|Oct 21, 2012, 06:34 PM|
Thanks Adam. If there's a dumb way to do things, I'll always find it.
I'll keep an eye on the roughness. I didn't really think about it, felt it and just thought I should clean them up. I hadn't polished them for quite a while. I've had some print happen in the past. Also I'm always experimenting with using Ampreg and now polyurethane expanded in the moulds. BUT ...thinking about it, it's probably just another dumb thing .... I reckon quite likely I've had them sitting open on a nearby bench when I was spray painting, and it may just have been overspray! I dunno but thanks for the advice, and I'll watch it.
|Oct 26, 2012, 10:40 PM|
Joined Aug 2010
I just use wax and spray paint the mould with a special 2 pack paint..
I always thought you had to wax 3 or 4 times but my friend waxed only once on a new mould and it popped out so easily. I wax 3 times though just to make sure I haven't missed a small area.
Something I have noticed is that if you spray paint the waxed part to be moulded it releases easily, if you brush it it can stick a bit. So maybe people are a bit rough when applying the gel coat with the brush.
In Thailand we have this 2 pack polyurethane paint and it is fantastic for making the release easy. Not sure why except that it dries almost instantly. You can spray it on and touch it 10 seconds later, it's not hard but it has gone off enough to touch it. It is always hot here so that may help?
We did a full size jet ski using this method and it just popped out real easy.
There is a bit of an art to painting over wax but easy enough I suppose. Never seems to fail.
|Nov 03, 2012, 12:07 AM|
Jim the 2pack polyurethane paint sounds very good.
Well I seem to have it sorted out. I have laid up 4 things in moulds. All of them I cleaned and polished and did 4 coats of sealer then 4 of Frekote. All popped out fine.
After vac bagging the skins in, before joining, I trim the edges and maybe I have too much protruding, but I do seem to have to work hard at the trimming and I worry that I am taking all the release off by being rough on the flange, working at it with a broad knife.
So I wipe some release on the flange before joining. I still find that the flanges need scraping clean. Not from normal epoxy bleed but from the expanding foam bleeding out (either foaming epoxy or PU). Same with the TE trench ... Usually needs some scraping out.
|Nov 03, 2012, 03:32 AM|
Wow Adam, that's interesting ... I pre-cut mine using templates too, but I let them overlap just a tad, so that I can cut them really flush to get a neat join line. So do you put a bead of splooge right up against the lip of both sides before joining??
(my moulds have lots of nicks on the flanges!)
|Nov 03, 2012, 04:18 AM|
Have you seen this video of wings?
How about this video that I did with a fuse?
They may be of some help in respect to not trimming.
|Nov 03, 2012, 07:07 PM|
Hey Adam, I'll watch those videos when I'm in a better frame of mind. Your video of the bladder technique was inspirational for me and it's my main method. No digressions into latex, balloons or whatever ... I still do mine with the thin plastic welded as per your method and have great results. Recently I made a new nose cone mould (yes, one of the moulds that had one side stuck up ... the inception of this thread!) and made it with a completely open end. A friend told me it wasn't worth mucking around with inflation bladders for a simple nose cone and just to roll the seam. I did the first one that way and wasn't happy with the seam being more bulgey than before and needing sanding etc to fit onto the fuse. Probably because originally, the fuse was made a close fit to a cone made with a bladder. So I made an "end plate" that screws onto the open end of the mould, has a foam seal and a spigot hole in the centre and converted it to an inflation mould! I used it a few days ago and it was the best nose cone I've ever made!!! The bladder does such a good job of squishing everything together and squeezing out excess epoxy.
But I'm (again, sigh ...) despondent about frequent failures after so much work. I am having so many disappointments and (seriously) I get to the point of deciding I'm just not cut out for this stuff ... there's something missing from my DNA, or I'm just thick and clumsy.
I could fill up a page ... but the latest downer is this. When the paint stuck to the Scratcho tail and stab moulds (as reported above) I cleaned them up and repaired various old chips and blemishes. Carefully wet sanded them flush with 800, 1200, 2000 grit (using shaped blocks) and then with G3 and then finish polish. I had some other stuff to polish (post-painted wings) so I borrowed a friend's electric rotary foam pad polisher and used it to buff out the polish pastes. They turned out excellent, so in a way I was glad that the stickup had got me to fix up the moulds properly.
Then as mentioned above I did the FMS sealer and Frekote routine. Two-pack paint, and was this time more careful to splooge the edges because I regularly get bubbling. Vac cured the skins, trimmed, then laid partial blue foam cores inside, and Sicomin PB170 foaming epoxy to fill the gaps. I'm playing with the PB170 because it's less dense than the Ampreg F230, and so far I'm really happy with it.
When I popped out the parts, they were the best result yet. A few paint masking blems (the mould release was so good I couldn't even get my good masking tape to stick!) but the edges are all solid, and best finish yet thanks to the mould polishing. But I had a double-take when I looked at the trailing edges of both fin and stab. Instead of tapering to a nice fine point as before, they were really thick. So thick that the skins weren't touching and you can see an epoxy foam sandwich between them.
At first I thought darn, I've trapped something in the moulds and they didn't close properly. I sandwiched blobs of putty in there and shut the mould, and the thickness of the blobs showed that it wasn't a closure problem ... the taper has been removed from the trailing edges! I'm not sure if it was from sanding or from the polisher or both.
Not sure whether it can be fixed. Maybe I can sand back the TE areas, smear some gelcoat on and press the plugs back in. I wonder if the gelcoat I'm using for moulds is too soft? It's Rengel SW10 and it seems to sand pretty easily.
(EDIT: I just measured the thickness of the finished parts ... they are 0.4 to 0.8mm thicker than the previous ones! So it's not just the TE area. I thought the polishing would take back a microscopic amount of the surface but in fact it's all been cut back considerably. Disaster!)
It's a bummer. As I said I feel like giving up again. Too many problems.
|Mar 31, 2013, 06:11 AM|
I had another stickup, and this time I'm bamboozled. I thought I did everything right. I can still feel the bitter disappointment from when I had those new moulds stickup late last year, and I knew it was from being slack about not using the mould sealer. So since then I’ve mended my ways and not taken any shortcuts. I have been using the method you guys described, all the time, with no problems up to today.
It's a well seasoned Scratcho fuselage mould. This time since I haven't used the moulds for a while so I wiped them with a couple of coats of the Frekote sealer, then did 4 coats of the release. I couldn't even get tape to stick, not even lightly.
I sprayed 2pak paint in and laid up the mould starting an hour later. It took just over an hour, so the paint was only 2 hours cured when I inflated the bladder to 25psi. Pulled it out this afternoon and it was stuck really bad. Really hard to split the mould because 95% of the paint was stuck hard to the mould. It broke a length of edge out of one mould side. I busted the (very good) fuz getting it out. I was gutted, and truly felt like quitting for good.
The only ideas I have could be:
1) I wonder if the bladder pressure combined with fairly fresh paint could be a problem. Reason I say that is that the flanges are fine - the excess lifts off them easily. But the whole fuz stuck to the cavity.
2) I’ve been using more thinners lately – I don’t get good flow from the gun and the guys at the shop pointed out that I need to thin the paint more. It fixed the flow problem, but maybe the thinners affect the Frekote?
3) I also changed brands of thinners (just cheap all purpose thinners). I wouldn’t think that would be it.
4) Maybe I did something stupid like pick up the wrong bottle of something ... who knows.
I just don't know what went wrong.
Some more comments and feedback from others on the SCratcho thread:
|Mar 31, 2013, 08:21 AM|
Hi Andrew a difficult experience. I think it is worth looking at the General Purpose thinner. This stuff is amazingly aggressive. I have just had to repaint a boat hull repair where I used general pupose thinner over an old surface which I later found out was a spray enamel. Off the gun the finish was good and I went to bed satisfied. The next morning, to my horror, the hull looked like someone had thrown sand over it. The paint underneath had broken down and had curdled into a sandy sort of mess. It seems like the GP thinners had penetrated, the surface of the new paint had formed and hardened, trapping thinners in the old layer. Like you I had a small gun and had used more thinners than with my larger gun.
I note that PPG even specify different thinners for their different hardners according to temperature, so I suspect that the brute force I can thin anything thinners might be a contributor.
|Mar 31, 2013, 05:14 PM|
You know, I've been starting to think the same thing ... I just wrote in the Scratcho thread that I am suspicious about that. I got told that it was OK to use the (much cheaper) GP thinners with 2K paint and I've been using it more frequently ... not thinking about whether it is for topcoats or in-the-mould. I've had a couple of times that small patches of paint have stuck, not hard, even on the wing mould which is unusual. I think I'll switch back to the proper 2K thinners.
Also Timbuck has been using Marbokote then a coat of wax on top before laying up ... I might do that as extra insurance. And spray the paint on very dry, with minimal thinners.
|Apr 01, 2013, 12:45 AM|
North OC, Ca.
Joined Jun 2005
AvB- What are the thinners? Acetone, MEK or lacquer thinner( reducer)?
IIRC the Freekote is in a solvent that is pretty agressive. If you are using a additional thinner that can solvate the silicone, you will have problems.
Also, how old is the freekote? it picks up moisture and goes bad failry quickly.
On old molds that have not been used for a while, we often clamp them together and dry them before prepping them( sealer and release like a fresh mold). Moisture in the tool can cause issues with the chemistry.
sorry for all the problems- makes you crazy.
|Apr 01, 2013, 04:00 AM|
Thanks Sarmoby. The thinners are sold as paint thinners - they're not pure acetone or MEK but I'm guessing they have a blend of those plus other things.
The Frekote is new. I put a lot of legwork into finding it and got a new tin maybe 6 months ago. I have only opened it once. I keep the smaller amount in a plastic dishwashing liquid bottle, for quick and easy dispensing.
The cheap GP thinners is sold for thinning standard acrylic one part paints. (cross posting stuff I've said in the Scratcho thread here) ... today I compared the GP thinners with the "Proper" 2K thinners. Firstly they do smell different. The GP thinners is a sharper smell, burns the nose a bit if you suck it in, but the 2K thinners is milder, smells oilier. Secondly, if you smear a stripe onto the bench, the GP evaporates much, much more quickly than the 2K. The 2K just seems to sit there and stays wet.
So they are quite different and perhaps the GP thinners are the cause, combined with the use of more thinners than previously. I can't be sure that's the diagnosis, but it's the best we've got.
But my mate Alan, who's done a lot of painting and moulding, is adamant that it wouldn't be the GP thinners and reckons that it should REDUCE problems, because it gasses off so fast. He reckons the stickup was from laying up too soon, trapping the solvents in the paint before it was fully cured.
I've got all the paint off the moulds now - it wasn't that hard once I got stuck in. I've glued up the broken piece and have some gelcoat setting in some small gaps.
|May 07, 2013, 01:45 AM|
Just an update ... I have got "back on the horse". The Scratcho fuse mould was cleaned after the tragic stickup. It was wet sanded and polished and I did some repairs where the edge had broken a bit.
I also have new fin and stabilizer moulds, which I got CNC cut by Mike F in the UK from CML978 epoxy tooling board. They had been sealed by wiping with low viscosity laminating epoxy resin, and also sanded and polished.
I prepped all the moulds with 5 coats of Frekote FMS sealer, and then used 5 coats of “Frewax”. This is the out-of-date stuff that my friend Alan got me originally – the first thing I tried after switching from wax, and at the time we thought it was normal “Frekote” but it’s actually a polyester release product that contains some liquid wax, and has an ammonia smell. I found it to be a fantastic release at the time. I ran out, but Alan has recently snaffled the remainder of the tin, so I got some too. I feel safer using it, despite having the proper Frekote 700NC on the shelf!
I spray painted into the moulds, but this time I used either no thinners (if the paint was runny) or a small amount of proper 2K thinners; and splattered it on quite dryish. Then like Tim advised, I sprayed some white 2K primer behind the top coat so I could leave it and lay up when ready.
It was easy to see that the paint wasn’t going to stick! The next day I tried to clean the overspray off the flanges but I couldn’t go near the lip of the cutout because the paint almost flaked right off!
The fuse layup went well and sat happily oozing out epoxy at 20psi.
Today I broke the moulds open and even the (tight fit) fuse pretty much fell out of the mould - the easiest release I've ever had. Very happy with the result.
Thanks for the discussion and advice. The take-home message seems to be:
1) use as little or no thinners in the paint.
2) If using thinners, use proper 2K thinners.
3) spray the paint as dry as possible … plenty of air, don’t gun too close, don’t spray too wet and thick.
4) good idea to back up with primer and leave it 12hrs + to really gas off the thinners.
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