Try and roll the resin out slightly smoother. Just enough resin to impregnate the fiber. The texture should be in the surface.
Sandbags are not really a help. They distort the surface, and compared to vacuum the effect is limited.
After demoulding, do only a very gentle postcure, ramping up very slowly. Your resin seems to be a bitch.
One more thing… IF I cannot find a low/zero shrink tooling resin that has a peak exotherm UNDER 175F and I’m forced to use the 404 resin that seems to have a shrinkage problem… How many layers of 3/4oz or 1oz CSM (one at a time… 24hrs between layers) should I apply before its okay to finish bulking with 1.5oz CSM? Or do you advise I bulk the entire mold with 3/4oz or 1oz (wow that will be a lot of layers (thats up to 16 layers since I was planning on 8 layers of 1.5oz CSM) and a long time to build the mold…)
I agree (resin being the primary problem)! Should I be using a different tooling resin in place of the 404 Isophthalic Resin from US Composites (something with less/lower shrink or zero shrink… must have a conservative peak exotherm of 175F or less)? I can’t imagine I’m the first guy that’s ever needed a low shrink tooling resin with a low exotherm.
Your not. Epoxy is the answer to that dilemma. With epoxy you could do that whole mold, outside of the surface coat, in one shot. I’ve had 1/4" epoxy layups never get above 80* in a 72*shop.
I wonder if some of your problems is all the staging that you having to do to keep the exotherm low. In a recent paper that I just read, they found that most resins shrink at a higher rate as the cure progresses. The later part of the complete cure ends up causing the most shrinkage. This is why post-cure parts have problems with fabric print-through. So, in your scenario, you have the first layers shrinking more than the later layers simply because the cure has progress further on the face due to time. This would cause the mold to cup towards the face of the mold. Ideally, after all the resin has fully cured the laminate wouldn’t be cupped. Shrinkage and mold instability always go hand-in-hand though.
Maybe epoxy tooling resin IS the answer??? If so, I have a few questions:
- Which epoxy tooling resin do you recommend (brand, type and where to buy) for a mold my size (21" x 32" with the total thickness of the laminate approx 1/4")
Adtech EL-301 would work fine. If shrinkage is a major issue then you can use the EL-302-PC (although it’s more difficult to work with as it’s a filled resin).
- Is the epoxy tooling resin (that you recommend a zero shrink resin? Or at least REALLY low shrink?
Low shrink
- Will the epoxy tooling resin have any problems bonding to the orange PE tooling gelcoat I’m using?
I don’t know. I would just use an epoxy surface coat
- What is the gel time?
Epoxies can range for 30 to 120 minutes. If the tooling isn’t going to be vacuum bagged then the working time isn’t all that critical. You can just work in multiple smaller batches.
The one issue with epoxy systems is that you typically can’t use CSM. Epoxy typically doesn’t break down the binder. You would need to use varying orientations of woven fabrics.
UPDATE: I just spoke to Scott at PTM&W and he recommended their Aeropoxy PR2032 laminating resin w/PH3665 hardener (2hr) which should give me about an hour before it gels in my 90-110F+ ambient temps. Scott did however recommend that I first confirm epoxy will work with my PE tooling gelcoat (even though the pot life is horrible in the high AZ ambient temps… I love the shine & finish quality of the PE tooling gelcoat!!). According to Scott, epoxy doesn’t bond directly to PE tooling gelcoat very well but it should “should” bond to VE resin so the solution if this is correct is to apply PE gelcoat, then veil with VE resin, then bulk with epoxy. Can anyone confirm epoxy will in fact bond well to VE resin… Scott suggested I call Duratec as he thought they make/sell something called “bond coat” that he believes is nothing more than VE resin… After this “bond coat” has been applied over the PE gelcoat, epoxy will then stick to the bond to the “bond coat”. I did a google search for “duratec bond coat” but couldn’t find anything…
Please advise,
An epoxy surface coat will be just as glossy as a PE gel-coat. It will identically replicate your plug finish. A PE gel coat will polish easier and better than an epoxy based one if you have to rehab the finish though. Any epoxy based finish is typically more durable than a PE one.
Hello again. I admire your efforts, and I respect that you are prepared to ask for help, but you are way overthinking what you are doing. The mould you are trying to create is a very simple shape. It is small. It doesn’t have any sharp corners. It is as simple as a flat plate. And it’s dimensions aren’t that critical. Moulds like this one are built in composites shops everyday using the most basic materials. I agree with everything Wyo and Herman have told you, and epoxy would be an excellent resin. But this is a simple job and you should be able to build a first class mould using PE Gel and VE resin. Unless you are planning on making a lot parts out of this mould, then you don’t need tooling gel. You don’t need to use a tooling resin either. Some things to think about :-
How much and how rapidly does your workshop temperature vary from day to night?
What is the pattern ( wing ) painted with? If it is 2 pack polyurethane, did you let it outgas for sufficient time before starting your mould?
10 coats of TR102 are more than enough, and as I said before, shouldn’t cause a problem. But changing wax midstream and adding more coats is a waste of time.
Gelcoat in the morning.
450 to 550 microns ( 0.020 " ) is plenty of gelcoat. You don’t need to give it a second coat.
Spray Gelcoat should not need thinning when using a bucket gun. The gelcoat should be coming out of a bucket gun in a much larger droplet size than the way paint comes out of a gun. If it is thinned so that it flows on the surfacelike paint, then the high solvent ( acetone, styrene ) content could be causing your pre release
No need to sand gelcoat. It will stay chemically tacky for weeks. Do not wipe it with acetone.
After lunch laminate ONE layer of 225 gsm ( 3/4 oz ) split strand mat with VE laminating resin.
Split Strand Mat is Chop Strand Mat, but each SSM fibre only has half the filaments of CSM fibres.
Make sure whenever you buy 225 that it is Split Strand. It is a basic material in any glass shop and is used for tie layers. I rarely use veil or tissue. It just gives a thick layer of resin with practically no reinforcment.
You seem to be using low catalyst percentages. Are you using summer grade resin and gelcoat?
When sanding the sharpies off before the next layer, it is just a very light rub by hand only for knocking the spikes off. If the laminate is well rolled there will only be sharpies on corners. The surface doesn’t need keying. Your job is so flat you should not need to sand it at all. No need to wipe with acetone. The resin stays chemically tacky for weeks too.
The next morning apply ONE layer of 450 gsm ( 1 1/2 oz ) CSM.
Now you are on your way.
The mould can be post-cured after release, if you intend on post-curing the parts in-mould.
What ever the problem is, it will be very basic. If you don’t solve the problem, throwing more expensive materials and more complex methods at it might create more expensive failures and more wasted time.
Good luck
Greg
ASB, why do you think that the mold is pre-releasing mid construction.
I appreciate your comments (Greg). I agree on some of your points and disagree on others… Follows is some clarification:
The dimensions of the molds and in turn the parts to be built from the molds is critical. I spent many hours building, shaping, sanding and polishing the plugs to get just the right shape so it seems logical then that any parts produced from the molds will not be dimensionally accurate if they’re produced from molds that have pre-released and lifted/warped 1/8" - 3/16" in areas. The resulting parts built from warped molds would be no different than if the molds were built off of poorly shaped plugs with no pre-release – the warped shape of any parts built from such molds would ultimately show when finished with a nice glossy paint job. Personally, if I was going to pay good money for a new set of gear doors I'd expect a quality product. The only reason I decided to build the molds vs building a one off set of gear doors was because I wanted the ability to reproduce/sell gear doors to other interested builders.
Ambient temps in my hangar vary approx 20-30F (85-95F in the early AM and as high as 120F+ by mid afternoon
The surface of the molds have been sprayed with Duratec PE surfacing primer, wet sanded and polished…. Then sealed and waxed.
The only reason that I switched wax (TR-102 to Dolphin Wax) was to eliminate the fish eye problem that I was having with the wax when spraying gelcoat. It worked…
The reason for the waxing overkill is because I was scared to death too have the molds stick to the plugs and ruin a $50K wing… overkill on wax.. absolutely… now it seems that I could have used a bit more “stick” because both mold making attempts have pre-released. Had I turned the wing upside down the molds would have fully released and fallen off the plugs from their own weight.
Re the gelcoat: I was simply following the instructions in the TDS “Apply 18mils +/- 2mils, wait until cured and apply a 2nd coat off 18mils +/- 2mils. Total thickness was ideally supposed to be 36mils but I accidentally exceeded this slightly (for reasons previously mentioned in another post). Also, for my 2nd attempt a true “spray” gelcoat was used without thinning. Other than spraying on a hair too thick it laid down beautifully. I waited 2hrs before applying the 2nd coat of gelcoat, then another 6hrs or so before applying the veil with VE resin. I did not sand the gelcoat or wipe with acetone before applying the viel/VE resin. The gelcoat had set up but yet was still slightly tacky as pressing my finger left a slight fingerprint in the gelcoat.
The next day (approx 20-22hrs after the veil was applied). I did “very lightly sand” the VE resin/veil and wipe with acetone. I did this because I’ve always been told that if you lightly sand VE resin and it makes dust (it did) you need to scuff the surface to get a good bond. If on the other hand it gums up the sandpaper then you don’t need to sand. I blew the dust off with an air compressor but some very fine dust remained so I saturated a clean cloth with acetone and wiped the veil before applying the first layers of CSM and 404 PE tooling resin.
The catalyst percentages were obtained from the gelcoat and resin TDS. It is VERY hot here in AZ this time of year.. That said, I don’t know if I purchased “summer” gelcoat/resin or not.
Am I over thinking this… Yes, quite possibly I am (my reasoning is simple… the more detail I share about my failed attempts the better all of you more experienced members will be able to diagnose what I’m doing wrong) That said, I’m just trying to learn how to build a quality mold (making plenty of mistakes along the way… as the next attempt will be my 3rd… each failure costing time and money). Composites Central is an awesome site with awesome members… I really appreciate everyone’s willingness to help out the “new guy”… all of the advice I’ve received thus far has been invaluable.
Now on to current events:
I’m very reluctant to try PE resin again for these molds… Logically speaking, I think Herman and Wyowindworks are spot on in that it’s my tooling resin shrinkage that’s the culprit. In one of my 3” diameter mixing cups this resin when ¼” deep (approx) is allowed to cure it shrinks so much that it pulls away from the edges of the cup approx 1/8”… that seems like a lot to me.
Yes, the shape of my parts are relatively simple but I’m also wondering if the slightly convex shape is contributing to the problem… It seems to me that any shrinkage at all would tend to release the part, especially since both past mold attempts practically fell off the plugs (super low stick) when I decided to demold and start over (after discovering the partial pre-release).
Question:
Can anyone confirm epoxy will stick to VE resin without any issues? I’d like someone to confirm this before trying the suggestion of the PTM&W tech (first spray PE gelcoat… then apply veil with VE resin.. then apply epoxy bulking with woven fabric). The thought here being that the VE resin will bond to the PE gelcoat (this is known) and then the epoxy resin will bond to the VE resin/veil (this I need to confirm).I only have questions at the moment Wyo.
JB Is the surface of the plug moving?
You have a fairly large daily temperature range.
Is there an air-cavity behind the hatch? If there is have you sealed the cavity so that the air can’t move in and out? If it is sealed the air pressure inside will rise as the temperature rises. If it is well sealed, can it cause the plug to bellow out? If it is not well sealed can the air escape and find it’s way in between the plug and the gelcoat? I can see a series of holes in the plug and it looks like they are covered by the mould.
To put the dimensional accuracy into perspective, I wouldn’t accept 1/8 inch warping in the bottom of my 20 foot boats. Your mould doesn’t have any sharp angles which tend to close up when you use PE. It has smooth curves which are easy to replicate. You are talking fractions of an inch. I am talking fractions of a millimetre.
Answers to your questions (ASB) below:
Is there an air-cavity behind the hatch? Yes, the wing is constructed of an upper and lower pre-molded skin. The plug was constructed over (with the wing upsided down) the landing gear bay (pocket the landing gear retracts into) using part of the lower surface of the wing as the plug. That said, there is no pressure change with temp as the underside of the plug is still open (vented) to the outter landing gear bay.
I can see a series of holes in the plug and it looks like they are covered by the mould. The holes you see are actually the holes for the screws that attach the belly pan when the wing is installed… they’ve been filled with modeling clay to prevent resin/gelcoat from contaminating the holes. Note also that the plug is EXTREMELY rigid with zero flex (I prob over did the number of laminates but I wanted a very rigid surface).
To put the dimensional accuracy into perspective, I wouldn’t accept 1/8 inch warping in the bottom of my 20 foot boats. Your mould doesn’t have any sharp angles which tend to close up when you use PE. It has smooth curves which are easy to replicate. You are talking fractions of an inch. I am talking fractions of a millimetre.
Following advice that I’ve received on this site, I’ve ordered an epoxy compatible gelcoat and epoxy laminating resin (along with woven cloth, since I cannot use CSM with epoxy) as I’m now confident the pre-release problem was primarily due to resin shrinkage (404 Isophthalic PE Tooling Resin).
Hopefully, my new supplies will be here in a few days… Fingers crossed, I’ll post my results.