mounting profile rail - Hiwin Manual vs. typical approach

[AdCNC]

I always incorporate a datum edge when i build a new machine i have done ever since i built my first machine.. and always used hi-win gear.

[Jonathan]

I always incorporate a datum edge when i build a new machine i have done ever since i built my first machine.

Where are they on the first machine, they look well hidden to me...
http://www.mycncuk.com/forums/router...tempt-cnc.html

To make a datum/reference edge you need a milling/grinding machine with as much travel as the length of the rail or maybe a long precision straight edge to use as a reference. Either way it's not realistic for the vast majority of people on the forum.

[GTJim]

So how do people get around this problem. I'm very interested as I will be facing this problem soon.

[dsc]

Gents,

thank you for the replies.

Looking at the manual, you can do without having a datum edge for the rails (ie. use the edge of the plate as datum), but the carriages still need a 'lip' and side bolts to secure in place.

Regards,
dsc.

[AdCNC]

This is how i mount my rails..

[dsc]

Few things I still don't get:

1. mounting against an edge assumes the edge is perfect, otherwise things go wonky. Surely there will be errors when machining the edge every single time.

2. with no side plates pressing the rail against the edge, I don't really see the point of the edge. Surely if the rail moves under load, it will move anyway. Sure the edge will spot the movement towards the edge, but the other way is still unsupported

3. the manual suggests simply bolting the rails down (ie. no edges) if there's no side space, but shows the carriages supported and mounted against edges. Again point 1 comes into play.

Regards,
dsc.

[Shinobiwan]

1. mounting against an edge assumes the edge is perfect, otherwise things go wonky. Surely there will be errors when machining the edge every single time.

Its for registration . A machined reference edge to butt up against makes getting your rails level far easier than without.

2. with no side plates pressing the rail against the edge, I don't really see the point of the edge. Surely if the rail moves under load, it will move anyway. Sure the edge will spot the movement towards the edge, but the other way is still unsupported

I'd love to see you bend a hardened steel rail that's fixed every 80mm lol Rails bending is the least of your worries when you constructing your machine out of only aluminium or steel box section. It ain't the weak link.

[AdCNC]

1. It all depends on what machine you use to mill the datum, so I'm fortunate enough to have a VMC at hand. (when i use this method i get a parallelism of 2um)

2. That would be true if you could exert a serious amount of side force to dislodge the rails, but in this instances its highly unlikely to happen.

3. Its tried and tested and works fine; all depends on the application and I think it would be necessary for the large machines that are doing heavy milling or moving heavy loads.