Linear bearing working
I've now had a go at making something like contraptors linear bearings.
Here's the result:
The t-slot I'm going to use in structures is integral to the bearings. I'm using the 3/8" x 1/16" angle because it's small enough to fit on this profile.
Each bit of angle is 25mm long. The bearings are centred roughly 5mm from each end. They are 3x10x4mm (ID, OD, W). They are fixed with M3x10mm button head screws and the nuts are captured against the angle. There's a washer between the bearing and the angle.
Drilling the holes for the bearings:
I wanted to capture the nuts, so I need the holes to be the right distance from the corner of the angle. The bearings also need to be a uniform distance from the angle outside edge. To do this I used a fence on the drill press. I set the fence as follows: I took a bit of angle, put the nut against the inside of the angle, and trapped the nut using the the bit in the chuck. Then I move the fence flush against the angle, and set it. Then I tried a few holes in a bit of scrap to see if it worked. If the nut fits flush against the angle, the result will be as accurate as the tolerance of the nut. The other axis doesn't matter much. I drilled without centre punching first. They were flush , so I went on to drill all my holes. Testing these I found I'd got a few too close. Be careful the fence is clear of debris each time and your pushing firmly against it. I fixed that by re-drilling, pushing more firmly against the fence. The slack doesn't matter, again because the nut flush against the angle is where the accuracy comes from. I held the work with an open pair of pliers straddling the hole, pushed into the angle. You don't want your fingers that near a drill bit...
Drilling the hole for fixing the angle:
There were a few failed ways of doing this, but I'll describe the one that worked first:
First I drilled a pilot using a 1x3mm centering bit from the inside of the angle. I held the angle using v blocks for drilling from the inside. Next I repeating with a 3.3mm bit. Finally I drilled from the other side using a 3x6mm counter-bore to get the flat surface for the bolt head. To hold the work for this, I used a piece of scrap angle as wide as my drill vice, with the corner pointing up, and then put the work on top of it. The clamp held both, since they are identical width.
Some other methods didn't work:
As per my linear motion post, I got an end mill. I used the mill to drill straight into the point. This worked fine, but left a sharp edge on the inside of the hole. When I tried to drill that out a bit for the screw, it caught and snapped the bit. I tried from the other side, and got stuck.
Then I tried drilling the hole first from the inside of the angle. When I came to use the end mill from the outside, my drill press proved inadequate: the post rotated, and even when I'd tightened it, the bit still jumped about a bit, and I wrecked a few bits of angle.
Further work:
The example above is the only one I've finished. It's just made with an off-cut of T-slot bar. I really need to finish another two units, attach a track to 2 bars and try capturing between the two tracks to show it's going to work.
It's also rather noisy. The contraptor version has delrin bushes around the bearings. I'm going to have a go at making these.
Here's the result:
The t-slot I'm going to use in structures is integral to the bearings. I'm using the 3/8" x 1/16" angle because it's small enough to fit on this profile.
Each bit of angle is 25mm long. The bearings are centred roughly 5mm from each end. They are 3x10x4mm (ID, OD, W). They are fixed with M3x10mm button head screws and the nuts are captured against the angle. There's a washer between the bearing and the angle.
Drilling the holes for the bearings:
I wanted to capture the nuts, so I need the holes to be the right distance from the corner of the angle. The bearings also need to be a uniform distance from the angle outside edge. To do this I used a fence on the drill press. I set the fence as follows: I took a bit of angle, put the nut against the inside of the angle, and trapped the nut using the the bit in the chuck. Then I move the fence flush against the angle, and set it. Then I tried a few holes in a bit of scrap to see if it worked. If the nut fits flush against the angle, the result will be as accurate as the tolerance of the nut. The other axis doesn't matter much. I drilled without centre punching first. They were flush , so I went on to drill all my holes. Testing these I found I'd got a few too close. Be careful the fence is clear of debris each time and your pushing firmly against it. I fixed that by re-drilling, pushing more firmly against the fence. The slack doesn't matter, again because the nut flush against the angle is where the accuracy comes from. I held the work with an open pair of pliers straddling the hole, pushed into the angle. You don't want your fingers that near a drill bit...
Drilling the hole for fixing the angle:
There were a few failed ways of doing this, but I'll describe the one that worked first:
First I drilled a pilot using a 1x3mm centering bit from the inside of the angle. I held the angle using v blocks for drilling from the inside. Next I repeating with a 3.3mm bit. Finally I drilled from the other side using a 3x6mm counter-bore to get the flat surface for the bolt head. To hold the work for this, I used a piece of scrap angle as wide as my drill vice, with the corner pointing up, and then put the work on top of it. The clamp held both, since they are identical width.
Some other methods didn't work:
As per my linear motion post, I got an end mill. I used the mill to drill straight into the point. This worked fine, but left a sharp edge on the inside of the hole. When I tried to drill that out a bit for the screw, it caught and snapped the bit. I tried from the other side, and got stuck.
Then I tried drilling the hole first from the inside of the angle. When I came to use the end mill from the outside, my drill press proved inadequate: the post rotated, and even when I'd tightened it, the bit still jumped about a bit, and I wrecked a few bits of angle.
Further work:
The example above is the only one I've finished. It's just made with an off-cut of T-slot bar. I really need to finish another two units, attach a track to 2 bars and try capturing between the two tracks to show it's going to work.
It's also rather noisy. The contraptor version has delrin bushes around the bearings. I'm going to have a go at making these.
