Bow Spring Hammer

[j.w.s.]

I think it's been a few years since I've been active on here. I've been lurking, mind you, just haven't been signing on or offering my 2 cents. Hope everyone is enjoying their lockdown!  So here's a little fun project I decided to throw together since I haven't been able to teach classes here at the forge for the past few months. Firstly, it's picture heavy. Second, it's not my first rodeo with building a hammer. In the past I've built Kinyon style hammers, this is my first mechanical hammer build though. Third, you're right, I could have just bought the plans from Clay Spenser instead of wasting my time doing things the hard way, I even spoke with Clay on the phone but still decided to remain stubborn. I like the challenge of the build, exercising my mind, the tool at the end is just a bonus. So here's my adventure thus far. It's still a work in progress, but very close to the finish line! It all started with a forklift tire...

I'm blessed to have a neighbor who has a 40 acre industrial scrap yard about 100 yards way from my forge. I've been handling the lockdown by taking a few walks back there, just wandering and wondering what sort of inspiration might hit. Then I found a pile of these. So I grabbed a few. Looked like a decent flywheel in my own humble opinion.

I had an extra pneumatic hammer project just laying around, instead of reinventing the wheel, I figured it'd be a decent spring board to work off of. 

For the tup, I had a some A2 bars. Played around with the configuration, found one I liked, ran with the idea and used set pins for alignment before plug welding the whole thing together. The center channel is for alignment within the tup guide.

Instead of using the tire as the clutch, I wanted to use a slack belt configuration, the tire is just a flywheel for the potential.

The first choice as far as spring configuration goes was a Bradley inspired design, as opposed to one placed between arms. This actually worked great for about 12 hours, but with the fulcrums being as short as they are, the design would be better off with rubber springs like those used on Bradleys.. They run about $90 each for what I needed. Yeah, I probably could have found some out back, but I chose to abandon the idea just because finding springs of my desired resistance/length/i.d. was going to be a bit of a pain in the future. Great for a one time project, but what if I actually had to repair it down the road? The solutions became cost ineffective and a little restricted on the supply side. So, I tried the next idea.

Eliminating the springs entirely was what happened next. Or, I suppose, more correctly, I eliminated a greater number of mechanical moving parts by replacing them with a single two-part spring I made of 1075. Let me just say, while this is a much simpler mechanical design, it is not a simpler technical design. You have to know and have faith in your heat treating abilities/capabilities or else you've just created something entirely dangerous/potentially deadly! There are extreme forces at work here, even a short 5" throw with a 35lb tup is generating some very awe-inspiring short term numbers! I'll just say this so no one blames me later, DO NOT make your own springs, catastrophic failure can result in catastrophic injuries! My own warnings ignored, this is what I ended up with. 

Here we have the hammer as she sits right now. I'm actually writing this to take a break from the cad work I'm doing for the CNC parts I need to make tonight. Everything between the springs and tup linkage is getting remade. I only pieced this hack together to make sure it would work before I invested the time and material on my table. I really like the action I'm getting from this design, however there is a point when the frequencies of rotation and oscillation meet and that does stall the hammer. To fix this, I tried reducing the distance between the tup arms. It delays the action and reduces it as long as I keep the hammer under a certain speed. Personally, it's not entirely acceptable. Why have a >50lb hammer if you can't do at least 270 bpm? My current thought process is working on a spring loaded bumper between the pillow block on the flywheel and the top of the tup to stop this travel based stalling from happening in the first place, but I'd be interested in anyones input. (except for Frosty, that guy can make up an answer for anything! lol You know I'm joking, Jerry!)

So, there you have it! Again, it's a project based around my sick enjoyment of the problem solving process. It works well as is, but there's still more progress to be done! I'll update this thread accordingly over the next few days as I work out the kinks. 

-J

 

[ThomasPowers]

Re-inventing the Champion style hammer?

[j.w.s.]

On 5/13/2020 at 4:49 PM, ThomasPowers said:

Re-inventing the Champion style hammer?

Not much else to do right now Thomas, might as well have a go at it, right?

-J

[ThomasPowers]

I have a basket case Champion that you could have started with!

[j.w.s.]

Sure, now you tell me! lol

-J

[ThomasPowers]

I find wandering through the scrapyard the most relaxing part of my week too.

[j.w.s.]

So this adjustable spring mechanism was the solution to my stalling problem and I'm happy to say it works! I've got to pick up a 0.75" shaft collar in the morning to keep the tup spring from drifting out on the offset shaft, other than that she's running fine. I did a few minor adjustments today which I knew I would but other than that, it was just some simple fabrication. Once I get the shaft collar in place I can trim some things down and tidy up the entire project. I've got a set of combination dies in the works as well - I''ve never been a huge fan of them, but I'm less of a fan of changing dies and I think in a class situation they might actually work better. I've got a bunch of Atlantic 33 square on hand so I'm sure there'll be some other fun dies to come! That's it for today, once I get everything dialed in I'll be sure to shoot a video.

-J

[Buzzkill]

Is the purpose of the vertical coil spring under the pillow block bearing to be a cushion for the ram on the upstroke or to add force for the downstroke or something else?

[j.w.s.]

Just a cushion to limit upward travel. It doesn't happen often, but it keeps the hammer in a consistent cycle at high speeds. While it'd be cool to add force to the downward stroke, physics just doesn't allow that. It takes energy to stop the initial travel and any gain would be completely lost plus the addition of the resisting force to compress the spring in the first place. Technically, it actually takes away from the potential performance of the hammer but at the same time makes the performance consistent. It's a fair tradeoff in my books.

-J 

[Buzzkill]

Thanks for the explanation.  I'm slowly building a similar style "junkyard hammer" mostly from what I had on hand or could source for free.  The bow mechanism is giving me the most trouble, but I'm planning to use a tow strap or other strong flexible strap instead of metal linkage to eliminate as many moving parts that require lubrication as possible.   Roughly how much side to side flex does one of your leaf springs experience in a complete cycle?

[j.w.s.]

I would say 5"+/-, my distance to center from the offset arm is 2.5" and I know there's some "whipping" (for lack of a technical term) going on there as well, just to be safe. I had considered a leather strap like on some of the Japanese style hammers but opted for 3/4" threaded rod for an easier adjustment of the stroke throw. 

-J

[Buzzkill]

The eccentric shaft on my build is 3" from center, so I can probably expect a little more flex needed.  I keep waffling on whether to do a DuPont style linkage or use leaf springs. It seems that the leaf springs are much easier from a fabrication point of view, but I'm guessing getting the right tension is a bit trickier.

[j.w.s.]

If you have faith in your heat treating abilities its not a huge deal, you don't want to however get 150k cycles in only to have a spring snap from repetitive stress! I made mine from 1075/80 from Admiral, only because I've got a few hundred lbs sitting around and had a problem to solve - the tempering was a bit tricky as far as being more precise. I quenched from 1525F after a 10 minute soak, tempered for an hour at 700F, naturally cooled to room temp, then a second cycle at 800F for half an hour. I'm obviously caring more about the overall modulus of elasticity over hardness at this point. I have molten salts as well and may have been able to quench at 650F/15min in the salts but didn't feel like the hassle of switching between low temp and the high temp salts I already have in the kiln. Resistance is the key though, the drop from base center will matter a lot too, however it's better to have perfectly heat treated springs that will take the extra flex to cover the travel to center than it is to have moderately heat treated springs that have too radius in them. I hope that made sense.

-J

[j.w.s.]

Here's the combination dies I whipped up today, I later trimmed them down because I know that I don't get along very well with sharp 90 degree angles when I walk by things in the shop and also  the foot switch that powers everything.

-J

[j.w.s.]

A quick video I shot with the new combo dies today with a little slow-motion so I could analyze the motion of the springs. The stock being forged is 1.25"x0.5". I don't think the results are too shabby for what is essentially a 35lb junk yard hammer.

-J

[j.w.s.]

I made one more revision to the hammer last night before leaving the shop. I needed to address something that has been nagging at me, adding a second layer/laminate of springs. I don't notice any change in overall performance but I do feel better in the event of a failure of the primary tines. Again I chose to use 1075, shaping it very close to the form of the primary and used the exact same hardening and tempering procedures - I don't think I need any more stiffness in the overall spring or the upward travel I'd probably get from it. I just wanted an added safeguard in case the primary fails. My thought is that the second layer should limit the potential hazards to the operator and anyone else in the shop should the primary break in use. There's also four bolts on the top of the hammer that hold down the 206 pillow blocks that I want to change out tomorrow, upgrade them to grade 8 because of the shock they get and I want to change the nuts over to ny-locks. Other than those small details I can't think of anything else that I need or want to change. Very content with the build as is and really happy with how she performs. If the little one gives me opportunity at some point tomorrow or Wednesday, I'd like to make a more detailed video of the hammer itself, otherwise I'll wait until she's back at her moms for the weekend. Hope someone found this post entertaining and/or informative, it's been a blast for me working on this build - while I make knives and teach people for a living, I have always preferred building new toys for the shop! lol

-J

 

[j.w.s.]

Had about 30 minutes to run down to the shop today and shoot a quick video. It's not perfect, but my 5 year old did her best to help with the creative processing in post. I'm actually shocked at how well she follows a final cut pro timeline! Now that I've gotten it all battened down, I've got a buddy coming over on Thursday to help stress test the hammer, obviously we'll christen it with some Irish whiskey before we begin for good luck.

-J

 

[j.w.s.]

Did a big change in design last night - just thought the spring set up was sloppy. Here's the new concept, and wow, what a change! The idea here was a set of springs made of 1095, just a slight bow to them and essentially the same heat treat as the main springs made of 1075. The speed is great, very little loss.

-J