How to: Duplicating a radio bezel. - Page 2

Giuliano · 12-31-2004, 08:53 PM

Quote: Originally Posted by mp3oplecarrier

Could you explain why the box has to be so much larger than the original part?

It looks like there will be a lot of space around the area that needs casting, but I'm sure there must be a reason for that, is it just strength of the mould?

Absolutely, I welcome any and all questions... this thread would be kind of one-sided if it were just me posting here.

This box has extra room around the sides so I can leave room for the pouring and venting channels, but normally it's reasonable to have an extra 1/2" to 1" of room around the sides.

In this particular case, I have left plenty of space above the part because I am expecting to rebuild and extend the duplicated part by about 2 inches in height.

The finished extended part will be placed back in the original mold, and the sections of rubber that lay under the extended sections of the part will be cut out and new rubber will be poured into the cut-out sections.

In this way, the original mold can be modified and extended, without having to re-pour an entirely new mold.

And to a certain extent, the box itself lends some strength to the finished mold, though in most cases the box is cut apart to remove the mold.

Giuliano · 12-31-2004, 09:35 PM

I'm nearly done trimming and shaping the rubber blank for the part that will be the right-side LCD mounting bracket.

The piece snaps in perfectly and fits so well, I may not even need to use screws to secure it!

With two of these pieces in place, and an LCD or a mounting plate screwed to the front of it, the lugs on the side of the bracket will keep the whole assembly in place.

Giuliano · 01-01-2005, 01:04 PM

I've cut some extra pieces of 1/2" foamboard to fill up some of the space around and under the bezel, so as to reduce the amount of rubber I will need to pour.

The addition of the 1/2" foamboard reduces the cubic inches by about 45 CI, reducing the amount of rubber needed by about 2 pounds. And for rubber, a single-pound of rubber can cost you about $15-30, so it all adds up.

The first picture shows the box with the extra pieces of foamboard in place, and the holes where the bezel's pegs sit.

With the bezel in place, the vertical gap between the board and the bezel is about 1/4", which is easy to fill with modeling putty.

The second picture shows how the pouring and venting channels will be laid out.

Normally, for larger (thicker) pieces, you can just have a wide opening at the top, and pour the resin in there, with enough room for the air to escape the mold.

However, for something thin like this, you need to create seperate pouring and venting channels so the resin can get in, and the air can get out.

The second picture shows the pouring channels in Red, and the venting channels in Blue.

Now you may be asking, why are the pouring channels looping down to the bottom of the piece?

That is because if you pour the plastic resin in this fashion, the resin actually pushes the air out of the mold out through the top, resulting in a perfect pour with less air bubbles in the finished piece.

The pouring/venting channels will be sculpted onto the posterboard with modeling clay, and will actually be molded into the rubber when it is poured.

MatrixPC · 01-03-2005, 12:51 PM

Man, this is one hell of a job... very nice ... stickyyyyyyyyyy a must.

Giuliano · 01-03-2005, 01:01 PM

Quote: Originally Posted by MatrixPC

Man, this is one hell of a job... very nice ... stickyyyyyyyyyy a must.

Thanks!

And I'm not even half done.. this thread is just on how to duplicate the bezel, but I'm also going to modify and extend the duplicate part in the process.

Right now, I'm waiting on my shipment of silicone RTV molding rubber to arrive in the mail before I can really continue.

I used to (and still will, when I have time) build anime models, and sold hobby supplies through a web store (I don't anymore), so I've become quite experienced with casting, modeling, and generally making things.

I've made resin copies of super-small parts before, about 1" long, with fine detail - it takes a little bit of thought and design, but in most cases you get good results.

Grayscale · 01-03-2005, 01:25 PM

I'm confused as to what the 'venting' and 'pouring' channels are. I guess you pour in the plastic in the pouring channels and then it exits the venting channels? or the air does? I'm not familiar with liquid plastic at all, but I'd like to know more about it. Also, where are these channels? I don't really see any special grooves for pouring into or anything. I guess I'm really missing something here.

brrman · 01-03-2005, 01:34 PM

yeah you pour into the pouring channel, but the resin would not go into the mold unless the air could escape - so you have venting channels for the air. You keep the channels as small as possible to prevent the amount of clean up after the mold has cured.

You put a small piece of material (mini straw/thick toothpicks, coat hanger, etc) to take up room when you make the mold. Then when the mold has cured, remove the toothpicks and you have an empty area that becomes the vent.

Grayscale · 01-03-2005, 01:35 PM

i see. where are the channels at? anyone have any good links i might could read to get myself more familiar with this stuff?

brrman · 01-03-2005, 01:36 PM

edited my above post about the channels

check this out
http://www.alumilite.com/howto.cfm

I have been fooling with molds the past couple weeks. very interesting and I love this thread.

Giuliano · 01-03-2005, 01:46 PM

Quote: Originally Posted by brrman

yeah you pour into the pouring channel, but the resin would not go into the mold unless the air could escape - so you have venting channels for the air. You keep the channels as small as possible to prevent the amount of clean up after the mold has cured.

You put a small piece of material (mini straw/thick toothpicks, coat hanger, etc) to take up room when you make the mold. Then when the mold has cured, remove the toothpicks and you have an empty area that becomes the vent.

Good answer!

The channels themselves don't have to be tiny, but it's usually a good practice to make the channel contact points (ie, where the channels contact the piece) narrow so that there's less material to cut off - the plastic that cures in the channels is usually referred to as the "sprue".

A channel width of 1/8" is usually sufficient, but for larger pieces it's not unusual to have a channel of 1/4" wide, which is what I'm going to be doing - it makes the pouring slightly easier.

The resin pours into the mold through the channels, and balances itself out by gravity.

For example, if you had a plastic tube shaped in a U, and poured water in, it would self-level at each end, which is why you need to have both the pouring and venting channels come out the "top" of the mold.

Giuliano · 01-03-2005, 01:50 PM

Here's an obviously photoshopped image of what I expect the modified and finished bezel to look like.

I'll probably end up painting it a pretty blue color to match the car..

I've got some specialized hobby paints that will do the job nicely - they're acrylic lacquers, so they go on real smooth and are real durable.

Giuliano · 01-03-2005, 05:45 PM

Quote: Originally Posted by Giuliano

I'll probably end up painting it a pretty blue color to match the car..

I've got some specialized hobby paints that will do the job nicely - they're acrylic lacquers, so they go on real smooth and are real durable.

On second thought...

What better way to make it look "factory" than to paint it using factory paints?

Subaru Touch Up paints, that is - they're about $5 for a 1 ounce bottle, and for my WRX, I believe the matching color is World Rally Blue.

Now, you might think.. 1 ounce of paint is not enough!
It is if you airbrush it! (which I can, I've got like, 3 of them)

Combine the radio bezel with the center, left, and right A/C bezels, and you've got a paintjob on the inside that will look factory...

Did I mention that if I spray the inside of the mold with primer, and let it dry before I pour the resin, the resin will bond with the primer? Instant pre-primed part, ready for painting.

antimatter · 01-03-2005, 06:05 PM

A quick post to say how great this thread is and i look foward to the continuation

Pudge · 01-03-2005, 06:21 PM

If you have an air compresser you can buy an airbrush kit for that dirt cheap from Harbor Freight tools, it should do the job.

Giuliano · 01-03-2005, 07:24 PM

Quote: Originally Posted by Pudge

If you have an air compresser you can buy an airbrush kit for that dirt cheap from Harbor Freight tools, it should do the job.

If you meant me, I already have at least 2 airbrushes now, both meant for hobby-size work:

The air compressor is pretty silent, and only runs when I press the airbrush trigger - I added a low-pressure regulator so I can dial down the pressure to 5-10 psi for detail painting.