Chain mortiser on hardwood

[nsm5096]

Having some issues with my chain mortiser. I had previously only used it on pine and hemlock and had no issues at all. Now im beginning to cut some ash, and will be cutting a whole pile more of it(entire house worth). Having trouble keeping it clamped in place as it wants to pull itself along the timber and closer/into the layout lines. Anything I can do to prevent this? its on planed white ash, so smooth surface and hard so the rear foot doesn't bite in much at all.

[DPatton]

I have limited experience with a chain morticer, but enough to know dry hardwood will make it jump and bounce in an undesirable manner if things aren't just so. It makes a big difference in control whether your doing your cutting with the downward edge of the chain or on the upward side of the chain as you progress through the length of the mortise. Hardwood also works better if you take smaller bites with the chain with a very steady and slow hand. These things taken into consideration if you are still having issues maybe you need a clamping surface with more grip or grit to it that will grab your planed sides of the timber better. 
Luckly for you I'm sure someone with much more experience than me will help with your question soon. Good luck!

[loganworks2]

I would try some psa 100 grit sandpaper on the foot if it is sliding.