Are my new rods defective?

I have been trying to upgrade many of the parts of my old printer. While replacing the bearings with better versions, I had to do a lot of work to dissemble/reassemble the printer, and was worried all this force I had to put on the printer could have possible bent the rods, so I decided to order new ones. I figured I might as well get rods that were likely more durable and accurate then the ones that came with my Chinese printer.

I was advised that these were good:

[www.ebay.com]

When I finally got around to installing them however, they seemed to be rather off. It took effort to get them to fit in the holes/retainers my old ones fit in, and my bearings were significantly harder to fit in them. When I tried putting on the bearings though is when they really seemed off. The bearings would only spin in one direction as I was aligning them, and even with copious amounts of lube, they were rather rough, not moving smoothly at all. When I tried the bearings on my older rods they were much smoother.

Any advice on what I can try to do to determine if they are accurate or if I am doing something wrong? Sadly, I don't have any precision tools that can determine sub-millimeter variances, in fact, I can barely get it down to a single millimeter, about the best I have is measuring tape intended for sewing.

Its unlikely the rods are inaccurate because ground rods have more or less become a commodity item. The chances are that your old shafts were a different diameter. Shafts come in a variety of tolerances ( [www.tribology-abc.com] ).

I would have expected g6 to work, but if it doesn't then the bearings were probably designed for something else. If you have a part number for the bearings the datasheet will tell you what shaft size they are designed for.

FWIW the chances are that if you put a Chinese cheese-steel bearing on an over-sized hardened linear shaft that their wear has been greatly accelerated.

The bearings work fine on my old rods though, which are specified as being 8mm, same as the ones I got. I find it hard to believe both my old and new set of bearings, as well as all my fittings, were wrong in just the right way to work.

I bought a Robo back in 2014 that was manufactured in China and it had 5/16 rods (.3125") on it. Dont remember the bearing fit but I believe they where appropriately sized. I chucked those for new 8mm (.315") rods and matching bearings. This might be what you are experiencing if, by chance the parts came from the same source. I have also found that getting rods and bearings from different sources (mainly in China) that quality control can be iffy at best. I had to buy at least 2 sets of bearings to get a nice fit. Buy some $15 dollar metal calipers off ebay or amazon so you can find out whats going on or better yet a $30 micrometer that can read to .0001". You could also for the same price get the bearings from that seller you got the rods from. No guarantees though

As they are still a few people using "inch", although a fast dying bunch, chinese mfg have decided simplify and produce metrinch rods, bearings, profile ... intended to fit both system, eg. 8mm and 5/16.
Therefore sometimes you get excessive play, others you need excessive force.

Excessive play is OK as most 3D printer frames are overconstrained, poorly assembled, aligned, flexible thus often cancelling it.
In the other case, as the materials used are usually soft, they will grind themselves to fit or seize. So you will get new ones as they are so cheap. Then back to above.

Don't trust any of their published specs, always measure.
Also lot of rods are stainless steel and not hardened then ground. The SS will quickly be damaged by the bearings.

Now if you use cheap chinese calipers, dials ... better check them first.

Note with some luck you can get useful parts and match rods to bearings for ex.
Don't forget to check if they are straight too !

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Yeah I'd second that. You need good measuring equipment sewing tape is okay for sewing, but for 3d printing you need at minimum some digital (or analogue) vernier calipers. And yes super cheap calipers often don't measure right. The first set I bought for £9.99 were innacurate in the range below 2mm which seriously messed with me.

Rods vary and bearings vary. Rods deflect even if the bearings run smoothly so you'll notice a hill in the middle of the bed.

---

Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Since when does the USA do stuff in Millimeters?

Quote
MechaBits
Since when does the USA do stuff in Millimeters?

Dude, really? Just because it's not the standard unit of measurement in the US does not mean the country and all manufacturers and stores are ignorant of it. I went and picked up Metric screws for my printer from Home Depot a few days ago.

Quote
Cyber Akuma

Quote
MechaBits
Since when does the USA do stuff in Millimeters?

Dude, really? Just because it's not the standard unit of measurement in the US does not mean the country and all manufacturers and stores are ignorant of it. I went and picked up Metric screws for my printer from Home Depot a few days ago.

[www.youtube.com]

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I'm obviously taking the piss. Y U So Ser we us

I was also thinking 20mm rods but no measuring device...

Edited 2 time(s). Last edit at 04/28/2018 05:54PM by MechaBits.

I tried measuring both the old and new rods with a pair of digital calipers I had, and they both seem to be the same diameter. Why do my bearings not move smoothly on the new rods then? Both my old and new bearings are smooth on the old rods, but rough on the new rods.

Quote
MechaBits
I was also thinking 20mm rods but no measuring device...

Yeah, I posted the wrong link, I ordered the 8mm rods, but I accidentally posted the link for the 20mm ones. Same seller and everything though.

Oil the new rods?
If that doesnt help the new ones may become smoother after breaking them in, OR the surface finish/diameter could be slightly out of spec

I tried oiling them significantly with Super Lube

Calipers aren't great if you are measuring small differences since jaw pressure starts to affect the reading.

You can check the relative dimensions of your rods by arranging three of them in a row on a flat surface: small - large - small. Then place a second flat surface on top (like the printer bed) and see if it rocks back and forth.