V Bearing questions

[Jkountz]

I was thinking of using some V bearings for a design Ive been working on and wanted to get some opinions from some of you in the know.
I have attached a picture of the bearing and a sketchup of how I want to to use them.
My question is, do you think that v bearings alone are enough to prevent racking of the Y axis?? Im not familar with them to know whether they provide any side to side support or not. Anyone know??

Of course there will be some sort of plate or something on the outer sides that the bearings would mount to and in turn the Y axis car would ride on. Does this make any sense?? LOL

[Kipper]

Will the racking be caused by axial movement in the the bearings or flex in the junction between the gantry and the uprights.....Vee rollers should have opposing AC bearings in them which makes them resist axial loads....some cheap versions don't!

[der_fisherman]

Hi,
are the bearings in question ball bearings? If yes, I suspect that their "axial" qualities are similar to normal ball bearings, not good. Only "Deep groove" ball bearings are (fairly) good with such side loads as well......
You could add an axial bearing either side to handle the axial loads, but it will eventually get too expensive and complicated I feel.....
The type of bearings that I have made for my CNC Router are similar to that as shown on some good web sites for CNC DIYers. The basic design I have copied and improved on I feel.....
They need more bearings but as the ones used are the ones that are the cheapest on the world market today (I sometimes get 12 of them for a couple of $$ on ebay) it does not really matter. I use Roller Blade bearings 22mm outside, 8mm inside 7mm thick......for heavy loads just use more, but don't forget that 4 in a roller blade shoe support very heavy and dynamic people.....!!
The end result is a cheap and stabil CNC linear bearing assy for very little money.....
I use stainless steel angle iron for rigidity to mount the bearings on and an aluminium angle iron as a track. I glue my alu track to MDF board edges which have been champfered to 45° each side (total 90°). Its easy and very stabil.....
If you need further help or infos just ask.
But don't forget that finding something out for yourself is also a great experience and your way may work well for you, so don't let me put you off trying something out, but if cost is important, come back to me as I am pretty sure I can help you.....
Have a really great day.

[ger21]

First, the V-bearings contain angular contact bearings, so their is no axial play in them.

When you say racking, are you referring to one side of the gantry moving without the other? If so, then no, the bearings alone probably will not prevent racking. Racking is a function of machine rigidity. With a long gantry, it's easy to create enough force on one side to flex something enough to cause racking. The easiest way to prevent racking is to drive the gantry from both sides.

[der_fisherman]

You are right, V-Bearings can take an axial load as well. In fact, other than the price of them, they look rather good......
They would probably work better on a wider rail with a 90° end form than on anything thin as you seem to want to use.
The site I found had some proper rails as well, look here:-
http://www.linearvguides.com/linearv...uidewheels.htm
Have a good one...

[MonoNeuron]

I use the V guide bearings and I love em. They are not completely self cleaning as some debris does cling to the rail but it is easy to clean off with a quick wipe of steel wool. If you are going to use the 30mm bearings and will use 8 of them and the axial load is around 150 lbs, then multiply that by 4 which will be the top ones that will be taking most of the load, and you have more than enough force to break a small endmill.
As Gerr said, Drive them from both sides and you won't have any problems and the small extra cost is really worth it and will give you a very rigid setup.
I say go for it.
Have fun with the build and post lots of pics.
Rich.

[mvd535]

I am at this very moment building a CNC home made machine, and I am using V type of bearings. In my opinion this is matter of cost, you should pay a little bit more, and get angular contact bearing that will allow your machine take axial loads. Refer to Techno-Isel to see on what I am talking about. Normal V type of wheel will not take axial loads, and will cause you a lot of frustation.

[ger21]

Originally Posted by mvd535 Normal V type of wheel will not take axial loads, and will cause you a lot of frustation.

All the V wheels I've seen have angular contact bearings.

[mvd535]

Some wheels that are designed for gates for simple linear motion has no angular contact bearing system, so we must be carefull when selecting wheels. There is no doubts that wheel designed for CNC particular use, all of them are with angular contact bearing system, like I said before at Techno-Isel link attached here. What I am trying to say is to advise our friends to take care when selecting a low price single rollers.
http://www.techno-isel.com/LMC/H860/PDF/H860P047.pdf

[Jkountz]

Wow the response here is fantastic!! Let me first say thanks to all who replied, you all have got my brain burning with ideas but I love it!!

Ok to answer a couple of questions some of you brought up, the side to side play I was referring to was the gantry itself going left to right, not back and forth. In other words, if you grabbed ahold of the router mount and pulled left to right across the table would the V bearing provide enough support to keep this from happening under load?

I do plan to drive my X from both sides to prevent the other type of racking mentioned above.

Der, I would be very interested to see the setup you spoke of, since Im so early in the development stage nothing is out of the question right now.

I had planned on using linear rails and trucks but my local scrap yard no longer allows folks to roam around and scrounge parts!! I was heartbroken man!! They have so much stuff just sitting there going bad its really a shame. Oh well!!

Thanks again everyone and if you think of something else please by all means chime in!!

[mvd535]

Jkountz,
I am available to help you as much as I can. Remember that I am right in the middle of my own CNC machine assembly process too.
In my case, I am using round bar cross section bars as guides (rails), so the wheels V must be in a way to get a good "seating" to assure that no Y slash will be present. A group of, at least, three wheels, two above the rail and one below the rail will allow to adjust the carriage package. The location of the upper ones can be fixed, and only the lower one should be able to be adjust it (vertically) by practicing for sliding drilled hole. In my opinion, a group of four wheel for each carriage will be even better but higher cost. My bars rails are also cromo-nickel surfaces hardened to prevent wheels damage on the surfaces rails. No problem that the whell can be damage itself after certain amount of time, because they are adjustables to eliminate any progressive gap.

[ger21]

Originally Posted by Jkountz the side to side play I was referring to was the gantry itself going left to right, not back and forth. In other words, if you grabbed ahold of the router mount and pulled left to right across the table would the V bearing provide enough support to keep this from happening under load?

Yes, but be sure not to exceed the axial load rating of the particular size your using. Download the catalog from Bishop Wisecarver for their DualV wheels. It has formulas for calculating loads, and load ratings for the different size wheels. Most people use #2 size, but #3 have much greater load capacity if you need it. Also, best price for #2 size is www.cadcamcadcam.com