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A Lawnmower Punch Press

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Robo_Pi

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I couldn't find a forum for lunatic ideas so I'm posting this here.

I'm in dire need of a small cheap punch press. I only need to punch out small pieces from thin brass sheet so I don't need to huge punch press. I'm looking to build one for FREE materials because I'm cheap. :grin:

Today I was able to acquire a free lawnmower. It doesn't run. I don't know if it could be made to run, but I already have several lawnmowers and don't need another one. It turns smoothly when pulling the cord so the crank and connecting rod are most likely in good shape.

Lawn Mower.JPG


My thinking is that this crank and connecting rod would make the perfect basis for a punch press the size I need. I can build the rest of the frame for the punch press from scrap metal salvaged from old farm equipment.

I searched YouTube and Google for examples of others who have built a punch press using a lawnmower crankshaft to get ideas. But low and behold I couldn't find a single solitary example. I confess that this kind of surprised me because I can usually find examples of people who have already built crazy things like this.

In any case, I thought I'd post the question here:

Has anyone ever seen a homemade punch press built around a lawnmower crankshaft or something similar?

I'm sure I can build one even without seeing an example. But it's always nice to see how other people might have done it. I'm pretty sure the stroke will be long enough to punch out 0.6 mm brass sheet.

I haven't taken this lawnmower apart yet. I doubt that I'll be able to use the bearing case. I'm thinking worst case I'll just grab the crank and connecting rod and piston assembly. Then make my own pillow blocks to hold the crank on the newly constructed punch press frame.

Surely there has to be someone out there who has done this? This is the first idea that came to my mind when I needed to build a punch press. Surely I'm not a pioneer in converting an old lawnmower into a punch press?
 

RJSakowski

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I'm going to take a shot in the dark and assume that this is in relation to the Curta build from another thread. In addition to the eccentric, you will need some sort of clutch mechanism, ram guides, flywheel and you are starting to get complicated. For the 42 parts you want to punch, the effort required to build the tool will greatly exceed the work required to make the parts. If it were me, I would look at getting a small arbor press. You might even be able to accomplish the task with a drill press.

If you are determined to set up a punch press, PM me. I have a small table top inertial press that is not being used.
 

Robo_Pi

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I'm going to take a shot in the dark and assume that this is in relation to the Curta build from another thread. In addition to the eccentric, you will need some sort of clutch mechanism, ram guides, flywheel and you are starting to get complicated.
Yes, I'm aware of how a punch press works. I used to work in tool and die. I actually made quite a few punch and dies. And also maintained the punch presses they were used on.

For the 42 parts you want to punch, the effort required to build the tool will greatly exceed the work required to make the parts.
First off, I'm not so sure I agree with you on this. Trying to make 42 microscopic gears all identical is nothing to sneeze at.

Also, my idea is that if I actually build the Curta I'd like to have the potential to build more than one of them. Maybe as many as 10 or more. Now we're talking more like 420 gears, or more.

Finally, I have been wanting a small punch press for years. I've actually had the idea of building one using a lawnmower crankshaft for quite a long time. Now I have an excuse to actually do it. :grin:

So it wouldn't be just for the Curta project. It would be nice to have this little punch press around for other projects to. I'm build robots. You can probably imagine how many small parts I could make for my robots with a nice little punch press.

So yeah, I agree, if a person wants to build just one Curta Calculator and quit, then building a small punch press might be overkill.

It seems to me to be a waste to only build one Curta. There are going to be a lot of special fixtures and jigs required to make even one. May as well take advantage of all that tooling and make some more too. In fact, I'm thinking that most of the work on the Curta project is going to be building the tooling to build it. Making the actual parts will be secondary.

We're working on making the transmission gears right now. But this part is a piece of cake compared with the next part we need to build -
The Setting Shaft.

When we set out to build the Setting Shaft we are going to need to build special tooling for that too. I don't recall exactly, but I think there are only 8 setting shafts required. But what a shame it would be to only make 8 setting shafts after having made the tooling to make them. May as well make 80 shafts and build ten Curtas. :grin:

Why stop at 8?

I openly confess that I'm thinking mass production here. Not serious mass production obviously, but mass production for a "handcrafted" item. These will all need to be meticulously hand finished. So making even ten will be a major undertaking. But hey, if done properly they could fetch a grand a piece. That could be a $10,000 pay off in the end. Finally a hobby that will pay for itself. :grin:

And yes, that's about all it will be doing - paying for itself. It's going to take a year to complete this project. It's not going to make anyone rich to be sure.

But what would I do with just one Curta?

Nope, I want ten of them. I'm GREEDY! :grin:

To be honest, I wouldn't have even bothered with this project at all if I thought I was only going to build one Curta.

Plus I want this punch press for other projects too. So the punch press isn't just for the Curta project.

But yeah, I'm talking about punching out more like 420 gears. Not just 42.
 

Robo_Pi

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If you are determined to set up a punch press, PM me. I have a small table top inertial press that is not being used.
Picking up an actual punch press is not "off the table". I might consider going that route yet.

But at the moment I have a FREE lawnmower in my backyard. and old farm equipment in the field that is calling to me. "Use us! Use us!"

Don't want to disappoint the poor things. :grin:

They want some love and attention.
 
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JimDawson

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Hey why not :) You know how a punch press works and how to build one, so no problem there. The stroke might be a little long for a small press, but it should make a 1.5 ton or so based on the journal sizes. Once you have the frame built, you can always build a new crank & rod if it doesn't work the way you want it.
 

Silverbullet

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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.
 

Robo_Pi

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Hey why not :) You know how a punch press works and how to build one, so no problem there. The stroke might be a little long for a small press, but it should make a 1.5 ton or so based on the journal sizes. Once you have the frame built, you can always build a new crank & rod if it doesn't work the way you want it.
That's what I'm thinking. I'm certainly not a punch press expert by any means. My experience as a tool and die maker was well over a half a century ago. But at least I do have some memories in tact. :grin:

I confess that I too am concerned slightly with the stroke size. I'm with you guessing that the journal size should easily handle 1 to 2 tons. And I'm also hoping that my small brass material will have perforating pressures well under that. I haven't actually done the calculation yet, I have the equations in hand. I'm just busy right now. I just cut down some trees and brought the logs into my sawmill for making lumber. Real life projects continue on in the background. :grin:

Edited: Here I forgot to post these pictures,...

Logs (1).JPG

Logs (3).JPG

I'd like to cut down one more large oak tree and bring those logs in as well before I set up to start cutting lumber.

Busy, busy, busy. No time to build any punch press one would think. But I don't think like that.

We'll have to wait and see what happens. I could very well be biting off more than I can chew. But the Curta project is just a hobby. I personally have no deadline to get it done. I know Racer would like to finish his in a year. But he doesn't even have access to a machine shop yet. At least I already have a lathe and mill. And I don't have the year time limit. I can just build it in whatever time it takes. No rush to build a Curta here.

I'll try to keep up with Racer. Don't ask me why, but I don't foresee that being a problem. Hopefully I'll be wrong about that and he'll beat me to completion.
 
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Robo_Pi

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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.
I just took an old 18 HP single lung tractor engine to the metal scrap yard last year! What a mistake that was!

I agree starting with a larger engine would provide a stronger punch press. But we're only talking about punching out 0.6 mm brass sheet. Surely this small lawnmower crank can handle this.

I also agree with the counterweight. I wasn't planning on using the lawnmower flywheel as the counterweight. I might use the original flywheel to mount the counterweight on though. I actually have a nice large heavy counterweight candidates on some of this farm equipment.

Again, I'll only be punching out thin brass sheet. I don't think I'll need to build a 5 ton punch press. I'm thinking 1 to 2 tons should be plenty.

I'm trying to get Racer to do the calculation for me in his homework. But I may end up needing to do the calculations myself. They are easy calculations. I might do them when I break to eat dinner.
 

RJSakowski

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Is that that same as a 'fly press'? Just curious, I've not heard the term "inertial press" before.

-frank
I hadn't heard the term fly press before. According to Wikipedea, a screw press is also known as a fly press. https://en.wikipedia.org/wiki/Machine_press https://en.wikipedia.org/wiki/Screw_press

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.
 

JimDawson

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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:
 

Robo_Pi

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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:
 

Robo_Pi

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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.
 

francist

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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
 

JimDawson

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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.
 

pontiac428

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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.
 

Silverbullet

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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.
 

JimDawson

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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.
 

Robo_Pi

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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:
 

JimDawson

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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.
 

Robo_Pi

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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.
I am certain that you are way more experienced than me. No doubt about it. My experience was back in my early 20's. Back in the late '60's. I worked "tool and die" in my brother-in-law's father's machine shop. He was teaching me the tool and die trade. I did make some punches and dies. He had a lot of business making tiny tin masks for an automotive parts company. We punched out the tin masks. These were then placed on things like plastic dashboard knobs so they could chrome them using a process they called "Luster Coat".

In any case, as young as I was I was often given a full project. I was handed the knob and told to make the punch and die to form the mask. Of course the boss gave me all the detailed clearances etc. All I had to do was draw up the punch and die, by hand, and then machine them. He would then have them hardened. And then I would need to set them up on punch presses so his female employees could sit there and punch them out all day.

So it was limited experience to be sure. None the less, it was experience. I did learn how critical clearances were, and various ideas about relief and cutting edge angles. Far from an expert to be sure. But it was still a valuable experience.

If you say half hard 260 blanks will work well, then that's what I'll do. I'm sure you know what you're talking about. :grin:

And hey, I was guessing at half-hard too. So gotta give me credit for a lucky guess. :cool:
 

Cadillac

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The crankshaft on a engine like that will have journals around 1". The block will be useless for you in that the "bearings" are aluminum. No bearings machined into the block. Forces the crank can handle? That's debatable I know for a fact they don't like the blade hitting something sticking out of the ground. I've replaced acouple cranks and side covers from people hitting the buffalo box water valve or such bending the crank like a banana. I would think in this application if properly laid out it could work but the crank is one of many moving parts to this equation. I think the flywheel weight would be the ticket.
 

Robo_Pi

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The block will be useless for you in that the "bearings" are aluminum.
I figured that would be the case. I'll just grab the crank, connecting rod, and piston. And build the rest from old farm equipment. I kind of figured that I would need to make my own bearing blocks. So that was already expected. I took a picture of the whole lawnmower, but I'm really only talking about using the crank, connecting rod and maybe the piston just to take advantage of the existing wrist pin configuration. I expect I'll need to modify the piston extensively. Possibly even remove it altogether and just use the wrist pin on an entirely new punch holder.

So I may be down to only using the crank, connecting rod, and wrist pin.

I will use the original flywheel, but only because it mates to the shaft already. I'll actually bolt a much larger and heavier flywheel onto the original for the inertial momentum I'll need for getting through the entire punch stroke.

Building this punch press will deserve it's own project thread. :grin:

But I won't start a project thread for this until I make more progress on it. I don't even have time to disassemble the lawnmower right now.
 

Superburban

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Have you considered a manual press? The crankshaft is likely between 1 to 2 inches of stroke, If I remembver things right, a 2 foot lever would yield you about 12 to 1 advantage. Yea, doing 260 manual punches is not simple, but neither is all the fab work to make up a power source, the clutch, if thats the plan, and all the control pieces.
 

rwm

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I like your idea but I have some concerns. I don't understand how you are going to get the individual blades of grass into the punch mechanism and align them accurately? They are too variable in size and shape?
Robert
 

Firstgear

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if you make something, make sure you are very aware of any safety issues...good way to lose some fingers quickly!
 

Robo_Pi

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I know. For some reason punch presses always make me squirm because I imagine getting my fingers punched off. There are obviously other many other places on the machine where you can loose a finger as well. But this is really true of most other machines as well. In fact, when I watch a shaper running it makes me feel just as nervous.

And what we often don't think about is that the lawnmower itself is actually quite dangerous. Typically when we mow the lawn we don't think about what would happen if our foot slipped and went under the mower. But that wouldn't be pretty either.

Life is dangerous. In some ways a punch press should be less dangerous than a lawnmower simply because you can visually see the danger more easily. But yeah, I plan on building a clear plexiglass guard around the die to make it impossible to stick anything in it other than the thin brass sheet.

If you want to have some nightmares watch this video.


These people think they have a better safety solution. I'm not convinced of that.


The compound die I'm hoping to build will most likely have a very tiny opening in it when fully open. You probably wouldn't be able to fit your finger in it if you wanted to. None the less I'll still build a guard around it leaving just a small slot large enough for 0.6 brass sheet to slide through.

But yeah, safety is always a major concern when using any power equipment, even the lawnmower itself.

In fact, I run a chainsaw pretty much daily. Talk about a dangerous tool! You can hurt yourself with a chainsaw pretty easily if you aren't paying close attention to what you are doing. My cousin is a professional logger and he put a running chainsaw blade through his forehead. Long story, and fortunately he wasn't seriously injury. Just resulted in some ugly looking scars. But I'm sure it didn't feel real great.

I slipped and almost feel off my tractor the other day too. Had I fallen I could have been seriously insured as the tractor would have kept going and run over me. In fact, I hear that farming is one of the most dangerous professions.

Yep, life is filled with extreme danger. Gotta watch your back to be sure. And even then you aren't safe.
 

Shootymacshootface

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You could pick up a used reloading press. The toggle system that most use can make a tremendous amount of force. The die bodies are almost always 7/8-14 so they can accommodate .50 cal or larger projectiles. You can even buy die blanks and make whatever you want with them. Production wouldn't be an issue either. Lots of people have automated presses that the designers never would have imagined would be.
 
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