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.Making a Pressure to Force Gauge

The Cheating Way

This article was inspired by Andy H's post on Passfire. Others have done this so this article is not originalWhy do you want to make a Pressure to Force gauge, that is, rig up a hydraulic gauge so it can measure how hard you are pressing something? 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 a hydraulic cylinder. You can buy a Pressure-to-Force (PtoF) gauge but it will cost almost $100 plus shipping. This setup will cost about $39 and be every bit as good.

Ok.. Here is how to make a Pressure to Force Gauge by Cheating

10 ton Harbor Freight short bodied ram. Part number |
Blunt the end of a metal screw and stick it in |

Brace the ram and take off the quick disconnect |
Pull the screw so the ram comes up out of the |

Refill the cavity with fresh hydraulic fluid - make sure there |
Put some Teflon tape on a 3000 psi gauge and screw it into the body. The gauge is available from many sources including Harbor Freight, Surplus Center, and eBay. . It should be liquid filled with a bottom opening. Note the hydraulic fluid on the table - left over from squishing the ram too hard (see the panel to the left). ;-} |

Calibrate the gauge (PSI will be approximately |
You now have a finished PtoF gauge - it took five |

Using the PtoF GaugeThe short bodied ram has a lip on the bottom so the ram acts like a bigger jack - you can see that in the picture below. The diameter of the cylinder is a tad over 1.69 inches. I rounded it to 1.7 inches and then found the area - which was ~2.27 square inches. I rounded that to 2.3 to simplify calculations. The rounding of values will make the actual readings a little high but the gauge accuracy will shadow slight differences anyway.

Here is a dissected ram:

Example calculations for typical rocket sizesLet's say you are using a 3/4" ram and the readout on the gauge is 1000. That means the actual pounds per square inch is 2300 and because the 3/4" ram is only .44 square inches, the actual pressure is 2300/.44 or about 5227 on the composition. That is usually good enough for most rocket mixes but, on this 3/4" example, you might want to go to 7000 (1300+ on the gauge) for whistle - especially if you are going to store them for any length of time.

The following calculations are approximate but close enough to give you consistency.

ram=3/8 (0.375) area = 0.1104

217 on the gauge = ~4527 on comp

326 on the gauge = ~6790 on comp

434 on the gauge = ~9054 on comp

ram=1/2 (0.500) area = 0.1964

326 on the gauge = ~3819 on comp

434 on the gauge = ~5092 on comp

543 on the gauge = ~6366 on comp

652 on the gauge = ~7639 on comp

760 on the gauge = ~8912 on comp

ram=5/8 (0.625) area = 0.3068

434 on the gauge = ~3259 on comp

543 on the gauge = ~4074 on comp

652 on the gauge = ~4889 on comp

760 on the gauge = ~5704 on comp

869 on the gauge = ~6518 on comp

1086 on the gauge = ~8150 on the comp

1304 on the gauge = ~9778 on comp

ram=3/4 (0.750) area = 0.4418

652 on the gauge = ~3395 on comp

760 on the gauge = ~3961 on comp

869 on the gauge = ~4527 on comp

1304 on the gauge = ~6790 on comp

1739 on the gauge = ~9054 on comp

ram=7/8 (0.875) area = 0.6013

869 on the gauge = ~3326 on comp

1304 on the gauge = ~4989 on comp

1739 on the gauge = ~6652 on comp

2173 on the gauge = ~8315 on comp

2608 on the gauge = ~9978 on comp

ram=1 (1.000) area = 0.7854

1304 on the gauge = ~3819 on comp

1739 on the gauge = ~5092 on comp

2173 on the gauge = ~6366 on comp

2608 on the gauge = ~7639 on comp

3043 on the gauge = ~8912 on comp (recommend 5000 psi gauge)

ram=1 1/8 (1.125) area = 0.9940

1304 on the gauge = ~3018 on comp

1739 on the gauge = ~4024 on comp

2173 on the gauge = ~5030 on comp

2608 on the gauge = ~6036 on comp

3043 on the gauge = ~7042 on comp (recommend 5000 psi gauge)

3479 on the gauge = ~7952 on comp (needs 5000 psi gauge)

ram=1 1/4 (1.250) area = 1.2272 (5000 psi gauge needed)

1739 on the gauge = ~3259 on comp

2173 on the gauge = ~4074 on comp

2608 on the gauge = ~4889 on comp

3043 on the gauge = ~5704 on comp (recommend 5000 psi gauge)

3479 on the gauge = ~6557 on comp (needs 5000 psi gauge)

3913 on the gauge = ~7334 on comp ( needs 5000 psi gauge)

4347 on the gauge = ~ 8149 on comp (needs 5000 psi gauge)

ram=1 1/2 (1.5) area = 1.767 (10000 psi gauge recommended)

3043 on the gauge = ~3954 on comp (recommend 5000 psi gauge)

3479 on the gauge = ~4527 on comp (needs 5000 psi gauge)

3913 on the gauge = ~5093 on comp (needs 5000 psi gauge)

4347 on the gauge = ~5659 on comp (needs 5000 psi gauge)

4782 on the gauge = ~6225 on the comp (needs 5000 psi gauge)

5217 on the gauge = ~6791 on the comp ( needs >=6000 gauge)

5652 on the gauge = ~7357 on the comp (needs >= 6000 gauge)

6086 on the gauge = ~7923 on the comp (needs >=7000 gauge)