skate bearing linear rails...adjustment??

[.xXACEXx.]

i would like some input from someone who has built several diy machines ive been looking at the skate bearing linear rail design,and am likeing it more all the time.mainly because of price.other linear bearing are sooo expensive,,enough to scare most people away from making a machine at all!so cheap skate bearings are a great alternative,but i am sorta stumped,bear with me here. lets say you groove your mdf with a router to say .125 deep(not a cnc just manually) now if you goof up only slightly and drill a hole in the angle iron off from the rest..say .010 off from the rest...do you just throw it away and start over??..im gonna exagerate now...if you drill a hole on one side of the angle and the holes are exactly the same distance from the "bend" but on the other end you goof up...and drill the holes .125 to far apart..this side will need to go closer to the pipe to let each bearing touch, at least in relation to the other side which was drilled correctly ..so one set of bearings on the angle is closer together,and one side if farther apart follow me so far?? so if this "closer" side is set as the "master running bearing",... woulndn't the "farther apart" set of bearings need to be shimmed out of the groove in the mdf ??..so as to get all bearings to touch the rail or pipe?? any bit of error drilling the holes will make the bearings diffrent so they will touch the rail or not touch at all..(im talking about a few thousandth of an inch here ,of error drilling)...now the other part of the question....is there a method for setting the bearings "exactly" the same distance apart ,..or for drilling the holes the same distance apart??...i have acess to all kinds of machines,but the diy'er most likely dont,so i was just wondering
im sorry for the long post...but this has been bugging me for a long time about this design

[Coogrrr]

i think if the left side is .125 too low or too close compared to the other side that you dont have to shim. The strut/support/gantry that sits on these rails will technically be move or shifted left or right but that wont matter if it is level as all it means is that 0" and 25" are .125 shifted over is all.

If this is a bearing the is in a verticle support method like the one that the gantry rides on and it bears the wieght... Well if the left is a little higher than the right side YES you need to shim to level it. its all about level. Whether or not you shifted forward/back/left/right only shifts where you can place your router. shifted up down will make it cut improperly when the gantry moves to the end that is higher. This could be fixed by leveling your table to the gantry as mine has adjustments for that but starting level as possible is the goal.

make sure your Z car is aligned verticle too and that the bearings are all set the same.

Last thought. The little piece of miss drilled angle is much cheaper to thow away and start over than is the messed up Teak or Mohogany or HDPE or AL you might router badly due to misalignment.. sooooo I might suggest scrapping that piece.

David Sosylva's plans actually make several oval holes for bearing mounts so that the slack and leveling can be somewhat adjusted out.

Coogrrr

[CurtisU]

Ace, I'm going to say you must to have a method of snugging the bearings to the rail or pipe either by adjusting the bearing assembly or rails.

If you look at the JGRO design it appears as though tighten the X and Y bearings to the rails is by adjusting the rails.

The JOE's model relies on a sliding bearing assembly that tightens the bearings onto stationary pipes.

My machine has both options but only because the build didn't include the precision Joe used in cutting his pipe "saddles" (on the X and Y). He used a CNC router to make the parts, presumably a Joe's machine is pretty square right out of the box. I felt the need for pipe adjustment to correct for anticipated elevation problems.

All the bearings should be in contact all the time.

My adjustable bearing assembly is made up of the HDPE part that carries the angle and bearings inside a larger HDPE part that has adjustment bolts poking in from the other side. Just like Joe's but not as pretty.

With regard to drilling the holes, I'd say you need to have a drill press fitted with a fence to get the holes drilled as accurately as possible. If the builder doesn't have one, he or she should find someone who does... shouldn't compromise there.

Hope that explains, check out the Joe's and JGRO machines.

Curtis

[.xXACEXx.]

thanks guys i kinda figured you couldnt just drill the holes...and they will be "perfict" some error is always possable...i saw a thread on the zone somewhere..with reguards to ecentric bolts to tighten the bearings to the pipe...but was just wondering about the drill and bolt alignment with out a machine shop to get the holes strait and on perfict location...i work at a machine shop..so that shouldnt be much of a problem...but for the "diy'er" i figured shimms were in order if the holes werent "just right"...gonna go look at those free plans again.....