Japanese paper hemisphere tensile strength?

[wizard7611]

I've been wondering just how strong Japanese paper hemispheres are? I'm wanting to make my own but I don't know how strong to make them. Thanks!

[davidh]

I don't think they're strong at all. I think they are, however, quite brittle. If you look at a number of the videos and pictures of shell being assembled in Japan, you will notice that a large number of their hemis are made of newspaper, which is quite weak as far as paper goes.

[wizard7611]

I don't think they're strong at all. I think they are, however, quite brittle. If you look at a number of the videos and pictures of shell being assembled in Japan, you will notice that a large number of their hemis are made of newspaper, which is quite weak as far as paper goes.

 

Understandable. Does it matter what kind of paste you use? Do you paste one sheet at a time or can you do multiple?

[davidh]

I don't know what kind of paste they use, although I suspect it's some form of paste similar to wheat paste. I keep hoping there will be a video of them making a hemi, although I suspect it may be a guarded secret.

[Mumbles]

I'm not totally sure if you're talking about making the hemi or pasting the shell Wizard. Shimizu might have some information. I suspect they'd make the hemi all in one go. It feels like it would be a lot of work to do more than one session for anything except a giant exhibition shells. I've made news paper hemis a few times, but never for anything all that large or mostly for inner petals. That said, the real japanese newspaper hemis I've seen are thicker. For pasting, I'd imagine they use multiple sessions like with most hand pasted ball shells. I personally use a pasting scheme that lays down about 2 layers at a time. I typically lay down 3 of these per session, so 6 layers at a time, and let it dry before adding any more. If I go more than that I've had some issues with the shells getting a little spongey. I'll only do about 2-3 layers (max 4) on cylinder shells for the same reason. The crown and bottom can also get spongey due to all the overlap.

[Zumber]

On 12/7/2020 at 9:26 PM, wizard7611 said:

 

Understandable. Does it matter what kind of paste you use? Do you paste one sheet at a time or can you do multiple?

They paste multiple sheets at a time like two three or four.

And they are using very thin consistency glue ( almost like water )

Then it is kept in heater or sun then they are cutted and using sandpaper joints are cleaned to match them perfectly.

[Zumber]

On 12/7/2020 at 4:03 PM, wizard7611 said:

I've been wondering just how strong Japanese paper hemispheres are? I'm wanting to make my own but I don't know how strong to make them. Thanks!

I have read somwhere that Strength of inner hemisphere is not important ( it should be thick enough to joint at equator perfectly say 3 to 4 mm ) so in Japan shell above 10 inch size uses newspaper hemisphere than strawboard.

Kraft paper is costly than newspaper so it is only used for pasting of finished shells.

Tuning between burst charge strength and no of layers to be pasted should be optimum to get desired burst.

[Arthur]

A 16" hemi is about 10mm (3/8") thick that's a lot of volume that's not there for effects. The butt joint between the hemis is a weak point in the construction.

A paper hemi needs to be made inside a mould or outside a pattern, and needs to be dried carefully to make it properly round. I ONCE saw a technique of making small shells by using two sets of hemis put on with the equators at 90 degrees, lots of glue a little paper made for extreme confinement.

Making the moulds could be the hard bit of DIY hemis unless there is something retail that would do the job. 

[Zumber]

For moulds A wooden ball can do a great job this works very well.

If you dont have wooden ball then Second thing is just pour white cement mixture in plastic ball and let it dry then you will have ferfect globe this should be usful upto 6 inch else ball weight will be too high.

For bigger size say above 10 inch you can have plastic ball ( if not ) use commercial strawboard hemispheres joint both hemisphere having hole in one side and prepare mixture of sawdust and glue and fill it inside ball and dry it out and finally apply hardning gum above sawdust ball to increase surface hardness. Using these three methods you can paste papers dry it cut it and make paper hemispheres.

For mould design

Take hemisphere place it at perfect position in some plastic bucket or other plastic container and fill outer sides with concrete mixture or sand cement mixture and let it dry then remove hemisphere this will give you bottom mould for hemisphere in which you can put strawboard stencil and press it to prepare hemispheres.

For upper mould use same method prepare solid hemisphere made up of concrete or cement sand mixture.

I will attatch Its diagram.

Also watch this tutorial for work in action.

User have used wooden moulds

 

1 hour ago, Arthur said:

A 16" hemi is about 10mm (3/8") thick that's a lot of volume that's not there for effects. The butt joint between the hemis is a weak point in the construction.

A paper hemi needs to be made inside a mould or outside a pattern, and needs to be dried carefully to make it properly round. I ONCE saw a technique of making small shells by using two sets of hemis put on with the equators at 90 degrees, lots of glue a little paper made for extreme confinement.

Making the moulds could be the hard bit of DIY hemis unless there is something retail that would do the job.

 

[cmjlab]

Man, that's an impressive result.  Do you have a die cutter for those paper shapes, or do you cut them all by hand / scissors?  Either way, quality hemis! 

[Zumber]

You can design die cutter I cut them with scissors it doesnt make big difference as ultimately we are using sandpaper for final finish to match equator perfectly.

[Zumber]

The video link provided is not mine😀

I just have Impressed from it and Die design came to my mind and I just drawed it on paper and posted over here.

[cmjlab]

Well, thanks for sharing the video.  I'd never seen it before.  I respect that someone has the creative ability to come up with a method of making quality hemis.  I ont use them that often though, so I typically just order a couple hundred sets every other year or so.  Still cool though, and better quality than what I buy.

[Zumber]

Unfortunately we dont have access to hemisphere above 6 inch size.

I am gonna make 12 inch 8 inch wooden ball In upcoming days and I will prepare paper hemispheres using wooden ball by pasting newspaper over it.

[Zumber]

This was my last set up 5 years back But due to home renovation I lost wooden ball .

[Edwin]

(whole second half is about newspaper hemis)

[Zumber]

9 hours ago, Edwin said:

(whole second half is about newspaper hemis)

I already have downloaded this video and cutted wooden block and right now I am drying it before sending it to CNC operator to form wooden ball out of it.

I am curious about their very thin gum ( it could be Dextrin/SGRS glue?)

If anyone have idea please share.

Else I would go forward with thin wheat paste or other water soluble glue.

Thanks Edwin for reminder.

[ThunderEx]

Cool video. I wonder what the ball they pasted on was made out of? When he cut it in half it looked like newspaper under it??  Maybe it was wood after all with some sacrificial layer on top? My Japanese is really rusty  😁

[Edwin]

2 hours ago, ThunderEx said:

Cool video. I wonder what the ball they pasted on was made out of? When he cut it in half it looked like newspaper under it??  Maybe it was wood after all with some sacrificial layer on top? My Japanese is really rusty  😁

That's one of the questions I have too. U can use translated CC and although it may not be 100% accurate, you get an idea of what they're saying.

[Zumber]

9 hours ago, ThunderEx said:

Cool video. I wonder what the ball they pasted on was made out of? When he cut it in half it looked like newspaper under it??  Maybe it was wood after all with some sacrificial layer on top? My Japanese is really rusty  😁

Anything which should be hard can work as a former.

It should be light weight so that it is easy to work and flexible while pasting and handling.

I had discussion with Japnese technician he told that many factories uses wooden ball. There is ppssibility that few layers are pasted over wooden ball to withstand scratches during cutting it into hemisphere.

[ThunderEx]

7 hours ago, Zumber said:

I had discussion with Japnese technician he told that many factories uses wooden ball. There is ppssibility that few layers are pasted over wooden ball to withstand scratches during cutting it into hemisphere.

Sounds reasonable! It would need some sort of release agent on it also. That's another question 😁 Maybe it's simple as paraffin wax or something.

[Zumber]

39 minutes ago, ThunderEx said:

Sounds reasonable! It would need some sort of release agent on it also. That's another question 😁 Maybe it's simple as paraffin wax or something.

Last time I had covered wooden ball with thin wrapping plastic paper then pasted newspaper over it another thing is just dont use paste or glue for first 3 to 4 paper....just take 3 layers of newspaper damp it in plain water and apply it over wooden ball.