Gang rocket press tooling

[NeighborJ]

I've been kicking around ideas for a gang rocket pump which could be affordable to the hobbyist yet versatile enough to be used with almost any existing tooling.

 

The design I propose is a series of short stroke hydraulic rams similar to the PTF gauges, which can be piped together in parallel. They will be able to transmit equal force onto each drift regardless of variations of increment volume and a single gauge can still be attached to monitor the psi across all the motors.

 

If this seems feasible to others then I may ask Caleb to fabricate a PTF gauge rail for the purpose of gang pressing.

[lloyd]

That may be 'overkill'. It certainly will work, and exactly as you indicate, but 'lots' of small cylinders (and lines) mount up to become a large wallet outlay.

 

I've made many 'gang' presses that give excellent item-to-item consistency. When the relative pressure from one to the next was actually critical (would be, for rockets), I've used die springs on each pin, selected to give approximately 60% compression at the desired load. One really nice thing about that strategy is that if you end up wishing to change the pressure, there's some 'take-up' in the springs to accommodate small changes, and if they don't meet spec, you just change-out the springs.

 

They aren't cheap, either, but a lot less-expensive than quality cylinders and plumbing.

 

Lloyd

Edited April 23, 2017 by lloyd

[OldMarine]

I don't press enough rockets to justify anything like that setup. I can press up a dozen ¾" or 1" rockets in a Sunday afternoon and the same number of ½" in an hour or so. By the time I make it out to my shoot site I have plenty made up. I imagine if you were making strictly whistle rockets it would be good to be able to make them up as needed to help negate moisture build-up during storage.

[NeighborJ]

I appreciate the feedback guys. The hydraulic balance system would be the most accurate system but also the most expensive not to mention it would be added to the extra 4 or 6 sets of each type and size of tooling.

 

I like the spring idea and was thinking of using leaf springs. This idea would be very large and seems like it could be difficult to dial in to the appropriate pressure. I've also entertained ideas of abandoning the hydraulic force method in favor of a levered counterweight which could be dialed in by moving the weight further out on the lever. But this whole assembly would take up the space of an entire room.

 

OM I agree that many rockets can be made in a relatively short time as single motors. Yesterday I pressed 40 whistle inserts in about 2 hrs but I still want it to go faster and easier. I like to make them in an assembly line fashion where I load an increment in 40 inserts then press them all, then repeat until they are full. I am constantly trying to find ways of increasing the efficiency of my builds without sacrificing quality.

[OldMarine]

I've almost hit my self-imposed pyro spending plateau and have decided that if I can't build it on the cheap I probably don't need it. I plan on buying one more star plate and a couple of comet pumps then I'll have to be happy with what I have for a while. Good luck with the project and I'm sorry I don't live closer so I could help you experiment!

[lloyd]

Leaf springs would make it immensely-large horizontally. Die springs only increase the vertical height of the assembly. If you're really tight on vertical height, you can use Belleville washers, instead, increasing the numbers of pairs (MUST be used in 'facing pairs') in order to increase vertical travel before full-compression. I've done it that way, too.

 

LLoyd

[NeighborJ]

Belleville washers, had to look it up to see what they were.

 

There would be no height restrictions because this press would be completely custom fabricated and welded solid. The other components I had in mind consist of a electric log splitter ram and pump modified with an adjustable high pressure relief, dumping into the holding tank.

 

But back to the springs, it seems as though coil springs would be the best bet here but I just don't want to swap them out every time I switch motor sizes. I find myself thinking that the PTF rams would do the job quite nicely, and if I install a shut off valve between each one then I can press less motors if I want. It would be simple to start with two rams and simply expand to more as I raise funds for extra tooling and rams.

 

I want to build this thing rite, it would be undoubtedly the most used tool in my arsenal and I want it to be easy to use, last decades and still be 100% accurate. Worst case scenario would be that it wouldn't work as planned, at which point I could offer up the extra PTF gauges for sale, and still use the press for individual motors.

 

I've got a few ideas to chew on now and plenty of time to decide what to do. I'll keep an open mind to any ideas offered.

[lloyd]

If you decide to do it that way, I'd make a recommendation: Instead of a 'full-sized' cylinder on each position, have ONE cylinder that does the major job of moving the press-rod plate, and only very short cylinders for applying the 'final force'. Shorter cylinders are cheaper than long ones.

 

It's still expensive and unnecessary. A set of springs, if carefully-selected, would work for at least two (maybe three) sizes of motors. Remember that a good spring's compression force is in a linear relationship to its compression length. To compress it twice as far requires twice the force.

 

So one spring can suit a pretty wide range of potential pressing forces (and thus, rocket sizes).

 

Lloyd

[NeighborJ]

I'm nowhere near set on any design but yes there would be one ram pressing on a slider which would then press on all the drifts. The PTF gauges would be under each spindle base.

 

I'll do some research on both low profile portapower rams and appropriate sized springs. I'm certain the springs are cheaper but I'd need to install them in a way that they wouldn't interfere during the use of a star plate or could be removed to accommodate one.

 

I may be a little leary of using coil springs. I witnessed a coworker get his hand crushed while rebuilding a pneumatic valve head fitted with coil springs. I also witnessed my apprentice cut his index finger off when he accidentally triggered a spring loaded emergency shutdown valve with his finger inside the ball seat. Yuk!

Springs under tension can kick, break or just plain wear out, they just scare me.

[lloyd]

I have client's presses in service with tens of K-cycles on ONE set of good die springs. I've had them begin lose force after 20K cycles, or so, but never had one break. (just to be clear, that's 20K items pressed PER PIN). I'm not talking about cheap Chinese hardware-store springs, I'm talking about U.S.-made DANLEY die springs.

 

Changing to different-sized rods without having to re-mount all the springs is a complete NON-issue. And there's NEVER a reason to have a hand anywhere near one of those springs. If you just can't resist reaching into a bay of springs (with your THIRD HAND, because the other two are BOTH on the actuator controls) while they're being compressed, you could put a guard around them!

 

Do whatever you think is best.

 

LLoyd

Edited April 23, 2017 by lloyd

[lloyd]

BTW... I've just GOT to hear your story on how a spring that's got a solid rod inserted all they way through its bore can 'kick' (I assume you mean 'fly out').

 

I've seen die springs break (in punch-die service), and have never, ever seen one leave the shaft it encircled.

 

L

[NeighborJ]

I'm trying to visualize how the springs would be used. I'm picturing the main ram pushing on a slider, mounted overhead and the springs mounted underneath with separate sliding guides going thru the main slide bar. When stroked the spring guide sliders make contact with the drifts and compress into the main slide bar.

[lloyd]

C'mon! You've already made it perfectly clear that the method is unsafe, and you have the experience necessary to declare that, even without having seen mine or others' tools (that are used in OSHA environments) -- or even knowing anything about how they're built.

 

What could I possibly tell you that would change that?

 

I'll continue to do what I know works, and is safe for my clients.

 

You do what you want.

 

Lloyd

Edited April 23, 2017 by lloyd

[OldMarine]

I work with captured spring check valves in backflow preventers in which the spring pressure exertion is up to 1100 psi in single spring 10" devices. When these springs fail, and they do often hence my job, they don't go anywhere. They just go to pieces and hang limply on the center shaft like a bunch of little springs. These checks compress and open while maintaining a constant pressure.

[NeighborJ]

I don't mean to cause a stir, I am picking up what Lloyd is layin down but I don't have a clear understanding of where he is suggesting it be mounted (under the spindle base),(around the drift). Obviously with a shaft thru it (I'm sure it's safe) but not if I install it wrong.

[lloyd]

A "stir"? You declared my design inconvenient without knowing how rods are exchanged, and dangerous without even understanding the concept of 'captive springs'.

 

There are plenty of references about such designs on-line, and plenty of other folks who will ask about things they don't understand, rather than making sweeping declarations about how bad someone's design they've never seen is.

 

Just to be clear; this doesn't mean I won't offer advice where asked-for on other subjects, nor am I "in a bad mood". You let me know clearly how you accept advice on presses, so I'm now finished offering any. I have nothing more to contribute to the subject.

 

Lloyd

Edited April 23, 2017 by lloyd

[NeighborJ]

I think you must be reading a different thread than me, I never had a bad word to say about your methods. I suppose the reference to my personal experience was intended to be a line cast out because I was fishing for more info. I apologise.

[lloyd]

Ooookay... Not for nothin', but when I want information, I ask. I personally think you did condemn the idea -- no matter how 'diagonally' you did it.

 

You didn't ask, "will that be dangerous?" or "Will the springs fly loose if they break?" -- you launched into stories of how dangerous you've seen them be.

 

But your statement and apology seem heartfelt.

 

I'll continue with the old thread as if this recent disagreement never happened, when I can use your first name to address you.

 

Lloyd

Edited April 23, 2017 by lloyd

[OldMarine]

NJ, the springs will exert their rated load throughout their range of travel (except for a tiny bit of initial compression) and therefore allow a slightly underloaded tube to reach the same pressure as the properly loaded tubes around it. I have some schematics on an old Watts Regulator wobble plate device that explains the concept but I don't want to rip the manual apart to scan and post it since it's an antique!

[lloyd]

Patrick,

What do you call "their rated load"? Do you mean "the same pressure" over all of their useful travel length?

 

Lloyd

[NeighborJ]

OM, I'm trying to gain more understanding of what your saying. If a spring is rated at say 50# then it will exert 50# thruought it's entire stroke except when it is in its Initial stages of compression, when it is loading up.

[lloyd]

Patrick,

 

I don't know if your perception of it is right, but the way you expressed it is wrong.

 

The rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring.

 

If a spring exerted the same force over its length of compression, then it would compress FULLY the moment that force was exceeded by even a microscopic amount.

 

Think about it... you compress a spring between your fingers -- say 1/4" compression of a 3/4" long spring. Does it just 'mush flat' the very instant it starts to move, or do you have to squeeze harder to compress it further?

 

L

Edited April 24, 2017 by lloyd

[NeighborJ]

http://www.acxesspring.com/spring-load-and-rate.html

 

Found all the formulas here.

[OldMarine]

Alright math guy, explain what I meant!

[lloyd]

Patrick,

If a spring had a useful travel of 3", and a spring constant of 10lbf/in, then it would require 10lbf to compress it one inch. It would require 20lbf to compress it two inches, and 30lbf to compress it three inches.

 

In this case, not 'higher math', just simple multiplication of the spring constant times the number of spring constant units of travel it is compressed.

 

Similarly, if that same spring were compressed 1/2-inch, then it would be 0.5in*10lbf/in, or 5lb.

 

Lloyd