#1180509 - 08/21/07 05:55 PM
Fabrication
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SnakeBite
Never say No...Just over charge.
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Want to work with fiberglass, plexi, metal or exotic composites. Just ask! I have much experience building show vehicles and I am an artist on the side. I doubt I can be stumped, but I am up for the challenge. Try me.
Just remember one thing when it comes to fabrication. Vehicles should never be modified for its intended safety. Vehicles are designed today to save your life and let’s keep it that way. Also you never want the vehicle to inhibit day to day operation unless it is strictly a show vehicle. 
Edited by SnakeBite (08/21/07 07:09 PM)
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#1198961 - 09/12/07 09:15 PM
Re: Fabrication
[Re: SnakeBite]
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speakermakers
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First off let me say great pic with the monkey jamming on the guitar!
How do you deal with shrinkage issues when you are filling a seam between two materials close to a surface that will be painted. For example, blending an ABS kit into an ABS or PC dash trim on an American vehicle like a jeep liberty or a Chevy pickup?
I have some methods that I use but I am always looking for that ultimate solution. In the past I have asked qualified individuals from select products as well as various individuals that I have met at MERA. They never have a decent answer. The normal answer is use less hardener in your body fillers. That’s a cop-out. All popular body fillers and polyester resins shrink 7-9%. This is a tough one but I am curious. Do you have the solution?
_________________________
Performance first! I say what I do and do what I say. Deal with it. I don't know everything only because I choose to learn more every day.
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#1199058 - 09/13/07 04:35 AM
Re: Fabrication
[Re: speakermakers]
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SnakeBite
Never say No...Just over charge.
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When blending things to fit or what this industry calls " Beading" anything that has to be filled that is thicker than 1/4" should be filled with Marglass ( reinforced body filler) or something comparable. There is minimal shrinkage with Marglass and it will add tons of strength.
Then your bondo/ bodyfiller coat will be very thin where shrinkage is not an issue.
I always try to use the minimal amout of hardener for each situation i use it in. If you mix hardener to hot it can crack as wel, because of rapid shrinkage. If that area you are filling in is thin it will never create enough heat to warp or crack.
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#1200051 - 09/13/07 07:23 PM
Re: Fabrication
[Re: SnakeBite]
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speakermakers
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I am afraid that I was looking for a better answer. Not that there is anything wrong with your solution. It might very well be the only solution when butting up two parts where the seam between the two is very close to the surface that will be painted. The problem with using any polyester based product is that it will continue to shrink for several days causing a line to appear under the paint (even with Marglass). Even when using the correct amount of hardener. The manufacturers of all major brand fillers agree on this.
The two solutions that I have been using work great but involve considerably more work.
Solution 1
Cover the entire surface with modified twill (a very formable fiberglass cloth) and use vinyl-ester instead of polyester (much stronger and forms a bond to your project similarly to the type of bond that you get with epoxies). Use a spiral roller to roll out excessive resin and achieve a smooth surface. Then skim with body filler. Now all shrinkage will be forced side to side instead of sinking from the surface down and will be resisted by the fiberglass mat. The problem with this method other than the extra time is that you add a minimum of 1/16” to the thickness of your project. Some times you will find your self in a 0 degree tolerance situation where this simply will not due.
Solution 2
Build your entire project normally and then cast a mold over the top of it (this must be done the same day). Now that you have a negative of your project you can cast replicas. In the event that I need a part that is absolutely perfect with no shrinkage and high strength I will lay up a glass/epoxy part (1-2% shrinkage). In the event that I can afford a little shrinkage over all I will just use Vinyl-ester/glass. Doing it this way I no longer have to worry about seam lines showing through the paint because it is one solid piece. Also I now have a mold that I can use for future replicas. For example I have a couple of molds for Chevy pu A pillars with tweeter mounts in them. I use these all the time.
_________________________
Performance first! I say what I do and do what I say. Deal with it. I don't know everything only because I choose to learn more every day.
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#1200064 - 09/13/07 07:50 PM
Re: Fabrication
[Re: speakermakers]
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SnakeBite
Never say No...Just over charge.
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I am afraid that I was looking for a better answer. Not that there is anything wrong with your solution. It might very well be the only solution when butting up two parts where the seam between the two is very close to the surface that will be painted. The problem with using any polyester based product is that it will continue to shrink for several days causing a line to appear under the paint (even with Marglass). Even when using the correct amount of hardener. The manufacturers of all major brand fillers agree on this.
For perfect results option to is the best. But considering the money and time it will take (the average person) to achieve is not really an option in the normal everyday shop.
Polyester resin will shrink up to 6 months (total fully cured resin). Therefore shrinking will continue during the whole process. Also resin has a shelf life of 90days
There are different qualities of resin
Good- General Purpose: this is the most basic of all resins it is unstable and shrinks allot when cured
Better- Tooling: this is the best resin for our industry because it is still reasonably priced. It is far more stable the GP and it shrinks considerably less
Best- Casting: This is very expensive and the best resin you can use. Of course it to will shrink but I would say around 1% which is not visible to any human eye.
I use tooling resin and the methods I explained in my previous post. You will never find "a line to appear under the paint" on any of my work. Any successful fabrication job is 80% prep, which includes experimentation and learning the tolerances of the materials used.
Remember there is better ways to do this and I can think of 3 more (not including the 2 you mentioned) off the top of my head. Remember this stuff is part of a business most of the techniques used today are to make money.
Let me ask you a question? After your final coat of filler and before your final paint what do you do? How do you get it ready for paint?
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#1200076 - 09/13/07 08:12 PM
Re: Fabrication
[Re: SnakeBite]
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speakermakers
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Usually transtar urethane primer. So is tooling resin your answer to my original question or is it Marglass? Care do divulge the remaining three processes that you mention you know of?
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Performance first! I say what I do and do what I say. Deal with it. I don't know everything only because I choose to learn more every day.
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#1200190 - 09/13/07 09:53 PM
Re: Fabrication
[Re: speakermakers]
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speakermakers
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I should add that I agree that my second option is not for the average shop or individual. See I work on installs that are in the 10-50K range and last anywhere from two weeks too 6 months every day. I realize that this is not the norm. But an installer in my position can not afford to have a comeback every 6 months. You asked for a challenge and here I am. You obviously know your stuff and are in a unique position much like myself to be exposed to cutting edge technique. I appreciate any further info you might have.
_________________________
Performance first! I say what I do and do what I say. Deal with it. I don't know everything only because I choose to learn more every day.
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#1201548 - 09/15/07 10:15 PM
Re: Fabrication
[Re: speakermakers]
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speakermakers
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Performance first! I say what I do and do what I say. Deal with it. I don't know everything only because I choose to learn more every day.
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#1201750 - 09/16/07 12:33 PM
Re: Fabrication
[Re: SnakeBite]
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SnakeBite
Never say No...Just over charge.
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First let’s start with the remaining three processes. Then I will talk about why I think you are having seam bleed through issues.
Processes
1. Vacuum forming: This is something I am getting into right now, using plastics, carbon fiber, and laminates. Here is an example of a home-made way to do this Vacuum Vid . Once you make your “plug” (by making a negative casting) you can mold anything in few minutes.
2. Silicone injection Molding: This requires a two part negative cast to poor various composites into to form your part. Using a silicone mold gives you the option to cast 5000+ parts from one silicone mold. Here is a link of an example of what can be done Silicone molding demo . Also is a link to show the different kinds of plastics and mold materials you can use. http://www.polytek.com/products/poly_plastics.html
3. From Scratch: Well this is basically making the whole thing from scratch using the normal fiber glassing techniques. This is pretty self-explanatory
Now let’s talk about your bleed through. Do you use an adhesive promoter on whatever plastic pieces you are going to finish? What type of plastic do you have this issue with? What grit are you sanding your part to before you cover with transtar urethane primer, and how many coats? Also what do you sand the primer to before paint. Finally after you paint what is your next process?
I need the rest of the answers to the question above to be totally sure what your issue is. As of this moment I your issue sounds like it is the transtar urethane primer. I think it’s the primer because it is urethane based but it’s a very good primer for something other than you is doing. The reason I say this it polyester resin as well as vinyl-ester will continue to gas off (cure) for a certain period of time. The urethane primer probably is porous to the “gassing off” causing the paint to swell in those joints, sanding scratches, anywhere to unlike materials meet. I know it is a sealer as well but it is not the same chemical make-up as polyester based composites.
I use and have never used anything else except a high build Polyester primer like this Poly here , which hardener is MEKP just like the resin. The primer will fill n pin holes and 220 grit sanding scratches when sprayed properly. It is polyester based and has "0" shrinkage, also seals the part completely from the “gassing off” of the part. It is the same chemical make-up as polyester resins so no contamination, rejection effects will occur. I have been successful with this method for over 10 years and teach this every month in a fabrication class.
Just to add one more thing.
It could also be the bonding method you are using to bond the structure to plastic. There are several types of plastic and it requires knowledge on how to fabricate with them.
Edited by SnakeBite (09/16/07 04:35 PM)
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#1201920 - 09/16/07 07:23 PM
Re: Fabrication
[Re: SnakeBite]
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speakermakers
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You have brought up several very good points. All of which I have all ready investigated and rejected as the core problem. And let me say once again that If I did not think that you might have the answers that I am looking for that I would not be wasting my time. And thank you for your time. First let’s start with the material that I am bonding to. I have experienced this problem with numerous types of materials. I am convinced that the prep of the materials is not the problem. Last year I had some shrinkage problems when butting up two ¼” thick pieces of flat aluminum together. The two pieces where bolted together by placing another 1/4” piece beneath the joint. After that I was left with a paper thin joint between the two surface pieces. I filled the joint with Dynaglass, sanded with 80 grit and then smoothed over with Rage Extreme, sanded with 220. Then the piece was sprayed with the Transtar primer. After a month of being exposed to the summer heat the filler in the joint shrunk leaving a very visible line. Also I noticed that some 1/8” holes that I drilled (no dissimilar materials here) and filled on this same project did the same thing. I wish that I could post some pics but as far as I know this forum dose not allow that.
As far as how many coats of primer. I usually spray a single medium coat and then use guide coat to find imperfections, Fix them and then spray a final medium coat.
I have used Evercoat feather fill polyester based primer several times in the past. It’s a good primer and has its place. This primer dose shrink. Much like the Marglass shrinks. You can contact the manufacturer to confirm that. I did. I like the polyester based primer but the paint manufacturers will not guarantee the results when you use these primers. In short I have done my home work and the primer is not the problem. I have had the shrinkage problems even when I have textured and dyed my parts using sems products all around. I believe that the solution is a filler that shrinks 1-2% instead of 7-9%. I have found a product, Evercoat white marine filler. This filler shrinks much much less than other fillers. It is made to repair gelcoat both above and below the water line on boats. I have found dozens of uses for this low shrinkage filler around the shop. What I was hoping for was a solution along these lines. I thirst for knowledge and a value any additional information that I can get. I think that you have the ultimate job teaching this stuff. Thank you for your time and efforts. If you have any more information on this subject it will always be appreciated not only by myself but others as well.
_________________________
Performance first! I say what I do and do what I say. Deal with it. I don't know everything only because I choose to learn more every day.
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