In my experience, there are three basic machines, which become necessary as one gets deeply into fireworking: a ball mill, a star roller, and a hydraulic press. Ball mills were discussed extensively in Fireworks Tips #91, and I showed some options for star rollers in #92. Now it’s time to look more deeply at rocket presses.
Commercial Rocket Presses
In past newsletters I have shown several of my hydraulic presses in action as I’ve made rockets, comets, pressed stars, black powder pucks, or fountains.
Some devices, like simple gerbs or black powder rocket motors, can be made by simply hand-ramming them with a rawhide mallet and a pounding post. Or they can be pressed with a hydraulic press.
Other devices such as whistle rockets or strobe rockets utilize more sensitive fuels, and require hydraulic pressing for their manufacture. Hand-ramming these motors is simply asking for a disaster.
Since I’m about to present projects showing how to make whistles, whistle rockets, and strobe rockets, I thought an introductory essay on hydraulic presses would be in order.
In the previous articles mentioned above I’ve shown my small Hobby Fireworks press. It’s a nice press and was not too expensive. It sits on top of my workbench and is light and portable. I can take it to club events like the PGI convention. Unfortunately, Hobby Fireworks has gone out of business.
Over the years I made some modifications to the press so that it suited my needs better. I replaced the 1/4-inch-thick steel plate on the top of the bottle jack with one that is 3/4-inch thick. The thinner one started bending a bit, and I want that plate to be perfectly flat.
I replaced the original 4-ton bottle-jack with a fast-action 6-ton one. The new jack can exert forces up to 12,000 pounds, which is about all I ever need, even when pressing large 4-inch comets and large rockets. Additionally, the new jack raises very quickly compared to standard-lift models.
The jack is available at Northern Tool, and currently it sells for $28, including a nice, collapsible lug wrench.
When I showed an advance copy of this article to my friend, Dan Creagan, he sent me a photo of a jack he had just found at WalMart, apparently identical to this one except it was painted black and had the Torin Brand name on it. It only cost Dan about $19.
I had the welding shop reinforce the press’s adjustable cross “bridge” so that it would withstand the additional force exerted by the 6-ton jack.
I drilled holes in the back of each horizontal leg-support so that I could bolt the press down to the workbench to secure it during use.
The pressure release knob had a hole drilled through it and a 3/16-inch rod-handle installed for fast and easy operation.
This press has gotten a lot of use over the years, and if I had welding capabilities and I wanted a nice little press, I’d duplicate this model.
There are H-frame shop-presses available at various suppliers. In the past I’ve referred to one such press sold by Greg Smith Equipment. It’s a floor standing unit, and weighs over 150 pounds, but it looks like a pretty nice press, has a good range of adjustability, comes with a pressure gauge, and sells for only slightly more than $200.
Simple Do-It-Yourself, Hydraulic Press
Note: My friend, Jim B, has a favorite saying; “For every 10 pyros, you’ll get a dozen different ideas on how to do any task in pyro.” The ideas I present in the following project are designed to simply get your creative juices flowing. I seriously doubt anyone will build a model that is exactly like mine. But maybe these ideas can point you in the right direction.
In addition to the commercially-manufactured options described above, I got to thinking about a sturdy, relatively lightweight, bench-top press which did not require much welding. I’ll describe one possibility that came to mind.
The setup and operation of the hydraulic bottle-jack is similar to the Hobby Fireworks press. I had six, 4×4-inch, 3/4-inch-thick, steel-plate shims cut at my local steel supply, to augment the adjustability of the press. Between the 5.5-inch travel of the bottle jack’s piston, and the 4.5-inches of adjustability the shims provide, the press has a total of 10 inches of travel between all the way down and all the way up.
This allows me to adjust the press’s top plate with the hex-nuts only one time per the particular device that I’m pressing. I never needed more than that 10 inches of adjustability for any of the devices I make. I’ve tripled-up the top hex-nuts because of the forces they endure during pressing. I don’t want to be stripping any threads.
The Press’s Main Frame:
The main frame of the press is made from four 3/4-inch x 36-inch threaded rods, nuts and washers from Home Depot. I had my local steel supply-house cut the bottom and top plates, which are 12-inch long pieces of 1-inch (thick) x 9-inch steel plate.
One-inch-thick steel plate is obviously very strong, and that strength is necessary to withstand the forces, which will be involved in pressing fireworks devices. I wouldn’t want to use steel plates that are thinner than the ones I used, and I also wouldn’t want to make them larger and spread the threaded rods out farther. This could lead to bending the plates.
The PVC plumbing pipe sections on the threaded rod uprights are there to keep me from cutting my knuckles on the threaded rod as I insert and remove devices in the press.
Installing a Blast-Shield
When I’m pressing whistle or strobe rocket motors, which use pressure sensitive, powerful fuels, the installation of a blast-shield is a good idea. The 1/2-inch thick plastic sheet will offer some protection just in case a motor “goes off” while it is being pressed.
The blast-shield is attached to the press and held in place with 3/8-inch eye-bolts, large fender washers, and hex nuts. Polycarbonate plastic such as Lexan is used in bullet-resistant windows, and serves well for blast-shields.
The other benefit of the PVC pipe on the threaded rods is to hold up the bottom blast-shield, eye-bolt supports.
Jack Return Springs
The two 7-inch springs, also from Home Depot, serve to return the bottle jack to its “down” position when the pressure-relief valve is opened. The top of each spring is attached to the 4×4-inch plate that is welded to the screw-out jack-post. The bottoms of the springs are attached to eye-bolts that are mounted in holes drilled through the bottom steel plate.
I had my welding-shop weld on small hex nuts for the top spring attachment at the same time they welded the plate to the jack post. This was the only welding required in this project.
Pressure Relief Valve Handle
To create an easily-operated handle for the jack’s pressure-relief valve, a hole was drilled through the end of the relief valve. A piece of 3/16-inch galvanized steel rod, bent in an L-shape was inserted through the hole, and the small end was pounded flat on a vise-anvil to hold it in place.
Holes in the Steel Plates
The holes in the top and bottom steel plates were drilled using a drill-press. That was the only large piece of equipment that was necessary in the fabrication of the rocket press. The threaded-rod holes were drilled at 9.5-inch centers, side to side, and 5.5-inch centers, front to back.
The jack is attached to the bottom plate with three, 5/16-inch bolts, which go up through the steel plate and into holes I drilled and tapped in the bottom of the jack. (Threading holes in metal is done with a tool called a “tap.”)
Two extra holes were drilled toward the back of the bottom steel plate, through which bolts will go to attach the press to my workbench. This will make the press nice and steady as I’m pressing rockets.
I used a hand-held grinder to smooth all the edges and corners of the steel plates. Then I primed and painted the plates using spray primer and finish paint.
Hydraulic Pressure Gauge
There are a few pressure-to-force (PtoF) hydraulic pressure gauges available to the pyro-hobbyist community. These gauges employ a one-square-inch-area piston, so they directly read out the number of pounds of force being applied to the item being pressed.
For example, if the PtoF gauge is reading 2000 psi, the actual force being applied to the tooling is 2000 pounds, the equivalent of 2000 pounds of concrete sitting on top of the tool.
An advantage to using one of these gauges is that you won’t need to install a pressure gauge on the press’s bottle jack.
I personally like to use a gauge that is actually installed in the bottom of the bottle-jack. Doing so enables me to eliminate one loose, movable component, like the PtoF gauge, when I’m aligning and pressing devices in the press.
Using a gauge on the jack, though, requires that the gauge’s reading be multiplied by the area of the jack’s piston, in order to determine the actual force being exerted by the jack. I’ll show what that means in a minute.
Installing a gauge on the bottle-jack presents what is probably the most challenging aspect of this project–drilling and tapping/threading the bottom of the bottle-jack, and installing a hydraulic pressure gauge. But, it’s good to know how to do this, even if a PtoF gauge is going to be used.
Installing a gauge on a bottle jack requires the partial disassembly of the jack, drilling a couple of holes, tapping/threading the hole where the gauge will be installed, cleaning debris out of the jack, and reassembling it.
One of the nice things about the bottle-jack I’m specifying in this project is that it is relatively easy to take apart and put back together.
First, the rubber drain/fill plug on the back of the jack’s cylindrical body is removed, and the oil that fills the jack is emptied into a clean pot. This oil can be filtered through a coffee filter and reused in the jack when it is reassembled.
When draining the oil, it helps to remove the pressure-relief valve. This valve has a 1/4″ steel ball bearing down in the hole into which it is screwed. Carefully set the ball and valve aside, and finish draining the oil. Pumping the lever assembly a few times works the rest of the oil out. Now is a good time to drill the hole in the pressure-relief valve and install the L-handle.
The lever-arm has a couple of steel pins, held in with spring-clips, and is easily disassembled. (You are making mental notes of how all this goes back together, right?)
It’s time to remove the large hex-nut at the top of the jack now. This requires that the base of the jack be held securely in a vise or a rocket press. (Waitaminnit, I’m making my rocket press! How can I hold the jack in my rocket press? I have 3 presses, and this will be my fourth.)
The hex-nut is then loosened with channel-lock-pliers or a large pipe-wrench. It may be necessary to whack the wrench with a rubber mallet or similar heavy object. The nut is screwed off when it is loose, and the central jack piston and outer jack shell-body can also be removed. The nut has a plastic O-ring gasket on it where it hits the main body, but this gasket is usually “glued” on with paint and does not need to be removed.
There is a “tapered” large rubber O-ring which sits in the groove that the shell-body came out of. Remove this O-ring. Remember that it was in there with the thin edge up, and the wide edge down.
Inside the jack, there will be a small, wire-mesh filter shoved in one of the holes in the base. Make a note of which hole it’s in, and then remove it. Actually, this is a good recommendation, which has never worked for me in real life. Each time I’ve disassembled a jack, the filter has dropped out before I get to notice where it was in the first place. I’m not sure how they get the darn thing to stay in during shipping and/or operation.
I’ll show in a moment how to determine which hole the filter ought to go back into when the jack is reassembled.
The screw-post will only unscrew so far as it extends out of the jack’s piston. It is not necessary to remove this screw-post all the way. The whole jack can be taken to the welding shop when the 4×4 plate is welded to the screw-post. If one wants to remove the post all the way, some filing/grinding is necessary to remove the small “indents” which have been knocked into the top of the cylinder to hold the post in place.
Now is a good time to measure and make note of the diameter of the bottom of the piston. In this case it measures 1.375 inches. Squaring half that diameter (the radius) and multiplying that by Pi (3.1416) yields an area of the bottom of the piston of 1.5 square inches. (3.1416 x .6875 x .6875 = 1.5 square inches)
Because of that, when my new, jack-mounted pressure gauge is reading, say, 1000 pounds-per-square-inch (psi), I’ll multiply that gauge’s reading by 1.5 to determine the actual amount of force the jack is exerting on the tooling in the press, which in this example would be 1500 pounds.
Once again holding the base of the jack in a vise or rocket press, I now carefully use a pipe wrench to loosen the jack’s inner cylinder. I apply the wrench right down at the bottom of that cylinder in order to avoid crushing or distorting the tube as I loosen it.
Once the inner cylinder has been removed, another plastic O-ring gasket can be seen inside the base where the cylinder bottoms out. This O-ring does not need to be removed. Notice that there is a top and a bottom to the inner cylinder. The top is beveled on the inside lip to make insertion of the piston easy. The bottom has a flattened edge, which bears on the O-ring seal.
The small lever-operated jacking piston/cylinder should also be removed at this time. There is a metal washer and a 1/4″ steel ball down in the base’s recess which should also be removed.
And, now, finally we’ve arrived at the final disassembly step. There is another 1/4-inch metal ball in the bottom recess of the base, held in with a plastic retainer. This can be seen in the base’s large recess in the photo above. The retainer is removed by prying it with a screwdriver, and the ball is also removed.
I’m keeping all the little parts in a clean paper cup to prevent me from losing them as I go along.
There is also an over-pressure, safety relief valve, covered by a plastic cap. This assembly, including the cap, screw-out post, spring, metal-mushroom, and very small metal ball, is all removed and placed in the paper cup.
I can just hear ya hollering, “Crikey, Ned, what the heck have you gotten me into?”
It’s really not as bad as it all sounds and looks. If you keep track of all the little parts, and remember how they all go back together, this can be fun. Really! There’s learnin’ happenin’ here.
At this point, for my own education, I spent a bit of time envisioning how the jack works when it is being operated. The small jacking-piston and cylinder create high pressure using the principle of mechanical leverage. The pressurized oil is forced through the small hole in the bottom of that recess and up past the ball/hole/retainer in the large base recess.
All those balls in this device simply act as valves, sitting in nicely machined recesses, and only allowing oil to flow in one direction, pushing the ball slightly out of its recess. Oil pushing from the other direction forces the ball against the machined seal and shuts off the flow.
As it is needed, more oil is “sucked” into the small base recess from the main reservoir between the outer jack body and the inner cylinder.
The pressure in the cylinder jacks the piston up a small amount. The process is repeated as the piston gradually is lifted.
If too much pressure is generated inside the main cylinder, the oil can push the small ball and spring in the over-pressure relief valve and allow the excess oil to escape back into the main oil reservoir between the outer jack body and the inner cylinder. This acts as a safety to prevent the jack from being over-pressurized and dangerously rupturing.
And finally, when we want the jack to retract and go down, the pressure-relief valve is loosened. This allows oil to move past the ball at the bottom of that valve, and back into the main reservoir.
Since the only hole through which oil moves out of the main reservoir is the one leading to the bottom of the jacking-cylinder’s small recess, that is the hole that the small filter will be replaced into (so it functions to remove debris from the oil as it circulates). I find which hole that is by blowing into it to make sure the air is coming out of the ball-blocked hole in the bottom of the small base recess.
And, keeping debris out of the whole jack is why I’ve completely disassembled it. After the next drilling and tapping steps are completed, all the parts will be completely cleaned before any reassembly. Small bits of metallic debris are the enemy of a properly functioning jack. They can become lodged in the various ball-valve assemblies and allow slow leakage, preventing optimal performance.
Drilling and Tapping the Jack-Base to Receive the Pressure Gauge
You’ll notice, when looking at the jack base, that all the existing holes and inner “channels” that the oil flows through are located in the right side of the base.
Conveniently, this jack’s base has a nice flat area on its left side, and plenty of room on the left-inside of the large recess where a hole can be drilled.
This is the point we’ve been heading toward. I want to drill a 3/16-inch hole down from the bottom-inside of that main base recess, but not all the way through the base. I drill this hole about 3/8-Inch deep.
I want to drill in from the left-outside of the base with the same 3/16-inch drill bit, until that hole hits the first hole that was drilled. I only want to drill as far as that first hole so that I don’t hit any of the other inner channels in the base.
The hole coming in from the side is drilled high enough from the bottom to allow the fittings I’m going to install later to clear the press’s base plate. I also plan that hole so that it is centered in the bottom “thickness” of the base, so that the strength of the remaining metal surrounding my new fitting is maximized.
Drilling this hole, centered up 1/2 inch from the bottom of the base, accomplished all the above goals. And it kept the metal thickness between the hole and the bottom of the base no less than 5/16 inch, which is needed to withstand the internal jack pressures.
These two holes are gradually deepened until they hit each other, and no further.
The two holes will form a new channel which will allow the pressurized oil inside the inner jack cylinder to reach the new gauge which will read out the same pressure that exists inside the cylinder.
Warning: The main power tool I’m using in this process is a drill-press. Like Norm Abrams says, “Read and understand the safety precautions concerning this tool before you use it.” I do this drilling at low speeds. I firmly hold the piece I am drilling with a clamp and/or other tools. This drill-press can be my best friend, or it can slice my hands open and/or break bones. Be careful.
The hole in the side of the base is enlarged with a 5/16-inch drill bit (Q drill bit) enlarging a section about 3/4-inch deep. This side hole (only) then has threads cut in it with a 1/8-inch-pipe-thread tap.
This is also a good time to drill and tap the bolt holes, in the flanges on the base, which will attach the jack to the press’s bottom steel plate.
There, the hard part, the machining, is done. I now clean all the debris, excess paint, and metal shavings off of all the parts in a pot of clean kerosene or paint thinner. I pay special attention to the base to make sure all the small metal debris has been washed off of it and out of all its holes and channels.
After the parts have dried, the bottle jack is reassembled in the reverse order in which it was taken apart. Before adding the oil back into it, I attach the new pressure gauge using hydraulic fittings and Teflon tape. My local hydraulic-fitting supply-house was able to supply the fittings that I needed, and which would handle the pressure the jack will be exerting.
These fittings were inexpensive, and it pays to use fittings certified for hydraulic pressure, rather than plumbing fittings which might rupture under that pressure.
The gauge sells for about $22 at McMaster-Carr. It is a 2.5-inch diameter dial, glycerin filled, 0-10,000 psi range, 1/4-inch pipe-thread bottom-connected, Model #4053K16.
But, the same supply-house where I bought the fittings, had a very similar gauge for only $16. I bought one for a spare while I was there.
I have temporarily hooked up gauges to lower-pressure jacks with iron pipe fittings. But those plumbing fittings are not rated for the 8000 psi that will be developed in this new jack when it is putting out the full 6 tons of force.
Remember that when the gauge reads 8000 psi, that reading is multiplied by 1.5 to determine the force that the jack is exerting. That means an 8000 psi reading equals 12,000 pounds of force, the maximum force this jack is rated for. That’s why I chose a gauge with a range of 0-10,000 psi.
The Teflon tape is carefully wrapped on the pipe threads, in the direction that will tighten the tape wraps as the male threads are screwed into the female fittings. 4-5 wraps of the tape are put on each threaded section. I’m careful not to overlap the tape down onto the end of the fittings, where bits could break off and clog the channels or valves in the jack.
After the gauge was installed and all the fittings tightened up, I filtered the oil through a coffee filter and filled the jack back up with the oil through the fill hole on the back of the jack’s body. I pumped the jack up and down a few times to work any trapped air out of the system. Then the jack was installed on the rocket press.
I topped the oil off with more, new hydraulic-jack oil until it started to run out of the fill-hole in the main jack body. Then I installed the rubber plug.
I put my Pressure-to-Force gauge on the jack-plate, and jacked the press up to various pressures. This was to make sure that, indeed, the PtoF gauge read 1.5 times what the gauge on the bottle jack was reading. I also removed the PtoF gauge, and jacked the press up to its maximum pressure and let it sit there for a while to make sure it wasn’t losing any pressure through leaks or badly sealed steel-ball valves.
Everything worked great, so I moved the press into its permanent location on my work bench and attached it there with bolts which go through the two extra holes in the back of the bottom steel plate, and on through the workbench top.
Great! My fourth press is now up and running. Why the heck do I need four presses? I think I’ll paint and clean up my old Hobby Fireworks press and see if I can find a new pyro who wants to give it a good home.
There’s one final thing I thought about this press when it was done: “Hey, I built that thing. I know every part of it, and if anything goes wrong with it, I know how to fix it.”
I bought an extra bottle jack while I was working on the project, and drilled and tapped it at the same time as the main one. That way I have replacement parts, or the whole complete replacement jack if necessary.
This all results in a good feeling, and I suppose that’s why I do all of this in the first place.
Stay Green, and now on to more, ahh, Pressing matters.