Just wondering what options people use for installing linear guide rails. So far I have seen the following.
1. use taught piano wire and shims ?
2. Try and source a 10' engineers straight edge ?
Any other options available ?
14-10-2011 #21. use taught piano wire and shims ?
if your using profile rails im guessing the easyest way is to use a DTI guage
for my X axis rails that were mounted to the sides of my machine (80x120 aluminium slotted extrusion and already pretty straight) i fitted one linear bearing and a DTI on a magnetic stand and concentraited on getting the rails parrallel to the surface my bed would be fitted to, mine is only a short machine though (700mm) if i was making a much bigger machine id consider mounting my rails on the horisontal plane if i could and use epoxy
i cant remember exactly what its called now but there is a special epoxy that is thin and slow to set so if you make two channels where your rails are going to be fitted and another channel to join the two together when you pore the epoxy in, it will level to perfection (in therory) you will have to do some research on this though, im not sure anyone on this fourm has used this method.
the problem with a large machine and fine precision is you only have to stub your toe on it and it will go out of true unless its very heavy or bolted to the floor or both :lol:
EDIT: oops... i didnt realise... you have asked a similar question elswhere and got similar answers
Last edited by blackburn mark; 14-10-2011 at 09:21 AM.
Auto-collimator or laser Interferomter are options, but it all depends just how accurate you want to go.
No point going for guides in the accuracy of tenths over their length, when the spindle flexes a couple thou under any kind of load.
Also, unless you get the base heat-treated/stress relieved after welding, it'll gradually flex as the weld induced stresses gradually relief themselves over the next few years, throwing your original accuracy out.
For Y and Z you can do the same. Alternatively as the rails are closer you can attach a DTI to one rail, as Mark suggests, and indicate off the reference surface (there's sometimes an arrow to show which - check out the Hiwin linear rail guide). Look at how much it varies and tap it into place.
Before mounting the first rail you could just put one bolt in, then attach DTI to one bearing block and indicate off the frame to get it parallel to the frame.
Edit: This may interest you if you've not already found it:
Last edited by Jonathan; 14-10-2011 at 12:03 PM.
You could scrape the steel surfaces that the rail will mount on (after the frame is bolted down and has 'settled')...that would be ideal but I bet it takes forever. As you mentioned in the first post a taught wire plus optical magnification (with weights to tension and put them in bucket of water / oil to stop them swinging) can act as a straight edge to align from. This enables you to take out any bends is the rail, which there will be, but I'm thinking removing twist is going to harder to achieve?
Last edited by Jonathan; 14-10-2011 at 06:18 PM.
A lot of people don't require a great deal of accuracy on such a large machine. For woodwork, accuracy to a few thou is good enough, and a more typical use for that size in metal is a plasma table, where accuracy to 0.25mm would be acceptable.
You need to consider what exactly you want to machine, and what kind of tolerance would be acceptable. It's all very well aiming to build a very accurate machine, but will you need the accuracy, and will it be worth the additional cost?
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