Sorry it has been so long since my last update. I have been really busy with work and have been doing some traveling. Anyway this weekend saw a solid 20 + hours of work on the CNC. Early last week I decided that the 80/20 linear bearing I built for the X Axis, had too much play in it so I ordered some shims. I also ordered some 20 mm linear bearings from Glacern Machine Tools. They have them on sale for $12.95. They are rotating ball bearing units. Lastly I picked up some aluminum channel for the spacer to go under my rails. I already had several 20 mm rails that were kindly donated to me by my friend Brian.
OK, the first thing to do was tear the entire unit down. I decided that I had the uprights too high for the sides so I need to cut them down. Then it was time to work on that bearing. Let me stop here and say that I am very sorry that I don’t have pictures of all the work. My good camera was charging so I was using my backup camera. I took a lot of photos that didn’t come out due to overexposure and out of focus. Anyway, the shims I bought came in a stack of about 8 or so. They were all stuck together from where they were cut out. It was a challenge to get them apart without tearing. When I finally got them apart I started adding them under all the slides. After doing that I tried to slide the bearing back on the rail but it was obviously too tight. So now it was a game of trial and error until I got enough shims to tighten it up but hopefully, not so much that it will cause too much drag for my stepper.
Next I started working on reassembling the uprights and the X Axis rail. When that was done I had to attach them to the base. Until now I have just had the bottom rails setting on the base. The base is a piece of 1/2″ scrap aluminum plate. It wasn’t exactly cut square and I realy didn’t have a good way to cut anything that thick. So I had to square the rails without using the base as a guide. So if you notice the 1″ rails setting on the base don’t match exactly with the edge of the base, that is why. I will grind the base off square later.
The next order of business was to install the slide rails for the Y Axis. I first cut two pieces of the aluminum channel to length. Alignment here is critical. Not only do they need to be perfectly parallel, they must be exactly perpendicular to the X Axis. So in order to insure this I mounted a square to the X Axis and attached a pencil to the end and drew a line on the base. So now I had a reference on my base to the X Axis. Then I used a square to strike two lines perpendicular to the X Axis line. I used these lines then to line up my channel support. I then used C-clamps to hold them in place while I drilled the mounting holes. The positioning of these holes was also critical because my rails are pre drilled and tapped and these holes had to match up with the rails. After the holes were drilled I had to counter bore them from the bottom so my 6mm allen heads would set flush with the bottom of the base. Finally, I pushed the bolts up from the bottom and set the rails on them and tightened everything up.
Here is what the channel looks like.
Here is one completed rail
Table setting on slide bearings.
After the rails were done I had a decision to make. Would I use 4 bearings, 2 per side, or just 2 bearings, 1 on each side. My Y table is only about 12″ wide so I thought one bearing in the middle should be fine, and a lot less work to line up that the 4 bearings would be. So after a lot of measuring and math I had transferred the mounting patterns on to my Y table and drilled them out. Once I got the bearings mounted and the table installed, it would slide very well. However if you applied almost any force at all to either of the unsupported ends of the table, the bearings would thrust and bind. This obviously was not going to work. There was just too much play in the bearings for this type of set up. Also you could almost fill the movement of the bearings as the table slid, even when the pressure was applied directly over the bearings. I was about to pull the table and re-drill it for all four bearings, when I remembered that I had some 20mm slide bearings that another friend, also named Brian, had given me. I hadn’t thought to use them because I didn’t have a housing for them. My thought was, I wonder if they will fit in the same housing as the bearings I got from Glacern. The Glacern bearings were held captive by two snap rings at either end of the bearing housing. The slide bearings I had were a little longer so I Knew I would be able to use both snap rings. Luckily there is also an allen adjusting screw in the middle of the bearing that tightens down to adjust the tightness of the bearing. I simply installed the slide bearing and tightened the allen screw tight enough to leave a mark on the bearing. Then I removed the bearing and drilled a divot in that spot. Now I reinstalled the bearing and tightened the set screw into the divot and the bearing was now captive in the housing. After installing two of these to the table and sliding the table back on to the rails, I was amazed how much smoother the table moved and the bearings did not bind when a reasonable amount of force was applied to the outside edge of the table!
Over exposed image of the bearings
Sorry about the quality of this photo, but you can see the original bearing on the left, the removed ball bearing in the middle and the slide bearing on the right.
Next I had to attach a nut under the table for the screw to act on to move the table. I had a piece of scrap aluminum about 3/8″ thick that were cut into two rectangles 1.5″ x 2″. In the center I tapped them 3/8×16 for my drive screw. I am using just standard threaded rod for now. I then turned one of them on edge and drilled and tapped two holes for 6mm. I drilled the table to accept the two holes I just drilled in the nutand mounted it under the table. By the way, every thing you see here was drilled with a hand drill not a drill press. Originally took some pieces to a shop to use the drill press but found the accuracy of the cheap drill press was no better than I could do by hand so I decided to just do them by hand. Don’t get me wrong, if I had a good drill press, allot of this would have been much easier. Anyway to get back on track, I took a threaded rod and screwed it through the nut until it came out the back side of the table. Now I used a line that I had already drawn on the base, that was the center of the rails, to align the nut so that I knew it was straight.
Y Axis Nut
You can actually see it better in the reflection off the base.
Then I built the mount for the stepper. This was built with some aluminum angle.
Y Axis Stepper mount
After this was done it was time to reassemble the Z Axis. The original setup I had used for the Z Axis was not working out. The stepper motor didn’t have enough torque and it was very hard to get perfectly aligned. After a lot of thought, I rebuilt it using a different stepper, that I had from a tear down of an old dot matrix printer. I also inverted the mounting of the motor and the drive nut. The motor is now on top of the axis, rather than tucked away inside. Also for the nut I used the second piece of aluminum that I spoke of earlier. I used a grinder to get it to rough dimension then hand filed it so that I could press fit it into the aluminum mounting for the axis. I wish the pictures of this had turned out. It is hard to explain without the pictures, but I will get some in a day or so. Anyway, all I like on the Z Axis is finishing the stepper mount on the top.
Here is a picture of the unit as it stands right now.
Front view, Z Axis mount not complete
That’s all for this update, time to get some rest.
You must log in to post a comment.