Sunday, May 29, 2005


Polymorph moulding

Using some Wood's metal, I made a mould of the end gear on an HP printer motor; it's a toothed gear that engages directly with the drive belt. It took some effort to separate the mould from the original gear, and despite warming everything up with a hairdryer first, a large air bubble formed inside. You can see where some Polymorph got trapped in it in this photo:

Undaunted, I drilled out the hole left by the shaft to suit Meccano shafts, and tapped a shaft gently home with a large mallet. If I had been thinking, I would have sprayed a little oil in at this point, and anchored the shaft in the vertical position.

Hot Polymorph was pressed firmly into the hole around the shaft, and a 2-hole Meccano collar pushed in on top. One of the holes embedded itself nicely in the Ploymorph, and the other stuck out allowing me to attach the collar to the shaft with a grub screw. For a permanent fit, Adrian suggests puting a flat on the shaft.

Getting it out was a mission, as the Polymorph had invaded the cavity well. Consequently, the gear was slightly distorted after extraction, and mildly eccentric. This was fixed up with a hot knife, and re-centred after warming the shaft with a hair dryer.

The gear is now in use in the Meccano trolley prototype and will do until I can get a replacement FDM'd up. As it is on a collar with attachment grubscrew, I have been able to change my mind over the length of the shaft it is mounted on a couple of times. Emulating this in an FDM'd model will be fun!

Vik :v)

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