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Question about resin casting


stevenoble
08-04-2013, 05:30 PM
I need a little help or maybe a few pointers. Basically I'm trying to cast the wheels from the 1/24th Tamiya Ford Escort Cosworth rally car. I've made the mold already and it seems to be a fairly good mold, as I've managed a couple of reasonable casts from it with minimal flash. The only problem I keep having is the area where the wheel nuts are on the face of the wheel. I'm getting the odd air bubble, usually right where I don't want it. Or the resin is just not filling that area so good when I add it to the mold. I'm thinking of making a very small batch of resin and coating the wheel nut area first allowing it to dry and harden, then assembling the mold and with a second batch of resin finishing the wheel. My question is will the 2nd batch of resin bond onto the first..?? I'm using a general purpose resin, but the supplier I got it from do a lower viscosity. Would the thinner resin help to eliminate my problems at all..??
If anyone can answer my question or even offer some advice as to a different way of approaching it I'd appreciate it...
Thanks in advance :smile:

freakray
08-04-2013, 06:06 PM
To answer the question regarding trying to cast the wheel in 2 stages, the resin will stick to itself but there's no guarantee of uniformity.

One trick I learned from Chris (C1), is to coat the mold with talcum powder, it helps the resin flow through the mold - by what wonder of science I am not sure but it works so I am not about to question it.

Wheels are always tricky to cast, I've cast a couple myself and had the same experience as you, the wheel nuts are tough to cast. On one set, I actually added the wheel nut detail after the fact.

stevenoble
08-04-2013, 06:18 PM
One trick I learned from Chris (C1), is to coat the mold with talcum powder, it helps the resin flow through the mold - by what wonder of science I am not sure but it works so I am not about to question it.

Thanks for the quick reply and the tip about the talcum powder, I really appreciate it. I shall give it a try tomorrow. Do I just apply a light dusting of powder with a brush over the whole inside of the mold..??

freakray
08-04-2013, 07:01 PM
Steve,
That is what I have been doing based on what I understood from Chris to do. It appears to have helped as I don't seem to get as many dead areas/bubbles.

stevenoble
08-04-2013, 07:11 PM
Ok, many thanks. I'll give it a go and report back later...

JeremyJon
08-04-2013, 07:22 PM
a very light dusting of talc will help with the resin somewhat, I use that without any spray on release agent

instead of pouring over the center or full of the open mould, try pouring in a thin stream at one corner, allowing the resin to move into the center detail area on it's own, and helps prevent trapped air further

what casting resin are you using?

stevenoble
08-04-2013, 07:44 PM
a very light dusting of talc will help with the resin somewhat, I use that without any spray on release agent

instead of pouring over the center or full of the open mould, try pouring in a thin stream at one corner, allowing the resin to move into the center detail area on it's own, and helps prevent trapped air further

what casting resin are you using?

I'm using a resin called Easy Flo 60 which I got from eBay. I've also got some that I ordered from Sylmasta, their general purpose casting resin. I've had fairly good results with both of them, except for the bubbles. Is there anything better you'd recommend?

JeremyJon
08-04-2013, 09:10 PM
I'm using a resin called Easy Flo 60 which I got from eBay. I've also got some that I ordered from Sylmasta, their general purpose casting resin. I've had fairly good results with both of them, except for the bubbles. Is there anything better you'd recommend?

Smooth-cast 305 or 321, comes out much like white plastic in feel & workability, you want resin with a little longer working time IMO, it allows air to escape, some people say to shake the mould after pouring, but personally haven't seen that help really, pouring into the corner works well I find too

flyonthewall
08-05-2013, 10:51 AM
Steve, Talc is indeed your best friend when it comes to casting. Dust talc in the mold and blow away the access to leave a fine film. It will break the surface tension of the resin so bubbles can't stick to the mold surface and become trapped. It also helps to wick the resin into small nooks and crannies. By using Talc you can eliminate almost all bubbles. The area you are having trouble with is notoriously tricky with wheels, how the resin feeds in and vents out of the mold is also a factor though.

Is the Sylmasta resin you use the G26 one? If so, that's a good resin, all SAS stuff was done using that but from another supplier. However, I would recommend the G27 low viscosity resin (also available there), but I prefer to use it with the white hardener. These are available at Resins-online and cheaper too.

The Easyflo-60 stuff is very common these days. It's very fluid but the cured casts continue to seep an oily residue for quite some time. Because of this I won't touch the stuff as it is not suitable to apply a painted finish to.

If you need any further help just shout.

stevenoble
08-05-2013, 11:42 AM
Steve, Talc is indeed your best friend when it comes to casting. Dust talc in the mold and blow away the access to leave a fine film. It will break the surface tension of the resin so bubbles can't stick to the mold surface and become trapped. It also helps to wick the resin into small nooks and crannies. By using Talc you can eliminate almost all bubbles. The area you are having trouble with is notoriously tricky with wheels, how the resin feeds in and vents out of the mold is also a factor though.

Is the Sylmasta resin you use the G26 one? If so, that's a good resin, all SAS stuff was done using that but from another supplier. However, I would recommend the G27 low viscosity resin (also available there), but I prefer to use it with the white hardener. These are available at Resins-online and cheaper too.

The Easyflo-60 stuff is very common these days. It's very fluid but the cured casts continue to seep an oily residue for quite some time. Because of this I won't touch the stuff as it is not suitable to apply a painted finish to.

If you need any further help just shout.

Firstly thanks for all the help from everyone, I appreciate it all. Chris, it is the G26 resin I have from Sylmasta. I may take your recommendation and get the lower viscosity G27. You're right about the Easy-Flo 60, it doesn't take paint so well..

flyonthewall
08-05-2013, 11:44 AM
P.S. You must use talc that is dry i.e. as fresh as possible. Don't use stuff that the wife has stashed away in the bathroom that is rarely used, talc soaks up moisture so if it has been there for a while it will be useless.

Capri-Schorsch
08-05-2013, 02:30 PM
To avoid bubbles from the surface,i always use a brush and brush a layer of resin into the mold.Than quickly close the mold and put the rest into the mold.
There are no bubbles on visible parts of the cast.
But best would be to show some pics from your mold and so we can find better solutions.

regards
Christian

stevenoble
08-05-2013, 04:41 PM
But best would be to show some pics from your mold and so we can find better solutions.

Ok, I have some pictures of the mold. Remember I've never made molds before so go easy on me.

This is the top half

http://i17.photobucket.com/albums/b61/stevenoble/Picture001_zps5a205e20.jpg

and this the bottom

http://i17.photobucket.com/albums/b61/stevenoble/Picture002_zps08c6f45f.jpg

The detail inside, the large hole in the middle is where the resin enters the mold

http://i17.photobucket.com/albums/b61/stevenoble/Picture005_zps01531eaf.jpg

The top hole where I pour in the resin

http://i17.photobucket.com/albums/b61/stevenoble/Picture004_zps7aa219a3.jpg

The cast wheel, this one was not bad, well by my standards anyway. Needs a little filler and a rub down on the outer rim where I still got a tiny bubble, but easy to fix..

http://i17.photobucket.com/albums/b61/stevenoble/Picture009_zpsd9becafa.jpg

Capri-Schorsch
08-05-2013, 04:53 PM
Hi Steve,
this should be no problem.
Use a big brush and brush both sides with a layer of resin.
Put everything fast together and fill the rest of the resin with a small beam(is this the right word?) into the mold.
Maybe you can shake your mold after the fill in a bit to put the air to the intake out.

Thats the way i make my castings.I never used any talc or stuff like that.
I only need a lot of brushes,but i got an big pack of them.

regards
Christian

flyonthewall
08-05-2013, 05:39 PM
This is my current method for male 'pin type' wheel fittings.

As the pin is a real bugger for trapped air, it's avoided altogether by using it as the inlet for the resin. My mold here is designed with a large reservoir built into the top half, I just fill each one and it's done! Vent sprues are located at four points on each wheel, I usually have to put the mold on a slight tilt to get the resin to vent properly.

My molds for 'female' fitments are done in a slightly different way using a central pour hole with channels to each wheel, and then vent sprues where needed.

http://i147.photobucket.com/albums/r286/scaleautostyle/2013-08-05222500_zps055797a5.jpg (http://s147.photobucket.com/user/scaleautostyle/media/2013-08-05222500_zps055797a5.jpg.html)

http://i147.photobucket.com/albums/r286/scaleautostyle/2013-08-05222537_zps8d1b4afc.jpg (http://s147.photobucket.com/user/scaleautostyle/media/2013-08-05222537_zps8d1b4afc.jpg.html)

http://i147.photobucket.com/albums/r286/scaleautostyle/2013-08-05222554_zpsa7f0c957.jpg (http://s147.photobucket.com/user/scaleautostyle/media/2013-08-05222554_zpsa7f0c957.jpg.html)

JeremyJon
08-05-2013, 07:31 PM
Steve, that mold looks fine, I would suggest then change the viscosity of the resin you are using, and if possible to one with more working time for you to have air escape before it starts to set

I can't comment on that specific product you quoted, as we get different stuff over here - across the pond - but as Chris suggested also, that should help you

Capri-Schorsch
08-06-2013, 02:16 PM
Thats how my molds of the BBS Style rims are look.

http://foto.arcor-online.net/palb/alben/73/3980473/3737636533316461.jpg


Easy to cast with.

regards
Christian

stevenoble
08-06-2013, 02:39 PM
Thanks for the pictures of your molds guys, that shows me what a good mold looks like..!! Got some good pointers now. I like the way you have nice clean molds and they lock together positively so you get a good cast everytime.
Christian, did you cast the tyres separately on your BBS rims..?? Is that just the same like a regular mold. I have the tyres to do for the Escort as well. Do you make a two part mold for the tyres as well..?? If you could post a pic or two of your tyre mold I'd appreciate it..

Edit: Now I look I think the tyre is cast with the wheel, all from the same mold..

Capri-Schorsch
08-06-2013, 02:57 PM
Hi Steve,
yes its all cast together.
I made the wheels/rims for my capri project.
So there is only one size to do,so i cast it together.
At the moment i cast some Porsche wheels with tires.The 5-spoke design in a 14"-15" size in 1/12 scale.
I made it in 14,5" size because so it fits on my current carerra rsr and a porsche 908 version.So i can use one mold for both cars.

regards
Christian

rgriffs
08-09-2013, 04:44 AM
i agree with the use of talcum powder, there is nothing wrong with your mould. a technique i use is to pour in some resin, work the bubbles out of the small details with a cocktail stick, then assemble the mould and complete the pour. it generally works for me.

MidMazar
08-09-2013, 07:41 AM
You can always invest in a vac chamber if your pouring resin a lot. http://www.ebay.com/itm/3-Gallon-Vacuum-Chamber-With-3CFM-Vacuum-Pump-purge-kit-for-degassing-silicones/111138258881?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%2 6asc%3D261%26meid%3D445304048741109755%26pid%3D100 005%26prg%3D1088%26rk%3D4%26rkt%3D5%26sd%3D2712545 63903%26

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