Smooth rods, cheap bearings, and grooves...

Like many noobs before me, I started building my Prusa i3 before I really had a handle on the potential pitfalls of sourcing your own parts. In this case, the parts in question are smooth rods. I purchased mine as a kit from a supplier on eBay. He had sold dozens of these and had 100% feedback, so I assumed I was good to go. What I ended up with was drill rod, but at the time I really didn't know much about steel hardness and linear bearings.

I've have my Prusa about 80% built, and noticed that there are already grooves worn in the 8mm rods on the Y-axis. This thing hasn't printed a single part yet, so this wear is just from me moving the bed back and forth a few dozen times by hand.

I've researched this on the forum and info is a little sparse. How big a deal are the grooves? Will it have a major effect on my prints? Right now, the bed doesn't exactly glide like butter, but if you tilt it vertically, the bed will slide down on its own.

I hate the idea of replacing the rods when I'm so close to being finished (and it has taken so long to get where I am), but if that's what needs to be done, I guess better now than later. Any thoughts?

If I do need to replace them, any suggestions on suppliers? There are UK and European 3D printer suppliers that will sell you stainless rod kits all day long, but I can't find anything here in the US, except eBay auctions selling the same stuff I've already got.

Do I just need to buy bulk stainless steel and cut them myself? If so, is there a source that won't bankrupt me? I checked McMaster, and for enough 8mm 316 stainless to replace everything, I'd be looking at 60 or 70 bucks - yikes!

Do I need to replace all three axes? (It seems like the Z-axis might not be as critical, but I could be wrong.)

Any advice is greatly appreciated.

Thanks!
David

Perhaps a set of these could be one of your first prints. [www.thingiverse.com]

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MakerFarm 8" Prusa i3v
RAMPS 1.4
0.4mm E3D v6 for 1.75mm

Quote
AbuMaia
Perhaps a set of these could be one of your first prints. [www.thingiverse.com]

I had definitely considered the possibility of using nylon bushings (or some other material), although I hadn't thought of printing my own. The thing about that is, once I get this printer up and running, I'm not keen on turning around and tearing it all back down to replace the bearings.

I've gone to printed PLA bushings on my Prusa i3. The "8mm" rods we get here actually 5/16th inch (which is bizzare, given that the rest of the country is metric) so LM8UU bearings rattle like a train on them. If you work the PLA bushings on a spare bit of rod to bed them down to the right size, and add a bit of light grease, they move pretty well. There's more friction than a ball bearing style, but the stepper motors I'm using (NEMA17) have more than enough torque to get over that.

Those might be rods from one of my kits. Drill rod is cost effective but has drawbacks. As you've found motion rod can get pretty spendy. My i3s have grooves but still work well almost two years on. I've build a few dozen for my use and have sold about 1500 kits in the last 19 months or so.

If you get your own, I don't recommend getting stainless in bulk and cutting it unless you have the saw to do it. A better value is to get some rods from Misumi. They'll be between US$8 and 12 bucks each plus shipping. You'll also need bronze bushings (known as press fit sleeve bearings) as well as a way to attach them to your machine. They won't zip tie to the machine. All of the LM8UU in that price range of of the same spec and quality. Unless you are willing to spend US$7-20 on precision linear slides/bearings (Igus, Thomson, etc) It won't do you any good to get other bearings. That's why we use the busings, a more cost appropriate solution. Unless those LM8UU bind, chew or rattle in which case they can be replaced as some of the cheap bearings fail after a bit of use. Unless they are catching and binding at this point they don't need to be replaced. If you take them off and a ball falls our (usually several balls) they need to be replaced. You can also use light oil to lube them.

My suggestion is to build what you have and start using it. If you add those premium componenets right now you won't see any improvement in your prints due to learning curve.

SDP plain bearings A 7Z41MPSB08M ( I use the 10mm version of these on Mendelmax 2 with Misumi rod) They've got a service charge they add when there is a small order.
[sdp-si.com]

The Misumi rods in chrome finish 1045 carbon steel are part # PSFG8-370 (the 370 is the length) and are US$8.44 each plus shipping. The other lengths will be about the same price.
[us.misumi-ec.com]

As always, if you got the kit from me and aren't pleased let me know and I'll replace or refund your money.

Dave
bluskreen on ebay

[www.banggood.com] Try these best cost effective quality rods I could find, I'm using them. I believe they're hard chromed tool steel optical linear shafts.