CNC Update 3: Assembling the 80/20 Linear Bearing

This has been a very busy week and weekend. I had a couple of PLC boards to refurbish so I didn’t get as much done this weekend as I had hoped. I did manage to get quite a bit done tonight on the X and Z axis but my camera battery is dead so I will create a new post in a few days with that progress.

So, back to the topic. I had decided to use a linear bearing from 80/20 for my X axis. I could have bought one ready to go for about $70., but I decided to buy the bare pieces and build it myself for about $20. I bought the bare bearing in an unfiled and deburred state for about $5. Then instead of buying the bearing pads individually, I bought an 18″ length of the bearing material UHMW-PE (Ultra High Molecular Weight Polyethylene) for $9.54. I then bought a bag of the screws to attach it to the bearing for $3.70.  I bought 1 extra piece that I new I wouldn’t use but I wanted to use it as a reference, that was a completed UHMW-PE bearing pad.

Here is a picture of the components:

Rough bearing lower right, UHMW-PE left, reference pad upper, Screws upper right

I originally was going to cut the  bearing material into pads just like 80/20 does, that’s why I bought the finished pad. However I decided that it would be better to make longer pads that covered the entire length of the bearing in one piece. This not only will make the bearing stronger and have less slop, it turns out it is much easier to make them this way. Now someone may jump in and say that you will create too much friction if you have that much contact area. I was worried about that myself but the finished product slides smooth as silk.

The first step was to deburr the bearing housing. I did this with a hand drill and a bit about twice the size of the holes. Since the housing is aluminum, you need to be careful. I ran the drill in reverse using the bit to deburr the holes with very little force. Then I finished deburring the edges with a file. Finally I used emery cloth to smooth all the surfaces. There is no need to spend time sanding or polishing further because the housing doesn’t come in contact with the rails.

Next I cut four lengths of the UHMW-PE bearing material, exactly the length of the bearing. I used a coping saw for this and it worked really well. One tip, I laid the bearing material in the slot of a piece of 80/20 rail then laid the bearing on top. I then scored it with the saw. Then I moved the bearing and slid the bearing material down to the end of the rail, leaving it in the groove but hanging over the end so I could saw it but it was supported and wouldn’t move around. I then used a razor knife to clean up any rough edges from the saw cut.

Cut piece of bearing material in slot of 80/20 extruded aluminum

Then I put the 4 pieces of bearing material into the slots of a 10 series 2″ wide extruded aluminum. Next I slid the bearing housing onto the bearing pads. After lining everything up I took a marker and marked all of the holes that the screws were going in with a fine tip permanent marker. This left a perfect center showing for lining up the bit on the drill. Then I took a small bit, I believe about 11/64″ and drilled out the holes where each screw was to be placed.

Here is what it looks like after drilling.

On the first couple I used a bit stop so as not to drill completely through the bearing, then I realized it didn’t matter if I went all the way through because that surface of the bearing doesn’t touch anything, so I just drilled the rest all the way through. Then used the screws to attach the bearings, making sure not to over tighten them and strip out the hole. Here is a picture after I installed the first pad then pulled it off to inspect it.

First bearing pad installed.

I continued on with the other three pads in the same manner. That was pretty much it! It was really simple and I saved myself $50.

Sorry I don’t have a picture of the competed bearing but this is where my camera battery died. After this I actually went on to drill out my Z axis mechanism to accept a 3/8 ” rod for movement then attached the it to the bearing. It is starting to come together. I will get some pictures up hopefully this week if I am not too swamped at work, it is month end so work will be a bear!

More next time…

Oh yeah forgot to mention, my optically isolated parallel breakout board came in from CNC4PC. If I get time this week I may do a quick write up on it.