I have recently purchased what might be called a "strap hammer", by which I mean it is a mechanical spring hammer with leaf springs, but where the ram of, say, a Little Giant has a solid toggle linkage, this one has a flat belt/strap. It is the system commonly seen on Japanese forging hammers. The ram weight is about 20kg and it is driven by a slack belt clutch system. It was designed for the forging of "arms, cutlery and for the heavier work of a coppersmith", and was manufactured by Bouhey sometime before 1914. http://www.archive.o...ge/162/mode/1up
It isn't in bad shape, but is in need of a little TLC, and I'll be posting some questions about foundations, set up, etc. as I go along. I am a total novice when it come to this kind of thing, and I'd be grateful of any help!


My first question; can anyone (preferably with experience) suggest a good material to replace the strap with? The current one appears to be made of leather, the last perhaps 100 years have not been kind to it, and it's gone a bit saggy.

Many thanks,
Dan

Leather is still my choice. Not just any leather, it must be cut from the correct place on the hide and be the right type of tanning to do what you want.
I think Stewart used strips of canvas and is very happy with that.

I never thought I'd say this in IFI, where people post pics that are so freakin' huge, but Stewart, do you think you could post some larger pics? Kinda tough to see what's going on in them.

I don't know how the thumbnail of the schematic got attached to my post, but thank you whoever did that!
Thank you also for the replies.
Peacock; From the sound of what you say, I think that the idea of leather straps might be difficult to realize. Just out of curiosity, and perhaps for the sake of posterity, could you explain what kind of leather is the right kind of leather, and why it is your choice?
Stewart, I have two questions; First, what made you think to replace the toggle arms with canvas strapping/belt? Second, why do you suppose it is that the strap allows or causes the hammer to hit harder?
I'm afraid the hammer is still in its box, so I have no detailed pictures at the moment, but here is one of it at its old home;

Sweet looking hammer!

My first choice for strap replacement would be ......... leather ... !

These guys in Newcastle will sell you as little as you need, they sell cut strip and width you want aswell

Phone them and have a chat, they are super helpful (website is terrible)

Heres the link.. My computer (or this site?) is acting super weird tonight, cant edit previous post...!

http://www.leprevo.co.uk/

Sweet looking hammer!

My first choice for strap replacement would be ......... leather ... !

I found it on the same website that I found the Beaudry that I posted over on BB.
Why do you say leather?

And, as it is a question concerning this hammer that I was going to post on BB, but one that you would probably know the answer to, do you know where one would pick up a suitable drive belt in the UK?

Thanks,
Dan

-Dan

it just flings the head harder!

Thats what I heard, but was curious if there was a discernable reason.
How tight did you wrap your strap?
-Dan

I use saddle skirting, it's stong & very little stretch ,easy to get. I like it because bits of hot slag do very little damage. You said the piece on yours maybe 100 years old. replace it once right and be done with it for your life time. The people who made them thought it was best.

I use saddle skirting, it's stong & very little stretch ,easy to get. I like it because bits of hot slag do very little damage. You said the piece on yours maybe 100 years old. replace it once right and be done with it for your life time. The people who made them thought it was best.

That's a persuasive argument. What weight (thickness) of saddle skirting are you using, and how many straps? I've only (in a very short search) been able to find it in sides. Is the whole side suitable?
Many Thanks for your help.
Dan

Look at the old straps on the hammer for the thickness and number of straps. I don't know about the U.K. but here in the U.S. a saddle repair shop sould be able to cut the straps you need. They need to be cut from the top of the side (along the spine) that is the least stretch. In the U.S. leather thickness is listed in ounces 1 oz.. =1/64th inch thick.

Look at the old straps on the hammer for the thickness and number of straps.

Thank you for answering my stupid question! These straps were a good 4mm thick.

I have been going over the hammer a bit this afternoon. I took out the ram. It is an absurdly heavy body for the size of the ram. I think it is over a ton for a 15kg ram. It is in pretty good shape for probably 100 years old. It turns very smoothly. The brass bushing or bearing or whatever you call it on the front of the crank wheel is a tiny bit loose, but that's about it. Oh, and some idiot has hammered the shim between the sow block and anvil and the odd looking shim fixing the die to the sow block TIGHT! And there ar some problems with the ram too.

Here are some photos;

This is the brass bearing that is loose, and this whole connection is a bit floppy. In my first post I added a link to a description of this hammer, in which the connection is described as being adjustable to alter the height of the ram. We shall see a bout that!

The sow block and die with the dodgy looking pin, all rammed tight as a drum!

Another shot of the shattered corner of the anvil. It is spalled of about 2" long. I don't think it should be a problem?

Thanks, Stewart. I would appreciate photos. I do have the original strap for this, but took it out because it was totally knackered.
One question for you; do you have an means to center your strapping on the ram? The strapping on mine has a sort of slot, and the top of the ram had tapped hole which I presume was to accept some sort of pin to center the strapping on the ram.
Another question; how tight is your strapping? The strapping on mine was very loose and I know that this was because of age and that it is wrong.
Many Thanks,
Dan

First, concerning speed, I have a flat belt pulley for a motor which is 110mm outer diameter, and the main drive pulley on the hammer is 210mm OD. Does that sound right to you?
Second, concerning the hammerhead you can see the threaded hole here, the large rectangular hole is where the straps go through;

The two smushed indentations are where the ram was slapping back up and hitting two nuts on the springs, which I suppose would indicate that the hammer was run with too loose straps for a while.

The slots in the old strap;

Dan as far as putting power to the hammer I would not necessarily limit your self to flat belting . I have happily run my goliath from two v belts directly onto the flat pulley of the hammer . I find this to be greatly improved on the flat belt drive I had on my previous goliath . If you were going to go flat i would suggest a continuos belt as opposed to a joined one as the noise and problems with the crocodile clips is a pain. a modern continuos belt will last a long time.
you can get belts from lathes .co.uk and joiners.
if you can get a 700rpm motor (8 pole) or 900 rpm (6 pole) motor you would be able to run the hammer strait from the motor mounted to the side and ignore or remove all the overhead belting tensioning pulleys any faster than that and you will have to run a jack shaft between the motor and the hammer.
with a 700 prm motor you would need a 100mm or so pulley to give you around 330 bpm (which is bloody fast but may well be the kind of speed a small hammer like this likes.) with a 6 pole 900 rpm motor you would be down to about 80 mm for the same speed. above that you are loking for an extra reduction stage.
it looks like a fine hammer small and robust . good find.

Thanks for the reply, Owen.
This one is a belt clutch, and I have a feeling that v-belts might cause problems.
I know this is something you have done on your coil springs, Owen, but I wonder if anyone has taken steps to isolate leaf springs (using leather or whatever) in case of failure, other than going with the cage method. Does anyone have experience of a leaf-spring failure? It must happen, but I wonder if the mechanics are a bit different, in terms of them pinging off.

You have more than 1 leaf on that spring odds are that 2 leaves would break at the same time and place help make this a little safer.
I have seen springs wraped with leather strips or even tape to contain broken pieces from flying around. Thanks for the latest pictures
I know how I would build that strap I might be persauded to make it and ship it to you. I would make the strap then install it on the hammer

so the hammer is a slip belt clutch ? hard core.. you might want to get a bigger drive wheel in that case or all the slip will be on the drive wheel wheel a bigger drive wheel will run the crocodile joiners more smoothly.. I would run a wheel that is similar to the one on your patent drawing and then reduce your speeds from there.

your spring assembly has 1 major structural spring . and imagine the flapping and flailing of sharp stuff if one of those arms broke , its also worth keeping in mind that springs do not break clean but often throw shrapnel around. I would leather sheath it from tip to tip . in a leather that would not rip if the spring let go. .I think I used 4mm .
your spring will fail ..... I have had 3 go so far .one on every old hammer I have had there was no real drama as they were well contained. getting a replacement before it happens would be a good idea I can dig up a manufacturer for you .

dan, ignore the threaded holes, and wrap the canvas, between the shackles, thru the rectangular head hole over and over again between shackles at the end of the springs, winding it very tightly.

would you pre tension the springs with something like a sash clamp so that in their neutral position the belt is being held taught ? this is the case for a toggle arm spring hammer . or are you allowing the weight of the ram to tension the belts?

Peacock, thank you for your kind offer, but I think this is something that really needs to be done in situ because there must be something to go wrong. Does your hammer have anything centering the straps. You can see what I mean here, where there is a slot in the belt and a hole in the ram;