resin casting problem question-rough finish

[busnproplinerfan]

I ran into a problem with my resin casting. I'm no expert and don't use a pressure pot although I have one. I made the mode form Smooth-On OOMOO-25, and the resin is Alumilite slowset 15. The cab I made has a rough looking finish but the mold is smooth. I did my best to mix the two parts of resin 1:1 by weight. I used a very light smear of vaseline to act as a demold.  I don't like the spray because I don't know if I can paint the parts after. I haven't had this problem before with resin and Alumilite is usually very easy to work with and good. This particular resin is over a year old, maybe that had something to do with it? I know this stuff has a good shelf life. Any ideas?

[Black Knight]

I think its more your vaseline reacting with the resin.

Try mixing some resin, a small amount and just leaving it in an aluminium bun dish or just on the smooth outside part of your mould, After its set peel it off and see what the surface is like

I use a Polycraft polyurethane resin. Its supposed to have a 3 month bottle life, the current bottles I'm using are from March 2000 and so far are ok. I find when my resin is going off it just doesn't harden anymore.

I also use a silicon two-pack rubber for moulds which is self-lubricating so I don't need or use a release agent

[busnproplinerfan]

7 hours ago, Black Knight said:

I think its more your vaseline reacting with the resin.

Try mixing some resin, a small amount and just leaving it in an aluminium bun dish or just on the smooth outside part of your mould, After its set peel it off and see what the surface is like

I use a Polycraft polyurethane resin. Its supposed to have a 3 month bottle life, the current bottles I'm using are from March 2000 and so far are ok. I find when my resin is going off it just doesn't harden anymore.

I also use a silicon two-pack rubber for moulds which is self-lubricating so I don't need or use a release agent

Good idea. I don't think I had problems with vaseline much but I might have put on a bit much. I try to rub just a little between my fingers to make them oily then rub it lightly in the mold. I usually do it for just the first pour. I tried again to but this time I filled the supplied shot glasses to exact amounts by calibrated eyeball. It seemed to work this time pretty good, made three cabs now that look ok. Looks to be a bit sensitive if your out by a tiny bit. The Alumilite I used this time was also a lot fresher, I know I got it recently withing this year. Might be the resin got old although Alumilite does last a long time. I used to used Smooth-On resin but it has such a short shelf life. The mold rubber they make is good, haven't tried the Alumilite mold rubber yet. I know there's others out there but i don't want to go crazy buying all of them, they get expensive fast.

[busnproplinerfan]

Think I got the problem worked out. I don't know what exactly the problem was. I opened new bottles of resin and it seemed to work. I also measure like the instructions said and used the plastic shot glasses that came with it.

My messy workspace, the parts with an X are scrap, they to soft, the mix didn't go right. That's when I started to measure by volume.

 

Lego makes great mold boxes. I use mostly paperboard. I don't have much lego, stuff's expensive. Also find newer lego breaks easier than the old stuff.

 

Most of these Kenworth parts are going into this wrecker, https://www.britmodeller.com/forums/index.php?/topic/235057045-2019-kw-t800-twin-steer-tri-axle-rotator-wrecker/page/2/

 

[Black Knight]

Good you got sorted

 

'Lego' is great for mould boxes.  I bought a mixed box of Lego-like bricks ages ago. Round my way they were far cheaper than the real Lego. Plus Lego has gone over to a lot of specially shaped bricks and its hard to get the plain ordinary ones now

When I build u[ the mould box I paint a coat of Copydex glue on the inside walls. Copydex is a rubber based glue. It seals the 'Lego' joints so my moulding rubber doesn't seep thru. The Copydex just peels off the set rubber mould

The polyurethane resin I use is mixed by weight, 1 to 1, so I use electronic scales. I try to be 100% accurate but the resin is quite forgiving if I get it wrong by a wee bit

[busnproplinerfan]

5 minutes ago, Black Knight said:

Good you got sorted

 

'Lego' is great for mould boxes.  I bought a mixed box of Lego-like bricks ages ago. Round my way they were far cheaper than the real Lego. Plus Lego has gone over to a lot of specially shaped bricks and its hard to get the plain ordinary ones now

When I build u[ the mould box I paint a coat of Copydex glue on the inside walls. Copydex is a rubber based glue. It seals the 'Lego' joints so my moulding rubber doesn't seep thru. The Copydex just peels off the set rubber mould

The polyurethane resin I use is mixed by weight, 1 to 1, so I use electronic scales. I try to be 100% accurate but the resin is quite forgiving if I get it wrong by a wee bit

I prefer measuring by weight especially when you don't have a clear container. But this stuff works better done by volume. Haven't heard of copydex.

[dickbarton99]

have u ever used fillerpowder in your resin  and do u know if  resin g26 is compat with g27 resin this is sylmaster resin

[busnproplinerfan]

On 10/23/2021 at 6:05 AM, dickbarton99 said:

have u ever used fillerpowder in your resin  and do u know if  resin g26 is compat with g27 resin this is sylmaster resin

Never used it, I heard of mircoballs, (maybe the same thing?)once but never tried it either.

[dickbarton99]

ok thanks

 

[Cheshiretaurus]

On 10/20/2021 at 7:29 AM, busnproplinerfan said:

The cab I made has a rough looking finish but the mold is smooth.

 

That texture on the cab looks like the texture of the layer of Vaseline I think. I've found I never need any mould release unless I'm making a 2 part mould and need to create a barrier between the 2 parts but that just in the mould making process.

 

On 10/23/2021 at 12:56 AM, Black Knight said:

Lego has gone over to a lot of specially shaped bricks and its hard to get the plain ordinary ones now

 

Lego have a 'pick a brick' service so you can get exactly what you need instead of buying a set. 

 

https://www.lego.com/en-gb/page/static/pick-a-brick

 

[busnproplinerfan]

6 hours ago, Cheshiretaurus said:

 

That texture on the cab looks like the texture of the layer of Vaseline I think. I've found I never need any mould release unless I'm making a 2 part mould and need to create a barrier between the 2 parts but that just in the mould making process.

 

 

Lego have a 'pick a brick' service so you can get exactly what you need instead of buying a set. 

 

https://www.lego.com/en-gb/page/static/pick-a-brick

 

Thanks. I think I did to much of the vaseline. I usually just rub a tiny amount on my fingers and very lightly wire the inside of the mold where I can reach. I found I had good parts without using it to. As toy said, yes you do need it between in two part molds especially when pouring the second because it will fuse otherwise. I do have a lego store here, just have to get to it sometime. They are pricey when buying individual pieces, guess that's how they make their money. But I also avoid amazon as much as I can, so I will likely pay more. It's a tool and we need tools.

[JPuente54]

@busnproplinerfan check Micro-Mark's website, https://www.micromark.com. They offer parts and supplies for resin casting. They may not be able to send the chemicals for the resin; but, can mail everything else needed to include measuring cups/beakers for the resin ingredients and the mold release chemicals. HTH

Joe

[busnproplinerfan]

2 hours ago, JPuente54 said:

@busnproplinerfan check Micro-Mark's website, https://www.micromark.com. They offer parts and supplies for resin casting. They may not be able to send the chemicals for the resin; but, can mail everything else needed to include measuring cups/beakers for the resin ingredients and the mold release chemicals. HTH

Joe

Thanks, I'll see what there is.

[Rob de Bie]

On 11/25/2021 at 8:07 PM, busnproplinerfan said:

Thanks. I think I did to much of the vaseline. I usually just rub a tiny amount on my fingers and very lightly wire the inside of the mold where I can reach. I found I had good parts without using it to. As toy said, yes you do need it between in two part molds especially when pouring the second because it will fuse otherwise. I do have a lego store here, just have to get to it sometime. They are pricey when buying individual pieces, guess that's how they make their money. But I also avoid amazon as much as I can, so I will likely pay more. It's a tool and we need tools.

 

I too would suggest deleting the vaseline, or any other release agent. Silicone rubber releases by itself. It does suffer from degradation by the chemicals in the resin, so after maybe 30 castings, it discolors and starts to stick more and more to the castings. With my combination of materials, I decided on a 20 piece production limit. If you're casting for your own use, 20 is usually way more then you need, so it's generally no problem.

 

Here's an example of one of my casting projects. No release agent was ever used, just silicone rubber and polyurethane resin.

 

 

 

Rob

[busnproplinerfan]

5 hours ago, Rob de Bie said:

 

I too would suggest deleting the vaseline, or any other release agent. Silicone rubber releases by itself. It does suffer from degradation by the chemicals in the resin, so after maybe 30 castings, it discolors and starts to stick more and more to the castings. With my combination of materials, I decided on a 20 piece production limit. If you're casting for your own use, 20 is usually way more then you need, so it's generally no problem.

 

Here's an example of one of my casting projects. No release agent was ever used, just silicone rubber and polyurethane resin.

 

 

 

Rob

Thanks, nice castings. There are a few small parts that I just put resin in the molds and they came out ok. I just had the mold rubber get stuck on a bit of the very small undercuts but nothing major. The parts you made here, did you pressure cast them? I have a pressure pot for painting but haven't used it yet. I was bugging Alumilite to make a resin that won't harden until it's maybe heated or something. Just so I'd have more working time. Might be years before that ever happens.

[Rob de Bie]

4 hours ago, busnproplinerfan said:

Thanks, nice castings. There are a few small parts that I just put resin in the molds and they came out ok. I just had the mold rubber get stuck on a bit of the very small undercuts but nothing major. The parts you made here, did you pressure cast them? I have a pressure pot for painting but haven't used it yet. I was bugging Alumilite to make a resin that won't harden until it's maybe heated or something. Just so I'd have more working time. Might be years before that ever happens.

 

I use a vacuum chamber for both making the mould and casting the resin parts. I consider that the 'European' method, and pressure casting the 'American' method. Both work well.

 

You make an interesting point about the pot life of the resin. Nearly all have a ~3 minute pot life, and that's too short to my taste. Luckily, Smooth-On makes a Smooth Cast 300 series resins with different pot lifes and curing times. I selected 305 as the most suitable for my method, and it has a 7 minute pot life. 310 would give you 15-20 minutes. Demoulding times are correspondingly longer, the brochure says 0.5 hour and 2-4 hours respectively. But again, if you're casting for your own purposes, that's not a problem.

 

Rob

[busnproplinerfan]

5 hours ago, Rob de Bie said:

 

I use a vacuum chamber for both making the mould and casting the resin parts. I consider that the 'European' method, and pressure casting the 'American' method. Both work well.

 

You make an interesting point about the pot life of the resin. Nearly all have a ~3 minute pot life, and that's too short to my taste. Luckily, Smooth-On makes a Smooth Cast 300 series resins with different pot lifes and curing times. I selected 305 as the most suitable for my method, and it has a 7 minute pot life. 310 would give you 15-20 minutes. Demoulding times are correspondingly longer, the brochure says 0.5 hour and 2-4 hours respectively. But again, if you're casting for your own purposes, that's not a problem.

 

Rob

I was using smooth-on resin, it is nice but it's short shelf life turned me off and would get very porous parts. I guess vacuuming or pressurising would help with but they don't tell you that. I still like their mold rubber. I can get smooth-on locally from an art store for very cheap but the alumilite I have to get from the company itself and the shipping across the border gets you, but it has a long shelf life. I've been trying to get that store to bring in alumilite. I also was never trained on it just learning as I go. Both are good in their own way. I see the pictures of smiling casters with gallon sized amounts in massive molds and wonder how they do that without it hardening while pouring.