What PSI should 70/30 benzo whistle comp be pressed at?

[SSHPyro]

I plan on picking up a press soon along with some appropriate tooling to make some whistle rockets. I want to grab a pressure to force gauge off woody and was wondering the proper amount of force needed to press them so I can avoid katos. I'm making 70/30 perch/benz comp and pressing 4oz rockets.

Edited November 16 by SSHPyro

[Zumber]

Plus one question I need to add here on your post.

I don't have remote operated press but have manual one. Is there any safe and tested way that I can proceed for whistle or do I just postpond it till I have remote operated press.

[FrankRizzo]

I wouldn't go any lower than 8800 for 70/30. The slower mixes like Dan Thames' super whistle fuel can be pressed at 7000 PSI.

For a 4oz rocket (1/2" bore), 8800 PSI would be ~1700 lbs of force.

Edited November 16 by FrankRizzo

[LiamPyro]

If I were you, when it comes to picking a press, I’d pick one that has the ability to press with plenty of force for your future pyro needs (larger diameter rockets, comets, star plates). Run some quick calculations around force /pressure for a given surface area. Total force required to achieve the same PSI scales exponentially with the radius of the surface. Think ahead to the biggest devices you can see yourself wanting to press. Presses are big and bulky, so it’s nice not to have to make space for more than one… coming from someone who owns a 1 ton arbor press and wishes I’d just bought a 10+ ton hydraulic press instead.

[cmjlab]

On 11/16/2024 at 10:20 AM, Zumber said:

Plus one question I need to add here on your post.

I don't have remote operated press but have manual one. Is there any safe and tested way that I can proceed for whistle or do I just postpond it till I have remote operated press.

Most people in the U.S. in the hobbyist realm consider "remote" to be a commercial requirement and expense.  For a lot of us, a plexiglass shield, or a shield of some sort between you and the comp you are pressing is the main safety factor.  If you can afford to buy a premade powered hydraulic press geared towards pyro, then extended hydraulic lines to get the motor away from the como by 8-10 feet (a different room would be better) often come with it, as well as a plexiglass shield (usually a couple sheets laminated together).

Another thought I read about is making sure your two halves are oriented that in case your rocket explodes during pressing, the largest chunks of metal may be directed off to the sides instead of towards you.  I have no idea if that's true, but it seems to be a fairly simple step, so I do it anyways.  

So after all that, I think it largely boils down to your risk tolerance.  Gold standard would prob be a steel shield, and a means of remote pressing.  Next would be an affordable shield if plexiglass with a couple layers, ir even thick plywood - anything to slow down any shrapnel.  Not very smart would be no shield at all, and sticking your face right in front of the rocket you are pressing.....:-)

[cmjlab]

On 11/16/2024 at 3:09 PM, FrankRizzo said:

I wouldn't go any lower than 8800 for 70/30. The slower mixes like Dan Thames' super whistle fuel can be pressed at 7000 PSI.

For a 4oz rocket (1/2" bore), 8800 PSI would be ~1700 lbs of force.

8800 seems to be incredibly high, is there a reason for this?  7500lbs on the comp has served me well so far, and all I've ever used is the 70/30/+1% Saly and K Benz.

Edit:  I should clarify I'm not arguing with you or doubting your methods.  LaDuke I think has mentioned using 9k before, but I've never understood why.

Edited November 17 by cmjlab

[Zumber]

5 hours ago, cmjlab said:

Most people in the U.S. in the hobbyist realm consider "remote" to be a commercial requirement and expense.  For a lot of us, a plexiglass shield, or a shield of some sort between you and the comp you are pressing is the main safety factor.  If you can afford to buy a premade powered hydraulic press geared towards pyro, then extended hydraulic lines to get the motor away from the como by 8-10 feet (a different room would be better) often come with it, as well as a plexiglass shield (usually a couple sheets laminated together).

Another thought I read about is making sure your two halves are oriented that in case your rocket explodes during pressing, the largest chunks of metal may be directed off to the sides instead of towards you.  I have no idea if that's true, but it seems to be a fairly simple step, so I do it anyways.  

So after all that, I think it largely boils down to your risk tolerance.  Gold standard would prob be a steel shield, and a means of remote pressing.  Next would be an affordable shield if plexiglass with a couple layers, ir even thick plywood - anything to slow down any shrapnel.  Not very smart would be no shield at all, and sticking your face right in front of the rocket you are pressing.....:-)

Thank you for response..!!

[Guernica]

Not to be pedantic, but speaking of blast shields of various sorts, my understanding is that if you go the transparent route, plexiglass (which is acrylic), should be avoided in favor of the significantly more impact resistant polycarbonate options (lexan etc). Please correct me if I'm wrong, as I'm actually wanting to build a blast shield myself right now & have a bunch of thick plexiglass I'd love to use if the community consensus is that it's safe enough...

Edited November 19 by Guernica
Grammar

[cmjlab]

2 hours ago, Guernica said:

Not to be pedantic, but speaking of blast shields of various sorts, my understanding is that if you go the transparent route, plexiglass (which is acrylic), should be avoided in favor of the significantly more impact resistant polycarbonate options (lexan etc). Please correct me if I'm wrong, as I'm actually wanting to build a blast shield myself right now & have a bunch of thick plexiglass I'd love to use if the community consensus is that it's safe enough...

You are probably right on the polycarbonate vs. plexiglass, since i believe the military makes "bullet proof" or ballistic glass from laminated layers of glass and polycarbonate. I'd still argue that plexiglass is better than nothing at all, and a thick plywood or layered plywood shield with a small window covered with polycarbonate would be affordable option.

Thanks, good catch!

[FrankRizzo]

On 11/17/2024 at 4:07 PM, cmjlab said:

8800 seems to be incredibly high, is there a reason for this?  7500lbs on the comp has served me well so far, and all I've ever used is the 70/30/+1% Saly and K Benz.

Edit:  I should clarify I'm not arguing with you or doubting your methods.  LaDuke I think has mentioned using 9k before, but I've never understood why.

That's just where my whistle motors stopped failing. Lots of theories on taking the elasticity out of the tube wall, harder grains, etc. I'm a student of Duke's methods (if it CATOs, press it harder).

Edited November 19 by FrankRizzo

[cmjlab]

Fair 'nuff