Making The Y-Axis Bearing Block, End Mount, And Ball Nut Flange · Sep 23, 12:00
Firstly, let us say that if you ever have the chance to buy an appropriately sized bearing block and end mount for your desired ball screw, do it.
While it’s certainly lots of fun machining (especially CNC’ing) the parts for your specific application, nothing beats being able to bolt-on this setup directly to your mill and getting to the good stuff – machine design and prototyping!
Here we see a picture of the Y-axis bearing block with the ball screw inserted for fit. This was the nicest fit we’ve made to date – slight resistance but not quite such a press fit that you’d have to use an arbor press to remove them back out. These are two angular contact bearings (already tightened to no-play) inserted and spaced just right so that when the cover plate is placed, the ball screw assembly will have zero axial play (aka “backlash”). This, coupled with the already zero-backlash nut, makes for a nice assembly. It should also be said that as a cost-savings measure, we used regular radial ball bearings (aka “skate bearings”) for the same effect. We’ll talk more about this in our components section of the website.
We first drew up the part in its assembly mode:
If all the pieces mate and fit in assembly mode (with all constraints in place), then the underlying component, when drawn out and converted into G-code for machining using a CAM program, will turn out exactly as you’ve drawn it (minus the inaccuracies of your machine itself , tooling, etc.)
So, we chucked the 6061-T6 aluminum chunk that was first squared off manually (though using CNC in jog-mode for a consistent finish) and then went to work. Click on the picture to view the video of this piece being made:
After some time, we end up with this piece:
Then we turned our attention to the end mount (which we won’t show here) because it’s basically the same procedure as making the bearing block.
We next had to make the ball nut flange. After taking some dimensions of the ball nut (finding specs on the THK website yielded no results), we machined the flanged, drilled, tapped some holes and then mounted the flange to the ball nut – nice fit!
We forgot one thing! The bearing block mount actually was going real nicely until we had to finish off one end. Technically, we could have left it as-is since the extra width wasn’t going to interfere with anything, but in haste, we used a 7/16” 4-flute end mill and ran it hard until it gummed up and ruined the look of what would have been a nicely-finished part:
Oops! So, take your time and remember not only to measure twice-cut once, but also take it easy and don’t rush things.
One more thing we had to make were spacer blocks to increase the height of the Y-axis base since the ball screw/but dimension was greater than what we had in the X-axis:
In this final picture of this article, you have the X and Y axes nearly put together just like what was shown in the CAD drawing above:
Now we’ll turn our attention to the Y-axis NEMA 23/34 combo mount. This time we’re going to simplify things and use just two pieces of 4” wide 1/2” thick aluminum extrusion. Stay tuned…’
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