Casting a 3D Print

[Bearwood West Yard]

As it’s the weekend I’ve been working on my own resin projects rather than maintaining iron casting patterns. A bit more complexly shaped this one but it is mounted at 45 degrees. The runner and riser system took me a full afternoon and evening to do, though I did waste an hour on the lathe trying to face off part of some sprue plastic to use as a runner (in the end I gave up). 
 

All the runner/riser system for this casting is 4x3mm styrene strip, with the exception of the runner feeders into the pattern which are 1x2mm strip in two layers and given a radius. There is a choke point on the main runner and also on the runner feeders, to enable air in the difficult spots time to escape. Admittedly, the pattern I am using here is part of an existing C88 Salmon kit by Cambrian.

 

For pouring the silicone, I have previously used one of the clear Oxford vehicle boxes, though this is rather large for that. I’ve cut up some 2mm greyboard and stuck the box together on the outside with sellotape. The sides are 50mm high. For added strength on the joint lines and to prevent the silicone being absorbed by the greyboard, I have treated the box interior with some neat PVA glue via a large modelling brush. I put this over the radiator last night to cure quicker given how cold the modelling/bedroom room is and it only took an hour and a half to fully cure. This morning I’m planning to raise the pattern to about 30mm below the the top. Hopefully having a silicone pour by mid afternoon. I will add the locating dowels prior to pouring. 
 

[regme]

Thanks that's pretty informative, the plastic sheet is that about 1 to 2mm thick can it be anything.

[Phil Traxson]

14 hours ago, regme said:

Thanks that's pretty informative, the plastic sheet is that about 1 to 2mm thick can it be anything.

I have always used clear plastic as you can see that you haven't squeezed out too much resin and so allowed air to be drawn back into the casting. I look out for "Javis" clear sheet as it seems to release of the casting better even if you have been economical with the wax polish (must be wax, not wax free polish). "Slaters" just doesn't want to let go. Hard plastic packaging is often quite good too, a rough guide, I find, is that if you look at the edge of the plastic and it has a slight blue/purple cast to it it will usually do the job. For more delicate stuff like my various window castings I use really thin stuff, I was given a wad of overhead projector film about 10-15 thou thick some time back and it is excellent for the more delicate castings, Georgian multi pane & 1950's steel frame windows etc.

Edited January 11, 2021 by Phil Traxson

[Phil Traxson]

A follow on to the last two video's, showing de-moulding the castings, words to help understand it will be to-morrow.

https://flic.kr/p/2kqSrgp

 

Edited January 10, 2021 by Phil Traxson

[regme]

Thanks, it makes it easier when you see it being done.

 

I had another go, I took a vid but at 500Mb just a tad too big, so I took a screen shots to the best quality but the idea is there.

 

I also asked the supplier of the resin and they recomended using industrial talcum power to line the mould to help with reducing an static electricity and realeasing any air bubbles, however I'm thinking its the chemical reaction between parts A and B that creates the air bubbles.  I tried being gentle on the mixing but I'm not sure.

 

When casting the mould how do you stick the master down, I used super glue on some xray film, but it doesn't come off very well when I seperated the xray film, it left a residue on the master and I ended up cutting into the master.  Tried bee's wax that didn't work very well either, didn't stick the baseboard.  So any ideas would be great.

[Bearwood West Yard]

On 21/01/2021 at 10:56, regme said:

When casting the mould how do you stick the master down, I used super glue on some xray film, but it doesn't come off very well when I seperated the xray film, it left a residue on the master and I ended up cutting into the master.  Tried bee's wax that didn't work very well either, didn't stick the baseboard.  So any ideas would be great.

I've got some mould boxes I'm getting laser cut at the moment from 5mm Perspex, along with pattern plate inserts for these. I'll be sure to make another post once these are assembled. The way i have produced mine is by the good old double sided tape. 

 

I stuck mine to the bottom of the greyboard (same as what ill do on the pattern insert plates) and sprayed Macwax over it before casting the silicone first half. Macwax is essentially a wax based aerosol release agent. I just follow the instructions and usually all is well. Its the stuff we use at work as well so I can vouch for it over talcon powder.

 

Depending on how you plan to make your second half, it may be worth taking the master out (if you have detail notches that can be used to retain the pattern again) giving it a wash with a toothbrush to get rid of any tape residue, putting it back into the mould, Macwax-ing it all and then pouring the second half. This is the approach i have planned to take. I would also recommend the use of rubber bands to hold the mould together or quick release clamps and pair of small wood sheets to prevent excessive flashing and leakage. 

[regme]

Here is the molding box I made from 10mm acrylic it's a 100mm high by 100 x 300mm in length.  I used a PVC priming fluid it join it all up.  I use clamps to hold it together, so now I can have any size box I need.

 

When I made the two part mold I just brushed on vaseline on the silicone before pouring the second half on the mold, which worked pretty well.

 

I'll give the double sided tape ago, I guess there will be a little bit extra to sand off from the model due to the thickness of the tape.

[regme]

So after a few more failed castings, I went to see a mate who had a vacuum chamber and did that make a difference, so I'm looking into getting one myself.

 

After a quick look on ebay I found these are there any thoughts.  I know you get what you pay for, I'm more interested in the specs they are providing, will this be enough to degass the resin and silicone moulds.

 

Vaccum Pump and Chamber

[regme]

Well finally got the vacuum pump and did that make a difference.

 

Thanks for all the help and insight into casting, just have to work on the moulds and things should start to work out.

 

Cheers