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Old Nov 23, 2010, 01:45 AM
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wyowindworks's Avatar
Cody, WY
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Originally Posted by skinnydoc View Post
Where's your bolt throughs on your pics above Adam? As the guru of bladdering your departures from the dogma are noted. Am I missing something? Maybe you just clamp?
No bolts....I use 15 clamps to hold it together. There are 15 pieces of 1/4" plywood that help distribute the clamping pressure and allow me to slightly change the clamping locations so the pressure isn't always in the same place. The ply is done in pieces because the CTE is different than the mold which could induce warping. The mold construction is: Surface coat, carbon tow in the corners, 30 ounces of glass, 3/4" of tooling compound around the flange and 1/4" everywhere else, 30 ounces of glass. This mold has to be shipped to the customer once the production run is complete so it had to be lighter than my typical molds. It's very stable and light. The method isn't cheap though. The materials alone are somewhere around $350.00. I thought that the method would be fast, but those tight corner and shapes made for around 30 hours of labor in the mold.

Adam
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Old Nov 23, 2010, 05:23 AM
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Alex.Schweig's Avatar
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Adam, which tooling compound did you use for this particular mold?
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Old Nov 23, 2010, 11:34 AM
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Cody, WY
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Originally Posted by Alex.Schweig View Post
Adam, which tooling compound did you use for this particular mold?
Adtech EL-323-TC
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Old Nov 23, 2010, 12:08 PM
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not easier...

whew, that sounds like a PITA. I guess the sand/fill backing is a lot faster and cheaper. Poraver may have been good for this, given its lightness. Hard to get though. I want to get some to try out.

so tooling compound is somehow tougher for the flange.. vs surface coat, homemade by you?

thx for the info. back to Jim's build....

Ben
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Old Nov 23, 2010, 12:12 PM
Entropy is happening!
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Bellingen NSW Australia
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Cte

Quote:
Originally Posted by wyowindworks View Post
The ply is done in pieces because the CTE is different than the mold which could induce warping. Adam
What's the "CTE" Adam?
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Old Nov 23, 2010, 12:32 PM
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let me guess...

coefficient of thermal expansion??

is there really that much heat dynamic going on? Outside of hotboxing?

oops I just faced my mold backing with a solid piece of masonite... I guess we'll see what happens. On the other hand with all the glue and random orientation of the particles of wood, I'm not sure if there is any significant expansion.

still learning....

Ben
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Old Nov 23, 2010, 01:12 PM
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Cody, WY
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Originally Posted by skinnydoc View Post
whew, that sounds like a PITA. I guess the sand/fill backing is a lot faster and cheaper. Poraver may have been good for this, given its lightness. Hard to get though. I want to get some to try out.

so tooling compound is somehow tougher for the flange.. vs surface coat, homemade by you?

thx for the info. back to Jim's build....

Ben
The issue with just back filling is a lot of strength potential is lost. Doing glass/backing/glass is much stronger and more stable. The tooling compound is used just like Poraver (glass/poraver/glass) but has much higher strength. I don't back fill with just sand/epoxy anymore. All my uses of sand/epoxy incorporate some kind of sandwiching (glass/sand/glass). I also use full length keys on everything mold now.

CTE is coefficient of thermal expansion.

Adam
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Old Nov 23, 2010, 01:28 PM
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Oh now I see! The ply is incorporated into the mould structure, is that correct?
I was thinking that the ply was loose and assembled onto the backs of the halves while clamping up.

And do you use conventional slip clamps Adam? I am wondering about using some threaded rod and stout pieces of timber across top and bottom to clamp. (rod through each end with nuts etc.). Maybe 2x1 hardwood and 8mm (5/16) rod.

And why the full length alignment keys?

Jim.
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Old Nov 23, 2010, 01:36 PM
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technique?

Quote:
Originally Posted by wyowindworks View Post
The issue with just back filling is a lot of strength potential is lost. Doing glass/backing/glass is much stronger and more stable. The tooling compound is used just like Poraver (glass/poraver/glass) but has much higher strength. I don't back fill with just sand/epoxy anymore. All my uses of sand/epoxy incorporate some kind of sandwiching (glass/sand/glass). I also use full length keys on everything mold now.

Adam
thanks Adam, as always. If you have a sec (prior to dvd release), do you mean like this: surface coat, 2-3 layers, then reinforcing glass x several, then sand, then glass on top? or, are there some more interim glass layers in the sand backing? Are you not using the through bolts anymore? How do you keep bolts from getting glued in by extra epoxy? a little grease in the threads?

@Jim: I think the full length keys are for the bladder technique, collecting excess epoxy. I cut mine the other day with a 1/2" plunge bit, I had a pretty ugly looking key, I think I need more router time! Thanks for your patience with my questions.

Ben
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Old Nov 23, 2010, 01:46 PM
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Cody, WY
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Originally Posted by Jimbello View Post
Oh now I see! The ply is incorporated into the mould structure, is that correct?
I was thinking that the ply was loose and assembled onto the backs of the halves while clamping up.

And do you use conventional slip clamps Adam? I am wondering about using some threaded rod and stout pieces of timber across top and bottom to clamp. (rod through each end with nuts etc.). Maybe 2x1 hardwood and 8mm (5/16) rod.

And why the full length alignment keys?

Jim.
The ply pieces are glued onto the back of the mold so the clamping force is fully/evenly transferred to the mold....and I don't have to fuss holding them in place. I use C and F clamps.

The full length alignment keys improve the stability of the mold and double as a trap for the excess resin that is expelled by the bladder. The resin has to only migrate 1/4" to the trap allowing the rest of the flange to be clear of resin. This allows the mold to close further resulting in tigher seams that don't step. Also, the mold doesn't drip and ooze all over the bench and hot-box.

Every mold that I have made using intermittent keys (even the beefy molds) have had small stepping issues after many uses. The full length keys seem to have helped with this issue.

Adam
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Old Nov 23, 2010, 01:58 PM
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Originally Posted by skinnydoc View Post
thanks Adam, as always. If you have a sec (prior to dvd release), do you mean like this: surface coat, 2-3 layers, then reinforcing glass x several, then sand, then glass on top? or, are there some more interim glass layers in the sand backing? Are you not using the through bolts anymore? How do you keep bolts from getting glued in by extra epoxy? a little grease in the threads?
Yes. Surface coat, tow in the corners, glass, sand, glass. I do cheat in some ways. I hate the laminating of all the corners and such, so on some things I do: surface coat, tow in the corners, sand/epoxy to just past the highest point of the plug, 3 layers of 13 ounce glass (S-B-S), 3/4" more epoxy/sand, then 3 more layers of 13 ounce glass (S-B-S). The sides of the mold also get 3 layers of 13 ounce glass (S-B-S). This allows all the laminating to be done on flat surfaces. It's fast and stable, but heavy and a bit more expensive.

I've been doing some inflation bladder molds by just reinforcing the flanges with sand/epoxy. It goes: surface coat, tow in the corners, 30 ounces of glass everywhere, 3/4" sand/epoxy just around the flange, then 30 ounces of glass everywhere. These molds are good to 30-40 psi. This is my absolute bear minimum mold construction for two piece molds even if no bladders is used. I often use this technique with molds for joggle gasket tools.

I keep the bolts from sticking to the epoxy by putting them in a cup, shooting them with WD-40, pouring them onto a paper towel to soak up the extra, and use. I do that about every 15 uses. I tried the whole process with Frekote, but the WD-40 was more effective.

Adam
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Old Nov 23, 2010, 03:16 PM
Entropy is happening!
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Bellingen NSW Australia
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Cte

I am catching up on some of the rcgroups acronyms! (this one is not peculiar to rcgroups though, I am sure!).
The idea of using a steel reinforcing frame in my mould has concerned me for the very reason of difference in the coefficient of thermal expansion.
It may in fact be counterproductive! I an thinking of abandoning the idea and building much like you have done Adam.

Jim.
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Old Nov 23, 2010, 03:27 PM
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Using steel is fine in either small molds or molds that are not going to be heated to really high temps. The CTE of steel and fiberglass laminate is actually pretty close. On large molds it's important to add the frame after the mold has cured for several weeks. The mold shrinks as it's cures. Adding the frame too early can cause tension to build-up with the structure causing issues. It's pretty common for large molds to have steel back-up structures. Typically the mold interfaces with the steel in a way that they can expand independently.
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Old Nov 23, 2010, 03:29 PM
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Disregarding the CTE issues, the steel supports seam very helpful as a medium to permanently attach the nuts to. I've been attaching mine with JB weld to the fiberglass back but I only get about 2-3 uses before they crack and I have to replace them.

I been thinking of using some steel as a backer on the fiberglass and then tack weld nuts to it but so far it has been easier to just continuously replace the broken ones with more JB. Adam's clamping idea on holding the mold together sounds like an elegant solution but I wonder if they clamps would get in the way.

Alex ( Just thinking out loud)
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Old Nov 23, 2010, 03:36 PM
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Cody, WY
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Alex, it's possible to glue ply-wood peices to the perimeter of the mold and use a 1/4" blind nut into the plywood.

I glue washer and nuts to molds all the time using resin and WS 404 Filler. It's important to soak them in acetone and abrade them to facilitate the bond. I use a wheel in a dremel tool to abrade them. I also use nuts with those attached "goofy teethy washer things". The resin seems to really hold onto them.
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