uhmw runners in birch plywood. should they slide on sides AND bottom?

[Cory filder]

I built an "over table" for my bandsaw. it is an 18mm thick table. I bought uhmw runners(3/4") wide and 3/8" tall at lee valley.
Should the uhmw touch the sides of the table only or touch the bottom and the sides.

my intuition is touch the sides only as I will almost certainly not get the depth of cut exactly right. which is the correct way to do this?
thanks

[William Hodge]

I like the aluminum runners, because they adjust width, and aren't plastic.

The aluminum ones are thin, and just touch the sides of the grooves. The band saw ones wok great. I cut joints with a sliding table on the band saw.

[Cory filder]

I like the aluminum runners, because they adjust width, and aren't plastic.

The aluminum ones are thin, and just touch the sides of the grooves. The band saw ones wok great. I cut joints with a sliding table on the band saw.

That's for aluminum. with the same apply for plastic?

[Eric Arnsdorff]

My view of a "sled" design (if I understand your "over table" correctly it is equivalent to a table saw sled) is that you have the table support the flat plywood while the runners use the sides of the slot(s) to stay aligned to the plane of the blade.

[Lee Schierer]

Most of my runners for sleds just touch the sides of the miter slot.

[Keegan Shields]

Just sides. No reason for the bottom of the rail to touch the bottom of the miter slot. The sled should reference off the saw table, not the bottom of the slot.

[glenn bradley]

Just the sides here. UHMW, aluminum, steel or wood; same deal.

[Dan Cameron]

Just sides. No reason for the bottom of the rail to touch the bottom of the miter slot. The sled should reference off the saw table, not the bottom of the slot.

It only makes sense to have one (and only one) right edge and one (and only one) left edge contact to guide the sled. If the runner width is precise, save one runner for another project.