Linear Bearings

linear brass bearings fitted to Genmitsu z-axis

I think this post should actually be titled “cheap linear bearings” as I don’t think all are equal. However, the bearings found in low end CNC machines are effectively parts from the inkjet printer industry.

sainsmart genmitsu spindle play

You will find this type of bearing in PC inkjet printers and in low end CNC machines.

This Sainsmart Genmistsu 3018-Pro is a good example of the low end CNC machines that are available on ebay and Alibaba for around£200 in 2020.

The linear bearing as you can see in the middle of the image with the arrow pointing at it operates on a round bar. The linear bearing contains 3 rows of ball bearings that are contained in a plastic housing.

Essentially they reduce resistance and maintain alignment.

Linear Bearings

The parts on the right are those installed each side of the z-axis. As you can see though, originally two parts are fitted to do the job of one.

Searching for a replacement I could only find parts that were 45mm long (part on the left of the image). This would protrude 5mm top and bottom from the plastic carrier.

At this point I really should have taken notice of Carbon Details as they sent me images of some homemade bearings. Anyway the replacement linear bearings I bought were rubbish, no different to the original parts and so I had to go back to basics. Or back to the message sent to me by Carbon Details.

My version of these bearings were to be made from brass, basically because I just didn’t have any phosphor bronze of this size in my materials bin.

Brass Linear bearing
fitting bearings using engineers vice

I machined the brass to 15mm OD, drilled the part through at 7.6mm and then hand reamed to 8mm. As I said, this was from brass, so great to machine.

They were machined 35mm long and then pushed into the plastic Z-axis motor housing using the vice and two pieces of MDF to protect the brass and plastic.

linear brass bearings fitted to Genmitsu z-axis

The parts fitted into the housing. Then in the next image on the 8mm z-axis runners. I assembled them with some graphite dust on the rails.

I have to agree with Carbon Details, these really work and are so simple to machine. Thanks Fernando, a great idea.

z-axis od genmitsu 3018-pro
About Nigel 355 Articles
I've been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.


  1. Excellent point, and maybe an almost-universal truth about buying a cheap machine (i.e., not a machine that’s lower-priced than an apples-to-apples competitor, but lower *value*) and modifying it to fix the problems. (I’ve fallen for it myself too often as well).

    Good on you, mate, and best luck going forward!

    • Thanks Mark, I really could have spent double and it would still have been cheaper, but then again I’m learning and enjoying the whole process. I should have learnt from the XJ12-300 milling machine experience that I bought on the cheap, spent 5 years improving it and then sold it to buy the Sieg. I just should have bought the Sieg first. However, I learnt about ball bearings versus tapered rollers, springs vs gas struts and gear vs belt drives.

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