Mould Construction
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25th September. We finished fibreglassing on Friday evening with three layers, mat, cloth and mat. We added a few extra layers of cloth and mat to the flanges and called it a night. Two hours work and 5Kg of resin mixed. On Saturday I went flying in the glider. Got four 30 minute sessions in all. The day was warm and muggy with no wind to speak of so flying was possible in both directions (at 40mph). Most enjoyable day.
Got home at 9 o'clock and couldn't resist visiting the mould. I should have gone to bed. I trimmed the flanges and started prying. The nosepiece came off really easily followed cleanly by the starboard half. The port half was a different story. I tapped in about two dozen thin wedges and lifted the mould about 6mm, over about 90% of the edge, without separation. It was obvious that the mould was firmly attached to the plug and - short of violence - seemed determined to stay there. At midnight I went to bed in a cloud of gloom.
Sunday morning I made some long (500mm x 30 x 6mm) timber strips with tapered leading edges and tapped them into the problem area. Crackling noises announced a separation, but the mould was still attached. I enlisted the assistance of my daughter and we applied some pull. Slowly the mould tore away, taking a layer of paint and plaster from nearly half the surface of the plug. Clearly, I hadn't used enough PVA. We chipped and chipped at the plaster until it was thin enough for the paint layer to be peeled away. To my immense surprise, it peeled cleanly and after an hour of careful work, we had a perfect mould. I just couldn't believe it. All those coats of paint, amounting to 25 thou ( I measured it) had saved me.
What relief! With all the hassle, I didn't take any pics until the end, so all I have to offer is the final result and the devastated plug.
So ends the mould saga. I think a small break from glass is indicated so we'll probably move to metalwork next, it's less strain on my heart.
21st September. Started late last evening and got just two more layers of glass laid up. One of cloth and one of chopped mat. We wetted out the cloth on the flat and used just 1Kg of resin for the layer. The chopped mat, on the other hand, took 2Kg+. My 4Kg statement of yesterday obviously refers to the layup (tissue+mat+mat) rather than individual layers. Early start tonight and work until finished.
20th September. Almost there. After Saturday's gelcoat fiasco, I chickened on gelling Sunday night so I left it to dry another day. Before dinner on Monday evening, I poured on the gelcoat and left it to go off. After an hour, it was firm but tacky, so we went ahead with one surface tissue and two layers of the 450gm chopped strand. Tissue is horrible stuff to work with, it sticks like crazy to the brush and delaminates into cotton wool if you just look at it but it does wet out easily. We added some extra layers to the flanges, just to use up mixed resin. We're mixing batches of approx 1Kg and each layer takes about 4 mixes.
No work Tuesday due to chapter meeting and none last night, as we went to inspect a new field where we intend to base gyro ops. Three layers tonight and three more on Friday, followed by the great cracking open ceremony.
Flying the glider on Saturday ;-)
17th September. Finished the first side of the mould. Total thickness approx 8mm. Added thickening pads to the bolting flanges to allow drilling dimples for location. Trimmed off the flanges and turned the plug around. Pics show the rear quarter, a view down the middle showing the thickness of the flange and extra pads, a side view of the last area to be moulded and the heath-Robinson method of holding the fore-deck mould in place. We really shouldn't have removed it, we weren't thinking.
The pics were taken before the drilling. I drilled dimples 12mm diameter just deeper than the lips of the drillbit. I went ahead with waxing and PVA on Saturday. After allowing sufficient (I thought) drying time, I poured on the Gel. More progress - not. Before I popped off to bed, I checked the set. At the bottom corner, between the plug and the baseboard, the gel had started to separate from the base. I think there must have been some PVA in the crevice which had not dried fully and reacted with the gel, causing gassing. I decided that if there was no further separation, I'd go ahead with glass, on Sunday. Unfortunately, Sunday morning, the separation had moved up the side of the plug about an inch. I debated carrying on but decided not. I stripped off all the gel and re-applied a coat of wax and then PVA. That was midday Sunday. I'll gel this evening. Another lesson learned the hard way. Luckily no damage done, just time - and some gel - lost.
13th September. Just got one layer of 450gm chopped mat done on Tuesday night. I was working in a daze really after the NewYork disaster. The pics show me trimming the edge of the first layup, the dry layout of the chopped mat and the current state after the second layup. It really pays to pre-cut all of the glass and lay it out in order. The mould is beginning to take on the typical green colour of cured polyester. We're planning for about six more layers, four of mat and two of 600gm cloth before we start the second side. This should give us a mould thickness of 8 - 12mm. We may add a layer or two to the joining flanges for extra strength.
10th September. Lashed on the Gelcoat before dinner last evening and by the time we were fed, it was ready for glass. We reckoned that the most important thing was to ensure that the gelcoat was well supported, so one layer of surface tissue and one of 300gm cloth went on as the first layup. The surface tissue wets out really quickly, so it's very easy to see and eliminate any of those nasty airbubbles which would leave voids under the gel. Very small pinhead sized voids are not a problem, but larger ones may collapse during moulding with disastrous results.
7th September. Progress at last. Worked last night setting up the fence to separate the main portion of the mould along it's centreline. The pics tell the story better than I can. We cut strips of 3mm perspex as close to the contour as possible and fixed them in place with modelling clay. We had to create buttresses all along the back so that the strips would survive the brush stippling during the first layup. We filled all the small gaps with the same clay, being careful to cut the edges to match the plug.
5th March. Just a word on progress. Not much. We've been polishing nightly since the 22nd with mostly frustration to show for it. It seems that, the better the polish, the more small scratches reveal themselves. We've reached the stage (of insanity) where we've convinced ourselves that it may be easier to polish some small scratches out of the mould than to continue trying to perfect the surface of the plug. So, we're moving on to glass tonight - tomorrow night latest.
22nd Feb. These are the pics of the Foredeck mould after separation. So far there are three layers of glass and no bracing. The intention is to add three more layers, extend the radial flange to at least four inches to accomodate the vacuum bagging attachments and add several ribs for stiffness. It's fairly stiff as it is but the vacuum bagging exerts a lot of force in directions that cannot easily be anticipated. The Epoxy primer is on the entire plug now but there's insufficient illumination without a flash, so I couldn't get a good pic with the Sony last night. I'll have to wait for Ken with the Olympus tonight.
21st Feb. I separated the foredeck last night and was quite pleased with the result. The surface is sound and it'll just require a little polishing. Our experience with the EP40 Epoxy primer has convinced us that it would be a good idea to go the extra mile with the remainder of the plug, so tonight we'll invert again and apply more paint. This will mean another round of sanding but we reckon it'll be worthwhile. Ships and tar and such.
20th Feb. Here are the Pics from last night. From the left, the final polish application . Three views of the foredeck with release film sprayed on, ready for Gelcoat. Then a view of the Gelcoat partially removed. I measured the Gelcoat last night and it varied from .015 to .035". Advice from the supplier is to stick with just one brushcoat which is what we've now done. The coat we applied on Sunday evening seemed OK so last night we applied two layers of 8oz chopped strand and one of 10oz cloth. So far so good.
19th Feb.
Well, the weekend wasn't a total success but neither was it a total failure. We're finally at the Gelcoat stage.
Saturday morning, we started to wet sand using 1200 grit paper. At about lunchtime, we decided that we would use the forward deck as our first mould section, so we inverted the plug for better access. Due to the poor paint finish (all the spraying was done upside down) we decided to apply a few coats of epoxy primer. This is a high-build primer and sprays beautifully. I'm very sorry now that I didn't use it throughout. It would definitely have saved alot of time and effort. Another lesson learned. Unfortunately waiting for it to harden really wasted the rest of the day, taking us to Sunday morning.
Having passed through the 180 grit dry, followed by 400 and 1200 grit wet sanding, we were quite taken aback at the number of fine scratches which surfaced with the 'final' polishing. So much so that we returned to 1200 grade wet sanding for several extra passes and polished again. We followed this with wax and finally spray furniture polish.
Then we set up parting lines, built fences of modelling clay and sheet perspex and sprayed six coats of mould release, allowing ten minutes drying between each coat. We applied one layer of Gelcoat and retired for dinner.
At 20:00 we returned and applied a second Gelcoat. Almost immediately we realised we had a problem. In one small area the Gelcoat began to blister. As we watched, the blister grew and travelled over about six inches and spread several inches wide. We drank coffee silently for an hour while it all went pearshaped.
At 21:00 we stripped off the Gelcoat, (building confidence in the release agent) sprayed another coat of release and applied the Gelcoat once more.
I've got some pics but they're too big to post. I'll reduce them and upload them tomorrow.