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Grogyan
12-27-2010, 04:02 PM
I have a large problem, my original idea to use 608 bearings on 5/16 rod came unstuck when I found that in most cases it won't be constrained enough plus it sags substantially in the middle, because it is a Y gantry holding the Z axis, thus it has a lot of mass, which I have done my best to minimize.

http://farm6.static.flickr.com/5083/5297969278_19cd386738_z.jpg

Such that two people have suggested using proper linear bearings, I believe this is the way to go now, as it is impossible to eliminate all the problems of spanning 500mm on 5/16 rod.

The two options I have found are

linear bearing slide SBR12-1000mm (2rails+4 blocks) (eBay item 250610973493 end time 02-Jan-11 14:05:21 AEDST) : Business Industrial (http://cgi.ebay.com.au/linear-bearing-slide-SBR12-1000mm-2rails-4-blocks-/250610973493?pt=LH_DefaultDomain_0&hash=item3a5993fb35)

and

Uni-Guide Precision Linear Slide (http://www.pbclinear.com/Uni-Guide)

The top supporting aluminium angle will be replaced with 20mm 3mm thick aluminium angle.
Ideally the rails will have to be mounted vertically, however I don't know how to affix the belt to it when it is vertically mounted from where it is mounted now.

I'd appreciate any ideas anyone might have.

Else i'll have to mount them horizontally and hope that I can mount the Z axis via some box aluminium

louieatienza
04-06-2011, 07:56 AM
I have a large problem, my original idea to use 608 bearings on 5/16 rod came unstuck when I found that in most cases it won't be constrained enough plus it sags substantially in the middle, because it is a Y gantry holding the Z axis, thus it has a lot of mass, which I have done my best to minimize.

http://farm6.static.flickr.com/5083/5297969278_19cd386738_z.jpg

Such that two people have suggested using proper linear bearings, I believe this is the way to go now, as it is impossible to eliminate all the problems of spanning 500mm on 5/16 rod.

The two options I have found are

linear bearing slide SBR12-1000mm (2rails+4 blocks) (eBay item 250610973493 end time 02-Jan-11 14:05:21 AEDST) : Business Industrial (http://cgi.ebay.com.au/linear-bearing-slide-SBR12-1000mm-2rails-4-blocks-/250610973493?pt=LH_DefaultDomain_0&hash=item3a5993fb35)

and

Uni-Guide Precision Linear Slide (http://www.pbclinear.com/Uni-Guide)

The top supporting aluminium angle will be replaced with 20mm 3mm thick aluminium angle.
Ideally the rails will have to be mounted vertically, however I don't know how to affix the belt to it when it is vertically mounted from where it is mounted now.

I'd appreciate any ideas anyone might have.

Else i'll have to mount them horizontally and hope that I can mount the Z axis via some box aluminium

I too am in the process of building one, though my goal is to make it as light as possible for the smallish steppers.

I would check out the DIY woodworking machines section to see ho others go about it. There are many guys (myself included) that use skate bearings for their machines.

For my reprap machine, I'm using 3/8" water-hardening drill rod that I'm polishing to make the surface even smmother. They're ground to exact diametr, and are harder to begin with. I found a lot of 15 3/8" linear bearings on eBay for $5.99 total shipped! Normally they'd be about $20 each!

With what you got now, you might be able to use square rod (at a 45) or another L angle as your linear guide... That's a pretty big z carriage, you probably could drill out sections to lighten it up as well...