8mm square to 15mm round adaptor

#1

I mentioned this in my introduction but it’s proving hard to fabricate. I need to connect three actuators which are designed to clamp to a round spigot max. 16mm:

http://www.neptronic.com/Actuators/pdf/BBM.pdf

to three damper valves which have 8mm square spigots:

https://www.ductstore.co.uk/cgi-bin/sh000088.pl?WD=dampers%20closing&PN=Damper-Units---Actuator-Cont.html#aDATML200

I have tried to use wedges around the spigots, but as the torque is quite high (the actuators rotate 90 degrees in only a few seconds, and the valves have stiff bearings and rubber seals), there is quite a lot of twisting between the two.

As it’s difficult to make square holes, one option is to drill a cylinder with a >=11.3mm round hole and clamp the faces of the spigot with grub screws. But the wall thickness would be <2.5mm so there would not be much thread depth. A thicker bar partially turned down to 16mm would have to be used instead.

Another option might be to use a cut-down door knob, and grind down the spigots slightly to fit.

Is there anything else I could use, like some sort of very strong resin which I could mould round the spigot, perhaps after covering with cling film to allow it to release?

Thank you.

#2

Have you tried 3D printing an adapter? Might not take the torque.

Personally I’d drill an 8mm hole in the end of a bit of 16mm bar, chuck it in the forge and then drift it out to square. But I’ve got a forge…

#3

You can certainly mill a square hole in the face of a 16mm round piece. Or laser cut it? Depending on torque requirements

#4

Laser cutting in something tougher than acrylic might work - delrin/acetal? Maybe even MDF?

Or cut a slice off the end of a piece of 16mm round steel, drill an 8mm round hole and file out to square?

#5

Thanks for all those great ideas! Funnily enough we have both a 3D printer and a laser cutter at work, but I’ve not acquainted myself with either. I think the material used by 3D printers is going to be too soft/weak.

The people I’ve approached said they can’t make square holes in brass (brass being my guess at a material).

I’ve had another idea: 15mm copper pipe offcuts filled with epoxy putty. It doesn’t matter if they’re permanently attached to the spigots. Anyone played around with epoxy putty? Is it going to be easy to fill a few cm of pipe with it and then push the spigot through it?

#6

Actually stand down - I’m getting brass-and-grub screws after all!