23 replies to this topic

[parabolic]

Just starting this thread as I was taking the other one off topic;

I'm seriously thinking about casting a resin block. I have plenty of tooling available but to make an aluminium clam shell for 3lb rocket tube will require 1.5inch bore or slightly more and 10 inch length of aluminum block. As we know alumimum is not cheap and boring a hole that long will be time consuming and just not pratical for me.
I also don't want really want to use plastic block due to cost too.

Has anyone or know of anyone that has made a resin clamshell before? and will it hold up to the pressure to keep the tube from splitting I know Dan williams made or had made for him resin bp puck die's

I won't be slicing it in half to make the traditional 2 piece clamp to remove the tube but instead will press the motor out after the last increment of fuel has been pressed.

Edited by parabolic, 03 August 2011 - 06:26 PM.

[helix]

Just starting this thread as I was taking the other one off topic;

I'm seriously thinking about casting a resin block. I have plenty of tooling available but to make an aluminium clam shell for 3lb rocket tube will require 1.5inch bore or slightly more and 10 inch length of aluminum block. As we know alumimum is not cheap and boring a hole that long will be time consuming and just not pratical for me.
I also don't want really want to use plastic block due to cost too.

Has anyone or know of anyone that has made a resin clamshell before? and will it hold up to the pressure to keep the tube from splitting I know Dan williams made or had made for him resin bp puck die's

I won't be slicing it in half to make the traditional 2 piece clamp to remove the tube but instead will press the motor out after the last increment of fuel has been pressed.

I haven't cast one but would have thought it would be ok. What about casting one out of scrap aluminium and machining it rather than buying an expensive block and then machining that?

[parabolic]

What about casting one out of scrap aluminium and machining it rather than buying an expensive block and then machining that?

casting aluminium requires it to be melted and a proper mold to be made and will involve a huge amount of saftey issues. by the time I found enough scrap, made a furnace/foundry, made a propper mold... it would be way cheaper to buy a block and bore it out.

helix, one of the main reasons I want to get away from machining a hole is because I don't have tooling to bore a 1.5mm 10" long hole.. thanks for your imput but I really want to avoid metal clamp system and stick with the resin idea.

Edited by parabolic, 03 August 2011 - 10:01 PM.

[dr thrust]

im thinking a two piece affair,, molding box on its side supporting a tube in the middle, pour resin to the middle of the tube, let set then place grease proof paper over the molded block/tube and cast over side?

Edited by dr thrust, 18 August 2011 - 05:45 PM.

[parabolic]

Dr thrust, that could be quite good way, only thing is I'd like to go one piece so I don't have to machine and use fixings to clamp the lot together around the tube.

the grease proof paper would be good for the block sides to stop them sticking, but if you just used one piece of grease paper and tried to cover the tube like you suggest, I reckon you would probably end up with air gaps at the corners of where the tube meets the resin block. I dont't think the resin would be heavy enough to make the paper press tighty against the tube and block sides when pouring the second cast, unless you helped it along by pushing and poking something on the paper. I think you may need 2 sheets of paper, one for each side of the block, then smear release agent on the tube, I bet that will give you a good tight impression.

[dr thrust]

i suppose you could try a little resin on some grease paper just to see if it sticks, how about just wrapping around the tube/mandrel in grease paper and casting around it simples!

[parabolic]

ahh well, ebay here we go for some resin 5kg for around 30 squid seems not bad

[dr thrust]

im no expert on the matter, but dont they have "aluminum casting powders" that you add to resin to bulk it up?, so you could end up with an ali clamshell after all

[Peret]

IMHO, simple cast resin won't have enough tensile strength to do the job. It would be a pity to do all that work and see it crack on the press. Why not use a piece of PVC piping and metal hose clamps?

[parabolic]

Yes this is what I'm wondering if it will hold up to the pressures. I do not want to use PVC and hose clamps. I just don't like that idea. Dr thrust, yes there are many powders available, but sand is free , it just means that if I had to mill it it would kill my tooling very quickly, but I'm hoping it won't need any maching given that I will be presing the motor out.

I think I will just go a head and do it as experiment and test how much pressure it can handle before the resin block gives up?

Edited by parabolic, 04 August 2011 - 09:34 AM.

[a_bab]

I'm fairly sure it won't hold up well enough if you use sand. You'd rather need some chopped fiberglass, so you create a proper composite. Also, the resin is quite brittle by itself. It will eventually crack.

If you don't like the idea of PVC/clamps, I can tell you for sure that at least 2 of the "rocket God's" are keen about this system (Steve La Duke and Dan Thames). The explanation is simple: should the motor explode, a clamshell will hurt you in a more efficient way to say so then some PVC pieces along with some clamps pieces. This is obviously true for an Al clam shell you DON'T want to know what it can do to your press shield.

I'm also thinking more about whistles/strobes then BP rockets.

[dr thrust]

i wonder if one could me made out of a nylon block, instead of ali?

[parabolic]

i wonder if one could me made out of a nylon block, instead of ali?

that's what Gareth has already done, he mentioned it on the 'brass turning thread' look towards the bottom and you will see his post.

[dr thrust]

duh! my bad, i was thinking of it being used in a two piece design, i guess an ali one going off on the press doesn't Ber thinking about

[Vic]

Parabolic, what sort of rocket motors are you thinking of pressing?

I think you could have problems extracting BP motors with a solid sleeve and especially with motors in the 3lb range and nigh impossible with the loading pressures of whistle mix.
You may prove me wrong though!