#31
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https://www.allmetalshaping.com/showthread.php?t=20580
Here I try solved one of the problems. During a consultation with a supplier of professional materials, I was informed about long-term properties. At the same time, knowledge from practice was shared. One block of polyurethane was used for 20 years in production - molding. The properties of the material have not changed much. Unlike the samples that were displayed in the office where we were. On the glass shelf, there were marks under some of the displayed pieces and the material was visibly changing the color of the surface. It was the effect of light and not using - not compressing. That's why I asked about longer-term experience. Polyurethane degrades even in my tools that I don't use. Is there another type of polyurethane that is stable?
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Jaroslav |
#32
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Quote:
I'll be happy to try, but since I didn't document the process with pictures it might be a little difficult. First of all, I took a good NOS horn that I wanted to replicate and cleaned it. Silicone rubber has the nice property that it doesn't really stick to anything but it self, so no need to prep the part with any kind of mold release. If I remember correct I think I might have given it a super thin wipe with vaseline or car vax - I can't remember. Next part was to figure out how to create a split mold. I decided to split the mold the very same place that the factory did it. That's where it's least visible and also what makes sense in terms of draft angles (ability to get the part out of the mold after casting). Fortunately silicone rubber is also very flexible, so in that sense also forgiving in case one create a "bad" mold with interlock - you simply just pull and the mold will flex out of the way. I build a small box out of some plastic sheet. big enough to accommodate the part + the extra wall thickness I deemed needed. I had a 1 kg silicone kit, so I had to do some simple calculations to ensure that the box minus the part wasn't bigger than what I could pour with the 1 kg kit. I've seen more than once that people has built similar "bounding box" out of Lego bricks - simple and smart if you have them at hand. I used this product: https://www.easycomposites.eu/as40-a...ilicone-rubber Silicone rubber comes as "condensation cure" and "addition cure" variants. Addition cure silicone rubber is stronger and more durable and only costs slightly more. So that's what I chose. Now the mold has to be poured in two steps to create a split two piece mold like mine. I did that by hot gluing "flanges" onto the horn where I wanted the split. The flanges being as wide as the inside of the box. I also glued 4 random plastic caps to one side of the flanges to create index tabs to accurately assemble the mold afterwards. Then positioned the part in the box and glues the flanges to the inside of the box. This random picture off the internet should explain what I mean by index tabs You can also see them on the picture I posted earlier Setup ready - now onto mixing the first batch of silicone and degas it. I think a video explains degassing better than I can. Here's one from Easy Composites https://youtu.be/GKddrZI4qAo Pour the silicone and let it cure After it had fully cured I carefully removed the flanges and index caps, trying to let the horn stay in the silicone part without disturbing it too much. Then I smeared a layer of vaseline on the part of the silicon the would mate to the other half, so that next batch of silicon wouldn't stick to it. Rinse and repeat - mix silicone, degas, pour and let cure. And that's it. Horn could be removed and mold ready to cast it's first part. This is the vacuum pump I got: https://www.easycomposites.eu/ec4-co...es-vacuum-pump And this is the degas chamber I got: https://www.easycomposites.eu/dc26-v...ng-chamber-26l (there is absolutely no reason why you couldn't make your own - it's a simple part) I bit pricy but I use it for other endeavors such as composites stuff. I wanted something I knew would work. Casting the new horns First I bent some strips of stainless and welded the fasteners to it. That assembly I simply just pushed into the bolt holes in the mold. As mentioned earlier this turned out to be a bit tricky as the PU I use has a very short pot life. It would simply set in the cup before I could manage to mix properly, degas and pour it into the mold. I eventually succeeded by doing 2 pours. I set up two cups and put in the required amount of PU part A and the black pigment. Mixed that thoroughly. Then I made sure I had everything lined up ready to go and put PU part B in first cup. Mixed really well, put cup into degassing chamber and degassed just enough to leave me with enough time to pour. Poured into the mold and immediately started preparing second cup. Mixed, degassed and poured. After a few hours the horn could be removed. The point/line where first pour stopped and second one started is completely invisible and it doesn't seem to have any impact on strength of part once fully cured. Again, I used this PU: https://www.easycomposites.eu/xencas...-casting-resin And this pigment: https://www.easycomposites.eu/black-...ethane-pigment I could cast exactly 4 horns from 1 kg kit - if I hadn't screwed up Oh, and to determine how much PU to mix, I took a big measuring beaker and filled it accurately to an index. Then submerged the horn and took a reading of the water level. The difference between first and second reading is the volume of the part and the volume of PU to mix + a little extra. Anyway it is difficult to explain in text, but please just ask questions.
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Sune Oestergaard Opel Kadett c Coupé build thread: https://allmetalshaping.com/showthread.php?t=21216 Last edited by Sune; 08-10-2022 at 03:14 PM. |
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Alright onto next installment of patching up the old Kadett.
I found that I just jumped a bit around and did a bit here and a bit there. I needed to attack it in a more systematic manner. For now I believe that starting from the rear of the car and working my way forward makes sense, as there is a lot to be addressed in the rear wheel wells and arches before I can recreate the rocker panel and associated inner structure. But along with inner wheel wells in the rear goes the boot floor. So that's where I focused. Now, I don't know if I'm overreacting with my aversion to pitting. The boot floor obviously had places where it was badly corroded but the majority of the boot floor area wasn't rusted through - it was just badly pitted. I just couldn't bring myself to called it "fixed" and cover the pitting with filler. I ended up cutting so much out that I was left with no boot I don't have any good pictures of the pitting in the boot, but you can just about see it here on the chassis leg in the boot (new floor under installation) Would you have left it as it is? Anyway decision was taken. At the time I didn't have the courage to try to make my own floor from scratch. I found a NOS boot floor from a Brazilian Chevette thinking that it would be the same since the car is basically the same as the Kadett. It turned out it was not - a far cry from. It LOOKS the same but the location of features was different. So, instead of trying to modify a 400€ panel that didn't fit, I decided to bite the bullet and look for an original Opel replacement. I managed to find one at an old German guys attic. I won't tell you how much I paid, but ouch The real deal At the same time I found a NOS rear panel, so I bought that instead of fixing the old one. Old rear panel cut out and new floor loosely fitted The "new" flor had some surface rust from 40 years in an attic, so I sanded it down to bare metal and gave it a coat of epoxy. Used the holes left from removing the spot welds on the old floor to plug weld the new floor once positioned correct Now remember the pitting on the left chassis leg? It was also rather thin in some areas, so when I found a reproduction, I bought it. I left it in place until the new floor was welded in. But man, it had to be the worst reproduction. Full of wrinkles from pressing it. Poor definition of the features. And of course it didn't fit well. After a lot of time with hammer and dolly I could twist and bend it until it fit somewhat. Where it didn't fit I had to cut away and remake Didn't mate up to the rear panel either New end made Bracket from chassis leg to bumper mounting on rear panel needed some massaging. A bit of weld-through and spot welded back in place Rear panel then spot welded in place. Now I could bring it back into the rotisserie - nice. That was quite a few hours for me even though I "cheated" with new panels
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Sune Oestergaard Opel Kadett c Coupé build thread: https://allmetalshaping.com/showthread.php?t=21216 |
#34
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Well done on getting a NOS panel like that as aftermarket generally is as bad as you found out.
In case you are short of any parts that we have here, I live not far from them and can send things over to you if they wont. https://www.rarespares.net.au/raresp...rt=description
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Marcus aka. Gojeep Victoria, Australia http://willyshotrod.com Invention is a combination of brains and materials. The more brains you use, the less materials you need. |
#35
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Thanks for the details on the silicone mold casting!
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Larry |
#36
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Pehr Norström |
#37
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Thanks for the link, Gojeep. I can recognize a lot of the panels. I think that the majority of them are the same ones that circulate here in Europe.
Next update: Boot lid fitted and adjusted. Close to being okay. But the lid it self needs more work (evident form the marks after running a sanding block over it). One of the rear quarter corners have had a smash repaired at some point. The shape is not right and a lot of bad marks from a pick hammer. I tried to massage it back into shape. The area where the epoxy is ground off: It's missing some crown at the back I slowly bumped and smoothed and checked with body file I have to admit that it is difficult for a rookie. It's not all there yet, but I decided to stop and have a think about it. I'm afraid of overdoing it and create more trouble for my self. Onto the rear inner wheel wells. A lot of work here. First on the portion facing the boot. Rotten bits cut off and flange on outer half repaired New corner for outer half made Then a patch for the inner half. Tried these cheap clamps for holding the piece in place. Not sure if I like them or not Then the outer lip of the inner arch needed attention. I cut the outer arch off - as little as possible. I'm not very confident in having to tackle the outer arch as I'm afraid of creating a lot of warpage. I can't get to the back side and planish, so TIG is out of the question in my opinion. I've marked 100 mm from edge on arch before removing so I have a reference if I f... it up too badly. Don't know if it is going to help me anything, but better safe than sorry As you can see inner lip is quite crusty but only the part that meets the outer arch. Folded a piece of sheet 90 degrees and shaped with shrinker/stretcher. Used replacement outer arch for reference Spend a lot of time fitting it up so that dimension/placement is as close to original as possible. Tag, weld, grind. Rinse and repeat on the other side (only inner arch so far. saving the outer to all repair in wells are done)
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Sune Oestergaard Opel Kadett c Coupé build thread: https://allmetalshaping.com/showthread.php?t=21216 |
#38
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The forward side of the wheel well also needs quite a bit of work including the floor that meets up to the well. From this previous picture, you can see that I have cut out a piece (both sides) due to bad old repairs and corrosion
a few bits needs repair before I can patch that hole up again Recreating the corner of the floor A bit of shape in it, hard to see on picture Cleaned up well Patching the outer half of well The other side was a bit worse Patch on inner rear seat structure (followed by brushing phosphoric acid and neutralizing the rust spots before priming them) The recreating the part I cut out Fitting up and welding in Fitting the big patch on the inner well. There's an indent made where a hook is spot welded to, for mounting of rear seat foam/upholstery Spot welded along the edge/flange That's how far I got this time around. I don't get to "visit" the car that often. It's in my parents garage and it requires some logistics every time I go
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Sune Oestergaard Opel Kadett c Coupé build thread: https://allmetalshaping.com/showthread.php?t=21216 Last edited by Sune; 11-13-2022 at 11:07 AM. |
#39
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Good stuff there.
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#40
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Great work! I just found this thread and will continue to follow. I think putting a Mazda rotary engine in that car is a great idea! Good luck!
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Rock. Able |
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