[sa7o]

I'm thinking about going for linear rails for x and y axis. I'm from Poland, and I think it would be easier for me, because right know thinking about momus steel rails /bearings give me headace (what kind of steel? what is equivalent for 1018? Metrics are way of... etc ).
So does anyone tried going this road? Some examples? Maybe some ideas?

[Mac.CNC]

You are on the right track, but that will be a bumpy road, once you start cutting and drilling..
There are several members on board that converted this machine to metric, I hope they will chime in, and help you out.
From what I heard so far, that involves some considerable leg work, sourcing close enough steel and aluminum stock is another challenge - as you already pointed out for yourself.
It'll be rough, but it's not that it can't be done, there's several metric builders already around here that did it already - hopefully they'll chime in on your question.
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Mac

[sa7o]

so after another day of looking at plans I got more clarity right now (in context why this part is that thick, what coresponding dimensions I have to change etc) so I think i will just go with instructions. I won't start building mine til october, so I got some time to learn sketchup and make mock-up in 3d before starting.
Your build was inspiration for me to build mine, but I don't think I'm going to deviate to much from original plans. Maybe increase Y axis. When (at what additional length) should I worry about adding another slave motor?
Are you using that hole in bed often? Is it useful addition?

[Mac.CNC]

To be honest, I haven't used it for a while and it's currently covered up. I'm still glad it's there and I'm sure there will be a time to use it some more down the road.
I feel like I'm still not advanced enough to fully utilize it effectively, but hopefully that time will come. Machining parts vertically on the end grain is a whole different (and more complex) world in terms of blowing out fibers and calculating the tool paths for I found, but I'm really looking forward to doing more in that area. It's like the "icing on the cake" for me, lol.
Is it useful? Well, I wanted to go 360 with this machine and that was like the last 10 degrees for me, so I'd say unless you can already think about projects that require vertical parts placement - I wouldn't worry about it too much. Also, if you won't extend it on the x, I actually wouldn't recommend it because it takes up a good amount of space in the reachable machining envelope.

For the left side x axis slave motor, I've always promoted that as a great thing to do and it helps the machine perform a whole lot better overall - but it really depends on what you're planning to do with the machine - how bad you are planning to tax it. For example, if you're going to do small parts for model building or small molds that don't involve a lot of material removal, you'll probably be fine without it. On the other hand, if you want to be able to plow all the way through a 3/4" oak board with a 1/4" end mill at 120ipm, profiling parts out for your projects, you'll find that the slave motor is an absolute must have, it just wont work without it. Think about it, most of the load is on the upper four right side x axis bearings, and you're pushing and pulling on those four bearings with a lever if the carriage is all the way to the left.
When you're already thinking about extending the y axis gantry tube, that'll only get worse - so yes, in that case you should definitely plan for the slave motor.
Alternatively, just make the parts to accept the upgrade while you're at it and leave the motor off - try it out and add it later if needed. I wish I'd done it that way and didn't have to tear it down to install the upgrade.
Good luck with your build when you start,
Mac

[sa7o]

Thanks, so I'll skip on that, I want to keep it desktop size.
considering steel for rails- thickness. More in relation to bearing size. In plans there is 6mm steel, which is about the same size as bearings, I found source for 5mm and 8mm steel. Can I use 5mm, or keep to look for other sources?

[Mac.CNC]

I'm certainly no expert at a metric Momus build conversion, although I'm originally German - I understand the challenges to go metric with it.
Generally, thicker is better than thinner - your enemy is always flex in the steel or aluminum on any part in the conversion.
This is just my personal opinion, but I think you should stick to the original plans as close as possible.
The rails are probably the most trickiest part in the whole conversion, because that will change the location and diameters of all the mounting holes for the bearings.
Bob did an awesome job with that in the original plans and that's gotta be difficult to translate to metric.
I guess going 8mm is possible (again, lean towards the thicker stuff you can get), but finding 6mm stock would be much easier down the road.
I do have to say that you picked an excellent starting point for a conversion, because the rail thickness pretty much governs where everything else needs to be in the end.
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Mac

[sa7o]

other thing that bugs me in design- wouldn't be it beneficial to add some gears to belt-motor?