I'm not punching cleanly...

[Beanwood]

I've been making some punch and dies - and have had some success with multile holes on smaller tins.
I've now come to do the same thing on larger tin lids (With larger punch rods) and have run into a few problems.
I suspect the problem is two fold - but would welcome any guidance.

Problem # 1 - I'm not cutting the silver steel which (Used as the punch pins) cleanly enough. These are 4mm and 5mm.

To get the pins from the 'main rod', I've tried:
Grinding them with a cutting disc (Leaves a burr)
Bolt cutters (Leaves a rough end here the silver steel 'snaps'
Hacksaw (No - just no...)
Lathe (Too much deflection when trying to part off)

All of these all lead to some sort of malformation or burr, which I've been taking off with a grinder, or with sandpaper - and I think is leading to a tapered (i.e. pointed) pin going into the die - causing the tin lid to stretch more than shear - so leaving sharp edges.

Problem #2 - perhaps the die holes are too large, so allowing the 'stretch not shear'. I've been making the holes with short drill bit (Trying to minimise hole drift). Would I be better making a smaller drill hole, and finishing with a reamer? I've never used a reamer - don't even know if they come in different types - so what size drill/size and type reamer do I need for 4 and 5 mm holes?

I'm doing the holes in punch and die with my pillar drill - as I don't have a vertical mill which I guess may be slightly stiffer?

I know you all love a picture - so here are some demonstrating the problem tops - in tin and aluminium. The upper side showing various nicks and deformities from pushing/pulling through the material. The underside showing the 'stretch' rather than shear of the pins - and I must say those thin slivers of stretched tin are viciously sharp!

 

[Erie Fred]

How are you aligning punch & die ?

 

[Kram]

Hacksaw (No - just no...)
Lathe (Too much deflection when trying to part off)

I would suggest your doing it wrong on both.IIt looks only a small diameter and take seconds with hacksaw. Followed by a few seconds with a file to clean up the edge.

Do you have a photo of your punch/die?

Consider how these knockout punches are shaped, they have a pair of leading edges which pierce and start it off so that its not trying to cut all at once, lowering the force required.

https://www.amazon.co.uk/KATSU-22-Hydraulic-Puncher-Hole-driver/dp/B00BKXVRTO/

 

[s410man]

I would maybe suggest putting a slight negative taper on the punch aswell-not sure if that's the right word

So as soon as its punched through its not dragging and causing more of a burr

 

[Beanwood]

How are you aligning punch & die ?

Lining them up in the fly press (Interlocked), and locking them in place before liting the press arm.

 

[Beanwood]

I would suggest your doing it wrong on both.IIt looks only a small diameter and take seconds with hacksaw. Followed by a few seconds with a file to clean up the edge.

You may well be right - didn't realise I could use a hacksaw wrongly - but it literally just skids on the silver steel, and won't cut it
Pick any size you like from 3mm 4mm or 5mm - I have the same issue with each.

 

[Pete.]

Looking at your punched holes you have too much clearance from punch to die. There's an allowance that you apply according to material thickness, I don't know it but I know that it's important from my sheet metalwork days, we had several sets of dies according to the material being punched. I'd say that it's possible your die is blunt too, the inside edge might be rolled a bit (if it wasn't it probably is now). Also how are you getting those holes so close to the inside lip punching from outside in?

I would make the die again but this time ream the hole from behind sliftly under-sized with a taper reamer then harden. Surface grind it to a tighter clearance.

 

[jsf55]

I would maybe suggest putting a slight negative taper on the punch aswell-not sure if that's the right word

So as soon as its punched through its not dragging and causing more of a burr

As above, try making the punch concave so it holds it's position

 

[Beanwood]

If I’d known I would have to show it off I’d have tidied it up
The saving grace is I can replace each pin individually now as they’re retained by grub screws - once I work out how to cut them precisely.

 

[Pete.]

Jesus wept I'm surprised you got as good as you did. Punches are usually dead square on the end and sharp edged.

 

[Pete.]

Grind those pins flat with a mini-grinder, harden & temper them then if you don't have a surface grinder put them in your battery drill and grind them flat against your bench grinder wheel to remove the edge burr.

 

[Beanwood]

Jesus wept I'm surprised you got as good as you did. Punches are usually dead square on the end and sharp edged.

But HOW do I get the silver steel dead square and sharp edged - it's only 4 ot 5 mm???

 

[Beanwood]

Grind those pins flat with a mini-grinder, harden & temper them then if you don't have a surface grinder put them in your battery drill and grind them flat against your bench grinder wheel to remove the edge burr.

Is there a best way of cutting silver steel rod of 4 or 5 mm please, to give my grinding wheel the best chance of survival.

 

[Beanwood]

Does anyone sell pre-cut/ground silver steel??

 

[Pete.]

Here I made one in a couple of minutes.

Cut off with mini grinder and 1mm disc





Stick it in your battery drill



Run grinder and spin it end-on against the wheel lightly



Remove remaining tiny burr by running it against a stone (held flat to the stone)



Pin ready to go

 

[Agroshield]

However you cut it, you can square the end by holding against the abrasive surface of a disk sander (https://www.machinemart.co.uk/p/clarke-cs4-6e-belt--disc-sander/), guided by the fence.

This page tells you the required shape of the punch (1/4 degree back taper), the die (tapered underside so slug does not get trapped) and clearance for material and thickness combinations:

The formula for successful punching

While the first step in successful punching is to pay close attention to the quality and features of punching tooling, other factors come into play. Punched slugs are clues, and examining them can reveal whether the punch and die clearance is too loose or too tight and whether the machine is...

www.thefabricator.com

These are cut to length and hardened, but the ends are not at all suitable to use as punches:

Metric Dowel Pins Hardened and Ground | Shop4Fasteners

<ul> <li>Steel metric dowel pins</li> <li>Through-hardened and tempered to 60 ±2 HRC, HV 550-650</li> <li>Precision ground diameter to ISO tolerance m6 for interference fit</li> <li>DIN 6325, ISO 8734</li> <li>Chamfer ground on one end (a), ra

shop4fasteners.co.uk

 

[Maker]

These are cut to length and hardened, but the ends are not at all suitable to use as punches:

Metric Dowel Pins Hardened and Ground | Shop4Fasteners

<ul> <li>Steel metric dowel pins</li> <li>Through-hardened and tempered to 60 ±2 HRC, HV 550-650</li> <li>Precision ground diameter to ISO tolerance m6 for interference fit</li> <li>DIN 6325, ISO 8734</li> <li>Chamfer ground on one end (a), ra

shop4fasteners.co.uk

Then why suggest it?

Lathe (Too much deflection when trying to part off)

You want as little stick out as possible, the parting blade can be literally 1mm from the face of the chuck jaw. Not that you even need a parting blade now you've chopped them up, just use a regular turning bit, HSS will cut silver steel just fine provided it's sharp and on centre. Spindle speed probably as high as you can go for such small diameter work.

Even just cutting them with an angle grinder and ignoring any burr that forms would be an improvement, I'm surprised (Or horrified?) the bolt cutter'ed pins cut as well as they did. The first cut would probably knock the burr off for you.

 

[Agroshield]

Then why suggest it?

I am responding to the direct question of the OP, quoted below in case you missed it:

"Does anyone sell pre-cut/ground silver steel?"

To be sure, the dowel pins only answer half the question (pre-cut) but it is a start and might provide inspiration for someone else to chip in with something that fully answers the question.

---

A lot of useful information is here:

punch and die design-1.pptx

punch and die design-1.pptx - Download as a PDF or view online for free

www.slideshare.net

 

[Screwdriver]

Do they need to stick out that much from the punch holder? If they can be pushed in to leave a feww mm you could put the whole thing in a lathe and dress them up.

I would cut the ends with a Dremel and then grind a slight concavity (with the Dremel). You could spin each individual punch in a drill then use a Dremel disk at right angles to give the tip a concave cutting edge.

If that's too much of a faff and you want to leave a squared off cut, cutting them at a slight angle would help.

 

[Ton-up]

You havn‘t got anything to hold the plate flat whilst punching. Surely you would need a pressured plate when doing that many holes?