On Tue, 28 Sep 2010 15:21:23 -0700 (PDT), Robatoy
wrote:

On Sep 28, 5:30*pm, GarageWoodworks
wrote:
I'm still struggling with my X,Y tables for my H-mortiser. *I've tried
full extension drawer guides and they had way too much vertical
slop. * I also looked at under-mount slides today at Woodcraft and
they too had too much slop.

I am thinking about using 4 steel rods (2 per axis) and using guide
bushings. *Four bushings total inserted into two separate equal
lengths of wood. *The wood would support the table (two per axis).
If I lube the crap out of the steel rod do you think this would work?


I have tried similar approaches and found it less than ideal.
Mind you, you are not looking for a lot of travel so you might be able
to bang the stuff around so it will work for a bit...but linear
bearings are a breed on their own. The bushings have the wrong aspect
ratio to the rods, even when using two. The slightest bit of skew and
you jam.... and you just need one of them to do that by a couple of
thou.

I quite like Mike's idea.

Instead of guide bushings, consider linear plain bearings. Ones made
from Teflon are not very expensive (3/4" for $5-10). They are long
relative to shaft diameter so they avoid the jamming problem mostly.

They don't need lube and can handle high loads as long as you are
moving them relatively slowly and can tolerate more friction than you
would get with linear ball bearings (which can be quite pricey).

For a bit more money you can get self aligning versions which are a
lot more forgiving when mounting....

As this is a key part of your cool project, you don't want something
you will be constantly cursing..

HTH,

Paul Franklin