<p>A common metric for straightness of shafts in industrial equipment is Total Indicated Runout (TIR). The shaft is placed in V-blocks or ball bearing rollers at its bearing journals. Runout is checked at various positions along its length with a dial indicator as the shaft is rotated.</p>
<p>This method could be easily applied to guide rods supported at the same axial locations where they are held in the printer.</p>

CC BY-SA 4.0
2023-12-07T14:10:09.583Z
2023-12-07T14:10:09.583Z
allardjd
<p>A few closely related questions about the straightness of linear rods. The 'straightness' of linear rods is vital for a 3D printer to function correctly and prevent things like Z-Banding or Z-Wobble. So, how do we measure the 'straightness' of linear rods? What measurement method or metric can be used?</p>
<p>I can imagine using some reference material (a piece of wood or a table), but then again, how would we know the reference material is perfectly straight? Lastly, how straight does it even have to be? What's a standard or acceptable range they should be in, and is there a standard that defines, classifies, and indicates this?</p>

CC BY-SA 4.0
2023-12-07T16:21:22.983Z
It is hard to het a very straight object to verify your rods against. A regular household measure is to use a metal ruler on its side; not everybody has access to a perfectly flat slab of granite/steel as I had at my previous employer (e.g. used for mounting optics).
0scar
<z-axis><linear-motion><axis>
What defines the 'straightness' of linear rods and how to measure it?
Bob Ortiz
# What defines the 'straightness' of linear rods and how to measure it?

(Asked by: username_0 on 2023-12-06)

A few closely related questions about the straightness of linear rods. The 'straightness' of linear rods is vital for a 3D printer to function correctly and prevent things like Z-Banding or Z-Wobble. So, how do we measure the 'straightness' of linear rods? What measurement method or metric can be used?

I can imagine using some reference material (a piece of wood or a table), but then again, how would we know the reference material is perfectly straight? Lastly, how straight does it even have to be? What's a standard or acceptable range they should be in, and is there a standard that defines, classifies, and indicates this?

**Tags:** z-axis, linear-motion, axis
> **Comments:**
> **username_1**: It is hard to het a very straight object to verify your rods against. A regular household measure is to use a metal ruler on its side; not everybody has access to a perfectly flat slab of granite/steel as I had at my previous employer (e.g. used for mounting optics).  

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## 1 answers

### Answer by username_2 on 2023-12-07. Score: 4 | Accepted answer

A common metric for straightness of shafts in industrial equipment is Total Indicated Runout (TIR). The shaft is placed in V-blocks or ball bearing rollers at its bearing journals. Runout is checked at various positions along its length with a dial indicator as the shaft is rotated.

This method could be easily applied to guide rods supported at the same axial locations where they are held in the printer.


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