I'm still in for one.
Ed
Ed
Trunk Roundel Gasket
- Thread starter Ohmess
- Start date
TodB
Well-Known Member
I too would like 1
I'll take 4 please
Hi All -- An update on the process.
I continue to have trouble finding a vendor. Gasket makers want to die cut the part, which will not enable the lip. When I point this out, they say the gasket material will compress around the base, making something that looks like a lip. Alas, I tried this, cutting a gasket by hand and it does not look anywhere as nice as the lip. (In other words, Macha was right. When will I learn?)
Compression molding, injection molding and even casting all require a mold. If the mold needs to be made out of metal by a tool and die maker, the costs skyrocket.
I also looked into 3d printing the part, but I don't think the quality will be there given the little lines in the parts as they are formed. Post formation treatment and/or sanding adds a whole lot of labor to the process. And, I am not sure I have identified a suitable UV resistant material. I am looking into having a 3d printed mold made, but I am not sure this is going to work for the same reason.
One of the reasons I wanted to use 3d printing is so that I could modify the size of the original part to more closely conform to the elliptical shape of the bottom of the base where it meets the trunk. If a more flexible part could be created, however, the replacement parts could be made the same size as the original.
So, I am on to casting. I am going to attempt to create a silicon rubber mold, and cast some of these out of silicon. The material I have identified for the parts is very flexible and can be colored with a UV resistant coloring, so if I can get the quality right I should be able to also reproduce something close to the original gray. More later...
I continue to have trouble finding a vendor. Gasket makers want to die cut the part, which will not enable the lip. When I point this out, they say the gasket material will compress around the base, making something that looks like a lip. Alas, I tried this, cutting a gasket by hand and it does not look anywhere as nice as the lip. (In other words, Macha was right. When will I learn?)
Compression molding, injection molding and even casting all require a mold. If the mold needs to be made out of metal by a tool and die maker, the costs skyrocket.
I also looked into 3d printing the part, but I don't think the quality will be there given the little lines in the parts as they are formed. Post formation treatment and/or sanding adds a whole lot of labor to the process. And, I am not sure I have identified a suitable UV resistant material. I am looking into having a 3d printed mold made, but I am not sure this is going to work for the same reason.
One of the reasons I wanted to use 3d printing is so that I could modify the size of the original part to more closely conform to the elliptical shape of the bottom of the base where it meets the trunk. If a more flexible part could be created, however, the replacement parts could be made the same size as the original.
So, I am on to casting. I am going to attempt to create a silicon rubber mold, and cast some of these out of silicon. The material I have identified for the parts is very flexible and can be colored with a UV resistant coloring, so if I can get the quality right I should be able to also reproduce something close to the original gray. More later...
I’ve been following this thread. Making stuff is hard! Silicone is really rubbery so keep that in mind. You probably don’t need to alter the shape. Here is what I would do.
1. Model the part. This shouldn’t be more than one hour of dev time. If you need a modeler, I can give you the name of my guy. I like to mail the small parts to him.
2. If you do want to make the part oblong, trace the profile of the aluminum pedestal onto some card stock. Send that with the part. FYI - I’m going to trace this myself tonight, as I’m sending a roundel base to Ed tomorrow.
3. 3D print the part in vinyl and test fit. Examine your goals. If the goal is to serve as a bushing, the vinyl part can be your end product. If the goal is to be waterproof, proceed with step 4.
4. You don’t need a two piece mold. Using your file, machine a block of aluminum for the mold. The bottom of the seal is the very top of the block. So if you look down at your mold, you see the lip machined into the chunk of aluminum. You may try delrin in lieu of aluminum. You may also just 3D print the mold. If you use Vinyl you won’t get stepping (lines). Vinyl is porous though so you would want to use some mold release spray.
When you mold the part, you squirt the silicone into the mold then scrape the top flush. This is how you get away with having a one piece mold. You can use 100% silicone caulk or RTV to start. Give it several days to cure.
Last edited:
Hi Markos - Questions on your suggestion:
As to item 3, I had looked into vinyl and found a couple of problems. First, I am not sure the little visible lines that arise from the 3d printing process are going to be acceptable. And any processing after printing (either etching or sanding) adds substantially to the cost. Second, and more importantly, I am not sure the lip will come out looking right with a rigid material. I believe the tension created against the inside of the lip causes the top of the lip to press tightly against the base as the material seeks to return to its original shape. Without this tension, there will be a gap between the gasket and the base (just as there would be with a die cut part).
As to item 4, you seem to be suggesting that the model could be used to create an aluminum mold. I've looked into this, and if I have this right that would require CNC machining, which would be cost prohibitive.
As to item 3, I had looked into vinyl and found a couple of problems. First, I am not sure the little visible lines that arise from the 3d printing process are going to be acceptable. And any processing after printing (either etching or sanding) adds substantially to the cost. Second, and more importantly, I am not sure the lip will come out looking right with a rigid material. I believe the tension created against the inside of the lip causes the top of the lip to press tightly against the base as the material seeks to return to its original shape. Without this tension, there will be a gap between the gasket and the base (just as there would be with a die cut part).
As to item 4, you seem to be suggesting that the model could be used to create an aluminum mold. I've looked into this, and if I have this right that would require CNC machining, which would be cost prohibitive.
If cost is a concern I would 3D print the mold. 3D modeling time ranges from $50 - $150 /hr. I wouldn’t anticipate any alterations but you can add that into your contract.
I’m not well versed on molding. I’ve researched it as an option for this part as well as others that I am considering. I think that you want to avoid using a silicone mold with a silicone part. You want a soft mold with a hard part or a hard mold with a soft part.
To save money, cast the mold yourself with polyurethane. It will only cost $10 to make. Make a small box out of mdf. Hot melt glue the inside edges. Also glue the seal to the floor of the mold, face up. Then pour in the polyurethane. There are loads of youtube videos on the process.
I’m going to do the same when I repair my factory steering wheel. Mine will be a silicone mold with polyeurethane steering wheel parts.
i made one from a sheet of bituthane roofing membrane
took 5 minutes. 1/16" thick
took 5 minutes. 1/16" thick
Pictures please
The material choice may be worth investigating but I'm not sure how helpful pics will be. Alan doesn't have a traditional rear emblem since he is running a CSL spoiler. Here is the frond roundel from his build thread. I'm not presuming that there should be, but no visible gasket present.
Roofing membrane? Not for me.
I used it on my deck joists. It is *very adhesive on one side. I'm not sure how you use it on a car unless you left the brown wax paper on the adhesive part.
SET IT ON THE FRONT SO IT WONT SHOW
Do we have samples of an OEM seal that hasn't been ravished by age? It would be good to know just what the edge profile should be. I'm thinking that it really should have a lip and that something like what I've posted below would work well.
If these have been NLA for too long that no one has one, making a model to mold is the trick, but I believe it can be done in softer materials, working up to the final mold. Shrinkage must be monitored and adjustments made so that the final product fits correctly.
I'm feeling that molding the part is the best way, the trick is of course, making the mold. I like the idea of 3D printing, but feel it just can't hold fine detail unless you spend quite a bit for the best printer.
I have some Hi Temp molding material that is capable of taking high temperature, so can be used for injection molding, at least for short runs. Since we don't need a huge number of these, this should work. I have the plans and materials to build a small injection machine, I just need the time for such a project. It's on my wish list.
Final material to make these out of? There are many versions of silicone so that might actually be the best choice, which wouldn't need to be injection molded with heat. It is possible to make your own rubber, but I have no idea about durability. Silicone excels in many criteria. Certainly the OEM ones didn't last as long as we'd have liked as it is. Anyway, it all would be a lot easier if we had a good one to use as a model to create the molds.
ian
If these have been NLA for too long that no one has one, making a model to mold is the trick, but I believe it can be done in softer materials, working up to the final mold. Shrinkage must be monitored and adjustments made so that the final product fits correctly.
I'm feeling that molding the part is the best way, the trick is of course, making the mold. I like the idea of 3D printing, but feel it just can't hold fine detail unless you spend quite a bit for the best printer.
I have some Hi Temp molding material that is capable of taking high temperature, so can be used for injection molding, at least for short runs. Since we don't need a huge number of these, this should work. I have the plans and materials to build a small injection machine, I just need the time for such a project. It's on my wish list.
Final material to make these out of? There are many versions of silicone so that might actually be the best choice, which wouldn't need to be injection molded with heat. It is possible to make your own rubber, but I have no idea about durability. Silicone excels in many criteria. Certainly the OEM ones didn't last as long as we'd have liked as it is. Anyway, it all would be a lot easier if we had a good one to use as a model to create the molds.
ian
Sfdon posted a photo of a bunch earlier in this thread.
My seal is fine also. I don’t think they get ravaged by age. I think they simply lose their flexibility. I have a normal looking perfectly round gasket that has almost zero flexibility.
Material selection is the only hard part of this process IMO. I could have a precise mold in two weeks. I’m not going to pursue this but I’m happy to chat about this one if you want Chris.
Material selection is the only hard part of this process IMO. I could have a precise mold in two weeks. I’m not going to pursue this but I’m happy to chat about this one if you want Chris.