How do you install the new foam pad on the old aluminum plate?
It is not hard to do:
Remove as much of the old foam from the aluminum plate as you can with something like a putty knife.
You can grind the old foam off. I used some lacquer thinner to try to get it off. If you use lacquer thinner do it in a well ventilated area or outside and well away from any open flames.
I found the old contact cement was very hard to get completely off so I left most of it on the aluminum plate.
Coat both the aluminum plate and the new foam pad with some contact cement. Let it dry 10-15 minutes and then apply a second generous coat. Let it sit several minutes until it is dry to the touch but will stick to your finger. Do not let it dry too long or it wil loose it's stick and you will need to apply a third coat.
Lay the foam pad down with the glued side up. Carefully place the aluminum plate on the foam pad more or less centering it. I say carefully because once the glued surfaces touch it is permanent. You can not remove it and realign it.
Cut the excess foam off around the edges with a sissors.
To make the contact cement stick really well lay the pad on the floor and step on it.
How to make the holes in the foam.
It is not hard to do and this is an old trick that is also useful in other situations.
I used a steel rivet. Grip the steel rivet (or use a finishing nail etc) in a vice grips. Heat the steel rivet until it is red hot.
Push it thru the foam to open up the holes in the foam. Move it around to make the hole in the foam the same size as the holes in the aluminum plate. You will generally need to reheat the rivet or nail a few times for each hole. Do this in a well ventilated area or outside.
If you want to counterbore the foam for the heads of the screws use something like a steel rivet. Heat the rivet red hot and come in thru the foam side to make the counterbores in the foam.
Your new foam pad is now ready to be installed on your sander.