View Full Version : As usual I have another dumb question

03-24-2013, 03:17 PM
I have started the process of rebuilding my DIY CNC machine.

I had a fixed gantry and now going to a moving gantry. I had a ton of problems with one axis so time to make some changes and incorporate all the things I have learned from this forum.

But I have one question.
I am starting to add up the weight of the various parts. Two steppers there's 5 pounds, some railings there's a couple more pounds.
Add in a router and the rest of the hardware I must be pushing 12 plus pounds. What I can't figure out is what weight bearings like an SBR12 or 20UU can actually support. I had one on a 20mm shaft and twisted it slightly to line it up and quickly discovered I fubar'd it. I have since found you need to slide them back and forth while turning them so that they don't' get messed up. So now its got me wondering. These gantry's must be very top heavy which means not only do you have the weight of the components, but the stress on the bearings caused by the sudden stop and start motion and the desire for the gantry to tip one way or another. Now I see that most cnc devices seem to employ this type of bearing so I shouldn't worry.

But I am.

Is there documentation around that speaks to what they can handle, or someone how can say..don't worry grasshopper its all good.


03-27-2013, 10:57 AM
thank you internet
I found the specs for the bearings. It indicates 54(kgf), which I struggled with until I found this article.


Which is a very technical description of the force of gravity. when I was young, a KG of lead weighed a KG. Apparently there is more to it.
However at the end of a long technical description the author indicates that the following.
One kilogram-force is approximately 2.204622 pounds.

so 54(kgf) is 109.329588 lbs, I guess I don't need to worry. Especially since the load is over 4 bearings. to funny