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Old 10-10-2012, 06:02 AM   #136
ebrabaek
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Originally Posted by therivermonster View Post


Earling responded to my message about filling these pin holes and repairing the mold. He said just scrap it and make a new one which is probably the better idea, but I can't help to think that someday I'll have to repair a very important mold that has pin holes in it. So, (sorry earling) I'm gonna repair this mold...
I received an order today from US Composites that included some Cabosil epoxy filler. I think that I'll mix up some thickend epoxy to make sort of a putty, then just rub the mixture into the holes. Finally I'll sand with 800, 1500, followed by buffing and polishing.
Ha ha..... yeeeeeeessssss..... But that doesn't mean that you shouldnt try..... I just wanted to prepare you for what your in for.....
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Old 10-10-2012, 06:11 AM   #137
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Originally Posted by ebrabaek View Post
Ha ha..... yeeeeeeessssss..... But that doesn't mean that you shouldnt try..... I just wanted to prepare you for what your in for.....
I really appreciate the insight, earling, but I have to at least try...

In my mind, I just see myself rubbing a little thickened epoxy into the little holes, letting it set, then sanding it smooth. It seems (in my mind) like it will be doable. What issues have you had when doing this in the past?
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Old 10-10-2012, 07:44 AM   #138
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Originally Posted by therivermonster View Post
I really appreciate the insight, earling, but I have to at least try...

In my mind, I just see myself rubbing a little thickened epoxy into the little holes, letting it set, then sanding it smooth. It seems (in my mind) like it will be doable. What issues have you had when doing this in the past?
Nothing...... except you will be doing this step.....uhhhmmmmm...... should we just say.... more than once........ It is a good learning curve though.... Don't let me discourage you...... really... I mean that.
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Old 10-10-2012, 09:07 AM   #139
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Nothing...... except you will be doing this step.....uhhhmmmmm...... should we just say.... more than once....
Uhhhh, yup!
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Old 10-10-2012, 10:17 AM   #140
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Quote:
Originally Posted by ebrabaek View Post
Nothing...... except you will be doing this step.....uhhhmmmmm...... should we just say.... more than once........ It is a good learning curve though.... Don't let me discourage you...... really... I mean that.
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Uhhhh, yup!
Well, crap!!

Yup... I think that you guys talked me into it... I'll be making a new mold of the shroud...

I received some new epoxy resin from US Composites yesterday, so maybe I'll just lay up another mold using this.The new epoxy is quite a bit thinner then the stuff that I have been using, so it may do a little better dissipating the bubbles. It will also run off a lot easier, so this may be a problem. I guess we'll find out.

Also, I didn't like how the ends of the mold (the loose fabric) turned out on the last mold. I think that the next time around I'll build a nice flange to lay the fabric up against to make things a little neater.

I'll post on the new progress...
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Old 10-10-2012, 10:32 AM   #141
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OK......
So try the following.....
Mix the epoxy with slow...ehhhhh... motion.....
warm each parts to 80-90 deg.F. before stirring it....
if there is still bubbles...... elevate the temp to 100 deg under a heat lamp.... ( reduced pot life)
brush on first layer, making sure the brush does not run out of resin plentynes....as it will draw air.
lightly spray acetone on the top for any stubborn bubbles......
Repeat the above to achieve two coats before laying fabric..... Dry to a tack between layers.
Drink plenty of Coors premium brew....
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Old 10-10-2012, 11:15 AM   #142
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Originally Posted by therivermonster View Post
Well, crap!!

Yup... I think that you guys talked me into it... I'll be making a new mold of the shroud...

I received some new epoxy resin from US Composites yesterday, so maybe I'll just lay up another mold using this.The new epoxy is quite a bit thinner then the stuff that I have been using, so it may do a little better dissipating the bubbles. It will also run off a lot easier, so this may be a problem. I guess we'll find out.

Also, I didn't like how the ends of the mold (the loose fabric) turned out on the last mold. I think that the next time around I'll build a nice flange to lay the fabric up against to make things a little neater.

I'll post on the new progress...
For making moulds you will find using a filled polyester resin system, designed for this purpose, both easier to use and less costly than epoxy.
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Old 10-10-2012, 11:56 AM   #143
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For making moulds you will find using a filled polyester resin system, designed for this purpose, both easier to use and less costly than epoxy.
When I had a busines making laminate molds I opted for epoxy for a couple of reasons. The biggest reson was that my shop was in a detached building next to my house and I didn't want the fumes wafting unto where I lived. I also liked the ability to compleate the mold from start to finish in one lay up vs having to stop and let the heat disipate to avoid warpage. Add in the almost zero shrinkage of epoxy and sometimes the extra cost of epoxy is money well spent.
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Old 10-10-2012, 12:16 PM   #144
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For making a mold I highly recomend using a gel coat for thee mold surface. I have used different gel coats depemding on the application. while polyester gel can be compatable with some epoxies(you let the gel kick and cool before starting your lay up) I used to use an epoxy gel coat with a high alumina contend designed to be used in high heat applications. While it was much tougher to sand than standard poyester gel or even tooling gel it was sandable and more importantly it was repairable. I'd have to look in my files but the product I used to use was made by BJB enterprises.

Besides the repairability of gel coat another reason to use it in a mold is to isolate the fibers from the surface. You do not want the fibers exposed to the surface as they can wick moisture and cause problems not the least of which is delamination or blistering.

I have always prefered a dark colored gel as it helps when block sanding the mold and polishing it out. If you are only using epoxy resin and no gel you don't get the same visual feed back when blocking sanding a mold, a small thing but for big flat areas it is a help.

And last is that most gels are a bit more forgiving to impact than straight resin. I have never known this to be a problem except on the corners of the flanges and mostly from moving and storing the molds but is is something to be aware of.

And for repairing pin holes either in straight epoxy or in gel you might have better luck by enlarging the hole with a dremel. it seems counter intuitive but sometimes the air in the pin hole will not let you rub in any patch material but if the hole is a bit bigger there is room for the air to escape as the patch material is rubbed in.
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Old 10-10-2012, 02:29 PM   #145
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Originally Posted by redprimo View Post
When I had a busines making laminate molds I opted for epoxy for a couple of reasons. The biggest reson was that my shop was in a detached building next to my house and I didn't want the fumes wafting unto where I lived. I also liked the ability to compleate the mold from start to finish in one lay up vs having to stop and let the heat disipate to avoid warpage. Add in the almost zero shrinkage of epoxy and sometimes the extra cost of epoxy is money well spent.
Add to that, that polyester many times do not bond very good to epoxy......
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Old 10-11-2012, 07:07 AM   #146
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Originally Posted by redprimo View Post
When I had a busines making laminate molds I opted for epoxy for a couple of reasons. The biggest reson was that my shop was in a detached building next to my house and I didn't want the fumes wafting unto where I lived. I also liked the ability to compleate the mold from start to finish in one lay up vs having to stop and let the heat disipate to avoid warpage. Add in the almost zero shrinkage of epoxy and sometimes the extra cost of epoxy is money well spent.
It is nice to have this ability, as well as not having to stock as many different products.

Quote:
Originally Posted by redprimo View Post
For making a mold I highly recomend using a gel coat for thee mold surface. I have used different gel coats depemding on the application. while polyester gel can be compatable with some epoxies(you let the gel kick and cool before starting your lay up) I used to use an epoxy gel coat with a high alumina contend designed to be used in high heat applications. While it was much tougher to sand than standard poyester gel or even tooling gel it was sandable and more importantly it was repairable. I'd have to look in my files but the product I used to use was made by BJB enterprises.

I do think that using a poly tooling gellcoat to make molds seems like an interesting idea, and in all the videos that I've watched, it looks easy enough to apply, but it seems like people have a lot of problems with it cracking, wrinkling, and shrinking. These are not fun, expensive mistakes.

Besides the repairability of gel coat another reason to use it in a mold is to isolate the fibers from the surface. You do not want the fibers exposed to the surface as they can wick moisture and cause problems not the least of which is delamination or blistering.

It does seem like it would make a good barrier between the surface of the mold and the glass fibers. A nicely tacky layer of epoxy would do the same, wouldn't it?

I have always prefered a dark colored gel as it helps when block sanding the mold and polishing it out. If you are only using epoxy resin and no gel you don't get the same visual feed back when blocking sanding a mold, a small thing but for big flat areas it is a help.

I can see how this would especially be useful, especially with my recent experience trying to assess the condition of my shroud mold.

And last is that most gels are a bit more forgiving to impact than straight resin. I have never known this to be a problem except on the corners of the flanges and mostly from moving and storing the molds but is is something to be aware of.

I could see where this property could come in very handy.

I might have to try poly tooling gellcoat, and poly resin with mat glass to make the molds for the fenders.

And for repairing pin holes either in straight epoxy or in gel you might have better luck by enlarging the hole with a dremel. it seems counter intuitive but sometimes the air in the pin hole will not let you rub in any patch material but if the hole is a bit bigger there is room for the air to escape as the patch material is rubbed in.

This makes sense. I'll remember this tip when the time comes for me to fix an important mold.

Thanks a bunch redprimo for all the great info...
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Originally Posted by ebrabaek View Post
Add to that, that polyester many times do not bond very good to epoxy......

I'll keep that in mind. What about epoxy to poly? I thought you have done this before, earling?
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Old 10-11-2012, 07:26 AM   #147
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Mold repair, disrepair...

I decided to make a quick effort at repairing the mold. I also wanted to play a little with the Cabosil that I had received from US Composites...
Here is the Cabosil. It's weird stuff. I wonder if it's powdered Aerogel?


Getting ready to mix it with epoxy to make a putty. In this pic, I have mixed up a batch of the new epoxy from US Composites. I used the pumps that they sell for their epoxy systems. The ratio for this epoxy is 3 epoxy pumps to 1 pump of hardner. This makes a lot of epoxy. Way more then what I have been using for my projects lately, so I think that I'll just use the pumps to pump the liquid into cups on the scale and weigh out my mixes.


Here the Cabosil is mixed in. It doesn't take much to bring the epoxy to a mayo consistancy.


Next I rubbed this into ALL the tiny holes in the mold. Esentially the putty would go into the holes, but would be pushed right out. It just wasn't working well for the level of effort that I was willing to put into it at this time.


So I cleaned the epoxy putty out of the mold with acetone, then came up with an idea. I would apply some mold release to the mold, dump the rest of the epoxy into the mold, and if it came out in the morning, then I would make CF parts from this mold.


The epoxy has been poured.


And the following results from trying to release the epoxy from the mold. It didn't work out well and I think I know why...
I used the new Mcguires mold release wax followed by Partal PVA. The PVA fisheyes badly and does a terrible job covering the McGuires wax. I know this because I tried to apply PVA over the shroud plug this morning that I had just applied the wax to. The two did not work together at all which seems really strange to me.


So I got to work on the plug to prep it for laying up another mold today. I added clay to the ends in order to make a better flange on the ends. The clay will also keep resin from seeping between the plug and the plywood which was a small problem on the last mold. It should work better.




Here the plug has been waxed and PVAd. Like I mentioned above, the Mcguires wax didn't work with the Partal PVA, so I had to wipe all the PVA off and start from scratch with the Partal paste wax followed by the PVA.


Does anyone else have experience using the Mcguires wax with Partal PVA? Did you have this problem?

More to come as I lay up another mold. Cross yer fingers...
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Old 10-11-2012, 07:50 AM   #148
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I use it all the time
are you spraying light coats?

you might want to lurk here

http://compositescentral.net/index.php?
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Old 10-11-2012, 09:37 AM   #149
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I use it all the time
are you spraying light coats?

you might want to lurk here

http://compositescentral.net/index.php?
Thanks for the link! I'll head over there...

Regarding the PVA, I actually just wipe it on with a paper towel. I know, I know, I should spray it, but I don't have the equipment right now. Maybe someday soon.

I tried wiping the PVA in thick and thin layers but both fisheyed a lot. The PVA lays down just fine over the Partal paste wax.

On another note, I have just layed down the first layer of epoxy on the plug and it is nice, smooth, and bubble free. I swept a torch flame over the epoxy and all the little bubbles went pop pip pop. Now we'll wait to see if it fisheyes.
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Old 10-11-2012, 11:14 AM   #150
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You dont need to use PVA on moulds after the first couple times you make a part. Once the mould is fully cured, and used a few times, properly applied wax is all thats needed.

In regard to making moulds, filled polyester resin is what most pro GRP shops use for smaller moulds here in the UK, larger ones are generally vinyl ester. If you want to use epoxy no problem, but do bear in mind the cost of the mould will probably double, and you will need powder bound CSM for use with epoxy.

Its really a waste of time trying to make good a mould suffering from fish eyes, as by the time you have sorted these out properly, it would be possible to make 2 moulds using poly resin system, as long as your plug is 100%.

You can easily lay up about 6mm in one go with filled poly systems, which is generally all you would ever be likely to need for making bike parts.

Properly made poly tools last a reasonably long time, and I am still using ones that were made 5 years ago, with only very minor rectification work needed to impact damage caused by rough handling.
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