I am trying to make this style of punch for making leather watch straps.

I'm going to use 1/2" square stock as the punch base, drill, tap and solder to accept the five individual punches and allow for the punched divots to fall out.

 

For the punches I have used 1/4" O1 drill rod, center drilled with a #36 drill, and tapered and sharpen the end on a lathe. I made a drift punch to drive into the end to do the shaping. This is not very reliable as it sometimes destroys the metal and tears at the taper. I harden after shaping the hole.

 

Is there a better way? I was thinking of a drift punch that would drive all the way through, but maybe the hole will need to be a bit bigger? I haven't figured out how to calculate hole size and this may be cause for the tear-out if I am using a punch too big for the hole.

 

You're punching 5 holes at a time? I've never seen a leather punch with more than one punch, though I've never seen one in a commercial operation.

 

Were I making a punch I'd use the same layout as a hand squeezed punch and maybe anchor a small spring in the punch blade to push the slug back out.

 

Of course that's just me and this evening's WAG.

 

Frosty The Lucky.

I would make a metal template with holes in it and a guide to postion it over the leather..then use one punch through the guide to punch the holes one at a time....

You want the circumference of the hole to be the same as the perimeter of the slot.  Maybe a TINY amount smaller so that it has a small amount of stretch. 

Doesn't have to be 5 holes but needs to be at least two for indexing perfectly.

Make it five and you strike twice on a watch band and production speeds up.

 

I guess what I really am looking for is a relationship between round drill hole size and elipse size, so a drift can be driven through and reshape exact every time.

I don't know the math to figure. Maybe just a bit of trial and error. but I dont want to waste a bunch of stock and time in the process.

Use Clay to assist you with sizing! 

The holes in your example photo are pill or lozenge shaped, not a true ellipse. So you can do the geometry on paper for that rather easily, because that shape is a rectangle with two half circles scanned onto each side. So perimeter of lozenge= 2x*(length of rect.) plus pi*(height of rect.)

From there you just need to find a drill bit that will produce a hole with a circumference close to but less than the perimeter you just calculated.

Not having a lathe myself I would be inclined to forge the end down a little, drill/drift to the correct shape, and finish edging it on a grinder or with a hand file. Using the same methodology you could drill two smaller holes the desired distance apart and use a burr of some sort (or any other method) to chew out the sliver of metal in between the two holes to machine the correct aperture, then continue to grind or file the edge to taste.

As to indexing and the number of punches, I would make one actual punch and make one punch shaped peg at the correct distance that can maybe be detachable so you can start it easily. Then you can set your peg in the previous hole to index, punch the next one, reset peg, rinse/repeat/profit.

I'm not going to fight my phone, there may or may not be undesired autocorrect influence in the above =\

Make a second drift of identical size. Forge this second drift round and measure it.

second thought while i was finishing the dishes, drill it out, turn the edge down almost to final thickness on the lathe, take a heat on the tip and forge it lightly to collapse the circle down to oval.

 

i also forgot to ask why you are tapping threads as well as soldering?

 

if your drift is tearing the edge when you attempt to reshape the hole you might consider leaving the edge thicker and sharpening it afterwards, that way it will have more resistance during the drifting process.  it could also be that your drift is oversized to the hole you are drilling, causing the perimeter to stretch and therefore crack.

second thought while i was finishing the dishes, drill it out, turn the edge down almost to final thickness on the lathe, take a heat on the tip and forge it lightly to collapse the circle down to oval.

 

i also forgot to ask why you are tapping threads as well as soldering?

 

if your drift is tearing the edge when you attempt to reshape the hole you might consider leaving the edge thicker and sharpening it afterwards, that way it will have more resistance during the drifting process.  it could also be that your drift is oversized to the hole you are drilling, causing the perimeter to stretch and therefore crack.

 

Thanks so much for the help. Chatroom was wrought with salesmen:)

 

The most important part is the indexing of the tool. I was too focused on the sample tool.

I used a formula for an elipse and as you said, not exactly what I was trying to make. If I use a stud for the index, then repeatability is built-in.

 

Was going to thread and solder since there will be a lot of impact.

Will be using mild steel for the base and tool steel for the cutting.

I dont know if these weld together properly for long use. I have never researched this joinery.

You left something out in chat until later in the conversation.... that this process needs to be repeated competently one hundred times.  I still do not see that in this thread.  Since you want to sell these.  Which means you need to do this somewhere between 200 and 500 times depending on how many you place in each gang punch.  When you leave important information out, expect inexact results. 

you may have trouble holding a hardened cutting edge on your punch if you solder the pieces together as the temperature needed to solder may push the temper on the edge too far.  you will need to consult with one of the knife guru's or the knife making section for accurate information relating to heat treating and preservation (look for info relating to soldering on guards and habaki without affecting heat treatments) because i have only a fairly basic experience with the process on tooling, iv just read up on applications to bladesmithing (technically you are making a circular knife) but have no practice in the shop.

 

if by weld you mean along the lines of mig/tig you can hit up the welding subforum for specifics, but i think the response is usually along the lines of make sure you pre and post heat correctly to avoid the weld cracking.

 

consider utilizing the mild steel block as a guide rather than a base and shape the shank of the punch to fit in a certain orientation, think square peg square hole.  that way you can hammer directly on the tool steel (make sure the struck end is softened, or use an annealed or brass hammer to strike it) and not have to worry about any joinery, and you can recycle the same guide block with any number of different punches for varied shape/size holes.  you can also reduce the bulk of the mild steel portion as it will not be subject to impact, it just needs to keep the punch straight and lined up internally and in the same place relative to the indexing stud.

 

if you are so inclined you can also install wings (or equal) on the side that are the same width as the band to keep everything restrained horizontally too.

You left something out in chat until later in the conversation.... that this process needs to be repeated competently one hundred times.  I still do not see that in this thread.  Since you want to sell these.  Which means you need to do this somewhere between 200 and 500 times depending on how many you place in each gang punch.  When you leave important information out, expect inexact results. 

 

I hate chat. I usually spend upwards of an hour composing my thoughts. (and I still miss some)

 

However, I don't think it matters if i'm making 100 or 1. Buying retail is not a fair answer on this site.

 

I actually want to trade these.

 

(Only took 45 minutes:)

if its an item intended for sale or trade in return for real goods, currency, or services from others you want your craftsmanship to be clean and consistent, or risk running out of customers in a hurry.  so it behooves you to streamline your tooling and processes to produce the most precise and consistent output, which often requires a lot more forethought than just grabbing a nail and eyeballing it.

if its an item intended for sale or trade in return for real goods, currency, or services from others you want your craftsmanship to be clean and consistent, or risk running out of customers in a hurry.  so it behooves you to streamline your tooling and processes to produce the most precise and consistent output, which often requires a lot more forethought than just grabbing a nail and eyeballing it.

Hence the reason for my post on iforge. I know my weaknesses and strengths.

Thanks for the help tonight.

good luck, post pics of your tooling and process, be interesting to see what you come up with :)

You are creating an oval not an ellipse.   To calculate the perimeter of the oval you need the diameter of the radii on the ends,  the perimeter is  diameter x pi + 2 x (length - diameter)    

 

Rather than just driving your drift in to create your oval you should drive it in part way then flatten the punch then finish driving in the punch.  It will be difficult to do this while maintaining your heat as the parts are so small.  You might consider using a drift  and bolster to drift and squeeze at the same time seeing as you are making a lot of these.  I would consider making the drift out of high speed steel with a mild steel striking end because it is so thin.  You could then allow it to retain a lot of heat and it won't suck as much heat out of your work. 

Alright, here are my measurements for the final hole size:

W-.100

L-.150

R-.025

 

This comes out to a circumference of .4571. This calls for a #27 drill. Much bigger than what I was using. Closest I could get at the tool store is a 9/64 drill bit. I will make one up and report back.

Give it a whack, your bit is pretty close and erring on the small side so you should be in good shape.

If trying to drift it fails (are you doing this hot or cold btw? Inquiring minds want to know) just drill it out and lightly forge it to an oval cross section. I highly doubt anyone will be able to tell what size you were shooting for. Just use the same process if you make duplicate punches in the future.

Why not just buy one? Check out Tandy leather for multi punches. Also lots of info for leather tools on www.leatherworker.net. It is like IFI for leather.

another way to calculate and forge what you need.

first; often start with larger parent stock than what you may think you need.

1- calculate the area of the oval, you have all the data.

2- determine what size drillbit is equal to or slightly less than the area of the oval

3- make a tapered drift and match area to shape where drift is at max deapth.

4- your parent stock needs be dia of drill bit + 2x thickness of wall of your tool or greater for final finish and polishing.

5- drill, then heat stock, insert. drift and lightly forge to the shape of drift. drive drift in to mark for final sizing of the ID

Note: when forging shape you are moving material to the oval shape, not thinning the walks of the tool.

referring. to -4- above, your actual diameter of parent stock should be large enough that you can remove material and sharpen your cutting edges.

if tou do it this way you should be right on every time and not distress your cutters.

instead of using the drift to move the material out, you are using it to match two shapes of a given area at a particular cross section. thus no sttess or distress of the thin cutters.

This isn't an oval, this isn't an ellipse, but rather a true slotted hole?
At least that is the way the machinist in me would classify it.....

Alright, here are my measurements for the final hole size:

W-.100

L-.150

R-.025

 

This comes out to a circumference of .4571. This calls for a #27 drill. Much bigger than what I was using. Closest I could get at the tool store is a 9/64 drill bit. I will make one up and report back.

Little confused on the math here. You want .4571" which is real close to 29/64". Closest you can get is 9/64" (??) which equates to approximately .141" That's like over 3 times difference. Did I miss a decimal somewhere? BTW, my drill chart says #27 is .1440" which is only 3/1000 or .003 difference. That is some tight tolerances you are after for a leather punch :o

Dodge, his 0.4571 is circumference rather than diameter. ;)

My bad. 'Splains the 3 times diff LOL (pi = about 3.14 ;) )