I've seen a couple of solutions to the problem of using an xy sliding vise due to it's higher profile on a mortiser.
I bought the HF mortiser for 99 maybe a year ago and just recently got ahold of the 4 inch xy sliding vise.
The height of the vise of course required the mortiser to be raised and the base be turned backwards but this makes the whole thing much deeper and the base would need ot be secured pretty well to what ever base you came up with.
Well, one day I was looking at my 14" bandsaw and happen to glance at the riser block I got from Grizzly and it gavve me an idea.
Here's what I came up with. It is solid and very very stable. It's made of 4" x 1/4 steel plates from Lowes cut to size and drilled as needed.
The hardest part was getting the drill holes where the verticle rods inset into a 11/16" recess. I madde the recess a smidgen larger and still I was about 1 mm off but was able to adjust it using a grinder. The inset holes I drilled in the top plate had to be exact in order for the verticle rods to fit into place.
This set up has given me about 5" of extra space.
I am hoping to test it out this weekend.
Hope someone finds this usefull. (BTW, my welding seems to be getting better. )