[TheForge] Build a power hammer?

[Jerry Frost]

I've thought about mechanical hammers and looked at 
lots of plans and patent drawings for different types. 
Believe it or not a self contained pneumatic hammer 
really isn't that much more difficult to build. To 
offset the increased difficulty in construction, 
control is worlds better.

The toughest thing to do was come up with control 
valving and after looking at and reading at least a 
dozen patent drawings I discovered it's really simple 
after all. The control valve schemes presented in the 
H. F. Massey patent # 707,246 are very simple.

Don't be fooled by all the diagrams and pages of 
description, they cover several configurations and all 
their positions. Print it all out so you can spread it 
out on a table and use highlighters to keep things 
straight. Once you see how it works you'll slap 
yourself on the forehead and say, "AH HAH!" or some 
such.

In it's most basic version you can operate a self 
contained power hammer with 1 (one) 1/4 turn ball valve 
in the bypass air passage. At idle the tup will rest on 
the anvil, it won't strike single blows unless the 
operator is quick, it won't clamp or perform a dead 
blow. It's either at rest on the anvil or cycling under 
full control.

Put a check valve in a 1/4 turn ball (or other shape or 
type) valve and you get all the functions of a self 
contained pneumatic hammer. It'll idle with the tup in 
the up position, strike a single blow, a dead blow, 
clamp and of course cycle under full control.

A flat slide valve with check valve might be easier to 
fab at home though it'll be a bit harder to make air 
tight. There are also spindle valve schemes though 
they're more complicated. Anyway, there are lots of 
ways to make it work and patent drawings of them.

The next hardest thing to come up with was a good way 
to run the crank and connecting rod to the compressor 
piston. All three components comprise a serious task 
for the hobbyist. (me anyway) Untill I discovered the 
"Scotch Yoke." A scotch yoke directly converts 
rotational motion into linear motion so you don't have 
to have 3-5' long connecting rods, wide skirted 
compressor pistons, wrist pins, journals, all those 
bearings and oiling system. Just take a look at how 
complicated it is to get oil to the journal and wrist 
in bearings in an engine.

A scotch yoke has a crank with a bearing mounted 
contact wheel that runs in a track in the yoke. As the 
crank wheel revolves, the track (horizontal slot the 
same length as the outside of the crank wheel's travel, 
plus a bit for clearance) allows the crank wheel to 
move laterally without moving the yoke or connecting 
rod but the yoke follows the crank wheel 
longitudinally. It's better if you just Google "scotch 
yoke" rather than try to follow my description but that 
is how it works.

Anyway, using a scotch yoke instead of a crank and 
connecting rod eliminates a lot of the headaches 
related to home made self contained hammers. The 
compressor piston, connecting rod and scotch yoke are 
hard connected and can be as close together as the 
stroke allows. A scotch yoke also doesn't need as 
careful balancing as does a conventional crank and 
connecting rod because it rides in carrier bearings on 
both sides of the crank and the crank can have bearings 
on each side of the yoke. All very solid and robust for 
minimum space and weight.

The connecting rod is strictly a thrust member so it 
can be smoothly round like a hydraulic cyclinder rod. 
It'll run in carrier bearings, either linear ball or 
babbit, above and below the yoke. Oiling becomes 
reasonably easy, the crank wheel's bearing can simply 
dip into an oil bath and an old chevy oil pump can be 
rigged to run off the yoke. A little line and flexible 
hose and you have positive oil pressure anywhere you 
want to plumb it.

The connecting rod enters the compressor cylinder 
through a lubricated seal, there is NO lateral motion 
so there's no stress or wear on the seal, cylinder nor 
piston. The connecting rod threads directly to the 
compressor piston and is locked in place by whatever 
means. (lots of ways to lock it) Lubrication to the 
compressor is via an oil port through the center of the 
connecting rod. If lubricant does not migrate to the 
slave (tup) cylinder(s) with the air, positive oiling 
will be easy, just plumb a line. Returning excess oil 
to the oil pan might be harder, I'm not a fan of just 
letting it exhaust into the air.

I've been thinking about, drawing and scrounging the 
materials to build a self contained hammer for a number 
of years now, some folk will recall much of what I just 
said from a couple years ago. The ONLY thing I lack is 
a chunk of iron or steel the right weight and a 
reasonable shape for my anvil. Three years ago I had 
access to all the RR axels I wanted for $0.20 / lb. The 
heavy duty ones are 8 7/8" dia and about 4' long. It 
doesn't take many, cut to length and welded into a 
billet to make the weight. Unfortunately the recycling 
center no longer sells to the public and it has THE 
contract with the RR. Of course I haven't started 
showing up with donuts in the morning and beer at 
closing. <grin>

Of course anyone out there who wants to start mailing 
me scrap please feel free. Just make it good gray cast 
iron and if you'd be so good as to break it into small 
pieces, say 3/4", it'd sure save me some time and work. 
<grin>

Frosty
-------------------------------
If it ain't forged
it ain't real.
Wrought iron is.
The FrostWorks

Meadow Lakes, AK.

http://www.artmetalradio.com/


From: "Ron Childers" <munlaw2 at hcsmail.com>


> Frosty,
>
> You might consider making a mechanical hammer. You 
> can order plans from
> Clay since you can't get a compressor up there....Our 
> tire hammers are not
> Sahas, Big Blues or Khuns, but they do a good job and 
> would be even cheaper
> if you scrounge material. Are there junkyards or 
> dumps with worn-out heavy-
> (hydraulic) equipment near you?
>
> Ron C
>