Some arbor press questions

[mabuse00]

I wanted to get an arbor press for years, but somehow this never materialised...

Those of you who already worked with them, please help me out a little!


- There are models with handwheel and ratchet and simpler ones without.
How beneficial are these features for our needs?
Or in other words: is it very bad not to have them?


- Imagine somebody wants to work with smaller devices, spoletta, 4OZ rocket motors and such.
He uses a big 3 ton arbor press.
How serious would such a mismatch affect the user's feeling for his work?


- Especially concerning the cheaper models - what are the critical achilles heels?
Is there something that requires special attention?

[calebkessinger]

The bigger ones have a larger working height and most of the time don't need to be modified. They are still hard to pull due to the way the gears fit so over-pressing something shouldn't be an issue. especially if you fit it with a torque wrench.

I'm betting after using a pressure gauge the first few times you would get the "feel" for it.

[OldMarine]

I've got a 2 ton and am loving it. Got Caleb's 3/8" rocket tooling and have yet to burst one of those little tubes. Like Caleb said after using my PTOF a couple of times I could do the pressing by feel.

[lloyd]

The 'ratchet handles' are a convenience, but not a necessity. I have three such presses, and even though I do 'production work' on them, I've never found the need for the ratchets.

 

The issue is the depth of pressing. For a given item (say, a comet), the particular pressing height doesn't change much. So, you can just adjust the pinion to the rack to suit your particular pressing height, and 'go' with that.

 

Adjusting the pinion/rack only involves releasing the pinion capturing ring, sliding it out, and sliding it back in at the desired angle. It takes less time to do than to describe.

 

Lloyd

[mabuse00]

The problem is, I haven't found any offers for presses smaller than 3ton here in europe that are equipped with handwheel and ratchet.

 

In fact I found this one here:

to be the sole ratched & wheel equipped one I can get here.

 

This would be a 60Kg monster, I don't even think my workbench would carry this thing. I would have to construct something.

 

Has 280mm working height.

Now imagine I get the idea to step to 3lb motors. Ned demonstrated pressing a 2lb motor even on a 1ton press, so pressing 3lb motors on this baby does not seem to be totally unrealistic.

 

The tube alone would be 250mm, so the working height would not suffice.

 

 

 

This 3ton model would cost between 250-300€, and I would be very reluctant to cut off the bifurcating front part, thereby destroying the press for any further use outside the realm of pyro.

 

One could slip the engine tube between the two befurcating front "fingers", theoretically... if the tube fits... And create some support below the press.

 

The tube alone might fit... but with support sleeve? Definitely not.

 

 

 

 

 

 

A cheapo 2ton model without ratched would be around 120€. Has about 200mm working height, so not even usable for 1lb motors.

But in this case I would have little remorse just cutting the front off

Might not stand enough force for 3lb motors though. They state 2ton, but will the press really survive it...? A longer handle would be necessary anyway.

 

How are these geared anyway? A fellow pyro told me something with 20:1.

Well, i only weigh about 80kg, even hanging myself on the handle only gives 1,6tons.

Edited February 26, 2017 by mabuse00

[lloyd]

The 'ordinary' Chinese arbor press is set up so that with about 60Kg pull at the bitter end of the handle, it will give the rated force,

 

There isn't really a "gear ratio" in a rack-and-pinion setup. On arbor presses, there is a 'handle circle to pitch diameter' ratio for the handle-pinion assembly.

 

For instance, say the pinon had a pitch diameter of 6cm; then it's effective radius is 3cm. Say the handle extends 60cm from the center of the pinion: In that case, the effective mechanical advantage would be 20:1

 

The solution to the 'legs' of the base not being far-enough apart is to mount the tube support entirely under the base (rather than IN the notch in the base), and make tooling or ram extensions so that all the pressing can occur 'down there'.

 

Lloyd

[OldMarine]

Lloyd, with set up on my 2 ton press, how much leverage am I losing due to the offset of the handle from the axis of the shaft?

[lloyd]

Patrick, odd as it sounds, you GAIN some, but you'll have to determine how much is "some".

 

The effective length of the handle is the distance from the middle of your gripping point to the center of the hub, regardless of how the handle attaches to the hub.

 

I'll use some unreasonable (but 'trick') values to illustrate:

 

So... say the handle were 20 3/4" from where it attaches to outer end of that 'dogleg' element to the center of your gripping point.

say the dogleg is 12" long from where the handle attaches to the center of the hub.

 

Then the "effective length" of the handle would be about 24".

 

That trick was based on a standard 1 / 2 / sqrt(3) right triangle. The short leg is 1, the long leg (handle) is sqrt(3), and the hypotenuse is 2.

 

So... all that to illustrate that you don't lose length, you gain it.

 

LLoyd

[OldMarine]

Thanks, it's an odd arrangement so I wasn't sure.

[lloyd]

If Pythagorus weren't my friend, I'd have just measured it!

 

<grin>

Lloyd

[OldMarine]

I think I had PythagorAs one time while in the Philippines but Penicillin cleared it right up.

[starxplor]

If Pythagorus weren't my friend, I'd have just measured it!

 

<grin>

Lloyd

 

Pythagoras + Archimedes for all your pressing needs...

[mabuse00]

Thanks for your sharing your insight.

 

 

The solution to the 'legs' of the base not being far-enough apart is to mount the tube support entirely under the base (rather than IN the notch in the base), and make tooling or ram extensions so that all the pressing can occur 'down there'.

With a big 3ton Press that means one has to cover 25-30cm. That does not seem to be very practical to me.

I have no practical experience with such a press, but I can imagine that the sheer lenght of rammer + extension is likely to cause tilt problems... or does it not?

 

The brass shim sleeve method might fit between the legs though.

[lloyd]

Nah... if you mount the pressing mold rigidly, and make the rammer extension as large as practical to fit between the 'legs' of the press, then the press rod needs be no longer than necessary to bottom-out in the tube.

 

It's plenty rigid-enough in that configuration. Lots of folks have taken that strategy, and it works fine.

 

Some have gone to the extent of turning the bitter-end of the rack round, and threading it, so that it will accept a coupling to add various (large) extension rams, the other end of which are adapted to the pressing rods. Others drill the end of the rack, but that much-reduces the size of the extension you can use.

 

Lloyd

[MasterBlaster]

I just wanted to add that if you have access to a grinder, you can modify a cheap press so that it effectively has the ratchet handle just by taking the bottom two or three teeth off the ram. It's real fast and easy, and it works great, no need to spend the extra money.

[mabuse00]

I found another time to think about this...

 

Unfortunately I never had the oportunity to work with one or even touch one and I'm trying to imagine what working with it would feel like.

Imagine this, your pressing a motor and after some increments you end up with the rammer pointing perpendicular into the air. So you'll have to pull sideways.

 

Or put something under the rocket tool until the handle is more horizontal again.

Ain't that a pita?

 

 

Adjusting the pinion/rack only involves releasing the pinion capturing ring, sliding it out, and sliding it back in at the desired angle. It takes less time to do than to describe.

 

But not several time for each motor?

 

Sorry if this sounds stupid, I simply do not have a press in front of me, I can only try to imagine

 

 

 

And theres another thing:

After reading through several presse's figures, I found that most 1ton and 3ton units seem to have the same effective ratios, even if the 3tonners have longer handles. 60Kg on the handles tip is always some 1000-something on the rack.

 

As I interpret this, the 3ton models can survive stronger forces, but to achieve them, one must put more force on the handle. As my own weight is barely 80Kg, this would be somewhat difficult.

And all of the manufacturers forbid the use of longer handles of course.

 

So apart from the greater working height, under that point of view the "3ton" rating seems to me like a joke.

[OldMarine]

The 3 ton will have a larger throat allowing you to press larger devices with fewer rammer changes. My ratcheting handle returns to the up position upon release and has a comfortable point at which the pawls engage.

[mabuse00]

Yes, the larger throat - but if thats all, I could use a modified 1ton press and be as happy as with the 3ton model.

 

IF the force is sufficient...

[OldMarine]

I know I get nowhere near the rating pressure wise on my 2 ton but the ratcheting handle and quick adjustment wheel are nice. I can press up to 5/8" rockets with no modification.