Phil, I wish I had thought of your clever idea. I had a 5" tapered flagpole which was long enough for a mast, but we decided it was a bit too light so I cut it in half and I am using the tapered top half for a topmast. Your idea would probably have worked for me. Oh well...
I built my two bandages almost to completion yesterday, using wood strips over a base of three layers of cloth and epoxy. Here. This morning they have cleaned up nicely and I have bogged the gaps. I think this will be a little easier to sand and fit than solid epoxy, and it has been very easy to do, so far. I presume, from your description, that you let the epoxy bandages cure, then made a dry fit – and finally glued the two parts together afterwards, is that right? In any case I think it will stick permanently and Jami can be reassured too. Read on:
Arne wrote:
“Even with a compression force of 200kp (I doubt it will ever reach that on that Gallion), the glue joint will hardly see more load than 0.2-0.4kp/cm2. Now, glue two bits of aluminium together with a contact surface of about 1-2 cm2. and pull them apart. You will find that it takes several kilos force.”
I tried that Arne, at the same time as investigating or comparing a couple of release agents.
I made seven aluminium tabs, each with a glue surface of 4sq cm, and glued them all to a strip of aluminium angle, like this. A liberal amount of glue was applied, to one gluing surface only (the aluminium tab) except in the case of (7). Each of the glue-coated tabs was then laid on the aluminium strip and a small length of timber placed over them, in order to provide a very light amount of pressure, and they were left to cure.
(1) CRC had been applied to the aluminium strip
(2) Baking paper sprayed with CRC had been applied to the aluminium strip
(3) Spray-on release agent had been sprayed on the aluminium strip
(4) Baking paper sprayed with release agent had been applied to the aluminium strip
(5) Baking paper on its own had been applied to the aluminium strip
(6) The aluminium tab (with glue) was laid on the aluminium strip, with no preparation to either of the gluing surfaces.
(7) The two gluing surfaces were carefully cleaned, sanded and primed with epoxy resin. When the resin was half cured, glue was applied to the aluminium tab and it was laid on the aluminium strip
After curing, (2) (4) (5) simply fell off. (3) required a slight bump before falling off. Each of the tabs took the glue with it. Neither CRC nor the spray-on parting agent prevented the baking paper from being glued to the tab.
(1) was able to withstand a light tug but was probably not stuck very well – I did not get to test it because it came off at some stage, I did not notice when, and it has been lost.
Conclusion: Proper spray-on parting agent is probably better than CRC but possibly not much better. Baking paper is a total success as a parting membrane. Epoxy will stick to it – but unlike printer paper (which I have tried and failed) it seems not to allow the epoxy to soak through and reach the other surface, hence it comes away cleanly taking the glue with it. See photograph of these results here.
Adhesion of epoxy to aluminium.
I hung various weights from tabs (6) and (7) with a view to testing to destruction.
(7) whose surfaces had been prepared and primed, has not yet failed. Here is a photo of it holding up three car batteries, the tailstock of a large lathe, an anvil and a dumbbell. It was way off the scale (my scales measure up to 50 kg only – that’s slightly more than 3 car batteries). The total weight here is estimated at 75kg or more. Look at the bend in the 40mm x 20mm strip of angle. I had no more weights so I left it stuck on and turned to (6).
(6) which was the simple glue joint and no preparation, held two car batteries and when I added the anvil it held for a moment, then with a bang it let go and something went past my left eyebrow with enough velocity that I decided testing would be over for the day. (It was probably tab (1), hurled off when (6) failed and the aluminium angle strip unsprung.)
I think the glue joint (6) was holding about 40kg when it yielded.
This photograph shows the two failed glued surfaces – evidently half the glue stuck to one surface, and the other half of the glue had stuck to both surfaces. It think if glue had been applied properly to both surfaces, it might have held more.
I went back and did some further testing on (7).
Would anybody like to guess the total static weight this join withheld?
Come on, experts- if anyone is prepared to try a guess, I’ll give you an answer tomorrow.