SSB's General Log

[Fleafa]

AH - You have an epic toy problem! lol

[SSB]

[Anvils Hammer]

[SSB]

Here is the result of my first attemp. (after the photos, the questions..)

I tried 'as an exercise' duplicating the small balls included in the Blood Bowl game set. I hope there won't be IP problems. It' is only ment as an exercise. I have a lot of these balls so I can destroy some without losing something important to me.

So the mold is crappy, I am going to make another one. The 'vents' were too small, I had to cut bigger ones and more of them... There are some defaults to the mold too.

Silicone mould


The casting was not made with the pressure pot. I was in a hurry to try, but it would be to late for my neighbours to endure... ^^
I just injected the resin with a siringue to put some pressure.

Casting views


Hum,

I had another problem. Both sides of the mold stayed "glued" to each other.

I did put some vaseline on the surface before I did pour the second silicone part. But it seems the vaseline didn't work at all to prevent both mold sides to srick together.

What should I use ?

Will the tips of the spikes of the ball reappear when I use the pressure pot ?
What will be better with the pressure pot ?

What should I do better in my mold and in my casting ?

[mangozac]

It's not uncommon to still require some force to separate them even when you use vaseline. I really can't imagine it not working at all

[SSB]

[mangozac]

That casts actually looks really good for being done at room pressure! Yes, using pressure should help in recreating the tips of the spikes. I can't see any bubbles so the pressure pot won't make a big difference there.

How did you clamp the two mould halves together? You have got a lot of flash, which will be minimised when there's enough clamping force.

For small parts like the footballs I think you would be better off doing a single part split mould, as described . That thread talks about using vacuum and pressure with the split mould, but judging from your current results if you were to repeatedly squeeze and release the mould while pouring the resin and then put it under pressure you should also get good results.

[SSB]

Here is the way I did hold it while pouring the resin in :



Maybe I should get stronger rubber bands ?

[mangozac]

Definitely need to be stronger rubber bands! I use the fat ones and wrap them around a couple of times if need be.

[geomod]

I agree with Magozac on this one.

A split mould is your best option (I made quite a few two part moulds before discovering the joys of split moulding), and uses much less silicone.

An addition to previous comments is that I use duct tape to 'leak proof', aid in support of the mould (I use 3mm MDF) and to add the overflow collar. While not reusable, even cheap duct tape works really well.


Cheers,

geomod

[Fleafa]

The hardboard is fine, but not when it overlaps the edge of the mould like that. With stronger bands it will start to bow or bend resulting in excess pressure of the mould edges, leading to mould slip, and too little pressure in the centre, leading to excessive flashing.
This is not a problem with thicker board (3-6mm).

[paulson games]

I was just about to say the same thing, you can have some overlap ove rthe edge, but having it go that far out causes the board to flex and it doesn't squeee the middle properly.


When you build your mold you can use the spray on mold release to help keep the two halves from sticking. You will need to give it a couple really good sprays to make sure everything is covered. Let each layer of spray dry for about 15-20 minutes before doing a second or third coat. It works just as good or better than the vaseline as long as you get proper coverage.

[mangozac]

Yeah good points guys. I generally cut a new set of boards to suit the mould from 3mm MDF (unless I already have a set from another mould the same size).

I also find that you don't want to go too tight with the rubber bands though as this can warp the casting.

[Anvils Hammer]

You dont need a lot of force to hold the mold together, what is important is that the force is distributed evenly and flat.

you always want the rubber bands to be as close to the mold as posslble, even going over the top of the molds as well if they do not get in the way of the pour.

THe sprue design is very wastefull of resin and rubber!

see attached image I made-

On the left- optimum design for a single peice split mold, blue line indicted the depth of the split. for this style you would pour, squeeze, pour squeeze untill no more bubbles come out, then pressureise it, also hammer it on the table abit while you squeeze.

on the right- optimum design for a two part mold- pour into the fill channel while hammering your fist next to the mold, untill you see resin in the air vents, no sqeezing required for this style, just pressure ideally.

To help with mold alignment and make the mold quickier, you could actually pour it as a single pour if you designed hte sprue correctly, then cut it like a split mold almost to the bottom, so the two "halves" are actually still attached. the blue line on the right mold shows whre this cut line would go.

hope ths helps,

AH

[mangozac]

I was intending to draw you up some diagrams like AH has, but couldn't find the time. But his diagrams are exactly what I would do too. Follow his advice 100%