WARNING AND DISCLAIMER:  If you are underage, then consult with your parents or guardians before attempting any of this.  You are on your own - I'm not responsible for your actions or harm you may bring to others because of your actions.  Making the items described below  can result in injury or death to you or people in your vicinity. Some things mentioned here may be illegal to make in your city, county, state, or country so check the laws that apply to you before you attempt anything described here. These notes are not complete on purpose. If you are reading them and new to pyrotechnics, then you are making a mistake. Stop now - this page is not for you. Get a beginning book on fireworks (see Skylighter or American Fireworks News (very quick shipping)  for a start) and read up. You can't make any of this work without more information so read up or join a club or ask someone to help you.

Tapping a Jack

This article was inspired by Ned Gorski's article in Skylighter. Click here to see his article for how to tap a 6 ton jack

Why do you want to 'tap-a-jack', that is, rig up a jack so it has a pressure gauge on it?  Well.. mainly, you want to make consistent rockets and press BP and comets accurately.  You must use some sort of pressure measuring device. One way is to add a pressure gauge to your hydraulic jack. Making or buying a Pressure-to-Force (PtoF) gauge is another way.

Ned Gorski decided to write an article for Skylighter about tapping a 6 ton jack and I used his inspiration to tap a 12 ton jack. This instruction is slightly different than Ned's but tapping a jack is going to be similar no matter what kind of jack you use. See Ned's article on tapping a jack at: 


While you are there, look at some of his other articles. Weekly, he is documenting his experiences and techniques with pyro - it is a great resource made by a master pyrotechnician.


Ok.. Here is how to tap a 12 Ton Chinese jack - the kind that comes with Harbor Freight's 12 ton press

12 ton Harbor Freight jack

Clean off outside hardware

Drain jack through side vent (your jack may have
different placement of oil drain)

Remove outside pump housing

All outside hardware should be removed and
carefully saved

Secure jack in large vise or press and take off
the top - be prepared to use some force. I beat the crap
out of this one with a 4lb dead blow hammer

When top comes free it will look something like this. At
this stage measure the diameter of the piston you are
removing. Convert that to area. The result is the multiplier
for your pressure gauge. This piston was 1.7 inches.
The area was 2.27 inches (I rounded it to 2.3 inches)

Pull top off and you see inner chamber. This one
was put on by Hercules - I couldn't get it off so I left
it and did the drilling with it in place. There will be a 
gasket on bottom of the outer case. Remove it if you 
can - protect it from dirt and swarf.

Drill a horizontal hole from the sprue flat on the side
of the base to near center of the base. I used a
1/8" drill

Drill down from the top inside the high pressure chamber
and meet your horizontal 1/8" hole. I used a  long
shank bit and hand drilled it. The bit is 1/4".

Drill a proper tapping hole for a 1/8 NPT tap in
the side of the horizontal hole you drilled earlier
(a Q bit is recommended)

Tap the hole with a 1/8" NPT tap

Finished item - cleaned thoroughly with solvent
and blown clean with compressed air

You can see the vertical hole at the bottom of this
picture. It goes down and meets the horizontal
hole you made.

Reassemble jack. Use Teflon tape and install a
 1/8" NPT to 1/4" NPT adaptor. Be sure to use
only high pressure fittings do not use air fittings!
Get fittings  from a hydraulics parts place such as Surplus 
Center or eBay or perhaps a local place..

Using the Teflon tape to make sure there are no
leaks, put on a 90 degree elbow and a 5000 psi
oil filled gauge. You would need a 10000 psi
gauge for a 6 ton jack.

Open side of jack and put in fresh oil

Notice oil above - it came out of a new jack and it
was filthy. I elected to put in clean hydraulic fluid

The hard work is done! Time to get messy. Add 
1/2 pint of fluid then jack it up and down a few times to 
clear the air bubbles. You might want to loosen the 
gauge and bleed any trapped air out of the plumbing 
you installed. It is important to get the air out of these. 

Calibrate the gauge or use the multiplier you
 developed when you measured the diameter of the inner 
piston. For this jack the multiplier was 2.3 since the jack
piston was 1.7 inches in diameter - which made 2.27 sq
inches of area. I rounded up to 2.3 for convenience.