Newbie- linear bearing concept... good/bad?

[pencilneck]

OK, let me first off say I'm sorry for the bad artwork, would of done this in Sketch Up, but that would take me days to do instead of 30 minutes... and my caffeine high is wearing off now (3:37 AM)....

Making my mill using 80/20 T slot, 1530. I've already got myself a sack full of Butcher Boy bearings with new bearings. I'm trying to build upon what GeeksGoneBad has done with his mill.

So here is my spin on the linear motion.....



Starting at the left, the red parts are the Butcher Boy bearings, the black dots would be the 3/8" round rod that would sit in the slot of the 1530. The large "1" is the magic bracket, the circle in the lower right of it is a threaded hole for an adjustment screw.

The next part we are now taking a side view of the same thing, red circles for the Butcher Boy bearings, the yellow thing at the bottom is the adjustment screw. The 2 circles in it are threaded holes. The black bars would be the 3/8" round rod. Now the bracket I'm hoping to make, with the bearings mounted, there would be maybe 1mm of slop if you moved it up and down on the track. The 1530 here would be the base.

Taking a 4365 joining plate, as shown in green, from 80/20, and enlarge 2 of the holes, the lower left and right in this example.

Last part of the drawing now shows the 4365 plate mounted to the gantry with the bearing brackets mounted up. The adjustment screws would make contact with the gantry piece, so as you run the screws in, the bracket would tilt thus taking out the 1mm of slop, until the bearings are snug on the track.

Here is my very sloppy cardboard mock up:



Good plan? Bad plan? 4:03AM, I guess I should go to bed... darn you Diet Coke with lemon.

[der_fisherman]

I personally prefer the method using alu angle iron as a track on mdf or fiber board edges, cur with a router to 90°, for skate board bearings. These are the cheapest bearings around and come in many different quality versions and are really cheap.
You can double up on the bearings for heavy loads.
I am very happy with the results and the accuracy.
Make sure you get the boards cut on a REALLY accurate circular saw, otherwise you will lose accuracy!
I prefer fiber board with a plastic surface.
See my attachments. The first one shows thick fiber board (3 cm) with the edges routed to and bottom and alu angle glued on as the bearing surface. The secon one shows the way the bearings are mounted onto a thick piece of angle, 4 bearings per piece as wide apart as possible, two sets needed. If the parts are really heavy, then double up on the bearings to spread the load. Very free running and easy to adjust.
Look at this website, I got a lot of my inspiration here:-
http://buildyourcnc.com/latest.aspx

If you have further questions just ask.

[Khalid]

Great Idea.. We will see this built with interest...

[Drools]

I sort did what you are planning. I put 1" solid cold rolled round bar on both sides of my 1530 and used it for my Y axis. I used the same round bar on my X axis but just to one side.
http://www.cnczone.com/forums/showthread.php?t=86166

[der_fisherman]

That will work fine as long as you manage to mount them exactly parallel to each other. The mounting hardware needs to be really good too.

The method I mentioned, provided you get the pieces cut to size in a good shop so that they are exactly parallel, are easy to chamfer using a router and a 45° bit, leaving the middle for the little ball bearing on the bit.....then a good glue and a rubber mallet to tap the (cleaned with denatured alchohol first) alu angle in place and the job is done!!! Self aligning even...

Then the skateboard bearings are really cheap and actually fit well on 8mm bar or bolts....life is really easy.

But each to his own, what works for you is fine, I am not criticising!!! I stole the ideas from the website I mentioned in the previous post......they were not my own ideas at all.....

[pencilneck]

OK, I've ditched the first idea. Making the "1" bracket would be something that couldn't be made easily. I have access to a machine shop so I could knock enough of them in a evening, but most people just can't walk into a friends machine shop.

So moving on with version #2 and I think the bulk of it can be done with basic tools that people would have at the house and using parts that are easy to get, plus I think it a sturdier design.

Now in the photos, I've got the 6 hole joining strips, part number 4366 from 80/20. But for the actual design, I'd be using the 8 hole joiner strips, part number 4365.



Here are the 2 plates bolted to the vertical part of the gantry. Now just the middle holes would be bolted. So my example here, I don't have the 4 more holes at the bottom.



With the base up next to the gantry now, you can see the top 4 holes.



Now mocked up here would be a 3/4" or 1" block of aluminum that would be drilled out to the same spacing at the joining strips. There would be 4 bolts across here now, 1 in each bearing (and one would enlarge the holes in the joining strips for the bearing bolts), and 2 bolts going to the T-slot.



While cardboard brackets cost less, I think I'd be using a 4303 brackets, one on each side of the vertical arms of the gantry, that should really stiffen up the joining strips.



This type of T-nut fits in the gap between the base and gantry.

If the holes in the 3/4" or 1" block are oversized, along with the holes in the joining strips for the bearing bolts, one could adjust it as needed to get the gantry to be perpendicular and then secure the hardware to lock it all into place.

So does this look like a winning design?

[Jack000]

just wondering, is there any advantage to this design over eccentric bushings (like in joe's hybrid)? The purpose of this setup is to adjust the tightness of the bearings, right?

[der_fisherman]

Who are asking? I assume Pencilneck.....

But in case you meant me, the design is esy to set up using lengths of theaded rod for adjustment, which can be removed once the fiberboard "bars" have been installed and fixed in place.

I got most of my design from the website I mentioned previously. The design ideas can be easily handled with cheap home tools and the results are really excellent. It is also far cheaper in all respects.....the Guy (I do not know his name) is simply brilliant....

I hope this helps.

[ger21]

Imo, if you're going to spend all that money on the 8020, you should spend a little more and get Dual V style wheels. They use angular contact bearings and can handle much higher axial loads. Joe runs them on plain steel angle, or you can grind the angle to a V with a jig. See the Mechmate forum for the fig design.