Hemis from vermiculite and wallpaper glue

[pdfbq]

This is my way of making hemis. Its not perfect but for me it works better than making paper hemis because it is much faster.

 

The materials used are vermiculite, wallpaper glue and, as mold, some 2mm perspex.

I made a program to draw the shape for the mold. You can find and use it here: http://www.zaza-zebr...werk/hemis.html

 

First make very thick glue. Let the glue stand for an hour and then add the vermiculite.

I use 150 gram perlite and 200 gram glue (including water)

Mix well (with gloves) and let it stand for another hour or more.

 

Now you have to figure out how much of the perlite glue mixture you need for one shape.

Make a ball of it, put everything on baking paper, press the ball in the middle of the mold, fold the baking paper over it and press 1/2 to 3/4 tons.

Pull the paper off and gently press the shape out of its mold and push it gently over a round shape.

I use tennis balls here but I also make 4" hemis this way, see the last picture

 

I let everything dry and then 'paint' them two times with wheat paste.

 

It needs some practice but is faster for me than paper hemis.

Maybe somebody comes up with a better or different mixture.

 

EDIT: I made a mistake. I mixed up perlite and vermiculite. I changed it to the correct one now but in the quote below it's still perlite. Sorry for the inconvenience.

Edited September 1, 2011 by pdfbq

[allrocketspsl]

This is my way of making hemis. Its not perfect but for me it works better than making paper hemis because it is much faster.

 

The materials used are perlite, wallpaper glue and, as mold, some 2mm perspex.

I made a program to draw the shape for the mold. You can find and use it here: http://www.zaza-zebr...werk/hemis.html

 

First make very thick glue. Let the glue stand for an hour and then add the perlite.

I use 150 gram perlite and 200 gram glue (including water)

Mix well (with gloves) and let it stand for another hour or more.

 

Now you have to figure out how much of the perlite glue mixture you need for one shape.

Make a ball of it, put everything on baking paper, press the ball in the middle of the mold, fold the baking paper over it and press 1/2 to 3/4 tons.

Pull the paper off and gently press the shape out of its mold and push it gently over a round shape.

I use tennis balls here but I also make 4" hemis this way, see the last picture

 

I let everything dry and then 'paint' them two times with wheat paste.

 

It needs some practice but is faster for me than paper hemis.

Maybe somebody comes up with a better or different mixture.

 

well done mate I like the idea,I use wall paper paste on all my tubes because I can make rock hard tubes for say farfalles inserts thin walled but strong and my rocket motors when I roll them using wp in two days they are rock hard light weight,perlite?

[Killerinc]

Thanks I have been looking for a pattern for the last few days. Is the Mold diameter in mm ? what number would i need to put in to make 2", 3" and 4" Hemis I dont have any paper ones to measure so not really sure what the normal sizes are

 

 

 

EDIT: found sizes if anyone thinks they are wrong feel free to chime in

 

1" (actual size 7/8") paper hemis = 22.22mm

1-1/2" (actual size 1-7/16") paper hemis = 36.512mm

1-3/4" (actual size 1-5/8") paper hemis = 41.275mm

2" (actual size 1-3/4") paper hemis = 44.45mm

2-1/2" (actual size 2-1/4") paper hemis = 57.15mm

3" (actual size 2-3/4") paper hemis = 69.85mm

4" (actual size 3-5/8") paper hemis = 92.075mm

5" (actual size 4-5/8") paper hemis = 117.475mm

6" (actual size 5-5/8") paper hemis = 142.875mm

Edited September 1, 2011 by Killerinc

[pdfbq]

EDIT: found sizes if anyone thinks they are wrong feel free to chime in

Those are outer sizes. You need the inner size, the diameter of your ball shaped mold.

 

I will ad some manual to the program itself but for now, In short:

The inner circle should have the diameter of the inside of your hemi. So 'Mold diameter' should have for instance 65 (mm)

Then print it.

Then measure the inner circle (not the very small center circle) on your print and put what you measure (say 74mm) in 'Printer diameter*' and press 'Go' again.

Now print it again.

The inner circle should now be more or less be 65mm

Edited September 1, 2011 by pdfbq

[allrocketspsl]

Those are outer sizes. You need the inner size, the diameter of your ball shaped mold.

 

I will ad some manual to the program itself but for now, In short:

The inner circle should have the diameter of the inside of your hemi. So 'Mold diameter' should have for instance 65 (mm)

Then print it.

Then measure the inner circle (not the very small center circle) on your print and put what you measure (say 74mm) in 'Printer diameter*' and press 'Go' again.

Now print it again.

The inner circle should now be more or less be 65mm

 

worked perfectly thanks mate

Edited September 1, 2011 by allrocketspsl

[Killerinc]

I am going to have some molds made for me at a cnc shop. what size should the hemis molds be for a 1" , 2" and a 3" shell Edited September 10, 2011 by Killerinc

[pdfbq]

I am going to have some molds made for me at a cnc shop. what size should the hemis molds be for a 1" , 2" and a 3" shell

I never tried 1" and 2", only made 3" and 4" but the idea is that you need two molds, the ball part and the star shaped part.

 

Say if the hemi you want to make has an OD of 69.85mm subtract the wall thickness (say 2mm) of the hemi, so 69.85 - (2 x 2mm) = 65.85mm

Now this (65.85mm) should be the diameter of your ball mold and the size of the inner circle of the image that the program creates.

 

My tennis balls where a bit smaller so I used for the 3" hemis 65mm and for the 4" 86mm.

 

When they have dried I glue the segments together by painting the hemis with wheat paste.

 

[Arthur]

Just please help me to understand WHY you need to make hemis. Paper hemis when used correctly leave only biodegradable rubbish which isn't too hazardous to the environment. Plastic hemis leave sharp shards of plastic to litter the place for everwith the risk of hurting animals or children, vermiculite bound in a biodegradeable glue may not be all bad, but in a stable adhesive there will be bits of litter there for years, which in areas where fireworks attract the adverse attention of the law could be the very evidence needed to convict you.

[Killerinc]

Thanks pdfbq for the help.

 

@Arthur not sure who your talking to if it is me i will be using Kraft paper or newspaper to make my Hemis so i will leave only biodegradable rubbish which isn't too hazardous.

 

 

[pdfbq]

Just please help me to understand WHY you need to make hemis. Paper hemis when used correctly leave only biodegradable rubbish which isn't too hazardous to the environment. Plastic hemis leave sharp shards of plastic to litter the place for everwith the risk of hurting animals or children, vermiculite bound in a biodegradeable glue may not be all bad, but in a stable adhesive there will be bits of litter there for years, which in areas where fireworks attract the adverse attention of the law could be the very evidence needed to convict you.

WHY make hemis? Because i like to make fireworks. I know one can buy hemis, one can buy fireworks too.

Environment? My glue is starch based. Vermiculite is used in agriculture to improve soil.

Come on. I'm not in the US, The police crawling through the woods collecting evidence trying to convict a firework crook?

[Bonny]

WHY make hemis? Because i like to make fireworks. I know one can buy hemis, one can buy fireworks too.

Environment? My glue is starch based. Vermiculite is used in agriculture to improve soil.

Come on. I'm not in the US, The police crawling through the woods collecting evidence trying to convict a firework crook?

 

Neither is Arthur.

 

I REALLY doubt in the US that cops would be crawling through the woods etc...

[Mumbles]

If they can't catch you from inside their car, the likelihood of getting in trouble is greatly reduced.

[Arthur]

As you like! make hemis for the fun, but I still prefer paper hemis. From a construction point of view all the rules of thumb are for paper hemis to get good breaks and burst radius. Paper hemis with paper pasting is the conventional method, and I know that shell size, star size and burst powder are related numbers, I can get ideas from Shimizu and others. Plastic hemis break differently and need practise, vermiculite hemis will break differently again, you will have to make up your own rules of thumb.

 

One UK person had his run in with the law simply because he annoyed the neighbours, the neighbours complained and his house got raided, it's always best to avoid getting into trouble rather than trying to get out of it later.

[pdfbq]

If they can't catch you from inside their car, the likelihood of getting in trouble is greatly reduced.

Oef... just ALMOST got caught by motor police, have to think of those guys too here .

Anyway... he did not get off his motorbike to search for vermiculite . Guess I was not in his perpetrator profile... Lucky me!

[schroedinger]

Hi

Does someone have a copy of the program in the first post?

The site itself is down to a mysql error