JTModels - Mold Making Information

	Mold Making Hello! I'm in the process of making a mold that I will share information on as I make progress. I've placed the date at the beginning of each new section and will continue to update that page as I go. New information will be added at the bottom of the page and any changes/additions to the older information will be italicized to help it stand out. Please feel free to contact me at jimmy@jtmodels.com with any questions or comments. 11/29/04 -Plug preparation is probably the most critical part of making a mold because you'll be making an exact duplicate of it when you pull parts out of your mold. I like to use poplar or similar woods to make my plugs. Bondo makes a very good filler for making filets and filling in gaps (or fixing mistakes.) Once I have the basic design complete I spray the whole plug down with several coats of automotive filler primer. Let it cure out for a day or two and then wet sand it with 400 grit paper. Now you'll have a pretty good idea of how you plug looks. The next step is to fill the small scratches and dents with scratch and dent filler from Bondo. If you're doing a large area you'll probably have to fill it a few times since the filler shrinks as it cures. Once it's cured out sand the plug again with 400 grit paper. Plug primed and filled with scratch and dent filler. Next, re-prime again with filler primer and let cure. This time you'll sand with 600 grit paper. Check for imperfections and fill/sand as needed. Plug primed and ready for paint. If you're satisfied with the finish, paint the plug with a color coat of your choice. I prefer to use Rustoleum's professional paints or engine paint from a rattle can.Both can be found at Walmart and are very inexpensive. I use a different color than the primer because it helps me see when I'm getting close to sanding through the final coat of paint. Once this coat has cured you have a very good idea how your plug looks. I normally end up sanding and filling the plug a couple more times before the final coat of paint goes on. Next, carefully sand the final paint with 600 grit paper making sure that you don't sand through the paint and into the primer. You'll get a very smooth, dull finish. I like to hang the plug in the basement for a week or two to let the paint outgas and cure before I move on to the next step. Once I'm sure the paint is cured I start waxing. I put a coat of mold release wax on the plug and let it dry for about an hour before I buff it out. I do this for about a week to get several nice coats of wax on the plug. I'm currently using "Hi-Low" mold release wax from Aircraft Spruce and Specialty. It seems to work pretty well and I don't have any complaints. Next it's time to cut the parting plain which consists of a 3/4" thick melamine shelf. I use malmine boards because the epoxy used to make the mold separates from it very easily. Note that on most molds the parting plain will have to be built on a frame to let the plug stick out through the bottom. On this particular mold I don't have to make the frame since the plug is 1-1/2" thick, exactly 1/2 the thickness of the parting plain. Start by placing the plug on the board and tracing around it, trying to keep the outline as close to the size of the plug as possible. Plug outline being traced on parting plane. After tracing. Cut the outline out staying close to the inside of the line. Try to avoid leaving any sharp corners on the mold since you'll have to work them out later to keep from scratching the plug. I like to use a Rotozip with the appropriate bit. Unfortunately this is as far as I got tonight since my bit in my Rotozip broke and it was too late to buy a new one. I'll update the page as I make progress in the very near future. 11/30/04 - New bit purchased and ready to go, I finished rough cutting the parting plain. After the rough cut I take a wood rasp and bring the hole to the outline I drew on it. Make sure you get rid of any sharp edges inside the mold. Parting plain with finished cutout. Note: Be very careful when working with the melamine board after making the rough cut. This is what happens when working with a wood rasp in a tight space. The top edges of the melamine board are VERY sharp! Once the cutout is finished, carefully lower the plug into the parting plain. It's VERY easy to scratch the plug and end up doing a whole lot of repainting and sanding. Plug test fit into the parting plain. That's it for tonight. Will update this site later this week when I'll be outlining the mold area and filling the gap around the plug. 1/20/05 - FINALLY found my airbrush and can proceed with construction of my mold. Mark the centerline of the plug top and bottom to align it properly in the parting plain. I like to wedge a little clay between the side of the plug and the opening in the mold to hold it in place while filling the gap between the two. Once you've put the plug in its final position, press clay into the gap between the plug and the parting board. Make sure you press the clay firmly down into the void. Clay pressed in around the plug. Close up of clay before trimming. I use a piece of plastic to trim the clay from around the plug. The plastic is actually the material used to laminate business cards and luggage tags with a heat activated laminator. A credit card (my wife's works well too! ;) will work just as well. When removing the clay, hold the plastic at about a 10 degree angle from the board and pull it toward you, peeling up the clay as you go. Keep the inboard edge of the plastic up against the plug. Go back a second time with the card nearly parallel to the parting board and trim the clay flat. Check for gaps in the clay and repeat these steps as necessary. BE CAREFUL not to put too much pressure on the plug with the tip of the card because you can damage the finish. Also be careful not to push down on the plug because you will push the plug through the board and have to start over again. Once you're happy with the seal, gently scrape the extra clay from the plug. Don't worry if there is a residue on the plug. Waxing the plug will remove any clay that is left on it. Generously wax the plug being careful of the new seal. Carefully buff out the wax and let the whole thing set over night. Plug with seal completed and waxed in preparation for applying PVA. Draw an outline of the area that you plan to cover with the mold. Now you're ready to apply the PVA. For smaller molds you can use an airbrush to apply the PVA. Larger molds require a bigger gun such as a touch up gun. Set the air pressure to 50-60 PSI and adjust the flow the a find mist. I like to thin my PVA with water and found that a 60% PVA to 40% water ratio to work well. Mist a very light coat of PVA onto the setup and let it set for about 5 minutes. Now you're ready for a heavier coat of PVA. I like to put it no thick enough that it looks like it's about to run. Don't worry if you see air bubbles in the PVA. They will all disappear as the PVA sets up. Once the PVA dries you should have a nice shiny surface on your parting board and your plug. If you use colored PVA you should see a color change on the board out to the area that you marked for the edge of your mold. Mold outlined and PVA sprayed. Note purple color where PVA has been sprayed on the board. Close up of plug after PVA has cured. Notice the nice shiny finish on the plug. If you have fish eyes in your PVA you can easily wipe if off with a wet paper towel and re-apply the PVA once the plug has dried. If you continue to get fish eyes you probably have a compatibility problem with your PVA and wax. Waxes that contain silicon typically will cause a problem with the PVA. 1 2 Next > Please e-mail info@jtmodels.com if you would like more information.

Mold Making

Hello! I'm in the process of making a mold that I will share information on as I make progress. I've placed the date at the beginning of each new section and will continue to update that page as I go. New information will be added at the bottom of the page and any changes/additions to the older information will be italicized to help it stand out. Please feel free to contact me at jimmy@jtmodels.com with any questions or comments.

11/29/04 -Plug preparation is probably the most critical part of making a mold because you'll be making an exact duplicate of it when you pull parts out of your mold. I like to use poplar or similar woods to make my plugs. Bondo makes a very good filler for making filets and filling in gaps (or fixing mistakes.)

Once I have the basic design complete I spray the whole plug down with several coats of automotive filler primer. Let it cure out for a day or two and then wet sand it with 400 grit paper. Now you'll have a pretty good idea of how you plug looks.

The next step is to fill the small scratches and dents with scratch and dent filler from Bondo. If you're doing a large area you'll probably have to fill it a few times since the filler shrinks as it cures. Once it's cured out sand the plug again with 400 grit paper.

Plug primed and filled with scratch and dent filler.

Next, re-prime again with filler primer and let cure. This time you'll sand with 600 grit paper. Check for imperfections and fill/sand as needed.

Plug primed and ready for paint.

If you're satisfied with the finish, paint the plug with a color coat of your choice. I prefer to use Rustoleum's professional paints or engine paint from a rattle can.Both can be found at Walmart and are very inexpensive. I use a different color than the primer because it helps me see when I'm getting close to sanding through the final coat of paint. Once this coat has cured you have a very good idea how your plug looks. I normally end up sanding and filling the plug a couple more times before the final coat of paint goes on.

Next, carefully sand the final paint with 600 grit paper making sure that you don't sand through the paint and into the primer. You'll get a very smooth, dull finish. I like to hang the plug in the basement for a week or two to let the paint outgas and cure before I move on to the next step.

Once I'm sure the paint is cured I start waxing. I put a coat of mold release wax on the plug and let it dry for about an hour before I buff it out. I do this for about a week to get several nice coats of wax on the plug. I'm currently using "Hi-Low" mold release wax from Aircraft Spruce and Specialty. It seems to work pretty well and I don't have any complaints.

Next it's time to cut the parting plain which consists of a 3/4" thick melamine shelf. I use malmine boards because the epoxy used to make the mold separates from it very easily. Note that on most molds the parting plain will have to be built on a frame to let the plug stick out through the bottom. On this particular mold I don't have to make the frame since the plug is 1-1/2" thick, exactly 1/2 the thickness of the parting plain.

Start by placing the plug on the board and tracing around it, trying to keep the outline as close to the size of the plug as possible.

Plug outline being traced on parting plane.

After tracing.

Cut the outline out staying close to the inside of the line. Try to avoid leaving any sharp corners on the mold since you'll have to work them out later to keep from scratching the plug. I like to use a Rotozip with the appropriate bit.

Unfortunately this is as far as I got tonight since my bit in my Rotozip broke and it was too late to buy a new one. I'll update the page as I make progress in the very near future.

11/30/04 - New bit purchased and ready to go, I finished rough cutting the parting plain. After the rough cut I take a wood rasp and bring the hole to the outline I drew on it. Make sure you get rid of any sharp edges inside the mold.

Parting plain with finished cutout.

Note: Be very careful when working with the melamine board after making the rough cut. This is what happens when working with a wood rasp in a tight space. The top edges of the melamine board are VERY sharp!

Once the cutout is finished, carefully lower the plug into the parting plain. It's VERY easy to scratch the plug and end up doing a whole lot of repainting and sanding.

Plug test fit into the parting plain.

That's it for tonight. Will update this site later this week when I'll be outlining the mold area and filling the gap around the plug.

1/20/05 - FINALLY found my airbrush and can proceed with construction of my mold.

Mark the centerline of the plug top and bottom to align it properly in the parting plain. I like to wedge a little clay between the side of the plug and the opening in the mold to hold it in place while filling the gap between the two. Once you've put the plug in its final position, press clay into the gap between the plug and the parting board. Make sure you press the clay firmly down into the void.

Clay pressed in around the plug.

Close up of clay before trimming.

I use a piece of plastic to trim the clay from around the plug. The plastic is actually the material used to laminate business cards and luggage tags with a heat activated laminator. A credit card (my wife's works well too! ;) will work just as well. When removing the clay, hold the plastic at about a 10 degree angle from the board and pull it toward you, peeling up the clay as you go. Keep the inboard edge of the plastic up against the plug. Go back a second time with the card nearly parallel to the parting board and trim the clay flat. Check for gaps in the clay and repeat these steps as necessary. BE CAREFUL not to put too much pressure on the plug with the tip of the card because you can damage the finish. Also be careful not to push down on the plug because you will push the plug through the board and have to start over again.

Once you're happy with the seal, gently scrape the extra clay from the plug. Don't worry if there is a residue on the plug. Waxing the plug will remove any clay that is left on it. Generously wax the plug being careful of the new seal. Carefully buff out the wax and let the whole thing set over night.

Plug with seal completed and waxed in preparation for applying PVA.

Draw an outline of the area that you plan to cover with the mold. Now you're ready to apply the PVA. For smaller molds you can use an airbrush to apply the PVA. Larger molds require a bigger gun such as a touch up gun. Set the air pressure to 50-60 PSI and adjust the flow the a find mist. I like to thin my PVA with water and found that a 60% PVA to 40% water ratio to work well. Mist a very light coat of PVA onto the setup and let it set for about 5 minutes.

Now you're ready for a heavier coat of PVA. I like to put it no thick enough that it looks like it's about to run. Don't worry if you see air bubbles in the PVA. They will all disappear as the PVA sets up. Once the PVA dries you should have a nice shiny surface on your parting board and your plug. If you use colored PVA you should see a color change on the board out to the area that you marked for the edge of your mold.

Mold outlined and PVA sprayed. Note purple color where PVA has been sprayed on the board.

Close up of plug after PVA has cured. Notice the nice shiny finish on the plug.

If you have fish eyes in your PVA you can easily wipe if off with a wet paper towel and re-apply the PVA once the plug has dried. If you continue to get fish eyes you probably have a compatibility problem with your PVA and wax. Waxes that contain silicon typically will cause a problem with the PVA.

1 2 Next >

Please e-mail info@jtmodels.com if you would like more information.