From a thick sheet of synthetic felt, had glued two layers together to make a typewriter pad. The pad did do something for the amount of reverberation of the table, but the felt also was very smooth. This meant that with every character typed, the machine made a shuffle to the left. As if trying to sneak off-stage to the left, hoping you'd not notice.
Typewriters have rubber feet to keep them firmly in place, would be worth a try to give the felt a rubber coating as well. With a spray-can of plasti-dip that was very easy to do and give it a try.
Not wanting to spray the whole of the pad bottom and to keep the edges clean, taped off the edges and taped a mask in the centre. A typewriter's feet will be around the edges of the pad always - where the anti-slip is needed.
Placing it vertical, gave it a few layers of plasti-dip. Vertical is better for a spray-can of course, but was also worried that the very runny rubber paint would just soak through otherwise. Result is definitely not like an even layer of paint, but it is a full layer and does cling well to the 'felt'.
Removing the masking, a black rubber coating now around the black felt pad.
With the anti-slip coating under the weight of the machine, it sits on rubber again. The pad should now have coating for the position of any portable machine. (Haven't yet heard of a typewriter with feet in middle centre. Though there may be... :)
Net result is a typewriter pad that does reduce the noise of the table a little bit and also stays very firmly in place. This pad would also help machines with hardened feet that have lost their grip, to keep them in place.
No sliding the machine around the table anymore, the only way now to move it is to just pick it up :)