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Basic considerations about Delta printers

Posted by fma 
fma
Basic considerations about Delta printers
January 05, 2016 03:44AM
Hi!

I'm thinking to build a Delta printer from scratch (moslty for fun), and I would like some advices.

Here are some infos about the printer I plan to build:

- no need fo high speed printing; quality is the main factor -> must be rigid
- metal parts as much as possible (aluminium profiles, lasercut plates...)
- diam. 10mm (mini) for rods/linear ball bushing
- normal build volume (~diam. 250mm x h 250mm)
- option for 2 more axis (goniometer)
- option for spindle mount (PCB engraving, soft wood...) and laser diode
- double extruder (or hybrid, like E3D Cyclops)

My first question is: what angle should I use for the arms (when hotend is centered), depending on the diameter of the bed? What are the criteria to take into account? Stiffness and accuracy. in mind...

Thanks,

Edited 1 time(s). Last edit at 01/05/2016 03:45AM by fma.


Frédéric
Re: Basic considerations about Delta printers
January 05, 2016 04:23AM
The goniometer option would imply, you have two steppers and a spindle motor attached to the effector?! I would go much larger then to have enough room for that beast.
Actually the delta design is made for speed and not for precise spindle action. I would start with a coreXY design, if I had your plans.
-Olaf

Edited 1 time(s). Last edit at 01/05/2016 04:24AM by o_lampe.
fma
Re: Basic considerations about Delta printers
January 05, 2016 04:40AM
No, the gonio is under the bed, not on the effector... About the spindle, I'm thinking using a little brushless motor, like used in quadcopters...

Anyway, these are possible options only, and I really want to build a Delta winking smiley

For now, I need to determine the global size, so arms geometry is an important factor.


Frédéric
Re: Basic considerations about Delta printers
January 05, 2016 05:21AM
Quote
fma
No, the gonio is under the bed, not on the effector... About the spindle, I'm thinking using a little brushless motor, like used in quadcopters...

Anyway, these are possible options only, and I really want to build a Delta winking smiley

For now, I need to determine the global size, so arms geometry is an important factor.

The Arms should not be less than 20 degrees to the bed at the farthest extent of there travel and should be as wide apart as you can get but aim for no less than 45mm (that is around 40 mm wide fixing points on the effector/carriages which is the std for the Kossel if you can go wider then you will have greater rigidity)

Doug
Re: Basic considerations about Delta printers
January 05, 2016 05:28AM
In my opinion, the only reason to prefer delta to coreXY is the high printing speed. Otherwise delta has only disadvantages. It needs more powerful/expensive controller, it is harder to calibrate, and it is taller. But if you want a delta for the fun/challenge of it then go on smiling smiley

Make your design so that you have an option to avoid the long bowden. The bowden is a major hurdle for high quality of prints which need to retract very often (e.g. models which contain a lot of thin towers). If you are after really high quality of prints then you need get rid of bowden. The options are:
  • mount motor on the platform just next to hotend (you need stiffer structure and stronger steppers for this since the platform will be heavier)
  • use a thin flexible hard steel cardan/shaft and a speed reduction at the platform - you can design your own or buy e.g. flex3drive
  • use the flying extruder mod (search this forum if you do not know what it is)
Place the equidistant diagonal rod as far away from each other as possible. Use high quality angle ball joints.
Here are some thoughts about the diagonal rod length: [forums.reprap.org]
fma
Re: Basic considerations about Delta printers
January 05, 2016 06:22AM
Quote
dougal1957
The Arms should not be less than 20 degrees to the bed at the farthest extent of there travel and should be as wide apart as you can get but aim for no less than 45mm (that is around 40 mm wide fixing points on the effector/carriages which is the std for the Kossel if you can go wider then you will have greater rigidity)

Thanks for the tips!


Frédéric
fma
Re: Basic considerations about Delta printers
January 05, 2016 06:56AM
Quote
hercek
In my opinion, the only reason to prefer delta to coreXY is the high printing speed. Otherwise delta has only disadvantages. It needs more powerful/expensive controller, it is harder to calibrate, and it is taller. But if you want a delta for the fun/challenge of it then go on smiling smiley

Well, I find it simpler to design: only 1 axis, repeated 3 times. About controller, I'm waiting for a Replicape... Very nice to add new features (mostly written in Python).

Why is it harder to calibrate?

Quote

Make your design so that you have an option to avoid the long bowden. The bowden is a major hurdle for high quality of prints which need to retract very often (e.g. models which contain a lot of thin towers). If you are after really high quality of prints then you need get rid of bowden. The options are:
  • mount motor on the platform just next to hotend (you need stiffer structure and stronger steppers for this since the platform will be heavier)
  • use a thin flexible hard steel cardan/shaft and a speed reduction at the platform - you can design your own or buy e.g. flex3drive
  • use the flying extruder mod (search this forum if you do not know what it is)

Yes, this is what I planned to do; I designed a light but strong extruder, using a geared nema 14 motor. On the other hand, for dual extrusion, it will be difficult to embedded 2 extruders :/

I printed for a long time with bowden, and for the parts I'm printing, I don't have any issue; I switched back to a standard config to be able to extrude Filaflex. But I recently tried Flex PLA, and find it more interesting for my needs. So, I switched back again to bowden a few days ago, and I'm making more tests to see if I can still get good results (have to try Flex PLA).

BTW, I will use Nema 23 motors, and I also need to find strong belt, to avoid elongation under tension. Any suggestion? Does GT2 exist in 10mm width?

Quote

Place the equidistant diagonal rod as far away from each other as possible. Use high quality angle ball joints.

What ball joints do you suggest? metal ones? Or plastic (IGUS?) ones?

Quote

Here are some thoughts about the diagonal rod length: [forums.reprap.org]

Thanks! Feel free to send me on old threads if you have some in mind (but don't make specific search for me!).


Frédéric
Re: Basic considerations about Delta printers
January 05, 2016 07:52AM
Quote
fma
Why is it harder to calibrate?
Because the equations for delta are not linear. It is pretty obvious what is incorrectly calibrated from a simple printed cube if you use a cartesian printer. But bad calibration in delta leads to some "strange" distortions in the pritned parts. Regardless it is not so bad now as it was in the past since there are some public tools to help you. You need a Z-probe and then use some of these approaches: [github.com] or [forums.reprap.org] or dc42's firmware for Duet board.

If you want to understand more then play with this notebook: [github.com]

Quote
fma
BTW, I will use Nema 23 motors, and I also need to find strong belt, to avoid elongation under tension. Any suggestion? Does GT2 exist in 10mm width?
You want as stiff belts as possible. That means belts with steel core and as wide as possible. GT2 profile is better than T2.5 but steel core GT2 is rare. If you are very advantageous then go for about Ø 1.5 mm steel cable. But in this case you need big diameter drums to minimize impact of the errors because of varying position on drum. And that means you probably need a speed reduction from stepper to the drum. Anyway the common Ø 1.5 mm steel cable will be much stiffer than any common belt you can get.

Quote
fma
What ball joints do you suggest? metal ones? Or plastic (IGUS?) ones?
Plastic is enough, just get ones which are sold already completed and which are tight. For example: [forums.reprap.org]
Or maybe better a version V2 of the MP Jet joint should be more durable. Sorry I have only a Czech link for it: [www.mpjet.info]
fma
Re: Basic considerations about Delta printers
January 06, 2016 03:49AM
What are the feedbacks on the linear systems using plastic wheels on aluminium profiles? I see that on some commercial 3D printers, but I wonder if it provides good long term accuracy...

It is a very simple design, and very cheap compared to rods/ball bushing.


Frédéric
Re: Basic considerations about Delta printers
January 06, 2016 03:58AM
Quote
fma
What are the feedbacks on the linear systems using plastic wheels on aluminium profiles? I see that on some commercial 3D printers, but I wonder if it provides good long term accuracy...

It is a very simple design, and very cheap compared to rods/ball bushing.

I have only even used Delrin wheels on aluminium profiles, and they work well for me. I have seen problem reports form people with kits that came with cheap shower door rollers instead of the Delrin ones.I guess linear rails are theoretically better if they are of sufficient quality.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Basic considerations about Delta printers
January 06, 2016 04:01AM
Quote
hercek
Place the equidistant diagonal rod as far away from each other as possible.

I don't fully agree with that. Wider rod distance also leads to a longer lever for any play or wobble in the carrier trucks.
I'd suggest using wider aluminum extrusions ( eg 4020) and wider linear rails before you start thinking about wider rod distance.

Only my two cent
-Olaf
fma
Re: Basic considerations about Delta printers
January 06, 2016 04:09AM
Thanks, DC42; I'll dig that solution...

O_lampe, I plan to use 40x20 aluminium extrusion as vertical arms, and put the rods on each side of the 40mm lenght. So, I will have more than 80mm between rods...


Frédéric
fma
Re: Basic considerations about Delta printers
January 06, 2016 04:33AM
And what about such solution:

[www.motedis.fr]


Frédéric
Re: Basic considerations about Delta printers
January 06, 2016 04:37AM
Quote
o_lampe
Quote
hercek
Place the equidistant diagonal rod as far away from each other as possible.

I don't fully agree with that. Wider rod distance also leads to a longer lever for any play or wobble in the carrier trucks.
-Olaf

And I don't fully agree with that either. The longer lever at the carriage end is compensated by the longer lever at the effector end. A wobble of a given angle at the carriage will lead to exactly the same angular wobble at the effector, no matter what rod spacing you use. However, I agree that if you do have carriage wobble about a vertical axis when using wheeled carriages, using wider extrusion will reduce it.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
fma
Re: Basic considerations about Delta printers
January 06, 2016 04:37AM
Quote
dc42
I have only even used Delrin wheels on aluminium profiles, and they work well for me.

Like these?

[www.think3dprint3d.com]


Frédéric
Re: Basic considerations about Delta printers
January 06, 2016 04:45AM
Quote
fma
Quote
dc42
I have only even used Delrin wheels on aluminium profiles, and they work well for me.

Like these?

[www.think3dprint3d.com]

Yes, those are the ones I use, originally on 1515 Mitsumi extrusion, now on 2020 Motedis I-profile extrusion. They might be too narrow to work with other types of 2020 extrusion if the slot is wider than on mine (5.25mm).



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
fma
Re: Basic considerations about Delta printers
January 06, 2016 04:54AM
Thanks!


Frédéric
fma
Re: Basic considerations about Delta printers
January 06, 2016 05:28AM
Quote
hercek
[...]If you are very advantageous then go for about Ø 1.5 mm steel cable. But in this case you need big diameter drums to minimize impact of the errors because of varying position on drum. And that means you probably need a speed reduction from stepper to the drum.

What accuracy do we need on the axis?


Frédéric
Re: Basic considerations about Delta printers
January 06, 2016 12:30PM
Quote
dc42
Quote
o_lampe
Quote
hercek
Place the equidistant diagonal rod as far away from each other as possible.

I don't fully agree with that. Wider rod distance also leads to a longer lever for any play or wobble in the carrier trucks.
-Olaf

And I don't fully agree with that either. The longer lever at the carriage end is compensated by the longer lever at the effector end. A wobble of a given angle at the carriage will lead to exactly the same angular wobble at the effector, no matter what rod spacing you use. However, I agree that if you do have carriage wobble about a vertical axis when using wheeled carriages, using wider extrusion will reduce it.

Everybody has his own opinion. But did you notice fma wants eventually to place a spindle on the platform? That means there will be significant forces trying to tilt the carriage. If these forces are compensated by bigger lever then it means less loading on the ball joint and the rods/joints do not need to be that strong. Also if the rod end have a small bit of play then the play will be less significant if the diagonal rods are spaced more far away.

I say put them as far away as your platform allows. Your platform will be on the bigger side if you want to fit some spindle there. It may not be wise to increase platform size just to increase the diagonal rod distance. But to be sure you need to compute what the forces will be. My guess is that a Ø 7 mm plastic ball angle joint will handle about 40N. The distance between rods will tell you whether you can stay with plastic (rods far away) or you need to go for POS 5 (rods near to each other).

On the other end, it will not help him much if he plans to mount it at only 4 cm wide aluminium extrusion on simple rollers. Fma, just make sure your rollers have high quality bearings which do not have any noticeable play and ... heh ... maybe delrin will be stiff enough. I would go with either Ø16 mm smooth rod with good quality linear bearings (not a Chinese cheap crap which has play around 0.1 mm) or good linear guides (the specification for the linear guide will tell you what forces it can withstand and under what errors). I would go with thick linear rods (they are cheaper in my location). But I wish you will go with simple delrin rollers smiling smiley Let us know how it behaves when you put a spindle on the platform and try some soft wood or a PCB!

Edited 1 time(s). Last edit at 01/06/2016 12:31PM by hercek.
Re: Basic considerations about Delta printers
January 06, 2016 12:36PM
Quote
fma
Quote
hercek
[...]If you are very advantageous then go for about Ø 1.5 mm steel cable. But in this case you need big diameter drums to minimize impact of the errors because of varying position on drum. And that means you probably need a speed reduction from stepper to the drum.
What accuracy do we need on the axis?
Put it about the same as your desired accuracy at the hotend tip. I would go for step size of 0.02 mm or smaller.
fma
Re: Basic considerations about Delta printers
January 07, 2016 04:58AM
Quote
fma
Like these?

[www.think3dprint3d.com]

Are these profiles better, in combination with the above wheels?

[www.watterott.com]


Frédéric
Re: Basic considerations about Delta printers
January 07, 2016 05:25AM
Quote
fma
Quote
fma
Like these?

[www.think3dprint3d.com]

Are these profiles better, in combination with the above wheels?

[www.watterott.com]

Those profiles look to be the Same as the open builds ones so yes they should be ok but the Openbuilds ones may be better suited Openbuilds Mini V-Wheel and from your same supplier V-Wheel

I use this combination on My large Delta using 4 wheels per carriage of which 2 use the Eccentric spacers to allow for adjustment all mounted to a custom designed Printed plate that takes the wheels and is drilled with 4 holes to take std Kossel carriers.

HTH

Doug
fma
Re: Basic considerations about Delta printers
January 07, 2016 06:09AM
Compared to the standard profiles, like 2020 Motedis I-profile, is Openbuilds profile better? It has maybe a better contact whith the wheel?

BTW, I also plan to use excentrics...


Frédéric
Re: Basic considerations about Delta printers
January 07, 2016 10:48AM
Quote
fma
Compared to the standard profiles, like 2020 Motedis I-profile, is Openbuilds profile better? It has maybe a better contact whith the wheel?

BTW, I also plan to use excentrics...

If using Delrin Vee Wheels then yes the Openbuilds style is much better as it has a true Vee in it which the Wheels can roll on nicely (It reduces any lateral play and I think will also increase the lifespan of them)

Doug
fma
Re: Basic considerations about Delta printers
January 07, 2016 11:11AM
Ok!


Frédéric
Re: Basic considerations about Delta printers
January 07, 2016 11:56AM
Attached are my Design files and STL file for my Openbuilds Slider Cariages



openbuildslider.FCStd
openbuildslider.stl


HTH

Doug
fma
Re: Basic considerations about Delta printers
January 07, 2016 12:05PM
Thanks for sharing!


Frédéric
fma
Re: Basic considerations about Delta printers
January 10, 2016 04:12AM
Is the FSR (Force Sensor Resistor) under the bed a good solution for bed leveling (and printer calibration)? What are the pros/cons?

I like the fact that this is the hotend itself which is used to touch the bed, instead of an external switch/optical/inductive/capacitive/whatever sensor, introducing error... No more problems when chnaging nozzle, or when you just remove the hotend after jamming or so.


Frédéric
Re: Basic considerations about Delta printers
January 11, 2016 04:15AM
The nozzle has to be clean, before you use the FSR-leveling method. Any little drop of hardened filament will spoil the result. ( Easy fix is to heat up the nozzle, before you start ABL)
-Olaf
fma
Re: Basic considerations about Delta printers
January 11, 2016 04:21AM
Yes, sure. But is it a reliable method? Or does it introduce some issues?


Frédéric
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