Tom in Austin

Love following these projects ... keep it coming Jerry!

Jerry Feather

With a little refinement I have begun to assemble the stand. I have the grooves cut in the sliding bases for the sticks that the ***** will be put on to work with. Then I have the leather forms clamped in the vise to drill common holes in them where they will be screwed to the top of the stand and gradually screwed down as I form the leather on the **** tops. I'll epoxy the sticks into their bases, but first I need to refine the fit of the sticks in the formed ***** to be sure they will reach the tops, but without having to use much force.

Jerry Feather

These pictures show a little better what I have in mind for this stand and leather forms.

Jerry Feather

I got my vacuum setup set up to do some degassing and was going to inject another pair if *****, then I remembered that I wanted to fix a couple of tiny defects in the molds. Also I wanted to fabricate and install a couple of swivel gates that I can use to close off the injection holes so the compound wont run out when I stand them up to cure. I'll have to wait until tomorrow to do the injections.

Jerry Feather

Well, that was interesting. I gobbed the molds with wax and mold release and then put them together for molding. Then I mixed up enough compound to fill them and then put the cup nearly full into the vacuum chamber. The vacuum pretty much pulled a lot of air out, but the last bits consisting of very tiny bubbles merely foamed up at the top and stayed there. Applying more vacuum merely caused the compound to overflow. Nevertheless, when the vacuum was released the compound settled back to a very smooth looking mixture, so I used it that way. I think there will be some very tiny bubbles in the finished product, but probably too small to even see.

I did feel the injection of one large bubble into one of the molds, but I had opened up the top vent holes quite a bit and I think it escaped through one of them. I can see evidence of that anyway. I think these two ***** will turn out somewhat better than the first ones, but I may still need some refinement in the procedure.

One problem is that filling the syringe at the very end gets pretty difficult because the compound is starting to set up. I barely made it with the second mold.

I'll let you know how these turn out.

Next will be working up some leather for that aspect of this development.

Jerry Feather

That didn't turn out as I expected. The GTS **** came out with an even larger bubble than the first one. Given the cost of the material I think it will be worth while to try to inject the bubbles in both of these and put them back in the mold to cure.

Next, since the degassing seems to take quite a bit of time and the compound starts to set up, I am going to have to refine my procedure and mix up only enough material to inject one mold at a time. That will probably work out the best since I suspect that if I were to try to market this project, the GTS **** is likely to be the most popular anyway.

Jerry Feather

Here's a picture of the last two castings. My finger is pushing in on the large bubble in the small end of the GTS ****.

Jerry Feather

I haven't filled the bubble void in the last one of these that I made but now it looks like I need to get back to this project since someone can't find these GTS ***** anywhere.

GT6ixer

Reading your​ post #110 you said you applied vacuum then you applied more vacuum and the material started overflowing. From the degassing stuff I read they only fill the cup up to about a third to a half of it's capacity so they can apply a full vacuum for about 60 seconds without it spilling over. My guess is that it didn't get degassed all the way because you were only under partial vacuum. I haven't tried it yet myself but sounds like Hans has degassed before and maybe he will weigh in here.

Jerry Feather

Thanks for the suggestion, but I don't think that is the problem. Even with the first ones of these I molded there were tiny bubbles in them, or one of them, that did not float to the top and form together, but rather stayed throughout the compound as it set. Those are the ones I was hoping to eliminate with the degassing. And, I think I succeeded.

The big bubble in the bottom of the ****, the top as the mold sits for the compound to set, is the one that I need to eliminate, and not one that I failed to eliminate in the degassing. Where it came from is the syringe. In the process of sucking compound out of the mixing and degassing cup I must have sucked in a chunk of air, and then in the injection process I injected that bubble into the mold. It was big enough and had time enough to float to the top as the mold sat, and the compound has enough surface tension so that the bubble stayed a bubble rather than breaking and letting the air out the top. It has formed a nice shell that I think I can fill with compound with a syringe and simply fill it up and have it retain the shape it has already formed. I may not even need to put it back into the mold to fix it.

When I do these kinds of developments I usually am flying on my intuition mainly, and then these processes become a learning process for me, usually well before my intuition runs out. In the process, what many of you guys have to suggest becomes very helpful, and that is certainly the case with this process. Some of what I have learned, however, is the following:

1. This two part rubber compound is supposed to have a half hour pot life, and it does, but in that half hour it is still setting up to the point that it becomes very difficult to suck into the syringe.

2. The degassing process eliminates a lot of the air mixed into the compound, but not all. However, what isn't released in the process is very tiny bubbles and are of little or no significance.

3. Trying to make one of each style **** with each batch of mixed compound is too much.

Making one at a time is going to be both more successful and beneficial in the end because if there turns out to be any kind of market for these ***** it is most likely to be primarily the GTS ****. The mixing cup wont be as full so it will degass better and I can fill the syringe from the compound then pour the rest into the mold before closing it, then inject the compound to fill it up without a big air bubble going in at the end. The only added cost is going to be in a little more wasted compound and in the loss of one syringe for each **** rather than for two. However, they only cost about $1.30 each. The extra loss of compound can be minimized, however, and will be better than the loss of a whole early ****'s worth if it turns out that no one is interested in the early style ****.

Jerry Feather

I finally got around to mixing up some compound and injecting the bubble in the bottom end of the GTS **** I made a while back and then set up and injected another of the original ***** in the other mold. I'm going to go out and take those apart and see how they came out and then maybe do the same the other way.

By that I mean that there is still the first original **** I cast that has the bubble in the bottom end of it, so I'll inject that bubble and then cast another GTS **** from the same compound mixture.

I have the leather forming jigs epoxied together; so it is getting to be time to try to put my skiving machine into service. I think I'll go out to Doug's shop later and work on that a bit.

Here are some pictures of the first successful original **** after the flashings have been removed. It is the one on the left of an original factory ****.

AirtekHVAC

Looks good!

Jerry Feather

I have learned a couple more things about this project. One is that the rubber compound I am using gets quite a bit harder than just after only one overnight, but in a couple of months; so hard that it is difficult to even cut with a knife. Also, and related to this longer time cure, it is not a good idea to leave the shift stick shaft part of the mold in one of the molded ***** for very long because with the harder cure over time it is very difficult to pull out.

I had left the mold shaft in the GTS mold waiting to fill and reform the bottom end where the bubble was, but after I got it filled and formed I couldn't pull the shaft out. I was able to fabricate a kind of pulling tool and use it in my mill to pull the shaft out with the mill table crank. See the picture. It didn't take very many cranks to get it to pop loose, but more force than I could muster just pulling on the **** by hand with the shaft in the mill vise.

Jerry Feather

I am still trying to figure out how to cast the GTS **** without a bubble in the bottom of the handle, which is the top of the mold as it is injected. In the meantime however I think I have decided to add the late Auto T-handle shifter to this project and do some replications of those with this same rubber compound mold process.

I took one of the T-handles apart that Doug V. gave me while I was waiting in blocked traffic yesterday and then used what I learned about how it works to figure out basically how to replicate it. I have that pretty well figured out, but I am going to want to have some hard aluminum components fabricated to cast into them rather than trying to cast the inside passages in rubber. This will also give them an aluminum core that can be screwed to the shift lever and that wont break over time.

The only drawback is that I may also have to fabricate the shift button and shaft and the sleeve it fits in, and the plug for the other end of the T. In the meantime I am hoping that guys with failed T-handles don't throw them away so they can use the button, sleeve and plug out of the original in this new design.

I have the mold plugs for the two openings started and will work some more on that during the holiday. Right now I need to get some more rest to catch up from the trip to Doug's for the free parts.

Tom in Austin

New automatic T-handles? Now that's a swell idea!