A Lawnmower Punch Press

If your determined to use a lawnmower crank let me suggest you get a much larger HP engine and older is better cast iron block type crankcase.
The journals will be stronger and the counter weights heavier. You'll still need a heavy flywheel which on older engines is heavy duty cast iron . On mower engines the flywheel is aluminum , they use the blade as counter weight.


Simple, just leave the blade attached to the crank :grin::cautious:
 
An inertial press (my term) uses the inertia of a flywheel driving a eccentric to provide the force required to punch or form the material as opposed to hydraulic press or a mechanical press using levers, gears or a screw.

That sounds like something I might be able to use. Do you have a photo of it? Is it motorized, or hand-crank?

As embarrassing as this is to admit, I don't have any money.

I'd be hard-pressed (no pun intended) to come up with shipping costs, much less purchase the machine from you.

The lawnmower idea may be a pain, but at least it's FREE. :grin:
 
Please Check my Math

Here's the formula for calculating perforating pressure.

Perforating Presser Forumla.JPG

T = Thickness of Part Material = 0.6 mm or approx 0.024" (the above formula requires inches)

L = Length of Shear - the outside diameter of the gear is approximately 5.0 mm or approx 0.20"

S = Shear Strength of Part Material.

Soft brass = 30000 psi <- already in inches
Half hard brass = 52400 psi
Full hard brass = 81400 psi

Not sure which material to use. I'm thinking half-hard, but don't know for sure yet.

My answers after calculations:

P = Perforating Pressure in lbs.

Soft brass = 445 lbs. or about 1/4 ton
Half hard brass = 778 lbs. or just under 1/2 ton
Full hard brass = 1208 lbs. or just about 1/2 ton

So I'm thinking a 1-ton punch press should suffice.

I'm with Jim Dawson guessing that a lawnmower crankshaft should handle 1 to 2 tons. It should be plenty good enough.

Please double check all my calculations and conversions to be sure I didn't make a any huge mathematical errors.

Thanks.
 
Flypress is more a blacksmithing term I guess, at least that's where I know it from. Lots of Google images for them, sounds very similar to what RJ is describing. Also really good for knocking your teeth out if you get too close to the spinning ball...

-frank
 
I get 1227 for full hard brass. But we're close. So allowing for other factors, I normally add about 20% just because, it looks like about 1.5 ton would do it.
 
Is the Length of Shear factor supposed to use the perimeter of the part? For example, a plain circle at say 1/2" diameter would be much easier to punch than a five pointed star of the same size. At least the way I'm imagining it. Cool stuff.
 
Simple, just leave the blade attached to the crank :grin::cautious:
Simple yes safe no , the hubs are made to shear , and I've had hundreds with sheared bolts that hold them in. Weld it up well it's cast so braze may work fine.
 
Is the Length of Shear factor supposed to use the perimeter of the part? For example, a plain circle at say 1/2" diameter would be much easier to punch than a five pointed star of the same size. At least the way I'm imagining it. Cool stuff.

Yes, you have to use full perimeter length.
 
Yes, you have to use full perimeter length.

I LOVE this forum. You guys catch all the details and that's great.

I agree, in fact, I was going to have Racer do that as part of his homework assignment. :grin:

The actual max outside diameter of the gear is 4.4 mm. I put 5 mm in the equation to allow for a little extra length. And then hoped and prayed that no one would catch the lazy math. I was also hoping the lawnmower crankshaft would ignore the math error too.

But it is true, we need to take account for the entire gear profile. So we could be pushing the upper limits on the poor lawnmower crankshaft.

Although in truth, we're only guessing at what it can handle to begin with. I supposed I should actually look into what they can actually handle.

Just based on life's experience I can kind of tell that this should work. At worst case we might be pushing the crank to its limits. It'll be the battle between the crank and the brass to see who wins out.

My goal is 420 gears. If I can get it to punch out 420 gears before it goes kaput I'll consider that a win. :grin:

Just off the seat of my pants I'm confident enough here to continue with the build of the punch press. We're certainly close to being in good shape.

Obviously if we had a crank from a larger engine we'd have more leeway. But I don't have a larger crank. And I'm too cranky to go looking for one.

I trust this little lawnmower crank can pull it off.

I'm thinking of going with the half-hard brass anyway. These calculators aren't likely to be used extensively. Chances of them wearing out are slim. They'll probably end up being purchased to sit on a display shelf and only used on rare occasions to show how they can add a few numbers up.

As a practical matter we could probably go with soft brass gears. Not sure about that. But surely half-hard would be good enough?

What do you think?

Would full hard brass gears be better? Push the lawnmower crank to its limits?

I'm game. :grin:
 
We're not going to let you get away with anything :grin:

I think at least half hard would be better, full soft is pretty soft. Half hard 260 blanks pretty nice, I've never punched full soft. Full hard punches about like 1020 steel. I'm an old tool & die make too, built a lot of punching and forming dies.
 
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