Has anyone any experience with reworking a large screw type gate valve assembly into a fly press. The paper co i work for discards large ones when replaced. Mabey a 2" screw dia. Is the rate of thread workable? Any thoughts, anyone? Humphry. Oh and Merry Christmas Everyone.

An acme screw would make a passable press screw I think. Are the ones you have available acme? There was a discussion here a while back on the subject of the use of different type screws: http://www.iforgeiron.com/forum/f7/acme-screw-1775/

There's been a lot of discussion on making your own flypress across the street at anvilfire.com. The general consensus was that there was actually a lot more to it than a frame and a big threaded rod and a frame .

The thread form of the screw is pretty specific both for speed and power. The frame and screw must be very strong and yet sufficiently elastic to absorb the very high pressure spike generated.

Flypressses seem deceptively simple, but are actually quite sophisticated in how they work and the amount of power that can be generated.

The problem I see is the screw. Take a look at the "slope" of the threads on a manufactured fly press:
The lead angle of the threads is very aggressive, moving the ram much farther per revolution, therefore much faster. Not the same as an acme thread.

I have thought that one could engineer a cam actuated press to get similar results, (and I think there was discussion of this here) but the theory will need to be tested by someone else.



source:
Fly Press Page - FredlyFX.com

acme thread pic:

from Wikipedia

Fly presses use multi-start threads. Unlike a regular lead screw which is a single start thread.

I might be using the wrong wording, so correction is welcome.

Phil

The attached .pdf file, ""Fabricating a Fly Press By Steve Gschwend, Bruce Weakly" shows how they made a flypress using a 2" Acme thread screw.

Fabricating_a_Flypress.pdf

here's the discussion I was thinking of

http://www.iforgeiron.com/forum/f82/fly-press-lateral-thinking-4774/?highlight=flypress


http://www.iforgeiron.com/forum/f82/fly-press-lateral-thinking-new-idea-4812/?highlight=flypress

Edited December 23, 200916 yr by GOATMAN

A single lead press is called a vise.

Nice pic of the manufactured fly press, Goatman. I see what you mean about the aggressive pitch!! :)

Wouldn't an acme screw lock tight at the bottom of the stroke?. My flypress has 3 threads on the screw and I have always assumed that this feature gives the "bounce" at the end of the stroke preventing it from locking.

brad

I think the 3 or 4 leads are for speed not bounce.
Ken

Wouldn't an acme screw lock tight at the bottom of the stroke?. My flypress has 3 threads on the screw and I have always assumed that this feature gives the "bounce" at the end of the stroke preventing it from locking.

brad

Much depends on lubrication also. I put graphite powder on the threads of a c-clamp once. (Thought I was doing a good thing) Those threads are designed to lock up but with the graphite, the clamp was useless as a clamp. On the other hand, it would have made an excellent model of how a fly press should work; bounce and l LOL. I had to wash it in solvent to get it to work correctly.

This will, hopefully, help.

http://www.nookindustries.com/acme/acmeglossary.cfm

Of course, Ed Thomas doesn't need to read it. He uses his vise. :lol:

Steve, of course then I HAD to read it.

Okay, so maybe my post was a bit short; this topic comes up fairly often and sometimes I forget that the reply posts disappear or get too buried to find with a casual search.

The fly press is named that for a reason. Although sometimes called a "screw press", "fly" press is more accurate. The whole point of the design is to (as efficiently as possible) translate the inertia of the flywheel, through the inclined plane of the screw, into concentrated vertical pressure, capitalizing on the leverage of the flywheel arms.

This is why the fly-press has a mass of some sort. Older ones have a cannonball-looking weight; modern presses distribute the mass in a heavy "fly" wheel. If it were a simple screw press, the mass would be just an inertial inconvenience you would have to overcome every time you wanted to move the screw up and down. Instead, we accept that effort, unconsciously knowing that it is the real power behind the press as we throw it or nudge it, depending on how much we need.

The threads sacrifice some speed in favor of power, but need to be aggressive enough to avoid binding on impact, and also to provide a practical rate of travel. If the pitch isn't aggressive enough, the operator might have to cycle the flywheel more than a complete revolution, which is very clumsy.

In my experience, the best design allows you to pull the flywheel less than 1/2 revolution to be up to optimal flywheel speed and therefore, screw travel. A single lead screw would reduce the useful downward press range to nearly impractical for most of our applications. The multiple-pitch threading overcomes this problem.

A single lead screw, thrown at the top rating of a fly-press, would usually bind... which is why I said it is really a vise, acme threads not withstanding.

Eddie!
I knew I could get a response. And a big THANK YOU. Very well stated.

Now I have to go turn MY vise on its side and spin the handle cause EDDIE says I can. :blink:

I understand what Ed is saying.While an Acme thread is more geared toward clamping than it is punching that shouldn`t keep you from building new tools using whatever follows you home.
The "Acme press" would add more control to a pressing operation due to it`s reduced velocity.
It could also be used to more easily control incremental bending if a locking collar or stop nut was brought into play to limit the travel of the ram.

If you`re looking for a cheap alternative to a flypress to use for punching or embossing then why not just make the manual conversion to a punch press as per instructions elsewhere on this site?
If you`re in spending mode(as opposed to "followed me home" mode), may as well spend the money on a complete old machine that has multiple uses as spend it on new parts for a make do machine that may fall short of your expectations.
YMMV,it usually is calculated differently than mine.

The triple threads on my flypress always cause the screw to return to the bottom by gravity alone. No single lead acme screw will ever do that.

Having worked in the engineering department of the largest valve and fitting maker in the world, for valves 2" and under, I would offer the following on Gate valve stems etc. (BY the way, we did make up to 8' valves on occasion)

A gate valve stem is usually single lead, but I have seen smaller valves with double lead. Nothing is free in engineering, so twice the translation speed per turn equals half the axial force.
The flypresses use very heavy weight and inertia to get the force.
Gate valve stems, bearings, and the yoke nut/yoke are designed for low speed, with minimal force until that last little bit of stroke. If you took a standard valve bonnet and yoke and added a flywheel, you would simply shear the shoulders off the yoke nut and then no thrust. I have seen many returned valves with stretched yokes, sheared yoke nut shoulders etc with the marks on the handwheel from a cheater. The force increase is so powerful that almost any addition to the rotational torque will fail most any valve.

A simple example is a 3/4" gate valve I did extensive testing with. Had a 3/8" acme thread. At 20 footpounds on the pretty small handwheel the force exerted axially on the stem was 1200 pounds. One would only have to double that torque to fail all sorts of things in the system. Just adding adaquate lubrication in the form of moly disulfide, reduced the required torque to get that same 1200# by 40%.

So in short, I do not believe those big acme stems would make good flypresses. Laid on their side, a nice big vise yes.

Being that I'm only a welding educator who does some blacksmithing I'm not qualified to be an engineer.
However, looking through the Nook information I see an explaination and drawing that I interpret to show how load/torque could be loaded to one side of the starts/threads. One start, or lead as PTREE names it, obviously loads one side of the shaft. Two starts puts the load/torque on two places each on opposite sides of the shaft. A four start places the load/torque on four equally spaced areas of the shaft.

The next thing that I interpret as side loading is when a pully is used. This puts the load on one side (horizontally) of the shaft, which can bend the shaft opening the non loaded side of the threads and closing the load side of the threads. Something like a fly press has linear loading when free wheeling. When it contacts the stop I'm not sure if that would impart a side load or not. Of course, that hundred pounds tends to want to continue even though the ACME screw has stopped. Consider that if it has only one start/ lead/ thread it has that linear load on one side of the shaft.

I need to stop. I think I may take away all doubt if I continue. :huh: