Sounds like you're treating these as if they are to hold the Forth
Bridge together! They really don't need any great force to tighten.
You'd need to be just a little bit specific as to what your paericular
grub screws are for before anyone can advise you where to get replacements.
Your Caterpillar Tractor stockists will keep a good range, same for
engineering shops and R/C car stockists. ;-)
I sheared off the grub screw the first time I fitted a replacement
Ultrascale Mainline Warship gear. Luckily the gear was in the right
place and enough of the screw was left to hold the gear in place. It was
my fault and I didn't do it with the other three. So be careful! :)
By the way the Ultrascale gears transformed my Mainline Warships.
I use hex drive ("socket head") grub screws. And I prefer the ones
with ring tips to the pointed ones:
In real life we generally put two, at right angles, into the gear
boss, but I've only seen that a few times in models. One instrument
maker I know puts in two, at 120 degrees.
Like MBQ says, a flat on the shaft helps a lot.
Two useful sites there, thanks Bob.
I think the real reason why you should use a flat is that if you don't,
the point or cup on the screw chews up the shaft and you can't get it
off (or if you do, you can't get it on again).
If you want to avoid damaging a shaft but don't want to put a flat on
it, try putting a little disc of copper or brass in the hole, diameter
just below the clearance size, length need only be about the same or
less, This will avoid damaging the shaft but still grip quite well. If
you hit it with a punch it will swell and grip the thread just a bit and
then it won't fall out when you remove the screw or the shaft, but still
move enough to grip when you tighten the screw.
You also need to be careful to get the shaft a good fit in the hole, or
the grub screw will push it to one side.. If it's undersize (say if you
use stock mild steel in a reamed hole) you may be better using Loctite,
which has reasonable centring properties.
I *think* as well that the grub screw shouldn't be done up tight against
the flat, so that the flat and grub screw provide a key rather than a
friction fit. This is what avoids the gear going slightly eccentric.
I may be wrong though!
Still won't fly; if the screw has any contact with the flat, it will
exert a wedging action on the shaft and displace it. Also, if it is not
tight into the flat, the shaft can rotate somewhat, which you mostly
want to avoid.
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