Speaking of Appalachian PH's...(about the helve arm)

[don schad]

Hi all,

I was wondering about the helve arm setup of the typical APH (an inline helve). In most cases the helve is a pack of leaf springs with a pivot somewhere in the middle. The pitman arm drives one end and the hammer head is attached to the other (often using rollers).

On the other hand, the traditional helve hammers (those which travel in an arc) (e.g. Depew, irnsrgn's version of that (see BP0169)) most often have a solid arm on the head side of the pivot, and the spring on the driving end.

So in the first case you have flex at both ends of the shaft, which would it would seem to me would be harder to tune and/or require stiffer leaves to achive such tuning. In the latter case, your flex is only in the driving end, which would seem to make tuning easier.

So that said, is there anything to this thinking? Is there a reason for the predominant design? Am I missing something?

Thanks for your thoughts,

don

[frogvalley]

A solid arm? Wood is quite flexible and most helve hammers have wooden helves. Granted it is not as flexible as a spring, but it is not iron. A more appropriate comparison of hammer styles is not with the unguided helve hammers, but with a guided helve such as the Bradley's. There are flexible coupling at both ends of the helve, a large series of rubber cushion on one end and a rubber or leather connector at the ram end.

I own a 75# Appalachian style and a 300# Bradley guided helve. It is my opinion that the reason for the difference in flexible materials is simply that in order to fully transmit the force from the motor to the ram, a super heavy frame is required, the less flexible the helve, the stronger the frame/body needs to be. Otherwise they would just beat themselves to death and vibrate uncontrollably.

One other reason is that in order to make a wider range in your workable heights for the appalachian hammers it is necessary to allow more flex in the helve. Differing work heights and actual stroke length are fully adjustable on a more sophisticated machine such as the Bradley(stiffer helve). My appalachian has one adjustment, a sleeve adjustable crank, but no allowance for stroke adjustment(very flexible spring helve).

If anyone has any other information regarding this, please chime in.

[ptree]

I have a 45# guided spring helve and the flexible spring is indeed what makes these hammers work. The spring stores energy and provides a harder hit, where a unguided helve with the stiff wooden helve must use more stroke or bigger ram for the same blow.

[arftist]

What do you mean by "harder to tune"?

[jeremy k]

harder to tune means - harder to adjust so everything is running and working the way it is most efficient. - JK

[don schad]

I have a 45# guided spring helve and the flexible spring is indeed what makes these hammers work. The spring stores energy and provides a harder hit, where a unguided helve with the stiff wooden helve must use more stroke or bigger ram for the same blow.

Actually I appreciate the need for the spring (both to lessen absorb the impact of the blow and for the "whip" when changing direction), but my question was more related to whether or not having flex on both ends would make the system more complex, or if having only one end with flex would be simpler. I believe (although I'm not 100% on that) that the winding up/unwinding of having a spring on one end would be equivalent to that which occurs with both ends flexing.

BTW, thanks for your BP on the helve hammer.

don

[frogvalley]

The action of both types of helve hammers, those with full length spring helves and those with supposed solid beams and one end spring or cushion, is virtually identical. Where you put the spring(s) , whether it be one or both ends, makes little difference. The design of the controls and adjustments for the hammer make the primary difference in tunabilty. Ask anyone who has used both a Dupont/Fairbanks hammer with its stroke and height adjustments and a Little Giant without brakes or decent adjustments.

Once again, it is my opinion that the reason that we tend to build these using leaf springs is expediency and ease of construction, and the tendency towards lighter frames, hence requiring a more flexible coupling in order to reduce vibration through the frame.

Edited February 17, 2009 by frogvalley
Stupidity

[Warren Nakkela]

Let me see if I can get my ideas across. In the home built helve hammers the leaf spring, stores energy when the hammer reverses at the top of the stroke. Then as the hammer is on the downstroke the stored energy in the spring helps to increase the speed of the hammer. When the hammer strikes the spring allow some give to adjust for tooling and thickness of the work.
Under these conditions the spring is under constant stress reversals. If I remember correctly stress reversals are four times as destructive to the steel than if the load is in one direction. The Dupont motion gets around this as whether the crank is on the upstroke or down, the springs will be under compression. The Bradley uses opposed rubber preloaded springs so what ever direction the helve is moving one or the other rubber springs are under compression. Other hammers may use opposed and preloaded springs on the link between the crank and helve. These springs are in a cage. Here again the load on the springs are in one direction only, that is in compression. I believe that these designs allow a smooth running hammer.
The leaf spring helve, on the other hand bends one way at the top reversal and bends the other way at the bottom. I believe that this allows for no independent means of adjustment for the spring helve. One may have the spring tuned for the impact stroke but may find that any adjustment for the upstroke is wanting. So using leaf springs how can we design a spring helve to eliminate stress reversals in the leaf spring helve? First off, one needs two opposing springs. Then there must be slide or link mechanism to push on the top spring as the hammer starts down. as the hammer strikes and starts up the other spring comes into play as the helve is pulled down by the crank. Thirdly, we can't allow any slop in the slide motion. This means that the springs must be preloaded. so on direction reversals the opposing spring, that is, the unloaded spring is following the spring under load. Hence, the importance of a preload to prevent any pounding. I am sure designers in the past recognized this and employed various designs, some of which were quite elegant, to circumvent the stress reversal problem.
Thank you for bearing with me,
Warren

[arftist]

Warren, trying to understand what the issue is. Tune for the upstroke? First of all, the purpose of the spring is not "to adjust for tooling and thickness of the work". All power hammers have springs in one form or another. The purpose of the springs is to prevent the hammer from self destructing soon after it's use begins. To adjust a spring helve hammer for thicker materials, or higher tooling, one shortens the pitman arm, thereby raising the lower point of the tup stroke. Have I still misunderstood your question? Some people believe the "Dupont" linkage to be the ultimate, and they may be correct, but my spring helve has served me well for many years, and while I am sure it could be improved upon, it's operation is certainly adequate, and compares favorably with similar sized dupont linkage hammers, perhaps even better than some.

[Warren Nakkela]

Hey Arf,
I was just contributing to the discussion in the off chance that the single spring helve hammer could be improved. Don S. opened this thread. I was just expanding on his line of thought. It is not my intention to criticize present homebuilt power hammers but rather take an existing design and improve upon it. One can make little progress by focusing upon what works. To improve one needs to look to where improvements can be made. Didn't mean to dis your good hammer.
Warren

[Johnny Woolsey]

On my first spring helve I stayed pretty close to the design from Jerry Allen.Seemed to need more mechanical stroke to achieve an effecient hit.
When I built my second hammer I beefed up the bottom of my spring stack to get the hammer up with less "flex". I was able to increase the speed and shorten the mechanical stroke. In my opinion this was an advantage because my hammer seemed to flex more than I was comfortable with.

Warren, I appreciate your engineering challenge exercises and agree that the "Homemade" spring helve can be improved on.

[arftist]

Hey Arf,
I was just contributing to the discussion in the off chance that the single spring helve hammer could be improved. Don S. opened this thread. I was just expanding on his line of thought. It is not my intention to criticize present homebuilt power hammers but rather take an existing design and improve upon it. One can make little progress by focusing upon what works. To improve one needs to look to where improvements can be made. Didn't mean to dis your good hammer.
Warren

Warren, I didn't feel dissed, I am just trying to understand what this thread is about. Thankyou for responding. For example I am still not sure about tuning for the upstroke, and wonder if I am missing something.

[Warren Nakkela]

The upstroke, having to lift the hammer, has a different set of conditions than the down or striking stroke. The top reversal of the hammer and being connected to the spring helve would benefit the ability to adjust the spring load to optimize the recoil or "whip" which accelerates the hammer going down. With a different set of conditions following the striking blow, that is, lifting the hammer requires springs for cushioning any shock loads on the mechanism. I believe the two conditions are different. Therefor if a design allowed for independent adjustment of spring rate and stiffness, i would expect better performance.
Warren

[arftist]

Oh. Thankyou.

[unkle spike]

Here's my take on it....

It is true there is a stroke reversal, but with the round recipricating motion of the driven shaft it is more gradual than it appears, if the stroke reversal was that violent there would be no way a standard reciprocating engine would stay together. The motor in most cases is not to provide the power of the stroke, it just provides momentum for the weight of the head. The hammer blow comes at or should come at a sort of "lull" in the driving stroke at bottom dead center so to speak the motor is neither lifting or forcing the hammer head down.

The springs are sort of a dampner for the arm, if you look at the "Jr" helve the springs are relatively short providing less of a dampening or "whip" effect.

I am in the process of building my own Appalachian Style hammer, and one mystery is the springs, what rate spring is desired 1000lb 750lb? There is no data on this, there are some thinkness dimensions given, but thickness is not a measure of spring rate.

And while on the subject of springs, I have seen dead flat ones, and some with arch to them. The arch would make the arc of the end with more radius in its travel, so you would have to build in some travel to accomodate that, but other than that I see no difference, as long as you had a stack with a long leaf, and shorter leafs both top and bottom of the stack. A stack of leaf springs on a vehicle or trailer is designed for majority Up Force, hence the smaller leaves stacked below the main leaf. In this hammer design you have both up and down forces, so you need smaller leaves above and below the main.

It will be interesting to see what my final design ends up with for a spring pack, that is the greatest unknown to me.

[arftist]

Hey Spike, don't know if this will help much, but it is easier to build with flat springs. The guy at the shop where I bought my springs had no trouble staightening them cold in a press. As to the size of the leafs required, it would depend upon the size hammer you were building. If you are making the effort of building a hammer, please buy new springs. Used springs are not reliable. As a starting point for you, my hammer has a 75# head or tup, and my springs are about 5/16ths by 2" wide.

[unkle spike]

That is what I am leaning toward. A spring shop here wants around $60 for a 60 inch single leaf "de-arched" it has a hole in the center, so I would likely cut a 30 inch section out of the center with two 15 inch pieces off each end for the top and bottom leaves, leaving 7.5 inches of the center leaf "running Solo" on the ends.

Thickness would be 3/8" X 2 1/2" X 30 inches for the total spring pack.

The other thing with an arched spring I thought of, if you put a binding strap on the bundle where the ends of the leaves overlap, with an arched spring this could restrict the movement of the individual springs too much, thus you would be losing the action of the springs you needed in the first place.

Thanks for the input Arftist, it helps a bunch, I will let you know how things progress. The head on mine should be around 25-30lbs, so this is a good bit smaller than yours.

[DonS]

Uncle Spike:
I just measured the springs on my hammer, if that would be of any help:
Ram Weight: 34 Lb
Stroke: 7 inches (moving it by hand, without the overshoot at normal speed)
Spring material: 5/16 x 2-1/4 inches
Main spring: 39 inches long
Upper and lower springs: 24 inches long
The three leaves are clamped at the back end 9 inches off center
They are not clamped together at the front end.
The main and upper springs are in contact the full length
There is a 1/4 inch gap between the main and lower spring at the front of the pack,
so that the ram is not restricted by the springs as much at the bottom of the stroke.
At rest there is about 3/4 inch of daylight between the dies.

The pitman arm is attached 2 inches from the back end of the main spring, and the rollers are about 4 inches from the front end of the main spring.

I left the curve in the springs just as they came from the spring shop. The pitman arm is tilted back a bit so that it is still perpendicular to the spring. This move the flywheel foreward a bit, reducing the overall footprint of the machine. I actually added a bit of additional curve to the lower "helper" spring so that the hammer would still hit hard with a bit more daylight between the springs.

I have not seen anyone else use these relatively short springs. Everyone else seems to use longer springs and has had good success. I had some trouble initially, which I thought was due to the short springs, but it turned out that I had insufficient weight on the flywheel (only a cast iron pully) I added a one inch x 13 inch disk to the pulley and everything went smoother.

I had a 250 lb anvil initially, plus the weight of the 1-1/4 inch baseplate, but that was insufficent. Performance was poor, until I added an additional 300lb baseplate and bolted it all firmly together. Total equivalent anvil weight (of the anvil and metal within an 8 radius of the anvil center) would be about 350 lb or a 10:1 ratio, and that improved it significantly.

Hope that is of some help.
Don Sinclaire in snowy Edmonton

[unkle spike]

Don,

Thanks for taking all the time to give me the measurements. I had never thought of leaving the springs "loose" on the front end, but it makes sense that you would not want the front end restricted. I don't have the anvil built yet, I may have to look for some more material as all that I have at this time is a piece of 4 inch heavy wall square tube. I have not finished the head up yet, so I don't know the total weight of it, the base plate is around 120 pounds at present, and I may add some weight there too.

I hope to get the driveline and jackshaft done this weekend, and we'll see how far I get.

[SLOB]

I dont have a power hammer (yet) but when I get the room I hope to build one of the rusty/crusty designs. I haven't seen Jerry's plans but have seen one of those style hammers in use along with looking at several diffent builds online.

while speaking with Jerry at a recent ABA hammer in he explained he used bolt on spring clamps on the leafs to be able to tune the hammer......if I remember correctly he said he keeps the clamp closer to center on the front end to allow more flex while the back end is clamped closer to the connecting rod. this similar to allowing the front to fully flex with no clamp......but just another adjustment to keep in mind when tuning the hammer.

Rob