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linear rods VS aluminum extrusions and pulleys

Posted by pwave 
linear rods VS aluminum extrusions and pulleys
May 17, 2016 01:11PM
Hi I am looking for a cheep delta printer I found 2 that are almost the same the only difference is that one has linear rods and the other has aluminum extrusions and pulleys. I already have one with the aluminum extrusions and it prints really well so I was wondering if the linear rods version might be better ?

option 1: linear rods

[www.aliexpress.com]

option 2: aluminum extrusions and pulleys

[www.aliexpress.com]

Edited 1 time(s). Last edit at 05/17/2016 01:13PM by pwave.
Re: linear rods VS aluminum extrusions and pulleys
May 17, 2016 02:09PM
Linear rods tend to be fairly bendy. But if you want quality, use real linear guides, supported by aluminum extrusion.
Re: linear rods VS aluminum extrusions and pulleys
May 17, 2016 08:20PM
with reprap intrinsically focused on the use of 8mm rod because that's what everyone has always done then yes they can get bendy when supporting each end only. I won't argue that linear guide is not better as it is but at often significant greater cost when bought new depending where you are in the world......

To the OP: micromake seems to have a bad reputation based on multiple posts..... however I do like that particular design with the linear rod actually being supported at each end by the aluminium profile and not being full length thus reducing some flex potential... just the size if the rods is not mentioned but they look larger than 8mm.
Personally if the rods were 12mm I'd take the rod version.... also based on the linear rod attachments from the photos it may be a relatively easy upgrade to larger rods.

Toss a coin and pick one smiling smiley
Re: linear rods VS aluminum extrusions and pulleys
May 17, 2016 10:52PM
or

option 3 aluminium extrusion with linear rails


this is not the cheapest option but I feel its the best, and if you build a simple aluminium extrusion printer in the first instance you can always upgrade it later..... however, out of the two options you list above I feel the aluminium extrusion with rollers is actually the worst, and would opt for the linear rods instead



RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD
Re: linear rods VS aluminum extrusions and pulleys
May 18, 2016 04:49AM
I would go for linear rails or linear rods. But the rods must be at least Ø 12 mm, preferably hollow inside so that they are not that heavy. Belt elasticity will contribute bigger error to your prints than Ø 8 mm rod bending.
Re: linear rods VS aluminum extrusions and pulleys
May 18, 2016 06:56AM
If you read enough threads in this forum you will find the following:

- Aluminium extrusion with shower door rollers works poorly.
- So does aluminium extrusion with cheap linear rails.
- Aluminium extrusion with Delrin V-rollers works well, and isn't very expensive.

Aluminium extrusion with high quality linear rails is probably best, but also the most expensive.

I don't have any experience of building delta printers using linear rods. One potential problem I can see is how to make sure that each rod is at right angles to the bed plane in both directions.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
PRZ
Re: linear rods VS aluminum extrusions and pulleys
May 18, 2016 07:40AM
Linear rod have two problems :
- If the rod are 8mm diameter, this is too small except for a quite small machine
- If bearing/rods are of poor quality, it is difficult to replace them and you have to rebuilt a big part of the machine to replace them. This only can be used if they are sourced from a reputed supplier.

[edit] For average or large machine you need rods diameter 12 or 16 and bearings are much heavier than wheels.

Rods and bearings often have problem of diameter, hardness, straightness and bearing quality.

Extrusion with wheels are more controllable as you can modify the play and compensate for wear. Wheels made with shower doors rollers shall be replaced one day or the other, but this is relatively easy to do.

I don't like rods, but I have one machine using Fisher delta components which work ok, but this was from a kit with controlled quality and the rods are quite short (426mm).

If building a new machine, I won't use a rod system, I will use polycarbonate V-wheels on extrusions or steel ball bearings rolling on steel as on my other machine (D-Box) or as on the Beagle printer.

Edited 2 time(s). Last edit at 05/18/2016 05:49PM by PRZ.


Pierre

- Safety [reprap.org]
- Embedded help system for Duet and RepRap Firmware [forums.reprap.org]
- Enclosed delta printers Lily [rouzeau.net] and Lily Big [rouzeau.net]
- OpenScad delta printer simulator [github.com]
- 3D printing on my site [www.rouzeau.net]
Re: linear rods VS aluminum extrusions and pulleys
May 18, 2016 04:06PM
My preference for linear rod over linear rails is easy to explain. I do not want to buy this stuff from a shop which does not specify tolerances. And the rods are cheaper in the few shops which do specify them and which I checked out.

As for as buying cheap linear bearings from china: Looks like one must buy about two times the needed amount so that the better ones can be used and the rest goes straight to a garbage bin. My impression is that many 3d printer part sellers are buying rejects from normal production and sell it to us thinking: "Those noobs will not notice that these parts are completely out of spec." smiling smiley
Re: linear rods VS aluminum extrusions and pulleys
May 19, 2016 06:50AM
I designed a Delta Printer with 16 mm steel Rods and Teflon Glacier bearing bushes and this printer is sturdy as a rock; 8mm rods doesn't work at all.
My new design has 20mm steel rods.
Re: linear rods VS aluminum extrusions and pulleys
May 19, 2016 07:29AM
Quote
hercek
My preference for linear rod over linear rails is easy to explain. I do not want to buy this stuff from a shop which does not specify tolerances.

Rod manufacruers specify tolerances because rods have a huge range of uses where the tolerance is critical, this is not true for rails, the only dim thats normally toleranced is the mounting heights.



RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD
Re: linear rods VS aluminum extrusions and pulleys
May 19, 2016 09:48AM
Quote
bgkdavis
Quote
hercek
My preference for linear rod over linear rails is easy to explain. I do not want to buy this stuff from a shop which does not specify tolerances.

Rod manufacruers specify tolerances because rods have a huge range of uses where the tolerance is critical, this is not true for rails, the only dim thats normally toleranced is the mounting heights.
Not sure what rails you are buying but the ones I buy have most dimensions toleranced, not only that but the tolerance for the mounting surface is also specified.
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