[docmart]

Again, thanks Butch.

The site says:

Cure time can be reduced with mild heat or by adding Smooth-On "Kick-It®" Cure Accelerator.

XTEND-IT® Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life of unused liquid urethane products.

This is rather vague information but you can ask about it. Of course, it costs more to use these products.

 

[butch_n]

Again, thanks Butch.

The site says:

Cure time can be reduced with mild heat or by adding Smooth-On "Kick-It®" Cure Accelerator.

XTEND-IT® Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life of unused liquid urethane products.

This is rather vague information but you can ask about it. Of course, it costs more to use these products.

Thanks for taking the time to look this up and pointing them out. I'll add them to my list of things to ask about when I call.

 

[rude_ideas]

I'd be in for a couple pairs also.

 

[butch_n]

There is a Smooth-On distributor in Orlando. I see these people are experts in casting products.

I'd much rather speak to them in person than to call.
I'm going over there today. I'll take the old original bumper (I used as the master) with me.

 

[butch_n]

Well, not so good.
This video explains it all.

But never fear. Were there's a will, there's a way!
Figuring out what material to use, the hardness and putting together a vacuum chamber. I'll be ordering more poly soon. Lots of studying still to do.

These were made with McMaster-Carr 60 Shore A Urethane Casting Compound. Failure to degas is likely cause of breakdown of material.

60 Shore D is a very hard, simi-rigid material. It might be very good for these. Or it might be too hard.

80 Shore A may be fine too. It is hard, from seeing my engine mounts.

McMaster-Carr has either one. However, they both have very short work time, especially since degas is required. They say 15 minutes, but it begins to thicken up in much less than 15 minutes, (if it reacts like their 60A did). Degas would have to be done very quickly. I don't much like that.

I'm going to keep researching and order something by tomorrow evening.

Three things I'm looking for;
Relaxed working time.
Quick demold time.
Correct durometer to use, be it Shore A or D.

Anyone happen to know what durometer Energy Suspension Urethane Bushing are? Do you think it would a good hardness to use?

Here is a shot from Fibre Glast. It looks sweet, but is very expensive. Colors offered are Black or White.

 

[butch_n]

Bit of an update.
I've not given up! Just lots going on and too many things to do.

I've got a vacuum chamber together, along with a dedicated oven for post curing.

I'm going to try a 45 Shore D urethane. They will be quite hard, semi-rigid. They should be extremely durable. The color is transparent amber. It can be dyed black, but I'm not going to use any in the first set, at least. I like the idea of the poly being transparent, for inspection.

I'm going to do my best to get the set made the weekend of the 15th. If I can't get them made then, it will be the weekend after the 4th of July. I'm going to do my best to get them made and installed in the car I'll take to NC for 2 weeks. That will put at least a couple thousand miles on them, if not close to three. I'll probably be driving around a lot while up there.

 

[butch_n]

Got a pair of these made. I'll put them in the car Friday.

I like the long working time of 25min. It allows for a good, long, quite thorough degas. These being transparent lets a light to be shined through them. I see some tiny surface bubbles, but none embedded in the urethane. Also found I'd trapped air in the mold. I'll cut small vent lines in the mold to bleed any off in the areas. I'll rotate the mold as I'm filling it next time too.

I did notice the Part B (which says to shake well before using) introduces a lot of air bubbles along with it. I will degas Part B before mixing with Part A. Then once mixed, degas a second time before pouring. Learning from these will help improve the next ones.
I don't think these surface bubbles will hurt anything. You can really see in the pictures, but there are not any visible bubbles deep in the poly. Only these surface one. So, hopefully these won't tear apart.

I have enough to make some more, but it won't be until July 6/7 before I can make the next ones.

I'll let you know how these hold up when I get back from my trip. 45 D appears to be a very firm, though rubber. Hopefully this is the product to use for long life.

 

[butch_n]

Got almost 2,000 miles on this set. I haven't removed them but visually they look just fine. Sitting flat on the base plate, spring doesn't appear to have pressed into them. Looking much better this time.

I just poured the 1st one of a second set. Degassed Part B before mixing. Then degassed the mixture before pouring. There were still a few small bubbles slowly raising, but I understand that to be quite normal. Hopefully I don't have any air trapped, like the first run. I rolled it around slowly in hopes of getting any out of the base. I did not modify the mold. I want to see if rolling it worked. If not, I'll put vent(s) in the mold and pour the 2nd one.

 

[butch_n]

Used up the poly making 5 more. Learned a lot from it. I'm pretty sure this material is excellent for these. I'll be making new molds soon and begin making larger batches.

If you'd like to see them along with some info and chatter:

Actually, I started this Thursday at 4:30pm. In video I said I started Friday.

 

[Brad91Z]

They are looking good! You are putting in quite the amount of research and thought into these. Nice work! They look stiff as hell!

Brad

 

[butch_n]

Thanks Brad.

These are very stiff, but they still dampen spring oscillation just fine. I've felt nothing abnormal with them installed.

---------------
A two-component urethane casting compound that is specifically formulated for high abrasion and impact resistance. It is recommended for use in the casting of highly wear-resistant parts and linings...
Relatively insensitive to typical environmental moisture and will make good void-free parts.
---------------

These should last for years with no maintenance required. Though it may be beneficial to occasionally blow/brush out any grit that may settle on them. That would be the only thing they'd likely ever need.

 

[docmart]

Hey Butch I am sending you a pm.

 

[butch_n]

Hey all.

The test on the new bumpers is looking fantastic. Nearing the 10,000 mile mark now. Taking the most recent visual look a couple days ago, they show absolutely no signs of deformation. So, I'm now in the process of making a 4 plug mold. I'm taking another trip up to NC in a couple weeks. When I return I'll remove the test samples for a closer inspection. I feel quite confident all will be good. Once that is confirmed, I'll begin to produce them using the same material as the samples.

Does the Amber color matter to anyone? There are two reasons I'd like to avoid using dyes, if possible.
1 is the increase in cost.
More importantly is, from the manufactures web site. "Liquid pigments can often cause a negative effect on a material's physical properties if too much pigment is added."
Please let me know your thoughts.

I expect to have some ready by mid October.

 

[docmart]

The amber color is fine, given the reasons you gave.
Put me down for a pair when you get to making them.

 

[butch_n]

About the color. I suppose these could be painted with a urethane paint. Just clean them real well before applying paint. Might be a good idea to use an adhesion promoter too.

Here is a list of cars that use these bumpers.

 

[Brad91Z]

I would have no issues with the amber color.

Brad

 

[butch_n]

I'll begin making these tomorrow.

Once they come out of the mold I'll make a short video showing the bumpers, insulators and swaybar bushings.

 

[docmart]

Good to hear Butch. I was thinking of contacting you about the bumpers, as I am nearing the point of installing rear disc brakes and so would install new bumpers at the same time if you have them available. No pressure of course! Its interesting to follow your progress. Thanks for your research and hard work.