Aluminium Framed Router

[lucan07]

Been thinking about my pulleys and how to secure them over breakfast, it may be obvious that I have little or no engineering experience so is this an acceptable way to lock pulleys securely.

My problem:
Each pulley is drilled and tapped and fitted with opposing 4mm grub screws, but motor and ballscrew shafts to which they are mounted are both round so not an ideal situation and I sure they would eventually move at some point.

My intended solution:
To drill into the pulley and shaft from the end effectively making a semi circular keyway into which I can insert a pin, I am thinking that 2-3mm drill giving 1-1.5mm semi circular key slot in both shaft and pulley would be enough to lock these connections and prevent slippage.

I know keyways tend to be slotted and have vertical sides, but as an amateur who did not consider the amounts of torque involved moving weight at speed
a) is my solution viable?
b) is 2mm or 3mm with a steel pin sufficient to do job?
c) is there a simpler way I haven't considered?

[Clive S]

Each pulley is drilled and tapped and fitted with opposing 4mm grub screws,

From my understanding the screws should be at 90' to each other also if you clip a little bit of copper wire off and flatten it then slip it down the grub screw hole it will grip the shaft better.

Loctite will also hold them on.

[Neale]

Drilling into the end, cutting both shaft and pulley, is an established technique but you will find it difficult to do accurately with an aluminium pulley as the drill will start to wander. Also, it's a mistake to drill for grub screws at opposite sides. You are now balancing the force of one grub screw against the other. Much better to drill at 90-120 deg apart, so both grub screws and the bore of the pulley grab the shaft. That might give some useful extra grip. You could just file a small flat on the shaft for one grub screw to bear against?
Good luck - I haven't reached this point on my own machine yet!

[lucan07]

Drilling into the end, cutting both shaft and pulley, is an established technique but you will find it difficult to do accurately with an aluminium pulley as the drill will start to wander. Also, it's a mistake to drill for grub screws at opposite sides. You are now balancing the force of one grub screw against the other. Much better to drill at 90-120 deg apart, so both grub screws and the bore of the pulley grab the shaft. That might give some useful extra grip. You could just file a small flat on the shaft for one grub screw to bear against?
Good luck - I haven't reached this point on my own machine yet!

The pulleys are not aluminium they are Zync plated steel quite solid so I may try a test on the end of one ballscrew I have a small drill stand that I use for holding a tapping aid that I can fix in place with Lube ands patience it should be possible without to much wandering.

[Davek0974]

Drilling in from the end is a good method, if at all possible, drill in and tap a thread - M3 or 4, then fit grubscrews, that way the pulley is secured both directions - axially and radially. You will only get away with it if both metals are similar hardness, my concern is the hardened end of the screw - if one is softer the drill will wander into it.

And yes, grubscrews at 90 or 120 degrees only, never opposite and only two screws, always file/grind a flat on the shaft for at least one screw, better still drill a little divot the same size as the tip of the screw.

[lucan07]

You will only get away with it if both metals are similar hardness, my concern is the hardened end of the screw - if one is softer the drill will wander into it.

The shafts will be harder than pulleys, I could Dremell a half round into shaft and use mill to match this on pulley would not be identical in all honesty but should be close enough to be able to run a M3 tap. Alternatively with opposing grub screws would I be better to drill through shaft completely and use a split pin

And yes opposing grub screws an amateurs mistake lesson learnt will remember that once is a mistake twice is stupid!

Decision made I had seriously under estimated how hard the ballscrew material was going to be.

Significant flat ground on one side and loc-tite to ensure grub screws stay put will be my plan of attack for now, just dremelled first one and grub screw replaced by an allan head A2 stainless machine screw should be sufficient to prevent rotation and lock pulley in both directions.