Drop Hammer Questions from a Newbie

[Crunch]

Hello, all,

I would like to either make or buy some sort of power hammer. My plan has always been to fab up some sort of junkyard hammer, probably the "spare tire" type, but lately I've been considering buying a unit if the price was right.

In the Tailgate section here, I saw the 200# drop hammer that kerrystagmer has for sale for $1500 at

http://www.iforgeiron.com/topic/22165-200-lb-forging-drop-hammer-needs-a-home/

(there are also some interesting videos posted there of the hammer in use)

and that got me to thinking.

Can anyone clue me in on what the advantages and disadvantages are of a drop hammer like this, as opposed to, say, a tire hammer or Little Giant type?

Are there any common problems, maintenance issues, drawbacks or anything else commonly associated with drop hammers? I'm not sure how they work exactly...I guess there are a variety of ways of making one.

Thanks in advance for any information.

[forgemaster]

Drop hammers are not really classed as suitable for general forging, they are really designed for forging between closed dies (dies that have a impression or series of impressions in them), however if you have nothing else they can be made to do an OK job as shown in the video. Size for size weight for weight they don't stack up to general open die forging hammers in terms of stock size worked, and they are as seen in the vid, of a slower stroking rate than mechanical or pneumatic hammers.
But any powered hammer has got to be better than standing there bashing it with a hand hammer.

Phil

[Crunch]

That's interesting. In my research, I also see that drop hammers are limited in their speed by the 10m/s² acceleration of gravity, which hadn't occurred to me right off the bat.

Thanks for the reply, Phil.

[bajajoaquin]

They're limited in their speed by gravity (9.8 m/s/s, to pick nits), but they're also limited in their speed, as Phil mentioned. Because they're gravity-dependent, there is only so fast that you can raise the tup without its inertia carrying it up away from the lifting mechanism. Too fast, and the hammer can't stop rising, then fall in time to keep up with the cam profile.

In Pounding Out the Profits there's some discussion about the percentage of the rotational cycle you want to have for lifting versus dropping, but I don't recall it off hand.

Mechanical spring hammers change that, and will tend to operate best in a speed range that matches with the spring rate and ram weight. (Someone may want to check me on that. It may not be a function of spring rate.)