In an earlier contribution to this discussion,
Mathew J. Newton wrote:

Hi all,

I am hoping some kind and able soul out there with a lathe and/or
milling machine might be able to help me out here....

At the risk of sounding like I've got too much spare time on my hands
I am in the middle of project building a network-enabled cat feeder.
The current design is based around a cereal dispenser driven by a
high-torque/ low-revs motor, the latter being controlled by a
modified Cisco switch.

The following diagram shows roughly what I am doing from a mechanical
perspective:

http://www.newtonnet.co.uk/permanent/feederdiagram.png

The cereal dispenser contains a rubber flapper mechanism which
accommodates a plastic shaft connected to a knob. Whilst I have
managed to separate the shaft from the knob and connected everything
up I am concerned that over time the high torque required when food
gets caught in the flapper will cause the connection to the brass
coupling to fail. This is based on the fact that the plastic shaft is
rather soft and is not held all that firmly by the grub screw in the
coupling. I have considered inserting a metal shim of some sort but I
really can't see it lasting.

Hence, I am wanting to replace the plastic shaft with something made
out of metal. Unfortunately whilst my apprenticeship days taught me
the skills to do this I do not have access to the necessary machines
to do so.

Would anybody be able to help me out here? That kind person would be
suitably compensated as required. I have made a drawing showing the
necessary dimensions (using Word - my teachers would not have been
impressed!):

http://www.newtonnet.co.uk/permanent/shaftdrawing.png

As you can see, the coupling to the motor (right-hand side) is
required to be smaller the main shaft - I could not find a shaft
coupling any bigger than 6mm (the motor shaft is also 6mm). The
rather strange (specific) dimensions of the main shaft (which is
fully inserted into the flapper body) is, I believe, a result of it
being US-made and hence of imperial measurements.

Happy to provide further info and clarification if required. Indeed I
am all ears to alternative ideas too and/or suggestions as to
who/where might be able to make this shaft for me.

Regards,

Mathew


Does it really need to be as accurate as your specification, if it only
rotates slowly? Does anything have to slide along the D-shaped shaft in
operation, or only in assembly. If the latter, can't you:
* Start with a length of 8mm mild steel rod
* Rotate it in a drill chuck, and use a file and emery cloth to reduce it to
7.6mm
* File the flat all the way along
* Bore out one end of the coupling - thus avoiding having to reduce the end
of the shaft to 6mm?
--
Cheers,
Roger
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