Ok, I know lots of people are building their own rails or rail systems in a variety of ways. I've worked out a couple ways of doing it myself, however in doing so I've come across some issues and questions.
I'm planning to go one of two possible routes. First a couple points about my planned system.
It's to be a Gantry style mill/router system for machining foam and some MDF only. The entire system will be composed of sqr or rect HSS [steel] sections. The foot print is fairly large and this is a medium which I'm comfortable with. The basic structure is two HSS rails running the length of the 'X' with smaller cross tubes connecting them [parrellel to the 'Y']. There is some conciderable weight to the whole setup, currently in my design the Gantry weigh's about 1200 lb's. The entire system is floor mounted to a concrete pad. Accuracy from my system optimally would be in the 1/64"- to 1/32" range, this is tight for a large system like this, and maybe I'm totally out to lunch on these numbers, but the closer I can keep to this, obviously the better.
Basic dim's of my system are X=20', Y=10' and Z=~5'.
Now the options:
Route A:
The typical angle iron rails, there will be four on the x axis and two on the y axis.[ two on either x rail and 1 on each of the two y rails] The Z axis will be composed of actual linear rails [ THK or the like].
Route B:
A second idea was to place a heavy 'T' rail, composed from 2 pc's of CRS,on top of the X rails. Then run several roller bearings on the top, side and a few on the bottom side also, to create a completly controlled linear travel. Each bearing would be adjustable via an eccentric bushing [ thats another post in this forum]. The same basic idea would be applied to the Y axis also.
So whats my dilemma?
Well with Route A, I'm concerned that there will be some warpage of the X rails while welding. I've got several small laser cut jigs designed to temporarily place the angle iron in its proper position for welding, it would then be stitch welded in many locations in an alternating pattern to help reduce heat shrinking and warpage. The possibility of heat distortion of the X rails could lead to a rail which either moves up and down along its length, or it will 'roll' along its length [ twist] and cause binding in that way.. or it could do both. There is a certain amount of warpage which can be taken out when the unit is floor mounted, however this is rather limited.
So short answer is.. warpage and accuracy issues.
Route B is a bit negative simply because of all the extra connections required to keep the 'truck' on the rail. There would need to be trucks on all four sides of the rails which all have to be finitely adjustable to make it work. There will also be the requirment for joining the main rails because CRS doesn't come in over 12' lengths [ that I've found anyway].Another issue is simply weight, this route's linear system will way heavier than route A. There will be less worry about warpage [ as in route A] however this route leads to many.. many more headaches. Mind you, if a person could get it working.. in the end it may be the better system.
The short answer for this one, is cost, weight and complexity.
Ok, so I wrote that whole book to simply ask the following. Has anyone done a system similar to either of these in this large of scale [ 8 or more feet long in any axis]?? If you have, which route did you take? Did you experiance any of these issues while traveling that route, and if so, what did you do to solve these issues? Did you do something similar, yet different?
I know that I'm probably missing several more issues with both of these idea's [ if you see anything that would significantly impact these designs please speak up! ] However, either of these two designs will end up being many many dollars cheaper than going with a complete store bought linear rail system.
JerryFlyGuy