Binding of a linear slide

[Joshua Sicz]

We were finally assembling our linear side on Saturday and ran in to some trouble. We are using two 2 x 1 aluminum stock that the slides glide on. We have attached a bar in between the two slides. They move up and down as expected but what is happening is that with the slightest nudge of being off, not equally being pulled on each slide, they bind against the metal and stop gliding.

Thanks,
Joshua Sicz

Here is a picture of a slide and could post more later today if the desciption is not clear.

[MrForbes]

Do you have a picture of the whole assembly, with the two slides and the connecting piece, and the vertical parts it slides on?

Just so we can clearly understand how all the parts are oriented when it's assembled, and is getting stuck.

[Drew4564]

Originally Posted by Joshua Sicz

We are using two 2 x 1 aluminum stock that the slides glide on. We have attached a bar in between the two slides. They move up and down as expected but what is happening is that with the slightest nudge of being off, not equally being pulled on each slide, they bind against the metal and stop gliding.

From the picture provided, it looks as if there's nothing to space the bearings out from the two side plates. If this is true, a thin spacer the size of the inner race between each bearing and the side plates would stop the entire bearing from contacting the sides and binding. This worked very well for my team's carriage assembly, which uses a very similar slide.

[GeeTwo]

Can't see enough to understand clearly, but the problem has two general solutions.

First, is to provide some sort of bearing or glide or close fit (preferably without sharp corners on the leading edges) that act to prevent the rotation. The idea is to so constrain the moving part that it cannot get bound. This will require more precise machining, but usually fewer actively moving parts.

The second is to come up with some "self balancing" way to distribute the load across the piece so that it doesn't get pulled away far enough to get bound. This year on our lift, we used two chains about a foot and a half apart but driven by the same axle. We've only done a few lifts and lowers so far, but we haven't had any binding. We do need to do some more tests with off-center loads to determine how much is too much.

[Fields]

From the picture I would guess that the cross bar is positioned top-bottom from the cameras view.

What I'm seeing in here is over-constraint left and right and under-constraint top to bottom.
The over-constraint is nice when everything is lined up perfectly. More strength and such. You see it on a lot of equipment because it can be sturdy.
Unfortunately this is where parts bind.

Under-constraint has no binding issues, but does have alignment issues (your cross bar going on an angle)

Try drawing this out. Remove one axle (looks like there are 4 on the guide). Position the other three in a triangle shape with the axles at the points and if you connect the lines all the angles should be less than 90 deg. The triangle would be seen from the side.

o
. o
o

Take your 4th axle and place it to the inside of the frame (either above or below the triangle) Ideally if you have a 5th axle it would be placed one above and one below.

. =
o
. o
o
. =

I don't know how your guide is put together, but theoretically you could cut out one half of the axles and achieve the same thing without wrapping around the al stock.

[75vs1885]

From my own experience, using spacers and checking every messurment for squarness is the only thing that can be done, make sure that the slides have a tiny bit of wiggle room so the can self correct for small amounts of binding

[Aur0r4]

Originally Posted by Joshua Sicz

We were finally assembling our linear side on Saturday and ran in to some trouble. We are using two 2 x 1 aluminum stock that the slides glide on. We have attached a bar in between the two slides. They move up and down as expected but what is happening is that with the slightest nudge of being off, not equally being pulled on each slide, they bind against the metal and stop gliding.

Thanks,
Joshua Sicz

Here is a picture of a slide and could post more later today if the desciption is not clear.

In addition to the suggestions given, this is one way to look for binding points on a slide.

Extruded material has tolerances on variations in width/height/smoothness that can be large enough to cause binding at some points, but not others, in a well-built, tight slide assembly. One way to find these points is with a bluing ink designed to indicate bearing pressure. This is one of the best out there, and it is quite cheap:

http://www.artcotools.com/die-spotting-ink.html

The benefit to a dye like this is that it doesn't just show contact...it shows pressure points by areas of lighter and lighter blue. Just smear an even coat on your tube, run it through your guides in a way that causes it to bind, and it will show you where the tight spots are.

This is the stuff they use to check tight fits on machine tool parts.