On Thu, 9 May 2019 10:12:01 +0100, newshound
wrote:

snip

My goals here are to retain the ease of adjustment / takedown (you can
then carry it in an estate car / MPV or even on a roofrack / boot) but
to remove any of the clanking, especially when the trailer is lightly
loaded.

[1] The spacer and suitable washer could stay on the bolt, effectively
forming a bolt with a bigger shoulder.


That could work. The issue might be fretting, because you are always
going to get some "flex" at the clamped joints.

Understood.

FWIW, the axle stubs (independent suspension unit, mudguard, length of
'inner' gauge square tube) would 'normally' be inserted to full depth
because that still leaves the trailer wide enough for pretty well
anything we are likely to put on it. That said, the 'axle' would only
be held in at two points (bolts) which are only maybe 1/4 of the
length of the axle tube apart.

So, if the wheel was loaded it's possible that (because the bolt holes
are quite close), that the inner box could be rotated (on the mating
surfaces) until the outer end of the inner tube (or the sides of the
M10 bolts / holes AND spacers / holes on the non clamped sides,
whichever happens the soonest) and the inner end on the inner tube
does the same at the bottom. Once 'settled' however I can't see any
reason it would move further (It would look like some very slight
camber)?

I don't think I would worry about the loss of strength caused by the
larger hole.

Ok, thanks. I was hoping that a 20mm diameter hole drilled in one side
wall of 50mm x 50mm square tube (that was mainly under a vertical
bending type load) would put the hole in the least stressed area of
the section?

I once fitted a fibreglass "dolphin" fairing to an old British bike
without any of the proper fittings.

I made the same by using a 'bubble' screen from a racing bike as a
mould for a fibreglass copy, inverting the final form and fabricating
a joining strip to fix them both together to form said 'dolphin nose'.
This was then mounted on the bike using a home made sub-frame and the
fairing was held on with nylon number plate screws with rubber sheet
between the two. There was no engine vibration as this was an electric
'motorcycle' but there was quite a bit of road vibration because of
the highly inflated tyres (lower rolling resistance on the track). ;-)

I used fittings fabricated from
aluminium sheet, clamped with rubber sheet and penny washers but, even
so, they regularly failed from fretting fatigue at the contact sites.

Oh.

But ordinary "chassis" aluminium is particularly bad for both fretting
and fatigue.

How much actual movement to you need for said fretting though? Are we
talking even at molecular / granular levels?

I think you would be unlucky to fail your steel tubes in
the same way. I would, though, regularly look out for fretting if you do
this.

Again, FWIW, both tubes are galvanised and I'm not sure how 'smooth a
surface that gives? Would any high spots tend to get crushed at the
fasteners and so help bind the two surfaces together?

It is worth putting grease on the joints IMHO. Although this will
reduce the friction (and increase the chances of movement) it will also
provide a barrier to air access and reduce the risk of fretting wear.

Understood.

Thanks for the feedback. ;-)

Cheers, T i m

p.s. If I were to open up one side (the same side g) of each hole
for said spacer, I could pin one hole in place first (put a captive
nut into the inner section) and then drill the larger holes though
both tubes at the other point(s), (in the hope of making the holes as
concentric / unstressed as possible).

p.p.s. I think I might still go for some form of 'collar' to help
resist any movement of the inner tube in the outer and so also
minimise any fretting.