[Spikes]

Hi,

while putting together my own design for a "learning cnc", I've seen quite a few people using v-grove bearings on flat profiles or 45angle profiles of steel. This is different than what I've seen for kits sold of openbuilds.com for example which use profiles with special v edged of the same size of the bearings. On one I'd like to this it's gonna work on a normal profile too and I like the idea of a guided groove. On the other hand I'm pretty convinced that being the groove of different size and shape of the edge of the profile things aren't going to work well, with a lot of play and general instability. However mine are just guesses and wanted to confirm with somebody on the forum that maybe tried it out.

Two examples:
- done "right": http://www.qbcbearings.com/New/NewsImg/Hi_ISGW.jpg
- on a flat profile edge https://youtu.be/MVcCbdGZtcI?t=73
- on a 45deg profile edge https://www.youtube.com/watch?v=lA519UWFTj8
- building a whole x axis that way: https://www.youtube.com/watch?v=jHJ_n4l8ndE

so yeah, is it a bad idea or it would work as well as a carriage with 4 bearings at a angle on an anagled rail?

thanks,

Spike

[wizard]

Vee bearings can work fine on the cirners of angle iron or the support rails made specifically for them. We probably should define what works fine means though.

By fine we mean that the bearings work as expected but you need to understand they are not the mist rigid solution to begin with. Beyond that most of these implementations arent that great when it comes to alignment of the rails so performance as linear bearings suffers. Basically you need the rails as precisely parallel and coplaner as possible. Coplanner might not be the best word here but i couldnt think of another term but it is the problem when one rail goes north and the other goes south. It really isnt that easy to get run of the mill angle iron into a precise position.

I hope you followed that. In any event it might help to understand what you mean by a learning CNC. Is this for a school or is it a personal project? For a school, to introduce student to various technologies, a vee bearing CNC can be perfectly good. For a personal machine there are far more considerations.

Here is the thing, on a personal machine you likely would want to make things as you learn. For a router a Vee bearing machine is very much an entry level solution and will most likely perform well below even a round rail machine. My fear is that you will quickly out grow the machines capability.

That all being said economics is also a factor in a machine build. If you want to keep the costs down id look for rail implementations that easily leads to parallel and coplaner rails for the bearings to run on.

By the way unless you buy the purpose built rails for the bearings to run on you will likely be running on soft material (angle iron or extruded aluminum angle). That means wear will happen. There are exceptions, angle iron from bed rails is often harder than normal iron. Just somthing to consider. You can find Vee rollers these days with an acetal running surface that wears better but in the end wear happens.

In any event nail down your expectation for this machine! That will help you decide how you will want to implement this machine and how much effort to put into making it solid. In the end, even for a personal "learning CNC ", i suspect that you will want the machine to do something.

[Spikes]

Hello Wizard,

thank you for your input, it makes perfect sense.

This is a personal project, except that the objective is skewed toward learning the making of a cnc rather than that of parts so, to a certain extent, I'm actually interested in "making mistakes" so that I can know first hand the problems of some solutions and the benefits of others beyond purely hearing it from people. One example is the aforementioned wear, which I've heard a lot about, but only in one or two post I've actually seen people talking about details, saying for example that 1/8 aluminum rails become unusable after about a year of light use. Given that this machine will be far from operating 24x7 then that may be perfectly fine. Of course I'm trying to avoid expensive or really stupid mistakes.

When you say a round rail, do you mean SBR or even a round rail with a pipe? and yes, economics is definitely a factor, especially given the context of expecting ongoing changes as I test different designs (this is my very first one) and I most definitely can't afford SBRs now.

thanks again for your insights.