Linear rail question

[Nr1madman]

Hello to you all!

Long time reader, and I hope soon to be builder.

Just have a quick question.. You lot seem to hate/dislike the "V Wheel" way with V bearings and steel profile as a linear guide.
Over at other forums this seems to be the preferred option..

And the supported round rails often get shot down aswell.

This has me looking at the hiwin type rails, but I dont really think I will need it!

What would be the stronger option between supported rails (for example SBR20) and the v wheel solution? Using the standard w2 wheels with 3/8" bore. I realize that much depends on the steel profile, but for the example lets say you use perfect hardened steel in 90degree angle for full contact with the wheel?

The machine Im planning should work with hardwood and plastics.. But overkill is always better if something else shows up!

Thanx
the madman

[Wal]

You lot seem to hate/dislike the "V Wheel" way with V bearings and steel profile as a linear guide.

And the supported round rails often get shot down aswell.

I've used supported round rail on my mini-mill, I'll use profile rail on my next build (for added rigidity and easier maintenance). I don't 'hate' my supported round rails, far from it - I get all the accuracy I need, my surface finishes are good and my maintenance intervals are acceptable (I'm a weekend user) - I think it comes down to the simple fact that builds will cost you time and money, you may as well get as many things right the first time..!

Wal.

[njhussey]

I suppose it comes down to a few things really...how much you're prepared to spend, what you're going to do with the machine, whst you want to cut, how often you're going to use it, the accuracy you want from the machine. If you want to make pcb's every other weekend with the odd bit of V carving plaques/signs then V wheels will be fine. If you're wanting to make money from it making aluminium parts then they're the wrong thing....its horses for courses.

If you look at my rambling build you'll see i started out with skate bearings and unsupported pipe and the gantry made from 25mm Sq aluminium box section...what I've ended up with is something way different...but then the things I want to cut have expanded as I've seen what CNC Routers are capable of.....

[Nr1madman]

Tanks for the input! And I do understand that it would be stupid to underbuild!

This would be a hobby machine doing mostly hardwood routing. That beeing said you are probably right that I would find more uses for the machine!

But from what I understand you need a pretty rigid machine to route oak and similar wood?

Aaah decisions!

[Nr1madman]

I have been reading alot! Hiwin hgr20 seems to be everyones choice. Ive read that 15 is to small.. Is this purely in hight or is it width aswell? How about the egr series?
Or even better for the wallet, chinese hiwin copies.. How do those match upp?

Been looking at iko and thk aswell but they seem to have alot of series with only two ballraces and i guess that this inte ideal?

Regards
Madman

[Clive S]

I have been reading alot! Hiwin hgr20 seems to be everyones choice. Ive read that 15 is to small.. Is this purely in hight or is it width aswell? How about the egr series?
Or even better for the wallet, chinese hiwin copies.. How do those match upp?

Been looking at iko and thk aswell but they seem to have alot of series with only two ballraces and i guess that this inte ideal?

Regards
Madman

There is not much price difference between 15mm and 20mm the trouble with 15 mm is it can be very tight in the z axis unless a lot of material is milled away. The Chinese stuff is fine you can buy it all at the same place including screws and bearings etc this is one place BST http://es.aliexpress.com/store/314742

[njhussey]

There is not much price difference between 15mm and 20mm the trouble with 15 mm is it can be very tight in the z axis unless a lot of material is milled away. The Chinese stuff is fine you can buy it all at the same place including screws and bearings etc this is one place BST http://es.aliexpress.com/store/314742

I've got 15mm on my Y & Z and if I was doing it again I'd buy 20mm all round. The Z axis I've got round by using a 40mm thick plate and recessing it for the ballscrew and mounts so I could put the bearing carriages flat on the back plate...

[Clive S]

That pic explains the problem very well. ..Clive

[Nr1madman]

Hello again!
I understand the problem, but why doesnt ppl just use 25mm rail and thinner ballscrew?
If you use 1204 ballscrews with bk/bf10 you would get 3mm extra for ballnut clearence and just have to make a bracket?

Or am I missing something vital? :D

[JAZZCNC]

Hello again!
I understand the problem, but why doesnt ppl just use 25mm rail and thinner ballscrew?
If you use 1204 ballscrews with bk/bf10 you would get 3mm extra for ballnut clearence and just have to make a bracket?

Or am I missing something vital? :D

There are many ways to do the same thing but your way is adding expense and weight to an area where you want to limit the moving mass. The larger rails don't really add much strength but they are considerably more heavy.

Maching slots for clearence while trouble some if not kitted up to mill the slots does give the advantage of reducing weight without sacrificing too much strength. The lighter and shallower 20mm setup gives a very strong and low profile setup making for a nice balanced Z axis.

Either way would work.! Thou IMO the 20mm rails with lighter plate setup gives better balance of strength and acceleration/speed with nema23 motors.