Magnetic ball joint seat geometry... May the force be with you!

First I'd like to give due credits to Kees Koese who started with the idea of the magnetic ball joint and made the original design of the effector plate. Give his website a visit to have a look at his multispindle drilling machines. Technicians will like it :)

This post is a how and why about the geometry of the ball seat in the effector plate. Since the original effector plate was made with SLS printing we wanted to be able to print this with FDM printing (both being entirely different processes).

During the first test prints there was still manual rework needed. I wanted to end up having to do nothing at all regarding removing filaments, grinding etc. I think making geometry only with the printer without having to rework it is why 3D printing can be such a fantastic way to manufacture.

Before going into details I was amazed how rewarding and exciting it is to draw your thought/improvement in your favourite CAD program (mine is SolidWorks) and having it on your desk in 30 minutes... Every engineers dream.

The picture below shows the original geometry Kees drew a few (almost 6) months ago. It depicts the ball seat with the area (cylinder) where the magnet needs to fit. Because of the original being SLS printed there were virtually no limits regarding overhang or printing resolution. Notice the second (bigger and lower) sphere that ensures the ball will fit in the topmost seat.

magnetic ball bearing seat 1

When initially printing this test piece to check if the resulting dimensions were good enough to fit the cylindrical magnet (this situation needs a ∅10.5 mm diameter to result in a snug fit of the ∅10 mm magnet) I had a lot of problems printing because of 2 non-printing areas coming together in mid-air. Also the points where the 2 areas merged were sharp so the filament  kept sticking to the nozzle on it's way back. (a lot of words for saying the result was horrible...)

What to do... Make sure there were no pointy encounters so that meant closing the gap between the seat and the cylinder volume. See below:

magnetic ball bearing seat 2This was not the way to go. The wall thickness was so thin (wall thin-ness) that it could not be closed (and the ugly thin-ness needed to be drilled away manually... bah...). Because the overhang is at a 15 degree angle there is not enough previous layer to adhere to. Improving (but not really) solving) this could be done by adding wall thickness. But alas... Every solution frequently introduces it's own problem... The distance between magnet and ball was getting so big the magnet lost it's force-field on the ball... Thanks for nothing Master Yoda!

There had to be a way to ensure a minimal gap between magnet and ball without the overhang problem and without wall-thinness situation... If you have something you don't want: (re)move it... See below:

magnetic ball bearing seat 3

All that's needed is a defined sphere and a axial constraint preventing the magnet being pulled onto the face of the ball (creating friction when the ball is turning). If you add a partial ceiling coming from the side (instead of bottom or top) of the cylindrical hole then during printing you will see a very gentle alteration of the contour of the non-printing area. Then there is enough support from the previous layer to create the overhang.

Final measurement and test were done with calliper (measuring the distance over Ball and Magnet, subtracting the ball diameter and length of the magnet) and multimeter.

I measured a gap of 0.1 - 0.15 mm and when doing the beeeep testing for I got no beeeep. (measuring short circuit between ball and magnet).

This evening Master Simon helped me taking a picture of the actual force of the ball joint connection. Result: One connection can pull 1690 gram. Take that Master Yoda?

Below some pictures of the test, some prints and last but certainly not least the geometry of the connection.

Pulling water in Sigg bottles. I am holding the blue printed part.

pulling force of magnetic joint

Resulting weight being pulled:

Weight being pulled by magnetic joint

Seat of ball with magnet underneath (view from top):

Seat of magnetic ball joint (top view)Fit of magnet in area under steel ball (view from bottom):

Fit of magnet in area beneath steel ballMisprints being mentioned in this post, next to the result:

MisprintsFinally after having bored you to death the resulting geometry. First the cut-revolve of seat and magnet volume:

magnetic ball bearing geometry section view

Second the cut-extrude at ∅10.5 with a width of 8 mm. Seen from above. This prevents the magnet from getting in contact with the ball. I also added a radius of R1 at the inside of the cylinder making the sliced contour even more printer friendly.

magnetic ball bearing geometry axial stopENJOY !

 

 

 

 

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Magnetic ball joints on our printer

We are proud to show some photo's of our working solution for making very simple ball joints for our printer. A few months ago Kees came up with the idea of using magnets to pull ball joints in a ball seat. We have done some dry runs before but did not print because of the lack of an extruder. Because of us both being busy with our work we did not make as fast progress as we would have liked.

The big plus about this joint is the very limited number of parts that are used for this. You need a base (carriage or effector plate) for the seat, a steel ball (ball from a bearing for example),a strong rare earth magnet and a carbon fibre rod.

Furthermore there is no play because of the magnet pulling the ball in the seat, always in the same direction. Another advantage is the big angle that can be reached.

The making:
The rods were made by drilling a hole in the balls (no accuracy needed for this) and gluing 2 balls on the ends of the carbon fibre rod. The important thing is that all the balls on the rods have the have the same center dimension. By making a simple rig for fixing the balls while the glue sets this is relatively easily done.

The effector plate and the carriages that were made for this printer are made with an SLS machine because we did not have a printer ourselves at the time. I'm positive though that this can be made with the normal FDM printing techniques. That's the next goal for us... Making another effector plate and carriages because one printer is not enough for 2 people.

Below some pictures, enjoy!

ball joint with steel ball and magnet

ball joint with steel ball and magnet

It's alive!

This week I've spent my evenings getting the printer to run. The problem is that I want to print above all other stuff that needs to be done before you should be printing. Things like getting the homing to work (no end switches), a heated bed (we don't have a heated bed), leveling the bottom with respect to the x-y movement. The way to quick results is done in buurman-en-buurman style.

Yesterday I tried to use a big round mirror because I though the multiplex base was not level enough. Also with the mirror I could not get the settings right. When moving in the x-y plane the height from the nozzle should stay at the same height. I measured a difference of 3 mm between the middle (0,0) and the end of the working area... Hmmmmmm... I even thought that the mirror was not level. So I went to the hardware store to get some 15x15 cm mirror tiles... They are level. No doubt about that. But the error was still there. (then I double checked the round mirror, and lo and behold. It's as straight as an arrow).

After some measuring and searching I found that the dimensions of the machine that are needed for making the calculations were off. We used a slightly wrong dimension. After updating the firmware a 7 cm movement of the machine was actually 7cm. Further more all was (reasonable) level. Below some visual proof of the result:

Printing an internal spur gear in layers of 0.10 mm

20130526-000108.jpgThe result when I stopped the printer because the rest would take another hour:

20130525-234728.jpg

A movie of the printer in progress. The ticking you hear is the filament coil bouncing against a column:

The first filament!

Last thursday I worked with Kees on our 3D printer. It was long overdue because I have been busy working... Until wednesday we had a machine that was moving. We could give some commands, and the machine would move to the designated coordinate.

A few weeks back I had ordered an extruder because making one ourselves would take too long. Thursday we connected it to the electronics and after some modifications in the firmware we could see the extruder nozzle heating up, we could see the temperature, and the stepper motor driving the extruder moved. We only lacked filament.

A friend of Kees had an extruder and 3mm PLA material. So with this we could try to extrude. See below the result... Next week we'll get the steps per mm filament correct and I hope we'll be able to print something then more sophisticated. We're nearly there.

20130511-102355.jpg

First 3D printer output

Today Kees brought the 3D printer. After setting the dimensions to the correct sizes and recompiling the firmware it moved! "It's ALIVE!"

Accuracy needs to be improved, I do not have homing switches mounted yet so I guestimated the zero positions.

The first question I got from my kids after seeing the head move op 10 cm (G1 X0 Y0 Z100 F9000) was: "What else does it do?"

I took my bloc note, made a sketch and manually programmed the G-codes (with 2 hyper boys next to me testing the limits of my concentration) to show them what this contraption can do more.

Below is the result. Programmed in 15 minutes (with in-between-tests), printed in approx. 4 seconds...

3D printer besturing

Kees en ik zijn een 3D printer aan het bouwen en hebben de mechanische delen bijna klaar (geleiding, frame, aandrijving).

Ik ben afgelopen zaterdag aan de gang gegaan met de besturing van de 3D printer. Het doel voor mij was om beweging uit één stappenmotor te krijgen. Het is zaterdag wel wat laat geworden.

  • Ik ben begonnen met connectors pakken, draadjes knippen, soldeerbout aan, een stukkie solderen... Voor mekaar!!!
  • Daarna moest de firmware worden gecompileerd (de brains van het kaartje). Dit was met wat zoeken op reprap.org goed te doen...
  • Ook het uitzoeken van software die 3D modellen in plakjes hakt en vertaald naar G-codes (instructietaal zoals ook CNC draai- en freesautomaten worden aangestuurd) was best snel geregeld...
  • Voeding uit een oude adapter was in een mum van tijd gefixed...

Het lukte alleen niet om de motor in beweging te krijgen. Laat op de avond (eigenlijk heel vroeg de volgende morgen) kwam ik erachter dat de voeding die ik gebruikte niet voldoende was. Ik had iets nodig dat 12V kon leveren met een minimale stroom van 5A... Ga dan 's avonds laat nog maar eens in de zak met oude adapters en transformatoren lopen trekken.

Toen ik Pug ging uitlaten zag ik de acculader... effe kijken en.... 5 Ampére... Ajetoo!.

Zondag was het toen binnen 15 minuten geregeld. Alles werkt. en achteraf gezien viel het me 100% mee.

Volgende stap is de 3 assen aansluiten en "kijken wat ie doet..."

3D printer brains

3D printer stepper motor