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Post by portaler on May 6, 2017 9:42:37 GMT -5
Hello, I'm new to this site, but looks like I'm in the right place for experts. I'm wanting to mould the item shown in the picture. At first glance I thought easy, flat and not so difficult. However the mesh will make it quite difficult I think. Could someone please give me some tips how best to mould this ? I am planning a silicon mould, then a couple of parts with resin. I'll paint it after and screw to a base. I was hoping to do it with a single mould, however I may need to create a 2 part mould ? Or I guess I could simply create a one shot mould which is destroyed during demoulding due to the undercuts in the mesh ? I don't plan on doing a lot of parts. Maybe 3-4. Really interested in feedback on this somewhat tricky part. |
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Post by Brian on May 6, 2017 12:14:52 GMT -5
A 2 part mold is what is needed to do this project...... I am assuming that the 6 screw bosses are an intricate part of this piece, so the way I describe the process will be paying particular attention to them for alignment and fit up of the duplicate piece(s) I am also going to assume that you have already built the mold box or will be shortly......either way make sure that it is no less than 1/2" larger than the piece you are molding. It appears that the piece that you are molding is light weight...in that case take some modeling clay and roll it into 4 pieces...one for each corner...about the diameter of a pencil or perhaps a little bit smaller should do so long as it can support the piece that you are molding with out it collapsing. The length needs to be no less than 1/2". The legs will later become the pouring and vent channels. Sit the piece on top of the legs....the side with screw bosses will be down,the side with the many small holes will be up(visible)..... the legs support the piece so as to allow the mold rubber to flow underneath creating the first part of a 2 part mold. Be sure and apply mold release to the piece you are molding as well as the interior portion of the mold box to help prevent the rubber from sticking to places that you don't want it to. Pour the first part up to the edge of the mesh just before it starts to go over the mesh ...not over it...if you get some over it you can remove it once it cures with a razor or sharp knife. Once the 1st part has cured do any necessary clean up prior to pouring the 2nd mold. DO NOT REMOVE THE MASTER PIECE FROM THE MOLD. Again apply mold release to the piece and the surrounding rubber....this is very important..you do not what the second pour to stick to anything from the first pour. There may be some sticking around the edges that can be taken cared of with a razor or sharp knife. Pour the second part and allow it to cure....once it has cured, you can now carefully remove the master piece and do any clean up that is necessary...make sure that the 4 holes where the legs were are free and clear of any modeling clay as they are now the channels for pouring and venting. FALLOW ALUMILITES RECOMMDATIONS FOR MOLD PREPERATION BE FORE POURING RESIN 
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Post by portaler on May 6, 2017 14:57:00 GMT -5
Hello Brian,
thanks for the detailed explanation. That helps a lot !! Also a very good point about understanding what is most important on the part. i.e the screw points. On the moulded part I may need to re-bore them slightly with a drill but that's the least of my problems. Position is the important thing.
I don't have modelling clay, but have some thin wooden dowl (size of a thin pen) which I can hotmelt to the bottom of the fill box and mould part. These should also serve as nice fill ports/air out vents.
I did see in a You-Tube video that a 2 part mould can benefit from key-in points to align the 2 mould halves. These would be positioned on the split line in the silicon wall thickness (the 1/2" you mentioned). I guess I can gouge out some holes afterward in the cured first mould half. Anything to prevent misalignment of the 2 mould halves is good for this type of part I guess.
This is my first attempt at moulding. I didn't want to go to the extent of making a degassing chamber. Do you think this is worth the effort for a piece like this ? To be honest I wouldn't be too concerned if there was some roughness due to air on the top surface. It should be a space mesh grill plate.
Andrew
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Post by Brian on May 6, 2017 22:49:49 GMT -5
...I would not worry about a degassing chamber.....I cast some very small parts that even one air bubble would ruin things and have never used one nor do I see the need for one. Forgot to mention the alignment lugs...yes, they are very important to a multipart mold. The wood dowels will work perfect as you described them in place of modeling clay. Sounds like you have things figured out and ready for the first rubber pour. |
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Post by portaler on May 7, 2017 2:56:54 GMT -5
Yes, all ready to go, then I did the calculation and I don't have enough silicon !! Oh well, can get all the setup done today. That's the bit that takes the most time.
One last question. I was thinking about the exact split line location. You mentioned go right up to the upper side of the mesh. That would mean the top half of the mould would be more or less flat on top of the lower half. I was thinking would it be better to have the split line midway up the mesh ?
My only thought is that the silicon is flexible and there are quite a few mesh holes. Even doing this the mould halves may not match up with every "hole" ?? Or am I fooling myself that the silicon is too flexible ? Perhaps by lowering the split line any mould mismatch would be then "hidden" further down in the hole. But maybe I am missing something.
A flat top piece may also allow resin to flow into the split line. Which i guess could be cut away afterwards, but is extra work etc.
I have seen people use wooden sheets on the outside of the mould to prevent swelling and flow between the split lines. Maybe I could do that too.
What do you think ? The Devil is in the detail I guess.
Andrew
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Post by Brian on May 7, 2017 20:17:57 GMT -5
......The split line can be ,as you described, half way up. I cast very small parts compared to what you are doing (1:25 car parts) so I tend to go with just below the surface....like .25 mm. at times so it appears that it is to the top but not enough to start covering it........In your case you have more area to deal with ,so being able to visualize half way up is a whole lot easier than visualizing half way up on a hood pin and plate for a 1:25 stock car as an known example. It has taken me a couple of attempts on some pieces that I cast to get the right mold in the first place, so if at first you don't succeed, try it again......after a few successful molds, you will have the confidence to study a part and figure in your head what type of mold you will need to replicate that certain part. Don't over think or over engineer your project and you will be pleased with the outcome. |
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bill
New Member
Posts: 18 
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Post by bill on May 14, 2017 1:07:58 GMT -5
Hello, I'm new to this site, but looks like I'm in the right place for experts. I'm wanting to mould the item shown in the picture. At first glance I thought easy, flat and not so difficult. However the mesh will make it quite difficult I think. Could someone please give me some tips how best to mould this ? I am planning a silicon mould, then a couple of parts with resin. I'll paint it after and screw to a base. I was hoping to do it with a single mould, however I may need to create a 2 part mould ? Or I guess I could simply create a one shot mould which is destroyed during demoulding due to the undercuts in the mesh ? I don't plan on doing a lot of parts. Maybe 3-4. Really interested in feedback on this somewhat tricky part. |
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bill
New Member
Posts: 18
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Post by bill on May 14, 2017 1:11:33 GMT -5
Hello, I'm new to this site, but looks like I'm in the right place for experts. I'm wanting to mould the item shown in the picture. At first glance I thought easy, flat and not so difficult. However the mesh will make it quite difficult I think. Could someone please give me some tips how best to mould this ? I am planning a silicon mould, then a couple of parts with resin. I'll paint it after and screw to a base. I was hoping to do it with a single mould, however I may need to create a 2 part mould ? Or I guess I could simply create a one shot mould which is destroyed during demoulding due to the undercuts in the mesh ? I don't plan on doing a lot of parts. Maybe 3-4. Really interested in feedback on this somewhat tricky part. Attachments:
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bill
New Member
Posts: 18
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Post by bill on May 14, 2017 1:13:56 GMT -5
When making a part his detailed I would first see if there is any inhibitions to the silicone mold material. This can be done by purchasing the small "Mold Putty" kit sold by Alumilite and press it to your master. It saves a lot of time if you are planning on using the Platinum based silicone and you have a reaction. Then, by understanding the use of the part, decide on the casting material to be used. Reading the performance sheets on each of the products will give you an idea of what you need. Some have shrinking issues and others don't. I like to make wooden mold boxes; they keep the mold secure in shape. Preheating with your part will most likely be in an oven or microwave. If a microwave oven is used the mold will have to be removed from the box before pouring.
As has already been said, there will be air bubbles in the casting and they always rise. Therefore I would build the box to hold the part raised at one end when it is ready to pour. But making the mold lying flat so it can be made in two parts as Brian suggested. The type of mold would be like a "Squish Mold" when done as both parts are together and then using a syringe to inject the casting material (when pouring the mold material into the mold box with the master part suspended, check to make sure the surface is level then use a wire bent at a right angle so it can be used to wipe the under side of the master making sure there are no trapped bubbles, then pour the rest of the first part of the mold). When building the mold box make it so it will hold both sides and allow it to be raised at one end so the bubbles float to the raised end. Place the part in the mold box at an angle to allow the bubbles to float to the upper corner rather than the whole length of one side. Add a hole at the lower end (corner) to place a straw so you can see if the casting material is all the way into the mold. Cut wood to be added on the top portion of the mold to give it stiffness, drilling holes in the wood so the mold material can attach at several points. It will also give you a place to add a screw in the wood to lift it on and off the mold. If you are going to apply pressure to the top of the mold the wood top will give an even surface to apply pressue. See attached. The wood in the center of the part is to keep the pressure from being too much while applying the needed amount to keep the casting material from working its way out of the mold.
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