Lifespan of a Skate Bearing.

[Miata2k]

I've been doing a lot of reading and planning for a CNC project. I like the idea of using inexpensive skate bearings so they will probably be used on my design.

I see most of the people using skate bearings have some type of adjustment for wear and initial setup. Are they really used to adjust for wear after the machine is running or do they just keep on going after the system is up and running? Do you start to see groves in the surface of the bearing or the rail?

I'm just wondering if I need to design the adjustment features into my system, or just weld it together after it is working.

Thanks,
Chuck

[wcarrothers]

I'd say you should build in adjustment..

b.

[NC Cams]

Bearings are made of hardened steel.

What do you plan to make your rails out of?

Simple fact of tribology is the the softer material between the roller and/or rail will wear before the harder one.

If you take this into consideration, wouldn't it simply be prudent to build in adjustment for wear potential that may occur/exist in/between your parts???

[Geof]

Originally Posted by Miata2k .....I'm just wondering if I need to design the adjustment features into my system, or just weld it together after it is working. Thanks, Chuck

Never do the 'just weld it together' if it is at all possible to incorporate adjustment features into a structure with close fits. Welding always introduces distortion, stress or both. You might have something fitting and running nicely before it is welded but after welding it is almost certain to be too loose or too tight and you now have no way to fix it. Well maybe not no way, you can always attack with a SawZall of a grinder with a cutoff wheel and go back to square one.

[Rance]

Chuck,

Keep in mind that there's more than one way to adjust. If designed properly, adjustments could be made using washers (ie. shims) rather than a screw-type of adjustment. It all depends on the design though, but yes, adjustability is crucial.

[project5k]

this is just a little quickie crude drawing of one of the adjustment ideas that i had.. using angle iron as the rail, have holes every so often in the bottom, that are oversized, this will allow adjustment of the rail left and right, and then by adding and removing washers (shims) you can adjust the up and down....

[Miata2k]

Originally Posted by project5k this is just a little quickie crude drawing of one of the adjustment ideas that i had.. using angle iron as the rail, have holes every so often in the bottom, that are oversized, this will allow adjustment of the rail left and right, and then by adding and removing washers (shims) you can adjust the up and down....

I had the same type of idea, using a angle iron with tabs welded to it, but I haven’t figured out how to mount a top side, or make it adjustable.

I made a few of these brackets shown below. (or as an attachment sorry I'm new to this board) I found the design on a site somewhere; I'd have to look to find them. Sorry If I'm stealing someone's idea.


Sorry about the low quality picture, I left my camera at home, so I'm using my Phone.

The bracket is .097 steel, CNC punched and bent on a big break. It is pretty accurate (manual brake with DRO), so I didn't leave any adjustments on the bracket.

Its bolted together with 5/16 hardware and Skate bearings. I have one build using 8mm hardware, but I've use all that was in stock at 3 different stores. To tell the truth, I can't really tell the difference between the 8mm (.314) and the 5/16 (.312). What's .002 amount friends?

Anyway, in its current configuration the bracket rides really nice on any 90degree angle. It would work find on pipe, but I'd have to add longer bolts and spacers to get the flat of the bearing to ride on the pipe, right now the bearings ride on the very edge of anything over 1/2 inch rod.

So I'm into the question, If I use a angle iron on the bottom, what do I use on the top. How do I mount it, and how do I adjust it.

With the parts I have right now, my machine can have a 24" X, 18Y and 6" z. I'm not sure if I'm going to move the table or the gantry. If I move the table I'll use 4 of my brackets on ~48" of rail, 2 on each side and build a frame between them. If I decide to move the gantry I'll only need about half (~24") run of track and I'll only use 2 of my trucks for the X axis.

The Y axis will also run on this type of truck, but the Z will be a linear rail that I bought a while ago.

My biggest fear is that I have too many things adjustable and I can never get the system square.

Thanks for your help.

-Chuck

[project5k]

i dont guess i'm understanding your mounting question.. on top vs on bottom?

[Miata2k]

Originally Posted by project5k i dont guess i'm understanding your mounting question.. on top vs on bottom?

Sorry, I should have been more clear.

I took the idea for my bracket from this website:
http://www.rcmodels.net/cnc/bracketsystem/index.html

Here is the bracket.


From what I can tell in the design on that website, there is no adjustment for anything, but then again, I may just be missing something.

I'd rather not use round bar or pipe in my design because the bearings seem to be more stable on the angle iron.

If I use angle iron with the open side down so the 90degree angle points up then I have a nice surface for the bearings. That is great for the bottom, now what do I do for the top. How do I make an adjustable top brace?

I have a few ideas, but I'm looking for something someone has already done.

-Chuck

[project5k]

ok, now i understand.. i orivinally drew a backside angle design... you can see the pics here.. www.jpcustomcrafts.com/shopmachines.htm but i wasnt going to use an upper and lower.. only the lower... but i have modified this design so that i will be riding the edge rather than the backside of the angle... this way i can adjust the angle for straighness... as you will see in the drawings, i was going to use a pinch roller to ride the underside of the top rail to hold the gantry down against the angle...

im not seeing any adjustment either in that design, but my suggestion would be to do like i have seen done, and mount the angle in some fation so that it is adjustable, and not so much the bearings.. altho you could do this as well.. i forget who it was that i saw doing it, but someone build a metal router, and used round rod, to mount the roundrod they put the ends of the rod in these blocks that had 4 bolts comming out of it at 90deg apart.. this way you could adjust the angle up and down, and left to right to get it all square... maby if you welded some short peices of box to the end of your angle, then you could put the box inside this adjuster plate, and that would keep it from turning, and allow some adjustability...