Why not use unsupported rails?

[Jonathan]

I didn't fasten them down as the purpose of the check was to show that even before you mount the rails they are bent (I measured straightness for the profile rails) which is clearly true. The test was not intended as a realistic indicator of height accuracy in operation, as clearly either will conform to the mounting surface.

Sliding the gantry back and fourth and tightening the bolts to tweak out any tight spots also wont get the rails straight. It will merely copy any bend in the master rail to the subsidiary rail. Very few DIY builds rest the master rail against a reference edge, or indicate it to get it straight, hence for those any bend in the rail as shipped will remain (in one plane). For example if I just bolt down one of my 15mm rails to a piece of nice flat aluminum tooling plate, then use the sliding method to align and fix the other rail to the same plate, the error I measured will still be present so the measurement is relevant. That's what most people do and it's perfectly valid for supported rails.

Its as Jazz said, they're designed for precision and will give more of that over round rail but you have to exercise another level of precision when installing them to reap that.

Which is what I said originally; "the accuracy of a profile rail is not much different to a round rail - it depends how you mount them as how many of us correct the bend in a profile rail by comparing to an accurate straight edge reference?"

[JAZZCNC]

Sliding the gantry back and fourth and tightening the bolts to tweak out any tight spots also wont get the rails straight. It will merely copy any bend in the master rail to the subsidiary rail. Very few DIY builds rest the master rail against a reference edge, or indicate it to get it straight, hence for those any bend in the rail as shipped will remain (in one plane). For example if I just bolt down one of my 15mm rails to a piece of nice flat aluminum tooling plate, then use the sliding method to align and fix the other rail to the same plate, the error I measured will still be present so the measurement is relevant. That's what most people do and it's perfectly valid for supported rails.

In which case they have incorrectly installed them.!!!! . . . If the master rail reference edge is accuratly straight which it should be and is the whole point of having it then the subsidiary rail as you call it will be perfectly straight.!! . . If not used then you will have incorrectly installed them and defeated one of the main points of using profiled rails.!! Accurecy

I get the feeling Jonathan you haven't ever used profiled rails before.? Because if you had you wouldn't be so quick to argue with me about the bennifit of the master rail and having a straight reference edge. You would also know just how critical and intolerent the bearings are of miss alignment and poor mounting surface.!

If you have then you know I'm correct and pride is just making you deliberatly argumentative is all I can think.!!! . . . . either way your very wrong.!

[Jonathan]

I did not say they wont be accurate if mounted properly. I'm merely pointing out that most people don't mount them properly, and thus don't obtain the best possible accuracy. Nowhere have I said it's a good idea not to mount them properly.

We both already knew everything either of us has posted in this thread, so the only purpose in discussing is to let others know. Spreading the knowledge is the whole purpose of this forum, hence I discuss.

Your lasts post seems to be suggesting the reference edge of the master rail is perfectly straight? Which is surprising, as this simply is not true. The point of the reference plane on the rail is that is it parallel to the grooves the balls run in - you can't easily indicate off the grooves but can use a plane. You have to first straighten the master rail when mounting by attaching a bearing block and indicator and using a genuine straight edge as the reference for the indicator, or by clamping the reference plain to the straight surface.

Hiwin's document on the subject explains it all perfectly clearly, well worth a read:

http://www.hiwin.de/DownloadCenter/f...9TE14-1006.pdf

[JAZZCNC]

Your lasts post seems to be suggesting the reference edge of the master rail is perfectly straight? Which is surprising, as this simply is not true.

No you probably miss under stood.? I said "master rail reference edge" meaning the edge which the master rail butt's against be perfectly straight.

I've read the Hi-win document before and like wise fitted many hundreds feet of profiled rails, like tomorrow when I'll be drilling and tapping 160+ mounting holes for the 10mtr's of profiled rail so I feel I'm more than qualified to comment on all aspects of fitting them.!!

All that said and my original comment was that your statement that round rail and profiled are roughly the same regards straightness is incorrect. . . BUT for clarity's sake I'll ammend my statement to read "Rubbish total and utter rubbish" . . IF CORRECTLY FITTED.!!

Now lets go to bed it's 1 am. . :whistling:

[Lee Roberts]

I get the feeling Jonathan you haven't ever used profiled rails before.? Because if you had you wouldn't be so quick to argue with me about the bennifit of the master rail and having a straight reference edge.

I dont see that Jonathan has challenged the benefit of having a Master Rail or a reference edge directly, he has simply discussed the credentials of both and what those credentials will mean.

If you have then you know I'm correct and pride is just making you deliberatly argumentative is all I can think.!!! . . . . either way your very wrong.!

To be fair Jazz i think the shoe of pride fits the other man in the room, arguments drive discussions and that is what this is "a discussion on the fitness of unsupported rails for an application". So for me it is well done Jonathan for making full use of the forums.

You have both covered this topic very well and highlighted very good points, so thank you as i myself have taken away some knowledge from this discussion.

Keep up the good work guys as this is exactly what its all about - Education !

[JAZZCNC]

To be fair Jazz i think the shoe of pride fits the other man in the room, arguments drive discussions and that is what this is "a discussion on the fitness of unsupported rails for an application". So for me it is well done Jonathan for making full use of the forums.

Woooo who swallowed a dictionary then.!!!. . . . . Not me thats for sure. .:rofl:
Nah ME argumentative for the sake of pride. . .NEVER . . . Your wrong. . . . . . . I'm right thou has those who have ever fitted them "Correctly" will agree and wouldn't argue. :naughty:

Nite Lee.!