As I commented to the other Pete, I don't know a thing about
air/hydraulic. How come the instructions recommend squeezing the air
valve and pumping the handle at the same time? Hopefully you don't have
to rub your tummy too.

Noisy? Sounds like my press...

So the air/hydraulic uses air to turn a hydraulic pump?

Steve

spaco wrote:

Hello, Steve.
I am not a knife maker, but I have used the HF 20 air over
hydraullic jack in a 20 ton press to weld damascus billets. I don't
understand why you say to use the hand pump. I never do. The air
pressure does the same thing that the hand pump does and to the same
degree, as far as I can tell. We use two of these presses on a pretty
regular basis, one for general work (and the occasional billet); the
other for pressing bearings where we approach the 20 ton limit often.
I agree that you don't need a lot of tonnage to weld. A friend of
mine, Mike Blue, from Cannon Falls MN got me started with this HF
air/hydraulic press idea when he said that he turns his 50 ton press
down to about 12 ton for welding damascus billets.
As far as speed goes: certainly, if I had the money and the time,
I'd go with a "regular", noisy 50 ton all hydraulic press. The ones I
have seen, particularly those with the 2 speed pump, move a lot
faster, and as you said, speed is important.
My press is set up with two foot valves. One for down (the stock air
cylinder) and one for up (a 1 inch cylinder I added to the release
valve). I move down to the point where I am close to the thicknes of
the billet before I take it out of the fire. Then press, release a
little, press a little, etc. With the two valves, the ram only goes
up as far as I tell it to, not a full or large retraction. I get
about 4 "squeezes" per heat.

I just put a few pix up on my website. www.spaco.org/Press.htm

Not trying to be argumentative, just reporting,
Pete Stanaitis
----------------------------------

Steve Smith wrote:

John, I'm a blacksmith and I have a powered, hydraulic forging press
that I've used to make Damascus with. I haven't seen Steve Dunn demo,
don't know his techniques, but I don't think you're going at this in
a way that will work.

In my experience, the main issue in forging or forge welding with a
press is being able to drive the press tooling into the work faster
than the work cools. About the worst case is welding a Damascus
billet--big flat dies that soak up the heat rapidly. If your pieces
are clean and lightly fluxed, just squishing them a little bit (maybe
1/8" over a 2" billet) should make a good weld. This doesn't take a
lot of pressure; I haven't measured it when welding (paying attention
to the weld, not the press), but I bet my 30 ton press wasn't even up
to 15 tons. I think that for both general purpose forging and for
making Damascus, a 20 ton press will do the job. More tons are
always better , but I've never had much need to go over 30. For
typical size work, if your press is actually pushing with 20-30 tons,
it tells me that the work is getting too cool to forge nicely.

So why won't the HF press do the job?--speed of travel during
forging. It does have a means to move the press tooling up and down
rapidly when under no load (via air). The problem is that air can't
give you a lot of pressure in the dies. The manual on your press says
air at 100 psi; my press is at an internal pressure of about 2000psi
when the dies are at 30 tons pressure. Quite a difference. How the
HF press works is you use air to move the dies into contact with the
work, then switch to the hand pump, like with most shop hydraulic
presses. This is *very* slow, way too slow for forging.
Here's an example. My press has a hydraulic cylinder with a 6"
diameter piston. The area of the piston times the pump pressure gives
you the amount of tonnage the cylinder will put on the dies. In this
case, a 6" diameter piston has 28 square inches of area. Multiply
this by 2000psi and you get 56,000 pounds pressure, 28 tons (I guess
my press is 'almost' 30 tons). The issue is how fast you can move at
this pressure. My press moves 1/4" per second at 30 (alright, 28)
tons pressure. This takes a pump driven by a 3HP motor, not something
you can contemplate doing with a hand pump. Maybe you could motorize
the pump, but it isn't designed to work at this kind of speed and I'd
expect it would fall apart quickly.

This also means that modifying a 20 ton shop press (hand pump) won't
get you where you want to go. You could imagine adding a motorized
pump to such a press, but the cylinder has no provision for the high
pressure plumbing. You could replace cyinder and pump, but you might
as well build the whole thing at that point.

Being a welder, I recommend you build a press. There are some really
excellent plans available by Jim Batson. You can get these plans from
Norm Larson ). Norm has most every blacksmithing
book available for sale, and he's a great guy. I'm sure you could
also get the plans from Jim, but I don't have contact info for him.
Jim not only gives you detailed press plans, he also gives you a good
understanding of how hydraulics work and how to estimate mechanical
stresses in your press (if you want to use different material sizes,
or change the press tonnage). I think Jim has two booklets out now,
one on an open sided press (C style) and another on H style presses.
He also discusses converting a motorized log splitter into a forging
press.

Rather than using a combination of air and hydraulic, Jim's design
uses a log splitter pump to achieve fast motion when not loaded. Log
splitter pumps will pump at a high volume rate as long as the
pressure is low, switching over to a lower volume rate at high
pressures. This keeps your motor HP down. My press has a pump that
runs the 6" cylinder at 1" per second up to around 600 psi, above
that, the dies slow to 1/4" per second.

Some specific comments:
1. Don't bend over with your eyes right next to a billet being welded
in the press. 1800 degree F flux can unexpectedly squirt out from
between the layers. You don't want your face anywhere near this, even
with safety glasses.
2. I find 1" per second travel (unloaded) plenty fast. I do a lot of
different kind of work on my press. I originally set it up for 2" per
second. This is *way* too exciting if you're doing any bending,
almost out of control.
3. The log splitter pumps claim that they work up to 3600 rpm. This
was how mine was originally set up to get 2" per second. The pump
just screams at this speed; not only don't you need 2" per second,
but I don't see how a pump making that much noise can possibly last
long. I now run mine at 1750 rpm, much quieter.

Here's a picture of mine:
http://www.metalworking.com/DropBox/...iles/Press.jpg
http://www.metalworking.com/DropBox/...iles/Press.txt
It probably cost me about $700, given some careful scrounging. Note
that the email address in the text is no longer valid.

Steve


John P. wrote:

Gents,

After recently completing a week long course on Damascus at the ABS
school (Taught by MS Steve Dunn, incidentally) I am considering the
procurement of a forging press. However, I am a complete novice when
it comes to hydraulics, which limits my ability to make any sort of
decision.

At the ABS school, there is a press made by Uncle Al of Riverside
Machine (http://www.riversidemachine.net/item16342.ctlg). The two
features that seemed important were 1) it would accept interchangeable
dies and 2) the foot pedal would lower the press at a constant speed,
it would hold at a certain level, or if you took your foot off it
would raise up.

I was with MS Chris Marks (http://www.marksforge.com/) when he used
this press to create a demo billet of damascus and remember him saying
it wasn't strong enough. I believe his press was closer to 50 tons.

Anyway, this brings me to my question. Does anyone have any
experience with or opinions on the Harbor Freight 50 Ton press found
he
http://www.harborfreight.com/cpi/cta...emnumber=46768

My thoughts, questions and observations:
- What powers this press? Can you just hook up a compressor? I have
a 5hp / 60 gal / 13.3 cfm @90 psi unit. Would that work?
- How would one convert the unit to be foot pedal operated?
- It looks like one would have to raise the bottom table up quite
high to use this press on a billet of steel that was only 2-4" tall.
- The manual says that you basically use the air supply to lower the
ram to the material and then pump it by hand. Can't you just keep
using the air pressure to ram into the material? Or does it lack
sufficient force in that manner?
- It looks like it would be difficult to fit dies onto this unit.

I'm only aware of two commercially available presses. Uncle Al's, and
the one from Carolina Knives.
(http://www.carolinaknives.com/press/press.html) If anyone knows of
others I would appreciate a reference.

Finally, would I be able to build my own press using the $70 HF 20 ton
bottle jack discussed in the other recent thread? I am a good welder
and a reasonable metal worker and handy sort of guy in general. I
just don't know anything about hydraulics...

Thanks in advance,

John P.