Linear shafts
Traditionally, all movement is supported and constrained by bearings running on linear shafts. While alternatives are getting more common, this is also what I am going for on my CEVO. In this post I will compare a few different shafts.
Traditionally most 3D printers have used solid stainless steel shafts. They are available cheaply from China in quite good, but sometimes varying, quality. The major disadvantage of these steel shaft is that they are quite heavy, but they are also quite stiff and smooth. Quality suppliers like Igus and Misumi have alternatives in aluminium and as tubes instead of solid, but these tends to be quite expensive.
In later years quite cheap Carbon tubes have been available from China. Here and there people are experimenting with using these carbon tubes as an alternative to stainless steel shafts. They should be 3K roll wrapped carbon tubes. Their main advantage is that they are a lot lighter, and personally I think they also just look a lot cooler - for many the black carbon weave just signals high quality high-tech ;-) But are they any good? - many conclude that they are not, but some use them successfully.
For my printer I have bought traditional steel shafts as well as an assortment of carbon tubes. The general recommendation seems to be to buy more than needed, and then use the best. I have 8 mm and 10 mm steel and 8/6 mm, 10/8 mm and 10/6 mm carbon. All are just some of the cheapest available from China.
All of the shafts seems quite straight; that really does not seem to be a problem with any of them.
More interesting is the diameter. All my 10 mm steel shaft have a very consistent diameter of 9.97 mm +/- <0.02 mm.
However the carbon tubes are not nearly as good - they vary from tube to tube and they vary over the length of each tube. In general my six 10/8 mm tubes have an average diameter around 9.90 mm, but varies as much as +/- 0.07. I do think I will be able to select a coupe of these tubes that over 400 mm do not vary more than +/- 0.03 mm. My four 10/6 mm tubes are in general a bit thicker with an average just about 10.00 mm but with a bit less variance over the length of the tubes.
Variation in thickness is not good, but it should be seen together with how much the shafts flex when under load - such a flex will act much like variance in thickness. I rigged up a little test-bed to measure how much two shafts depress on the middle when loaded with 350 g (which happens to be the weight of a 12 mm shaft, and which I used for load).
When evaluating the bend values, you should consider the weight. Probably you will have a X-carriage that weights somewhat less than 350 g, or a lot less if you use Bowden or a Nimble. The weight of the full X-axis, that will be the load of the Y-axis, will be the sum of the carriage and the two X shafts, so the weight of that will largely depend on which shafts you use. Well, that is of course one of the main purposes of this exercise ;-)
The results are shown i the table below together with the weight of each shaft.
If you have a heavy X-carriage and a long X, I will conclude that you should go with 10 mm steel (or something equally stiff). However, lots and lots of people successfully use 8 mm steel for the X-axis. As I go for a light X-carriage with a Nimble, I will then conclude that with respect to the stiffness I will also be able to use 10/6 and probably also the 10/8 carbon tubes.
I am going to use mesh bed leveling, so I am no so concerned about a little variance in the the distance from the head to the bed at different positions. With that in mind, I think I just might get away with using the carbon tubes, but I will be prepared to give it up and go for something else if needed. But! Before my final conclusion I will have to look at the bearings together with the shafts, and that will be the topic of my next blog entry.
Traditionally most 3D printers have used solid stainless steel shafts. They are available cheaply from China in quite good, but sometimes varying, quality. The major disadvantage of these steel shaft is that they are quite heavy, but they are also quite stiff and smooth. Quality suppliers like Igus and Misumi have alternatives in aluminium and as tubes instead of solid, but these tends to be quite expensive.
For my printer I have bought traditional steel shafts as well as an assortment of carbon tubes. The general recommendation seems to be to buy more than needed, and then use the best. I have 8 mm and 10 mm steel and 8/6 mm, 10/8 mm and 10/6 mm carbon. All are just some of the cheapest available from China.
All of the shafts seems quite straight; that really does not seem to be a problem with any of them.
However the carbon tubes are not nearly as good - they vary from tube to tube and they vary over the length of each tube. In general my six 10/8 mm tubes have an average diameter around 9.90 mm, but varies as much as +/- 0.07. I do think I will be able to select a coupe of these tubes that over 400 mm do not vary more than +/- 0.03 mm. My four 10/6 mm tubes are in general a bit thicker with an average just about 10.00 mm but with a bit less variance over the length of the tubes.
When evaluating the bend values, you should consider the weight. Probably you will have a X-carriage that weights somewhat less than 350 g, or a lot less if you use Bowden or a Nimble. The weight of the full X-axis, that will be the load of the Y-axis, will be the sum of the carriage and the two X shafts, so the weight of that will largely depend on which shafts you use. Well, that is of course one of the main purposes of this exercise ;-)
If you have a heavy X-carriage and a long X, I will conclude that you should go with 10 mm steel (or something equally stiff). However, lots and lots of people successfully use 8 mm steel for the X-axis. As I go for a light X-carriage with a Nimble, I will then conclude that with respect to the stiffness I will also be able to use 10/6 and probably also the 10/8 carbon tubes.
I am going to use mesh bed leveling, so I am no so concerned about a little variance in the the distance from the head to the bed at different positions. With that in mind, I think I just might get away with using the carbon tubes, but I will be prepared to give it up and go for something else if needed. But! Before my final conclusion I will have to look at the bearings together with the shafts, and that will be the topic of my next blog entry.
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