Silicone mold help

[Slo_Snipe]

Sorry if the pics are blurry.






Hi this is my recent work. These are spoon SW388 im trying to replicate.

The first problem about the mold is that after Ive done pouring for the first 2 wheels, the other wheels seem to get stuck, resulting incomplete parts while having a lot of resin build up on top of the sprue.

Second problem I have is that the inside of the wheel where it goes on the fujimi uprights have a huge air bubble on each wheel. What should I do next time to prevent it?

The third problem is on the face of the wheel, where the rim is. There are another small air bubble on the rim of each wheel. I thought it would get filled up as it is not the highest point of the part.
I know some of you had experiences with replicating using silicone. Thank you in advance for any help. This is my second mold I made, the first one has failed. I use alumilite high strength 2 to make the mold.

[bill_kustomz]

use mold release

[simdel1]

the problem is that you are trying to make the resin work against gravity. pour it in from the two other holes and it should work better.

i dunno what to do about the bubbles though, sorry.

[dread_darven]

Maybe this link could help http://www.childofmecha.com/Modeling/Resin/Resin.htm

[bvia]

I work with Smooth-On products, but they should be all about the same.

1. The quickest way to make this mold work is to pour the resin into the open face of the wheel fronts, then close the mold and pour the remaining resin into your pour vents. This should allow you to complete the wheels using this mold

2. When creating a "complex" mold, you have to really think about how to get the air to escape. On the wheel backs, I attach a piece of alluminum tubing of the same diameter as the attaching pin (or hole) with clay while casting, and then remove it to allow the resin to flow into the hole.

What I think is happening with your mold is that you are either working too slowly (resin is blooming too fast) or you have the incorrect resin (try getting some that allows for a longer working time).

I'd bet that if you made a front wheel mold and a rear wheel mold and then used that to cast the wheels one at a time, you would have a much better product (instead of trying to cast all 4 at the same time).

hth,

Bill

[dag65]

Originally Posted by simdel1

the problem is that you are trying to make the resin work against gravity. pour it in from the two other holes and it should work better.

i dunno what to do about the bubbles though, sorry.

I agree, your mold looks fine , but you are trying to dill it through the vent hole. I don't agreew ith bvia however on pouring half and then putting the halves together to finish the pour, verfey messy>
Have you looked at the How To I wrote? There are suggestions there on limiting air bubbles

[Slo_Snipe]

I've read your how to, but I can't find some equipments I need, so I used foot powder instead of mold release (I also went through some websites in google telling me to use baby powder...which is foot powder I think...), a tip of an icing bag for a small funnel.

Alumilite suggested heating the mold before each casting and they said to microwave it for a few minutes. I did that as well.

They also tell on their website that refrigerating the B part of the resin before mixing/pouring/casting will give me an extra 60 seconds before its work time kicks in. I will try that now first.

My resin usually starts to harden within a minute of being mixed good. Would that be too little time for them to even go through the whole mold?

[JTRACING]

theres a section in the faq on casting your own parts, i was just looking at it today

http://www.automotiveforums.com/vbul...d.php?t=188447

http://www.automotiveforums.com/vbul...d.php?t=189039

[dag65]

Ahhh , now I can help you. You should be okay with the powder, but you could try something like PAM cooking spray for a release. Now the real problem, your resin is setting up before it has a chance to fill th emold. Mine doesn't start to kick for 45 minutes or so. That could be too slow in some cases.
Keep trying you are close, you just need the right resin. You r mold looks great, well thought out.
D

[Slo_Snipe]

Thanks dag for the help. I think I will need to buy some different resin now. These materials sure are expensive...So far i have spent around $80 already. This is actually how I pour the resin. The pic on my first post with the vent hole filled was because I was doing a desperate move after the resin never came back out for the 5th time.




I also took a few pics of the part being tested on the car. An example of a spoon CTR with unpainted SW388. Only the front wheels though, it was the best one Ive done so far.

before, those are just box stock wheels painted black.


after:



Alumilite makes a slow set version of resins that they claim to have a working time of up to 7 minutes. Do you think that would be enough for the size of my mold? Or are there better brands that I can look for?

Thanks and wish me luck!

[hirofkd]

You should have placed the wheels tilted, so that it would have made the air escape easily.

You can still tilt the mold when you pour resin, but I really recommend two stage casting instead.

First, mix very little amount of resin and apply it just thick enough to cover the rims and spokes, and also the plycap socket. After the resin is cured, put two halves together, and mix another cup of resin and pour it into the mold as you normally do.
That way, there will be no bubble and you won't waste any resin at all.

Cooling the resin does help, too. Next time, choose the right kind of resin to match the complexity of the mold. You need at least 5 min. of working time for hassle-free resin casting.

[bvia]

Originally Posted by dag65

I agree, your mold looks fine , but you are trying to dill it through the vent hole. I don't agreew ith bvia however on pouring half and then putting the halves together to finish the pour, verfey messy>
Have you looked at the How To I wrote? There are suggestions there on limiting air bubbles

Dag,
I use Smooth-On's 5 minute "Liquid Plastic" resin and have no problems using the 2-pour method. When I made the mold for my 5-spoke Speedline's to go on the F50 GT1, I had problems with air bubles in and around the wheelnut. By filling the lower portion of the mold (the face of the wheel as my mold is split at the back of the spokes), removing all the bubbles (breaking them with a pin) and then closing and completing the pour (through the gate which was created on the back sidewall of the tire at 3, air escape at 6 o'clock and also an air escape hole (directly in the center of the wheel, where Tamiya put's it's mounting pins) I was able to correct the problems I engineered in my molds.

Smooth-On also suggests that I can do a two-part pour in where I completely allow the face of the wheel to cure and THEN closed the mold and pour the back-half as the resin WILL stick to ther resin and be prefectly unnoticable in the finished piece.

Luckily I have yet to be forced to do this.

hth,

Bill

[bvia]

Originally Posted by Slo_Snipe

I've read your how to, but I can't find some equipments I need, so I used foot powder instead of mold release (I also went through some websites in google telling me to use baby powder...which is foot powder I think...), a tip of an icing bag for a small funnel.

Alumilite suggested heating the mold before each casting and they said to microwave it for a few minutes. I did that as well.

They also tell on their website that refrigerating the B part of the resin before mixing/pouring/casting will give me an extra 60 seconds before its work time kicks in. I will try that now first.

My resin usually starts to harden within a minute of being mixed good. Would that be too little time for them to even go through the whole mold?

I use Smooth-On's Omoo30 and have yet to be required to use mold release while casting. The silicone has oils which aid in demolding. I only use Mann's 800 Release when I'm creating a 2-part mold and then only to facilitate the removal of the lower silicone mold half from the upper.

If your resin starts to harden within a minute of being mixed...you've found your problem. Mine starts to bloom in 3-5 minutes (depending on amount of resin being used...more volume blooms quicker) and can be demolded in about 10.

hth,

Bill

p.s. Remember when you cool the resin that it is hygroscopic, so don't stick in the fridge and then pull it out into a really warm enviroment or it will literally suck the humidity from the air and go bad. Cool only the amount you need.

[Slo_Snipe]

Hey thanks guys! Reading you all's response Ive learned a some things I never knew before, or have missed out when actually making the mold.

I never tried brushing resin and then pouring resin to make a complete mold. I always had a doubt that once the part is taken out I would see my wheels come out in several pieces. I will try this method the next time I do resins.

Next mold I make, I will also slant the original to avoid bubbles too. I will show you guys some complete cast parts later after I achieve these things.