Sanding & Filling
I started to write up my day by day diary based on my workshop notes and it seemed to go something like sand, fill, sand fill so I didn’t think that would make very interesting reading.
I spent the bulk of this month filling both stabilizers, sanding them back and filling the pinholes. I have learnt a few tricks so far and I am sure that I will learn a few more.
The first thing I have discovered is that it is far easier to put on too much filler and sand it back than to put on many coats. The problem with putting on multiple coats is that it is very difficult to get the coats the exact same consistency. The second issue is that it seems to pull a bit of epoxy and form a slight skin. It seems far better to get the mix as dry as possible and put on a little too much.
If you sand it within 24 hours it seems to be quicker to cut back. I have found that if it is left for a few days the epoxy reaches its full cure and it’s a little tougher to sand back. I have also discovered if you work the material too much when smoothing it out it tends to draw a little epoxy to the surface forming a tough skin to sand through.
I have experimented with Superfil versus my Expand Cell / Carb O Sill mix and I can’t find any discernable advantage. The Superfil seems to sand slightly easier and it’s not as messy to mix up, but the advantage it not significant, particularly when you consider you get the Expand Cell with the kit.
I find the Superfil very handy for patching up what I call “big pinholes” after I have done the bulk of the sanding. For the smaller holes I am using something called Model Magic. It is intended for filling surfaces of model aircraft and it seems to work into the pin holes fairly well. I am hopeful that the Smooth Prime will take care of the rest.
Sanding tools.
I soon ended up with a vast array of these things. I used a palm sander and found that this was pretty quick to put on flat spots, so I only use it for taking off the rough spots such as the lines left by the “fishing line”. To get off the really high and rough spots I use a Surf Form plane. Once you get the hang of this thing you can work areas without taking off too much and its sure faster than sanding
I have 3 sanding splines that are made from 1/8 x 2 x 22 inch aluminum strip. These have wooden handles glued on them with Redux. I have each spline set up with 60, 100 and 150 grit paper. My only complaint with these splines is that they are not quite flexible enough, but with care they work well. I have a couple of smaller T bar splines that I use for the leading edges. The last sanding tool I find useful is a rubber backed sanding block used for sanding dry wall joints. These take a one third sheet of paper.
As far as sanding techniques go I am far from an expert, however, as stated in the Europa builder’s manual, it is very important to sand diagonally across surfaces. I find that the 60 grit paper for rough sanding is a little too coarse, but it very quickly looses its sharp edge. I haven’t used the smooth prime yet so I don’t understand its ability to fill. It may well turn out that 150 grit is too fine for this stage.
Baking oven
Before I put the undercoat on I needed to post cure the parts. Actually I believe that this is best done
soon after they have been made, however it needs to be done at some time. I constructed an oven out of 2 inch styrene foam. The oven is 80 x 36 x 10 internally with a
chipboard base. I glued it together
with PVC glue and sealed the edges with duck tape.
I was thinking of using a blow heater with an electronic regulator to set the temperature to 150 degrees F. I started to scratch out a design based on thermal sensors, operational amplifiers & a solid-state relay when it occurred to me that it didn’t need to be that sophisticated. Given that my workshop is a fairly stable temperature environment, all I really needed to do is to introduce enough heat so that the input + losses gave a temperature delta to the outside which resulted in an internal oven temperature of 150 degrees. By experimentation and by using a meat thermometer stolen from the kitchen, I determined that two 100-watt lamps gave a temperature of 135 degrees and three 100-watt lamps gave 165 degrees. What I did was to put in a 50 mm hole in the base of the oven, a 50 mm hole in the top, and blew in a small amount of cold air. I then determined by experimentation how much I needed to cover the top hole to set the internal temperature to 150 degrees. After a couple of hours of observation I determined that it was very stable, and good enough to trust putting in my first stabilizer.
Apart from generating quite a smell, I successfully baked the two stabilizers.
