VXB linear bearing systems???

[stag53]

Has anyone used the VXB linear bearing setups? (http://www.vxb.com/page/bearings/CTGY/LM)

Their 20mm systems are really inexpensive ($70 USD for a 55" cylindrical rail and two trucks), but I wanted to see if they've worked well in others' applications before I take the plunge. I'm considering using them for a CNC plasma table I have in the works.

Thanks in advance!

[LazyMan]

Where did you see the $70 one? Im using the $155 one with supported rails and 2 blocks on a cnc router build. My machine is not completed yet but the system feels pretty nice. For a Plasma cutter I would definately go for these bearings unless you dont mind waiting for some killer ebay deals.

[stevehuckss396]

I have ordered from VXB many times but never linear hardware. Never had a problem with VXB

[tumutbound]

I'd be interested in opinions on the 20mm stuff as well.
In the stages of planning my machine and the VXB stuff looks good for the price.

[stag53]

Lazyman, the $70 one is at: http://www.vxb.com/page/bearings/PRO...ystems/Kit7956

This is the end-supported version... not the fully supported one like the $150 version (not that 150 is expensive for this stuff).

You are pretty happy with the quality of VXB? How does it compare to Thomson or THK? Are the rails difficult to machine?

[LazyMan]

Man I never even noticed those. The VXB bearings are not THK quality but trust me, you wont need THK quality. Many people use THK slides for rails because thats what comes up on ebay. Im pretty happy with the Quality of the VXB bearing and I feel like they are a perfect match for my machine. The rails are not difficult to machine. All you need is cheap cut off saw (As low as $20) with an abrasive wheel to cut the hardened rod.

One thing to watch out for when ordering VXB bearings some of the bearings have an adjustable preload on them and others dont.

Overall, I would certainly reccomend them. I purchased three of the fully supported sets along with some extra bearings and cut them to lengths I needed for the x,y, and z axis.

[multiplex]

i have all VXB linear bearings on my machine, and have been happy.

unless its a for torch, you need the supported bearings. you would be suprised how much a 20mm rod will flex over 60 inches or so.

i'm using the 20mm supported for my X and Y

and 13mm for Z i believe

[steve323]

Unsupported shaft deflection can be reduced by rigidly clamping the ends.

Loosely clamped end pieces only have to bend in the center to deflect.

Rigidly clamped ends have to bend in 3 places to deflect. The deflection in my system went down considerably after tightening the end clamps. It is not as great as a supported shaft, but the cost of a few extra inches of rail is really small. Also consider a movable rail clamp for when you are only using a small portion of your available travel.

btw: I have received great service from VXB and recommend them.

[stag53]

Steve323,

Did you use the 20mm shaft? How much deflection are you getting? I totally agree about clamping the ends... gives the shaft the ability to resist a moment at the ends.

My plan is to clamp the ends rigidly (2" on each end) and use two blocks, spaced 10" end to end. I did some back of the envelope calcs and FEA and found that I got .010-.020" deflection depending on the weight of the gantry, location of the load, and several other factors related to my design. This causes some interesting things to happen at the torch head... specifically errors in the Y-axis from the Abbe effects (angle error)... some of this is due to the design I've been toying around with (check out the pics... prelim design... no details, Z-axis, etc. yet). I put one rail up higher that the other to allow the table to be accessed from the front. This makes its easy to place metal on the table, retrieve cut parts, and push the table up to a wall to save space. I've thought about shortening the shaft, but would really like to get at least 40" of travel. I also contemplated larger shafting, but VXB only sells the 20mm stuff at bargain prices. If only I had an unlimited budget.

Considering changing over to the supported shafts, but I am kind of liking this setup right now... although, I don't think it would work if I wanted to hook a router to the Z-axis. Plasma only for sure.

Thoughts on this design? Should I just throw in the cards and go with the supported shaft?

Thanks!

[stag53]

Here's the pics:

[steve323]

Originally Posted by stag53 Steve323, Did you use the 20mm shaft? How much deflection are you getting? I totally agree about clamping the ends... gives the shaft the ability to resist a moment at the ends.

stag53,

My setup is slightly different, but the concept is the same. I have 1" rails with 42" of span and 36" of travel. I was very dissapointed when building the system because I could easily bend the rail with one hand before it was clamped at the ends. I became happy again after installing the end clamps.

Sorry, I don't have measurements. My machine is still a work in progress due to a recent baby and moving to a new house.

I am also guessing that reducing the length with mid clamps (when cutting smaller pieces) should improve flex by at least a factor of length squared. i.e. a 4X improvement when the length is cut in half.

Steve

[harryn]

I don't have personal experience to answer your question on supported vs unsupported, but I have read a lot of threads on cnczone.

People with supported rails are a lot happier with the control they obtain. If you go to something like 50 ish mm rails, it might be different.