Re: Custom rubber parts

I'm not sure why my cell phone camera does that... reminiscent of old Penthouse magazine layouts where they coated the lenses with Vasoline to blur the image a bit... or that's what I heard anyway... ahem...

Either 60A or 70A would work well, 70 being the stiffer of the two. Be aware there is a Shore "D" scale as well, where 60 and 70 are getting into the bowling ball range, so order carefully. Some manufacturers offer "Wet" and "Dry" varieties, the "Wet" version exudes a mold-release-like liquid that works well in some applications. For your purpose, I'd stick with the "Dry" variant if offered the choice, that way you can make the mold from the same material as the part. Be sure to purchase a compatible mold release.

Most polymers can be colored using either a dispersion pigment (my choice) or tints. In my experience it takes a lot of tint to obscure imbedded steel brackets (or screws in hole pockets), which is why we use the dispersion pigments. Those bumpers being where they are, direct sunlight could make them appear a translucent purple when using a tint. Colors are generally added to the hardener component before mixing with the resin.

Paul, yes, 3D techology is becoming affordable, but for the purpose of making soft molds the pattern has to have a good surface finish that won't grip the mold material - for this type of work the hand finishing required generally makes CNC a more logical choice. We have even seen the 3D printers that print metal, but that won't be affordable for a while, and current technology would still mean leaving some finishing stock for final polishing.

The suppliers that sell urethanes and silicones will also usually have mold board available. It's a hard plastic board that's great for short run tooling and suppliers will sometimes have samples or scraps that might work well to make this pattern. That said the pattern can be acrylic, wood, aluminum, most anything you can whittle into the desired form. Do check the data sheet for the polymer you choose for any material interaction or incompatibility before investing time in a pattern.

On Sunday, April 27, 2014 2:52:54 PM UTC-4, Plucked Chicken wrote:

That looks more like an underwater shot from the Titanic. ; ) Another thing that could be molded is the plastic handle, mine is missing that too. Pic of a complete handle from a ’62 Fury wagon below.

Wonder what other years the bumpers would fit? If I did mold them, could give out a set to every ’62 wagon owner I meet. Think it’s the kind of part you don’t realize you need, out of sight, out of mind. My seat back is hard to release, I bet if the rubber bumpers had some give to them, that would help.

This site sent to me by Mark is very helpful, they list products along with hardness values and comparisons. The Flex 60 or 70 sound about the right hardness.

Flex 60

Caramel

1:1

5 min.

18-24 hrs.

760 cps

60 A

770

160 F

MSDS

Buy

Easy to use, extremely tough flexible rubber used for casting flexible parts and making flexible urethane molds. 60A hardness (similar to a shoe sole)

Flex 70

Ivory

1:1

5 min.

18-24 hrs.

780 cps

70 A

1,170

160 F

MSDS

Buy

Easy to use, extremely tough flexible rubber used for casting flexible parts and making flexible urethane molds. 70A hardness (similar to a car tire)

http://www.alumilite.com/

From: 1962to19...@googlegroups.com [mailto:1962to19...@googlegroups.com] On Behalf Of Steve Charette
Sent: Sunday, April 27, 2014 10:54 AM
To: 1962to19...@googlegroups.com
Subject: Re: Custom rubber parts

If I'm understanding your question correctly, yes, you can make a pattern from wood, pull a urethane or silicone mold from it, then cast the part into your new mold. The secret is to thoroughly seal the wood to prevent the mold material from bonding to it. Shellac or a polyurethane finish work well. Don't forget to use mold release... ask me how I know! If you use a relatively soft material for the mold, you can skip putting draft on the part (the slight angle that allows you to remove a part from hard tooling without the use of bludgeoning tools, usually destroying the part, the mold, or both).

With the addition of CNC machines we've gotten away from soft tooling, although we did a couple runs of Shelby Cobra engine mounts a few years back (2000-2002) using this method and a recent look at the molds reveals that they are still in good condition.

Most companies that sell mold-making products will have sampler packs of both the mold and part materials available so that you don't have to buy large quantities just to try a product out.

After reading this I went out to look at my '62 wagon - it was parked in 1979, the seats were folded down and the windows lowered so the owners (who also owned a marina) could use the car for an antifreeze buggy for winterizing boats. As a result, my bumpers are in comparatively good condition.

Let me know if I can be of assistance if you decide to mold these, or any other small pieces, for that matter.

SC

Flex 60	Caramel	1:1	5 min.	18-24 hrs.	760 cps	60 A	770	160 F	MSDS	Buy
	Easy to use, extremely tough flexible rubber used for casting flexible parts and making flexible urethane molds. 60A hardness (similar to a shoe sole)

Flex 70	Ivory	1:1	5 min.	18-24 hrs.	780 cps	70 A	1,170	160 F	MSDS	Buy
	Easy to use, extremely tough flexible rubber used for casting flexible parts and making flexible urethane molds. 70A hardness (similar to a car tire)