[GreenKeys] Rubber Feet

[Jones, Douglas W]

I've decided to take the plunge and try manufacturing replacement rubber feet for the missing and broken feet on my Flexowriter.  So, I removed one good rubber foot yesterday and set to work to create a mould for forming the replacement feet.

Step 1:  Cut a length of brass tube that fits snugly in the bolt hole in the foot.  I put a piece of steel wire through a crosswise hole in the far end of the tube to lock it into the plaster and then pushed the tube flush with the rubber on the wide side of the foot.

Step 2:  Coat the rubber with vaseline to make it easier to unstick from the mould.

Step 3:  Set the wide side of the rubber part on a smooth surface.  I used the lid of a plastic sour cream container, and I used some vasilene to stick the foot to the plastic so no plaster would get under the part.  I plugged the brass tube through the bolt hole with a bit of soft wax to keep it from filling with plaster.

Step 4:  Build a wall around the part to contain the plaster.  I used the rest of the sour cream container, with most of the bottom cut out (leaving a narrow rim to serve as a reference plane.

Step 5:  Mix the plaster of paris to the consistency of thick cream and then pour it to fill the mould level or a bit over level with the top of the mould.

Step 6:  As the plaster starts to harden, use a straight-edge to scrape off the excess down to the reference edge.

Step 7:  Wait a day to let the plaster set completely.  That's where I am now.  While waiting, I ordered some Versimold thermo-setting silicone rubber.

-- to do tomorrow --

The Flexowriter foot has a hollow in the wide (bottom) side, so I need to make a plug that fits it:

Step 8:  Make a rigid pin that fits in the brass tube through the bolt hole.  I used a piece of telescoping brass tubing for this, and drilled a small cross hole for a bit of steel wire to go crosswise through the pin to lock it into the plaster.  The pin-length should make the exposed end flush with the wide flat surface of the rubber.

Step 9:  Coat the exposed rubber surfaces with vaseline.  Try to avoid coating the pin, you want the plaster to stick to it.

Step 10:  With the pin in place, invert the plaster-encased rubber part, remove the flat bottom from the mould to expose the flat side of the foot, and insert the pin.  Plug the hole in the exposed end of the pin with wax and pour plaster into the space around the pin.

Step 11:  When the plaster starts to harden, use a straight-edge to scrape it down flat with the planar exposed rubber surface.

Step 12: Wait a day to let the plaster set completely.  Also wait for delivery of the rubber compound.

-- to do when ready --

Step 13:  Break loose the wax in the upper end of the alignment pin, grab the crosswise piece of wire that goes through the pin with a hook, and pull the upper part of the mould out of the original rubber foot.

Step 14:  Somehow (and carefully) pull the original rubber foot out of the plaster mould.  If the vaseline does the job, this should not be too hard, but it may involve sticking pins in the rubber to get a grip on it for pulling upward out of the plaster.

Step 15:  Coat the inside surface of the plaster mould with a thin layer of vaseline.

Step 16:  Press the clay-like thermosetting rubber into the mould, shape it with finger pressure to approximately the right form, and then put the upper part of the mould in place and continue forming it.  Use too much rubber so that, as a final step, you can use a straight edge to form the flat base of the new part.

Step 16a:  (Experiment may be called for here)  Either release the new part from the mould and put it flat side down on a cookie sheet, then bake at the curing temperature for long enough that the part cures or

Step 16b:  Bake the new part in the mould at the curing temperature and then remove it
from the mould.

The curing temperature for the rubber I purchased is 250 degrees F.  I will report on the success of this project when it's done.

		Doug Jones
		jones at cs.uiowa.edu