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TURK
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Warren (Staff) (14/12/2016)
looking much nicer now! Thanks Warren 
Morning folks, Last time I had a bit of a mare ! The body filler didn't quite cure for some reason, I finally put it down to not mixing in enough catalyst. This time I tried something slightly different ....... Basically my new plugs were the exact dimensions I needed for my final part, which allowed me to apply the Pattern-Coat Primer directly onto the PU foam plugs. Most of the plug has been flatted back, but low spots can still be seen, particularly the bridge between the top and the bottom surfaces. Because of the large distance between those two levels, that without a doubt is where I would of got 'webbing', so by making that part of my structure I'm hoping webbing will be eliminated completely >>  At this stage I've really flatted back as much as I dare go, in some areas the underlying PU foam can already be seen. So the thickness of the resin is probably thousandths of millimetres at this stage, but that gets fixed in the next stages. In this shot the gap that bridges the top of the plug with the bottom can clearly be seen. The goal here is to blend those areas together so a nice smooth curve is needed >>  The fix is applying body filler to the low areas, so a skim of body filler is used. Paying particular attention the that curve >>  The transition from the top and the bottom must be flawless, and you also have to blend the sides in. One skim of body filler didn't do it, two applications were required >>  And then everything was sanded down to a nice smooth finish >>  At this stage it's a good idea to double check your measurements, as it's so easy to sand down too much from one particular area, one millimetre from here, and one millimetre from there, and things begin to get out of hand. I also took the opportunity of checking the available space for mounting the Hella headlight carrier frames. The two round marks you see on the paper template, indicate where the mounting holes will be for the bolts that will secure the mounting frame. Not a lot of room as you can see, but the mounting frames are installed from behind the completed part >>  It's also a good idea to check that both plug bases are identical, and that the footing is square ........... so far, so good T: >>  Now onto the next stage ....... second coat of Pattern-Coat Primer now that I have a sound base layer. You'll also notice that I have blue painters tape around the base of the plugs, I noticed from my previous resin application and then the sanding, that I wasn't getting a nice crisp edge around the footing, the tape also helps to stop the resin from leaking under the plugs and creates a resin lip that'll be much easier to sand ......... that was the theory anyway ! >>  The following day, now that the resin has had ample time to cure ......... I'm ready for some more sanding >>  Flattening back this time was a little easier as I had a level base from my previous resin application. I began by sanding the footing and getting those measurements bang on. I'm not looking at adding any bulk to these plugs at all, the entire process is to achieve a nice smooth finish. And getting those dimensions as accurate as possible as they will sit inside the OE headlight retainers >>  After I'd gone round the entire footing I flatted back the sides, leaving the tops till last. Doing it this way made it very easy to work out the radii required for the edges, as you can clearly see the difference between the light grey and dark grey areas >>  Everything was blending in nicely ....... >>  At this point it's a good idea to start checking your dimensions again, you can never over measure that's for sure, check and double check. In this shot you'll see that the plug is sitting on a piece of card, that card ( cardboard template ) is the exact dimensions as the interior of the OE headlight retainer, the red 'frame' around the card is 3mm ( the thickness of the ABS sheet ), so my plug has to fit nicely on the inside of the red lines .......... simple enough. When vacuum forming you'll get shrinkage from the material ( 3mm ABS ) that's guaranteed, and judging by the amount of shrinkage I've had from previous vacuum forming attempts, I figure about 2 to 2.5mm, that should leave me with a gap of about 0.5mm .......... but I'm banking on that as I need a little space for adhesive in order to get a good bond between the two materials >>  These are as smooth as I can them using 120grit sandpaper .......... now I'm ready for the next stage >> |
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Warren (Staff)
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looking much nicer now!
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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TURK
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Hanaldo (14/12/2016)
Looking great mate! Thanks Hanaldo ! 
I'm currently at the sanding stage, doesn't look like I'll have to do much filling in.
Out of all the different methods and materials I've used in the past, this is by far the easiest ........ finding this very therapeutic actually ! |
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Hanaldo
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TURK
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Thanks chaps, makes a great deal of sense that
I tried to fix my previous plugs, but I think I was flogging a dead horse !  So I started again.
The nice people at 'Easy Composites' kindly sent me some more PU foam .......... I'm in a tiny village in central France, but it's not a problem for them .......... I had to pay for it thought !
I'm now using the slightly denser PU foam, 96Kg/m3. You could say it has the consistency of Balsa wood, great to work with. The final shape I'm trying to achieve is quite intricate, in order to have a vacuum forming friendly shape I can't have any negative angles, straight vertical side walls are also an issue, but I really need that 'footing' it's part of the area that will be bonded to the headlight retainer >>
And as advised, I applied the Pattern-Coat Primer directly to the PU foam ......... it's worked very well indeed. When that cures I'll sandback and fill any gaps and low spots with body filler, then a final Pattern-Coat Primer application >>
I'll let you know what happens .........
Many thanks all for your help and advice guys. |
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Dravis
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Ideally your plug foam core should be about 1 -1,5 mm smaller in all dimensions, and then the pattern coat filler should add a few mm to allow sanding it back to the perfect dimensions.
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Hanaldo
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Turk, there's no reason you can't coat with pattern coat straight away, however it isn't really any easier or more accurate than skimming with body filler. Keep in mind that when skimming with body filler, you aren't trying to build thickness yet. All you want to do is fill the porosity of the open cells of foam, as well as any gaps and cracks that may be present in the foam. Pretty much as you did in the photo of your 'original' skim of body filler. So you're on the right track. Then instead of applying more body filler to do the contours, apply the pattern coat. Flat down, fill any low spots that can't be sanded out, and apply another coat of pattern coat. Repeat until you have a thick enough coat of pattern coat for it to be completely flatted down. Then mould or proceed with gloss coat. It took me awhile to figure out that your foam form isn't really where you should be going for dimensional accuracy. Obviously it needs to be close, but you don't want it mm perfect yet as you will just continually sand through to it.
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Warren (Staff)
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TURK (07/12/2016)
What's the 'bumper filler' you speak of Warren ? You can get slightly flexible fillers for car bumpers and other flexible panels. However, it is still sandable.
Warren PenalverEasy Composites / Carbon Mods - Technical Support Assistant
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TURK
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Hanaldo (07/12/2016)
I'd wager you simply didn't put enough hardener in. Happens to me from time to time, despite having done this professionally for almost 5 years. |
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Hanaldo
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I'd wager you simply didn't put enough hardener in. Happens to me from time to time, despite having done this professionally for almost 5 years.
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