9 replies to this topic

[Rip Rap]

I have a rocket press which uses a pneumatic hydraulic jack - very similar to this - http://www.amazon.co...R/dp/B000WJ106W

Does anyone know how to drill & tap the jack to fit a pressure gauge, to enable accurate & consistent pressing? (Like the ones shown here - http://www.hobbyfire...com/Rocket.html )
I know that a few years ago there used to be a document on rec.pyrotechnics describing how to do it, but unfortunately I cant find it anywhere.

Alternatively, does anyone know the theory behind how to make a pressure conversion gauge, like the one on Wolters page? - http://www.wolterpyr...catg&cat=rocket or know of an alternative tool?

Many thanks for any advice.

[marble]

Its in a passfire article but I will get reamed by others here if I give it to you.

[cooperman435]

The theory is easy! You would need a short cylinder that had a piston with a 1" square surface area. This would have a small volume of hydraulic fluid in it and a threaded port for a hydraulic pressure gauge. 1 lb of pressure on the device would put 1psi into the gauge. 10lbs would give 10psi etc etc.

[FrankRizzo]

The theory is easy! You would need a short cylinder that had a piston with a 1" square surface area. This would have a small volume of hydraulic fluid in it and a threaded port for a hydraulic pressure gauge. 1 lb of pressure on the device would put 1psi into the gauge. 10lbs would give 10psi etc etc.

Apart from actually disassembling it, you can also tap into the jack from the outside. Drill and tap into the fluid channel between the pump piston (the small one under the rocking arm). Getting the jack apart takes a nice sized pipe wrench and a sturdy bench vise.

Another idea: Some front wheel brake cylinders have a 1.125" bore (.997 sq in). If you were to fill it with fluid, and attach a gauge to the hydraulic line input you'd get almost a 1:1 ratio of PSI to force. You'd have to make a base and pressing plate though to make the assembly stable.

EDIT: Here's another solution. This isn't quite as elegant as a Wolter gauge with it's 1:1 pressure/force conversion, but if you don't mind doing a bit of math and having a conversion sheet near your press (Wolters gauge requires a conversion sheet too)...

Just fill the cylinder slightly to extend the ram and add a gauge to make your own improvised P2F. The cylinder bore is 1.5" (~1.77sq in).



http://www.harborfre...temnumber=42830


OR



http://www.harborfre...temnumber=95979

OR

http://www.harborfre...temnumber=95978

Edited by FrankRizzo, 30 May 2008 - 01:45 AM.

[Rip Rap]

Just to say thanks for the replies - eventually went with - http://www.harborfre...temnumber=95979

Even with the shipping from the US, it came in at £25! (Good job the $ is weak against the £ atm)

Works great - now I know that I can keep a consistent pressure from rocket to rocket

[dr thrust]

thats great! i need on of those!! may i ask where you got the pressure gauge to fit to it? any pics of the finished jobby

[Rip Rap]

thats great! i need on of those!! may i ask where you got the pressure gauge to fit to it? any pics of the finished jobby

Here's a pic of it - http://pyrotechnics....es/img_0448.jpg

The gauge I got off Ebay for about a fiver. Search for "pressure gauge" - will get you things like this.

You may need an adapter as the fitting on the ram is 1/4" npt. You can easily get one from a place like Pirtek. Thankfully we have a local branch.

When I got the ram, I needed to raise the piston. I removed the hydraulic attachment it came with & drained the fluid. the top of the piston has a small hole in the centre. I tapped this & pulled it up with the tap. Then slowly refilled with fluid (making sure no air was trapped) then attached the gauge. "Jobs a good 'un!"

Now you need (or at least I needed it) this page to calculate the pressure you are applying to the comp in your motor. The smallest tooling I use is 10mm diameter. With this 10mm tooling, only 200 psi on the gauge equates to nearly 3000 psi on the comp!

Its nice to be able to "know" how much pressure is being applied - to be able to adjust that for different tubes, comp ratios etc.

[cooperman435]

Im hopefully gonna get one of these myself and it shouldnt be too much issue geting a 1/4" npt threaded gauge or adapter as Ive a hydraulic manufacturers down the road.

Btw its probably easier to usea hydraulic pump to pump up the cylinder first rather than pull it up and then fill it

[Rip Rap]

Btw its probably easier to usea hydraulic pump to pump up the cylinder first rather than pull it up and then fill it

Theres's no "probably" about it - It would be easier (even I figured that!) - but I don't have a hydraulic pump, lines, connector etc

[FrankRizzo]

Here's an updated reference for those of you looking to make one of these easy P2F assemblies:

The author took the time to put one together (and take it apart!), and found that the working diameter of the piston inside the ram is ~43mm (1.70"). This gives a P2F multiplier of ~2.3X (1000psi gauge = 2300lb force). Again, this isn't a perfect representation of the force applied, but will enable consistency (most important).

http://www.wichitabu.../ptof/ptof.html

Edited by FrankRizzo, 18 November 2008 - 01:59 AM.