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]

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 !

[greybeard]

Well, a year has passed, and I managed to produce the cuts I needed with a watchmaker's slitting saw mounted in a drill press.
I had a jig mounted on a huge bearing I found on the farm scrap heap, lined up on the drill press, and cut a couple of hundred bolts without any problems.

After a year of re-designing the instrument, I've settled on a slightly different requirement. I now have a slot cut in a socket grub screw, at the opposite end to the socket.
My set up still works while I'm prototyping, but if all goes well, I would be better employed with other parts of the manufacturing process if I could outsource the slotting.

Any suggestions as to what type of company might best be approached for this ?
I'd be looking for 1000 till I see what the market might be.

John

[Geof]

You are missing a zero, or two.

I think you might find if you try to get a machine shop doing it that 1000 is too many for them to consider with a simple setup and too few to justify a proper automated setup.

[greybeard]

Hi Geof,
That is `what I feared the reply might be.
I just hoped there might be some source I'd not known about that might fit the bill.

Just done a batch of 70 at about 6 per minute, so perhaps I'll stick with it for a while.

But if anyone does have a bright idea, please let me know. Just bear in mind my material cost per grub screw is about 2p, so I'm not looking to make a major investment

Regards
John

[Geof]

....Just done a batch of 70 at about 6 per minute,...

Even with a CNC I would be hard pressed to go much faster than that because the loading/unloading time would be large compared with the cutting time. Lets say I could do 20 per minute at the price I charge per hour they would cost about 8p each. But that is only 8000p for the whole lot and I am too lazy to get off my butt and turn the machine on for only 80 quid.

At your production rate you have less than three hours work ahead of you so you will be saving money at about 27 quid an hour.

[keebler303]

Couldn't you drill and tap a long row of holes in a block of aluminum or something and just go down the line cutting 50 or 100 in one go?

Matt

[greybeard]

Geof, now I'm saving £27 an hour, I could afford a holiday

Couldn't you drill and tap a long row of holes in a block of aluminum or something and just go down the line cutting 50 or 100 in one go?

Matt

Hey Matt, that sounds a lot safer than the way I'm doing it at the minute !

Will give that serious thought, and look at the timing involved.
Once I've got the jig made, loading and unloading with a small power driver could be very much quicker.

John