotting Saws

If you Google 'screw slotting saws' you should be able to find a UK supplier.

For stainless on a small manual mill HSS is probably the best. You will have to run quite slow; I would start even as low as 50 rpm. For the feed aim at about 0.01mm per tooth and do not let the cutter rub; either be feeding in or move clear. For lubricant use a tapping fluid that is good for stainless steel.

You are probably going to burn out or break a few saws before you get the hang of it but with luck you will be able to get about 100 bolts per saw. Doing 100 per hour may be a challenge unless you have a CNC machine and can load several bolts in a fixture per cycle.

[greybeard]

Originally Posted by RICHARD ZASTROW Do you have a freindly EDM shop in the area? Dick Z

Hi Dick,
I wish ! I had thought this might be the way to go originally, and also considered ECM as a possibility to the extent of getting some kit together to try out the principles. Might still be a goer, but I thought the traditional mechanical methods should be explored first.

There is a small complication, not mentioned till now, in that the path of the groove, though only ~ 0.5 x 0.5mm needs to follow the curve over the top of the button head, but straight in plan view.
It's going to be a track for a 0.45mm wire to bed into.

Geof, thanks for the cutting speed etc data. That gives me a good starting point.
I do have a diy cnc router which I might consider adding a different head to. That would get round the complication mentioned above.

I had also considered abrasive cut-off discs, but the dimensional change as the wore out might be a complication too far. The cost of one blade per 100 bolts would only add about 30% to the cost of the bolts, so that would be fine.
From your figures, a 90 tooth saw (as advertised in your link, thanks) should cut a single track of 10mm x0.5mm x 0.5mm in about 15 secs, or less. Some sort of carousel feeding the set up would seem sensible, I hadn't thought of that, so thanks again.

John
EDIT Just ordered the 0.5mm slitting saw, so off we go !