AussieJester said:
Could grease or one of the loctite variants be substituted in place of the Duralac Jeremy? Am i correct in assuming if aluminium has been anodized
electrolytic corrosion less of a concern when 'mating' the ali and steel? Or should insulating still be implemented.
KiM
Not sure about the effectiveness of grease or the Loctite stuff, but some types of paint do a reasonably good job if you're not living in a climate where condensation is a potential problem.
I built a big box trailer cover by riveting alloy sheet on to a 1" square, painted steel box frame and it was less than a year before the rivet holes corroded out badly, but then I live in a climate where alternating rain, cold, warm and dry weather is the norm. Walking into this trailer some mornings was like going into a rain forest, with condensation dripping off the roof inside..............
The Mk2 trailer was built with polyurethane car body adhesive/sealant between the panels and the frame (and had insulation added to keep the condensation down). The car body adhesive was great, that trailer is over 10 years old and still looks like new. The polyurethane adhesive also made the structure more damped and solid feeling and could probably have been used on its own to bond the parts together (aeroplanes have been made like this). It came in 300ml sealant gun tubes from the local auto parts stockist, under the brand name Tiger Seal, but smelled and looked like Sikaflex (except it was a lot cheaper, being a non-marine product).
I'd sort of assumed (maybe wrongly) that Costa Rica might be a bit challenging in terms of corrosion, as I guess the wet season tends to be very wet for long period and warm at the same time, both conditions that tend to accelerate corrosion, hence the zinc chromate suggestion. Over here a tube of Duralac is around $10, BTW, so relatively expensive but it does go a long way, as only a smear is needed.
If it were me making a bike this way I think I'd probably use the PU adhesive/sealant, primarily because it will bond the joint and tend to damp out noise from travelling through the structure a fair bit. This was really noticeable on the Mk2 trailer; when I was building it it was less like working in a big biscuit tin than the first attempt.
I agree with Gordo that bucked rivets are dirt cheap and strong. I'm a lazy sod though, so tend to use pop rivets (usually stainless steel ones, only because I inherited a big sack of them). These do the job OK on the sort of sheet thickness's we're likely to use, where the rivet strength is very rarely the limiting strength factor, the hole in the sheet is. The same is true of the majority of bolted joints, too, BTW. Bigger bolts are often used for higher loads not because the extra bolt strength is needed, but because the bigger hole massively increases the bearing stress limit in the material being joined.
Jeremy
