Another self build 3D Printer

[Dr_Ju_ju]

A variant on the CoreXY\DBot printer has recently been released, using linear rails, Duet control etc...  all the info can be found at https://www.thingiverse.com/thing:3382718 

The test prints look amazing & I may well be stealing some ideas for the bed, as well as the extruder head....

[Gina]

Interesting - looks rather complicated though.  Wonder if it's more accurate than my Concorde design or my Mini for that matter - it's between the two in size.

[Dr_Ju_ju]

nominally its 300x300x300, with Z stretching to 525, but as its based on extrusion\linear rails, more money would bloat the size....

[Gina]

Yes indeed.  Not sure I like those linear rails and bearings.  I get the feeling they could suffer from the same problems as the old round linear bearings and rails.  I prefer to have the little steel balls in standard round bearings and have these running on linear rails.  I feel it would be easier to seal them from the micro-dust produced by 3D printing.

[Dr_Ju_ju]

While using them doesn't guarantee better prints (too many other variables e.g. print head etc.), depending on manufacturing quality, they give you a good starting point where the XY axis should be running parallel to each other.

I see many of the 'pro' systems now seem to use them, and even some of the better self builds. Also, I believe, that even some of the Chinese clone makers have started using them, so they are becoming more common, albeit more expensive.

 

 

[Chriske]

I never use these linear ball bearings. To much play after a while. it is one of the reasons why ghosting appears on perimeters.
I make my own bearings. I can rule out all play on  X and Y axis + on the two extruder rods.

[Chriske]

4 minutes ago, Dr_Ju_ju said:

I see many of the 'pro' systems now seem to use them, and even some of the better self builds. Also, I believe, that even some of the Chinese clone makers have started using them, so they are becoming more common, albeit more expensive.

If I had to choose between linear ball bearings and rails I'd definitely go for these rails.
Using these rails there's absolutely no room for error. Meaning : the walls of the casing must be ab-so-lu-te-ly parallel..!
Linear ball bearings allow rather lots of error.. Except of course if you buy the very expensive linear ball bearings.

[tonyowens_uk]

40 minutes ago, Chriske said:

I never use these linear ball bearings. To much play after a while. it is one of the reasons why ghosting appears on perimeters.
I make my own bearings. I can rule out all play on  X and Y axis + on the two extruder rods.

My apologies Chriske - I think I misunderstood which type of bearing you were referring to! Almost no machine tool builders use round shaft linear bearings carrying cylindrical recirculating ball bushes anymore. Those MGN rails are from HiWin ( https://www.hiwin.de/de/Produkte/Profilschienenfuehrungen/Baureihe_MG/Laufwagen_MGN/21089 ) and for most practical purposes are as good as those from the populariser of this style of bearing, i.e. THK Tokyo. Static load capacity of each truck (in the 12mm MGN profile rail used in that printer) is 580 KgF and stiffness is far better than anything else used in 3D printing including ball bushes. There should be no problem with contamination and abrasive wear as they all have effective wipers. Life is measured in thousands of Km gernerally - there is an approximate calculator here: http://www.efunda.com/DesignStandards/bearings/bearings_linear_ld_life.cfm

The main issues with using this style of linear bearing are:

1. the need to fix them onto a flat stiff support surface and the problems of getting them and keeping them parallel especially in the flimsy structures typical of most RepRap.  That is what chappie in the Thingiverse video discusses.

2. the effect of the wipers on breakaway friction especially where multiple bearing trucks are used.

The second point could be an issue in high precision (but low stiffness) belt-drive machines like 3D printers which operate open-loop position control but aspire to carriage positioning repeatability to within a few tens of microns. It manifests as higher positional repeatability than one would like. Ballscrew drives ideally with servomotors will solve this. The poor man's solution is to just remove the wipers and substitute a block of wool/acrylic felt soaked in NLGI 2 grease!

Hope that helps!

Tony

 

[Chriske]

Correct about flimsy printer setup, many people tend to use. It's cheap, fast to build, but in the end well, it is a second reason why ghosting appears on perimeters.  That's why I always use 18mm plywood to build midrange printers. Planning to build a larger one,  it will be even thicker wood. 18 mm plywood is not thick enough for say 500mm high print capacity. As matter of fact I do have problems lifting my printers, but I dare to say all  parts do have superb perimeters. Except when I'm printing very fast, say 110+mm/s. Then again I do have perimeter issues from time to time.

Together with a few friends we've build 20+ different printers. Some of these projects only lasted a few days. Reason : flimsiness. And you don't want to us these rail bearings in these reprap printers at all.