After a couple weeks of testing and trying different methods, I finally got my linear bearing situation taken care of. Thought I would write up the process I went through.
update (10-16-2012) – if you go the drill press and template route, make sure your press table and any vises are square. i don’t believe mine was so the batch i didn’t do 100% on the cnc is off by 1mm, making them useless. They are going straight into the foundry… when i build one… I’ll try to post an update when I create the next batch.
They post the models for these small linear bearings from cncrouterparts.com. I had to increase the height of their design to full inch so I could use common 1″x2″ aluminum bars. I also changed some sizes of set screws and little things.
I’ve learned with CNC things can go wrong quick. Best to prototype out of cheap stuff first. Especially when you are creating a batch of parts. So instead of jumping straight to using the aluminum stock, I decided to create some mock ones out of 1/2″ mdf to test everything first to test the changes I made. So I cut some 2″x4.5″ pieces
I just had to glue them up in pairs to get them into full 1″ depth.
Here’s the finally test product.
Next thing I had to do was to create my jig for the mill so I could do multi-sided milling. I use 3/4″ mdf. My machine doesn’t have any homing or limit switches. To get things zero indexed I used a 30 degree v groove bit to find the top north west corner between milling. I really need to get some limit switches and learn to use offsets.
Here’s a shot of the test piece’s top milling.
I flipped it over to do the other side and re-zeroed.
I flipped it over to do the next side. Unfortunately I didn’t flip it the right way and ended up milling this piece the wrong way.
So that ruined that piece. Had to create a whole new one. And when I did I noticed that the nuts I had didn’t quite fit and broke off the stand offs created by the top milling. Not critical but it made me dig deeper into my cam stuff being generated. Turns out there wasn’t a hight enough tolerence in those tool paths and too much stock was being left for finishing operations. Increased the tolerances and when it came to the milling aluminum everything went of great. Another great reason to do prototyping in cheap stuff first.
Here is the underside. I’ll eventually replace these capped hex bolts with rounded over ones.
The whole system works with a pair of these ganged together. Here I wanted to show how it fits on the rail. The real rails will be much wider and made of 1/4″ cold rolled steel.
After I got things to reasonably fit I went ahead and created the first one out of aluminum. It came out great! All the test runs really paid off. Here’s the top side.
And here is the bottom
I went ahead and created 3 more making it a total of 4. But I noticed that this was really taking a beating on my carbide bits. After a while I was having to stop the machine and clean out aluminum from the bits that had turned to clay. Also, I didn’t have any bits with enough clearance for the deep hole drilling so that was causing things to jam. After a while I decided that I could keep the pocketing and profiling stuff on the mill but all the holes probably needed to be done on a press. So I created some jigs. Here’s the top one
Here’s the right one.
And finally the left one. This one might not have been necesarry if I had a drill press that had a greater than 2″ travel and I could do pilot holes all the way through.
Here they all are together to give you a better idea how they all fit together. All the holes are drilled out to 1/4″ to fit my 1/4″ transfer punch. This lets me mark up the stock and then take it to the press and use the appropriately sized bits to make the actual holes. More about this in the video above.
Here is a demonstration of how the top one fits. Notice I still drilled holes for the more oval shaped holes used for the adjustable post bearings. Since its oddly shaped, it couldn’t really be pulled off on a press.
Using the press sped up the time in creating all 16 of my bearings but required more time hands on creating them. If I could do it over again I would have only made one side jig for what I have labeled “R” for right. I would have used a smaller bit to drill a pilot hole as much of the way as I could through the 2″ of aluminum, then used the same bit to finish the pilot hole with a hand drill (since my press has slightly less that 2″ of travel). Then used the appropriately sized bits to finish off the holes. I believe this is called concentric drilling. If you notice in the picture below I had to actually increase the size of some of the clearance holes since they didn’t line up completely with the other side. Kind of heart breaking putting in all this work and having to do that.
All in all I’m actually impressed with the cncrouterparts.com design. Also with their pricing. With all the work and hours I had to put into this, I think its pretty much worth it to buy them from cncrouterparts.com. They come with abec7 bearings and all the nuts, bolts and split washers I believe. But since I’m cash poor and have entirely too much time on my hands, it makes more sense for me to make them. Plus, now I have the whole linear bearing situation taken care of for any other project I might need.
For the first 4 bearings I used screws and stuff at Lowes and got my bearings from Academy sports, which was the cheapest I could find abec 5 bearings in a physical store. But even then it was probably gonna break the bank. So I ended up buying my parts in bulk from amazon for the rest. Here’s roughly how it breaks down
$0.80 per linear inch of 1″x2″ aluminum bar x 4.5 = $3.60
$0.16 per set screw x 2 = $0.32
$0.31 per 50mm screw x 2 = $0.62
$0.22 per 30mm screw X 4 – $0.88
$0.06 per 8mm locking washer x 6 = $0.36
$1.00 per ABEC 5 radial skate bearing x 6 = $6.00
%?.?? cost in man hours machining, drilling and tapping (roughly 2 hours per bearing) = How ever much you value your time and your aptitude for machining.
So for about $11.78 I can turn out a bearing. But considering how cheap they have theirs priced and that it comes with better bearings, I don’t know how they do it. This also doesn’t factor in all the time it too and the fact that I had to buy a new set of end mills, a new set of drill bits and my first set of transfer punches. So if you are not a hard core DIY or super cheap person like myself, I recommend you just buy them.
But for me this was more of a write of passage. I figured if I couldn’t pull this off with a smaller cnc mill then I had no right building the bigger one. I setup a code to follow that if I could build it, I had too. Even if it didn’t cost less.
I did figure out a number of things doing this. How to create jigs for work pieces, especially for multisided milling. How to use transfer punches and screws (or what tranfer screws even really are). How to use a sharp pointy bit to zero my work without any kind of homing. How deep I can mill with certain bits. Oh, and to only ever use 2 flute bits with aluminum.
So for me it was a well worth it exercise