Testing Chinese AliExpress Linear Rail and Extrusion for Flatness
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- Опубликовано: 5 янв 2024
- When people say their Chinese aluminum extrusions or their linear rails from AliExpress are flat. How do we know for certain that they are flat? In this video, I am gonna measure flatness of these items purchased on AliExpress. See it for yourself the result. Are they acceptable for for intended use? For me, they are perfect for DIY 3D printer parts and 50 micron (0.05mm) flatness is nothing that I should worry about and I can sleep well at night.
For reference, here are purchased links for these items on AliExpress
▬ Shopping ▬▬▬▬▬▬▬▬▬▬▬▬▬▬
KGT Store: s.click.aliexpress.com/e/_DEj...
CCQ Factory Store: s.click.aliexpress.com/e/_DkX...
Aluminum Extrusion:
General 2020 Extrusion: s.click.aliexpress.com/e/_DlD...
For Voron 2.4 3D Printer: s.click.aliexpress.com/e/_DdQ...
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► Personal Website: www.thinhla.com
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ruclips.net/video/s72SvaYPc9w/видео.htmlsi=BoBqIDJKmHxG8ut2
Linear rails flatness isn't as important as people think, that's not a critical dimension for them most rails are also preloaded intentionally to be flatten out when bolted down, this includes even very expensive rails e.g. rexroth rails. The critical part of the rails is the channels in which either the rollers or the ball bearings ride in.
Assemble, level and tune at operating temperature and you're golden.
Exactly! There is a paper out there advising people putting titanium backing plate to prevent deflection from bimetal thermal expansion. 🤣 I just wanna do experiment!
I love the channel name 🤣
🙂
why is the high side always on the left? and always ~2 thou? Did you try flipping one of those parts end to end?
Yeah i should have in order to cancel out the effect. Tolerance is added. It's 2 thou higher than the other side
That's why i meant extrusion are not flat. It might just be that end opens up like a "flower" Regardless, .002" (~50 micron) over 450mm long to me it's FLAT enought. And its flatness may be better than that of table glasstop or kitchen countertop.
This a common problem when extruding material. The tech is improving but it's almost impossible to make a perfect extruded part. You could finish the surfaces but then the parts would be much more expensive.
You are measuring parallelism from the back of the rail. Nice inspection station though. Flatness is measured independent of any other feature.
You are totally right, I should have probed the underside of the linear rail and the extrusion when resting on the V block to check for flatness. Thanks for pointing it out.
@@lavithhcm typically you want to jack up 3 points 120 degrees apart evenly to define a plane. Your total deviation from that origin would be your flatness value.
Many of the comments posted here are silly. It is nice to see that the deviations in the rail is small. But that is as far as it should be taken. Even if they were less flat (bowed) the important thing is the deviation found when the rails are mounted to the final structure. And as long as you have not done anything dumb in that structure, the small deviation will be irrelevant in a 3D printer.
You are so 99% right. 🤣 wait untill I show you my next little "experiment" by heating those parts over 70°C which my chamber temperature would never reach. Should I worry? Hell NO. 😂
And this is exactly why , if you want something precise , you should not get cheapies from China. They are okay for a home edition 3d printer and so , but not for .02 spec routers , or when you make high spec tools.
Yeah i am happy with that tolerance for my 3D printer build. For $30 dollar linear rail from China, it is actually pretty good for just 25 micron (0.025mm) flatness. There is a band wagon where everyone puts another metal titanium backing plate onto the aluminum extrusion to prevent it from bending too much due to thermal expansion. And i am gonna show how much it will bend under influence of heat. Should we worry too much in that situation? Stay tuned!😂
Yeah you should be worried if you're using higher chamber temps. You can see the thermal deflection when probing. But it's usually within what a mesh can easily compensate for.
@@lavithhcm Yeah , that`d be interesting.
I think , depending on the mass and thermal expansion of the titanium , that it will create a bi-metal distortion , like in a thermometer or a thermostat. I wonder if that expansion would be linear , or create all kinds of artful but anything but linear distortion.
You`d probably be better off with just aluminium properly bolted down , that is at least linear and predictable.
Under 250°C cooking pan, they both experience some what 80-100°C as you see towards the end of the video. There is of course thermal expansion that would bend both. What do you think how much it deflects? How many micron?
.@@lavithhcm Titanium`s expansion is about half that of aluminium`s , so that would probably be a mil or more.
Did you measure the lateral distortion as well?