Howw do I put a square peg into a very small round hole....

[Beanwood]

Well not quite, but close.

I have a need for a punch and die - 6mm x 1.5mm. I managed to buy one , but the die was physically to wide for the part I needed to punch through.
So I need to make a new bottom die - 6mm x 1.5 mm with perfectly square corners.
I have my new milling machine (Hooray) and a 1.5mm cutter (This is going brilliantly!) and I now have a nice slot 1.5mm wide, and 6mm long, with the cutter radius each end.

But I have a square ended punch.

How do I make the corners of my new die square. I presume I need to file them with a really thin file?or is there an easier/better way?
Are files less than 1.5 mm thick available (I've seen something about Escapement files?)

Alternatively - do I make a punch with the same radius ends as my new hole - as the square punch ends might be easier to file round.

Thoughts please - I don't want to reinvent a wheel if there's already one out there....

 

[hotponyshoes]

Thin files are commonly available (or you can carefully grind down a thicker one. Half Round would be best to keep the grinding away from the edges)

If you haven't milled the slots yet drill a smaller hole in each corner first to save on the filing

At that size you could probably broach it. Pillar drill would work if you don't have a press.

 

[Kram]

What material and thickness are you punching? Edit I misread.. you are trying to make the die.

I'd suggest a broach which can be ground from a 6mm square HSS bit, or milled from tool steel.
You may need several radiused cutting edges on one corner to get the full square profile, do one corner at a time, flipping and rotating the die so you only need one tool. The other 3 corners would be filed to a matching radius.

Much of the advice from your previous thread would likely apply here...

 

[Nick67GT]

Spark erosion.

This will produce the exact size you need with as sharp a corner as you want.

(If I haven’t misunderstood the practicalities of your needs with my suggestion…)

 

[Beanwood]

Spark erosion.

This will produce the exact size you need with as sharp a corner as you want.

(If I haven’t misunderstood the practicalities of your needs with my suggestion…)

Looks like a great idea - but probably beyond my (As usual) limited budget.

I think @hotponyshoes and @Kram have cracked it - make my own broach!!! That's the answer chaps, thanks.
I can reduce the thickness of the die to about 1mm I suppose, in an area local to the actual die hole
I have some tool steel I can grind/mill.
Do I just put a few 'steps' in the broach to take out the corners a little at a time?

 

[hotponyshoes]

For something that size you'll probably get away with just one tooth on the broach and a set of micro drills to use as packing and work it through one spacer at a time

 

[voipio]

Jeweller's files. Something like:

https://www.amazon.co.uk/Needle-File-Jewellers-Files-Tool/dp/B00439E2MQ

The flat ones are usually less than 1mm thick.

 

[Agroshield]

1.5mm wide?

Hacksaw blade with the set ground off the teeth.

Too wide?

Junior hacksaw blade fettled in the same manner.

...ground from a 6mm square HSS bit...

He could actually make the die from that. Two pieces of square HSS lined up parallel to each other with a 1.5mm gap between them.

HSS parting blades are available in 1.5mm wide to form the two ends. They may need a slather of JB Weld to make them parallel as they will taper.

The die would have nice square corners on it and a sharp top edge and would not need hardening.

 

[DAPPH]

Photos required of the fabrication exercise & end product please , or we won't believe you did it.

 

[Beanwood]

Photos required of the fabrication exercise & end product please , or we won't believe you did it.

No problem.

I am unfortunately out this evening - so tomorrow night is the first chance I'll get.
I quite like the idea touched on by @Agroshield - with a slight variation - two pieces of tool steel - die hole profile machined into both halves, then joined together with screws or similar

 

[Screwdriver]

... two pieces of tool steel - die hole profile machined into both halves, then joined together with screws or similar

Machined into one half surely?

 

[Beanwood]

Machined into one half surely?

Oh good point! I was thinking 2 sides as I’m not sure how deep my 1.5mm end mill is. (For design reasons 6mm across the width rather than the length )

 

[oldbikedavey]

Might be able to notch that into the side of a bar of HSS, then make an appropriate stack of similar items in a supporting role ?
Bit of a surface grinder job, but it's do-able....

 

[Screwdriver]

Oh good point! I was thinking 2 sides as I’m not sure how deep my 1.5mm end mill is. (For design reasons 6mm across the width rather than the length )

You'll be making a 1.5mm deep slot surely if you want square corners. So long as the cutter is less than 6mm diameter...

 

[Beanwood]

You'll be making a 1.5mm deep slot surely if you want square corners. So long as the cutter is less than 6mm diameter...

Ah no you see - that would mean the 6mm running the length of the die. I need it to run side to side, so 1.5mm wide and 6mm deep.

 

[Screwdriver]

Not a straight slot then?? I thought the idea was to mill out a square corner? Why do you have to mill a 6mm deep pocket with a 1.5mm tool? Sounds fraught…

 

[Agroshield]

If you have a punch and die, measure their dimensions. Your finished slot needs to be 6 x 1.5. The tooling will not be that size as there needs to be clearance. The optimum clearance depends somewhat on the material (brass, steel, stainless) and thickness. The tooling also needs a little bit of back relief so the slug does not jam in the die.

Milling a narrow but deep slot would make it hard to adjust that clearance and hard to form the relief. Milling a shallow and long slot, as above, would allow you to slip a fag paper between the two parts of the die to adjust clearance and tickle the short edge with a stone or file to adjust in that direction. Also much easier to add relief when made that way.

 

[Barking Mat]

Lube, lots of lube.

Apologies, it's late.

 

[Beanwood]

Not a straight slot then?? I thought the idea was to mill out a square corner? Why do you have to mill a 6mm deep pocket with a 1.5mm tool? Sounds fraught…

Maybe I’m not explaining it well. I’ll draw a picture tomorrow.

In other news- how does one cut tool steel? Put it on my new automatic hacksaw and barely even a scratch!

 

[optima21]

make the die in 2 parts, one side can be milled with a slot 6mm wide by 1.5mm deep and the other side is completely flat, dowel the two parts together and you have a rectangular hole in a "piece" of metal.