By TURK - 12/7/2016 8:25:58 AM
Hi all,
I'm in need of a little help guys ........ I watched ( and learned a great deal ) from Paul's 'Airbox' video on YouTube, I purchased and currently using the Low Density 48Kgs/m3 PU foam blocks, to get my 'form'. I then put a skim of body filler to harden the 'form' that will eventually be my plug for casting a resin mould. After the initial body filler 'skim' had hardened, I applied a few more layers of body filler to build-up the form to the dimensions I wanted. So basically, my plug now has about 3mm of body filler on it that needs to be sanded down smooth. Unfortunately, that isn't what happened ........... the body filler ( known as 'Bonda' ) turned out to be more like a rubbery texture !!!  as we all probably know, it's impossible to sand down bubble gum !
Any of you know why it did this ? .......... did I overdo the 'skimming' of body filler ?
The plugs have now been drying for four days, but the texture of the body filler is still quite soft, to the point where I can push my finger nail into it. This was the original 'skim' of body filler >>  Then I applied a little more on to build it up as it were, so I could sand down the contours >>  So, another question if I may ......... As I've never had any troubles with this sort of body filler, I use it all the time ( mostly on MDF plugs ) and never had any issues with it. D'you think there's been kind of a reaction with the PU foam ? should I have applied a few layers of Pattern-Coat Primer to the initial 'skim' of body filler ? or can I simply apply Pattern-Coat Primer directly onto the PU foam ? ( sorry, that's three questions ! )
There's loads more info in the following link, and the entire procedure here > PU foam plugs
Many thanks for your time. |
By TURK - 12/31/2016 8:38:09 AM
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 >> |
|