46 replies to this topic

[ProfHawking]

I have some polycarbonate if you want, it's 6mm lexan. You would have to slice it up and laminate it i think.

[pyrotrev]

It mightbe worth going to your local plastics stockholder and seeing if they have any offcuts - mine sometimes does. Themain business of such people these days seems to be stuff for conservatories etc., but sometimes they have straight sheet polycarb.

[portfire]

Yeah thanx rob,just hang on to it for the time been i'm going to try pyrotrev's idea first.If i cant find anywhere i'll have it off ya


thanx guys
dean

Edited by portfire, 10 June 2007 - 08:45 AM.

[pudi.dk]

Made a plan of my press (Pictured without safety glass):



Do you suppose wood would stand a chance against the 8 t or can you see any problems contructing my press like this?
Please do not ask about the hydraulic jack, I don't know how it exactly looks, but my grandpa described it that way (he has it lying around, and I can get it for zero $). The handle is a swing handle and I'm thinking about connecting the handle to a motor, so it can be operated electrically with pedals or so.

My granddad also knows a toolmaker who might have some polycarbonate or channel bars I can have, keeping the total price of the press on a minimum.

Edited by pudi.dk, 11 June 2007 - 05:49 PM.

[ProfHawking]

my press is similar in design. I used wood originally, but it kept cracking. I had some nice aluminium plates made up in the end.


My BP is nice and fast, but not quite to the ideal density. A better jack has to go on the shopping list if i am to get it exact. Anyway, the aluminium doesn't compare to the the wood, it's def the way to go. Not as cheap though unfortunately.
If you have to use wood, i had the best results by using thick pieces of "Marine Ply", layered up and glued with extramite.

Edited by ProfHawking, 11 June 2007 - 01:53 AM.

[pudi.dk]

Edited by pudi.dk, 11 June 2007 - 05:48 PM.

[ProfHawking]

Ah i think i miss-read your diagram. So you have metal bars at the top & bottom, then yes i think the wood will be ok with that reinforcement, but perhaps a bit dented where it is under pressure. The springs are a nice touch i'd like to have as well, but i couldn't find any big enough...

[pyrotrev]

To give you an idea of the relative strengths of wood and metals:
shear compressive
Oak 3.7 5.....15
Steel 250 250
Aluminium 60....120 60....70

Since you've got metal "backing" pieces top and bottom, it won't fall to pieces, though you will have to be careful if you have large or off centre loads, since there's no metal backing piece on top of the ram.

Edited by pyrotrev, 11 June 2007 - 08:13 PM.

[pudi.dk]

Well I'm quite sure beech wood is a lot stronger than oak.

Since I only have beech for two boards they will be use as top and bottom besides the metal channels.
Then in the middle I might try to find a piece of metal, whatever I can find in the right thickness and price range.

[MFX]

The springs are a nice touch i'd like to have as well, but i couldn't find any big enough...

Big enough diameter, or big enough length (in which case use more than one )? Let me know what size you need I have a "selection box" of springs from R.S so I can see if there is anything suitable in that.

[dr thrust]

hi,may i ask what sort of pressure is needed to press say a 3/4 id rocket,then say if i moved up to 1" would the pressure need to jump a few tons ?,just asking for when i am buying a bottle jack. what are we talking 5-8 ton?

[dr thrust]

who's using a press put there and what have you got? i fancy a ten ton from machinemart but is it enough for a 6lb rocket grain? no point going over the top if i dont need it

[digger]

who's using a press put there and what have you got? i fancy a ten ton from machinemart but is it enough for a 6lb rocket grain? no point going over the top if i dont need it

I am using a press for all my rocket grains (30 tonne). I press 21mm ID rockets to about 4 tonnes which is probably a bit over the top as I can get away with 2.5 tonnes without problems. For your 6 pounders you would have 3.3 times the surface area so based on my experiernce I would be going to around 8.5 tonnes minimum.

There is a better calculation for the required pressures on the passfire site, however these pressures work for me.

[Draco_Americanus]

I use a 6 ton A frame press, it seems to be more then enough for 3lb rockets as i have split the case, I also use it with a 3 inch BP puck maker with out much problems, the plastic ram for the puck maker cost more then the press, it's solid delrin

Edited by Draco_Americanus, 28 December 2007 - 12:49 AM.

[Arthur Brown]

http://www.casupply....olidsheets.html

Has to be one of hundreds of suppliers of polycarb sheeting. They will cut to size and dispatch across the UK. Though there must be another one near you! Layers of 6mm will give added protection.