mounting profile rail - Hiwin Manual vs. typical approach

Gents,

this is mostly for the people who used or use Hiwin rails.

Looking at the Hiwin technical manual:

http://www.hiwin.com/pdf/lg/QE/QE-Li...ay-%28E%29.pdf

page 11 , there's a whole section on how to mount the rails and carriages.

I've seen many machines which use Hiwins and only a few times I've seen the rails mounted against a datum line, even rarer with side plates used for securing the rail. Curious how many of you followed the Hiwin manual and how many simply slap the rails on a flat plate and bolt it when everything is aligned? Am I correct to think the suggested mounting methods are for high loads, not normally seen on home built machines?

Regards,
dsc.

It's to do with ensuring the blocks/rails can't move, and allows easier assembly.

Relying on bolts alone means that under high loads (especially shock loads), the blocks/rails could slip. By ensuring they're mounted firmly against an edge ensures they won't move.

Also by using datum edges, it makes assembly quicker and more accurate. Most machines using linear rails will be getting machined anyway, so adding a datum edge isn't a major issue, and saves quite a bit of time in mounting and adjusting the rails/blocks. For one offs, it's probably not a major benefit, but if you're producing multiples of the same machine, that additional time mounts up.

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.

Quote:

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Originally Posted by AdCNC

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

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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.

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

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.

This is how i mount my rails..
Attachment 8504

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.

Quote:

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Originally Posted by dsc

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.

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

Quote:

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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

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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.

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.

Quote:

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

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Ah but what if the edges which are use to butt up against are not parallel? It does indeed make assembly quicker, but the assumption is that whatever is used to mill the edges is near perfect.

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I'd love to see you bend a hardened steel rail that's fixed every 80mm lol

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Not planning to:) I was simply referring to m_c post regarding shock loads and possible movement of the rails if not fixed against an edge. Surely this will not be a problem when milling MDF:)

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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)

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Lucky b*stard!;)

The reason for asking is purely to understand where the edge idea comes from, I do like the ease of assembly, when butting the rails against the premachined edges, but worried about parallelism.

Ad, how do you mount the carriages? similar approach against an edge with a side push plate via a block bolt?

Regards,
dsc.

So if your a DIYer building a router out of box section what method should be used.

Yeh bud, if your milling a datum edge in for locating the rails then the machine your using to mill the datum with will have to be cock-on!

Regarding the blocks you always mount the rails like this and let the blocks find there own parallelism. So for instance when assembling a z axis mount one rail up agains the datum edge then mount the second, as for when you aline the second rail to the first; mount a bearing block on the first rail thats correctly mounted the attach a magnetic block and gauge to clock the second rail! This is a method of checking if you have milled both rails a datum edge or a way of aligning if you are using a single datum edge. then mount all the blocks and attach the second plate then attach a gauge to this and align this plate to either the first rail or the first plate (taking in consideration that the plates have good milled edges.)

That's what I thought Ad (ie. rail against datum and 'floating' carriages), but for whatever reason the manual suggests going the other way, floating rails and fixed carriage.

Regards,
dsc.

Just a quick question again on the linear rail installation. Hiwin manual shows this:

Attachment 10961

So master rail bolted, three linear blocks bolted to the axis plate and moving the thing up / down, bolting the second rail at the same time to make sure it's all parallel. This assumes that the two left-hand side linear blocks on the axis plate are in the same line ie. same distance from the edge and the third one is on a line parallel to those.

I have the master rail bolted down and it's pretty much parallel to the edge (within 0.005mm). I also have one block on the master side bolted and it's also cock on parallel to the axis plate (within 0.002mm). Is it a good idea to loosely mount the second linear block on the master side, slide [both blocks + axis plate] on the master rail and then bolt down the second linear block to make sure both blocks are on the same line / parallel? The whole process would go like this:

Attachment 10960

This means effectively using the master rail as a reference line, according to which two linear blocks are set in the same line.

Regards,
dsc.