Build Thread- Linear motion: V-groove or skate bearings?

[hgularte]

This is my first post here. I've been reading this forum for a while, until I decided what type and details of my project.
Now I'm drawing the plants, and would like to have your thoughts about this topic.
Almost all design here uses carriages with 4 skate bearings attached to a v profile, running over a v-profile.
Why don't use a v-groove bearing running over a v-profile? Is the cost of the bearings the only reason?
What would be the pros and cons of v-groove bearings?

thanks in advance

[ger21]

The V-groove bearings are far superior imo. Most of the designs you see using Skateboard bearings are older designs. The V Bearings in the past were about $25 each, which made them about 25x more expensive than skate bearings. Only in the last year or two did they become more affordable, now about $12-$13 each. You'll see that a few newer designs are using the V bearings, including Joe's popular 4 x 4 Hybrid.

[hgularte]

That was precisely my understanding. It makes the building process easier, too.

[cerberos]

Hi,
I'm also interested on design a machine using V-Groove bearings. But what problems can be with this kind of design? Must i drill the guide and support holes with another CNC? I can use only hand tools....

Thank you

[amishx64]

Originally Posted by cerberos Hi, I'm also interested on design a machine using V-Groove bearings. But what problems can be with this kind of design? Must i drill the guide and support holes with another CNC? I can use only hand tools.... Thank you

Many of us on the forum have built our own machines without the use of another CNC. This makes things considerably harder, but still doable. I was able to build mine without a CNC, but I also used things like an out-of-square miter saw and a cheap drill press.

V-groove bearings would make your life a bit easier over skate bearings because you only have to worry about getting the mounting holes in a nice straight line. With skateboard bearings, you need many more, and the bearings need to me mounted accurately on three axises on another piece of angled material vs 2 axises on flat material with the v-groove.

[louieatienza]

My opinions are on the fence about this. I do like the simplicity of construction. And definitely tune up is easier, especially if you use eccentric bolts for adjustment. Even though multiple bearings have to be used, there could be a benefit of having the "load" of the bearings distributed, putting less stress on the system. Plus no one can argue the cost

While not necessary a problem, I do feel some design considerations should be considered to prevent overloading the bearings. For example if a design incorporates either a tall or heavy gantry, it might be beneficial to widen the bearing distance, or at least keep its weight centered between the bearings.

[amishx64]

louieatienza, I agree with your thoughts. Also though, if you are using a very heavy gantry, I don't think I'd recommend even using V or skate bearings.

Where are you guys buying the bearings? I seem to be seeing ~$8 for one bearing. Surly that can't be right.

[ger21]

I bought mine here. http://www.cadcamcadcam.com/v-groovewheel2.aspx
But I might go with larger ones from VXB for my X and Y axis, but I'll need to fabricate my own eccentrics, or find another source, as VXB doesn't sell them.

If you download the Dual V catalog from Bishop Wisecarver, it gives load ratings and how to calculate them for the different sizes of Dual V's. The larger ones have very high load ratings, but can be expensive.

As far as fabricating, I think a drill press would be the minimum requirement. By using a fence, it's easy to get the holes in a straight line, and perpendicular to the face.

[louieatienza]

Originally Posted by ger21 I bought mine here. http://www.cadcamcadcam.com/v-groovewheel2.aspx But I might go with larger ones from VXB for my X and Y axis, but I'll need to fabricate my own eccentrics, or find another source, as VXB doesn't sell them. If you download the Dual V catalog from Bishop Wisecarver, it gives load ratings and how to calculate them for the different sizes of Dual V's. The larger ones have very high load ratings, but can be expensive. As far as fabricating, I think a drill press would be the minimum requirement. By using a fence, it's easy to get the holes in a straight line, and perpendicular to the face.

ger21, I believe IMService sells the eccentric bolts, for a very reasonable price.

amishx64, the great widgetmaster had a build that used v-groove bearings, and though only 24 square by 9 high travvel in the z, the bearings still failed, despite doubling them in the direction of force. Granted it was an all-aluminum construction, but the weight, high z and relatively small bearing spread seemed to lead to their failure. He eventually rebuilt the machine with linear slides.

I think however, for the y or z axis, where there is less weight, the v-grooves might perform better, and you get the advantage of the low-profile design i.e. carriage tighter to gantry...

edit: Just noticed this thread must have one of the lowest reply to view ratios ever....

[ger21]

Originally Posted by louieatienza ger21, I believe IMService sells the eccentric bolts, for a very reasonable price.

They are even cheaper if you buy them with the bearings. I actually did purchase some with my bearings.

However, what I said was, that I want to use larger size bearings from VXB, and they don't have larger size eccentrics available.

Originally Posted by louieatienza amishx64, the great widgetmaster had a build that used v-groove bearings, and though only 24 square by 9 high travvel in the z, the bearings still failed, despite doubling them in the direction of force. Granted it was an all-aluminum construction, but the weight, high z and relatively small bearing spread seemed to lead to their failure. He eventually rebuilt the machine with linear slides. I think however, for the y or z axis, where there is less weight, the v-grooves might perform better, and you get the advantage of the low-profile design i.e. carriage tighter to gantry...

WidgetMaster used the small #1 size bearings, and imo his design far exceeded their load ratings. Also be aware that when using this size bearing with bushings, that the entire load is being carried by #6 size bolts.

It's really quite simple. The bearings have both axial and radial load ratings. Don't exceed the ratings, and they'll work fine. ShopBot's been using them for 15 years.

For the Z axis of the router I'm currently designing, I plan on using #3 bearings. The top (load carrying) bearings are rated for almost 700lbs each, and 380lbs axially. And by nit using a bushing, they are mounted with12mm bolts, which are plenty strong.