Mini Kossel arm Lengths

Hi

Im building a mini kossel k800 all Aluminium brackets




I have come to the point where i need to cut my carbon rod to size i am using the 10mm stainless steel balls and grub screw method,
I have read the problem people have had with the system so i ain't using the effector design as intend to install my flex3drive from my i3 to it so in my effector design ive made allowances so can use fishing braid to tie between the effector and carriage so theres no play and effector not falling of at furthest reach point.

I have used several calculators to try and calculate the rod length and several different results the measurements standard says 180mm but thats traxxas rod ends and the pivot point is in the centre, on a magnet sytems is the pivot at the end of the ball as?

ive read 80% rule and as my base is 300mm triangle it means my rod length should be240mm??

also calculations at 214mm and 190mm im so confused

ive asked several times in irc its the final obstacle and spent several days looking through forums and blogs

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The most important rule is the 20 degree rule, that is the angle between the arm and the print surface is never less than 20 degrees, if you want higher stability in print quality then maybe set this value to 22 or 25 degrees, but 20 degrees should be your absolute minimum, call this value A

Start by determining the pitch radius if the carriage and effector ball centers, call them Rc and Re

You also need the radius of the print area Rp, this should be less than Rc-Re

At the lowest point the carriage balls are Rc+Rp-Re apart, we will call this value Rl

This will then give you a MINIMUM length of the arms to equal Rl.cos(A)=L

Once you have your minimum take a look at your build height, you can calculate this by measuring the distance from the bed to the maximum height of the carraige balls centre -Hc and the height from the hot end tip to the effector balls centre He, your maximum full radius print height is now approximately Hc-L-He, if your finding this is more than enough try a new A factor, you can also increase your print height by just increasing the length of the verticals

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You may have a look to this reprap wiki page 'Delta_geometry': [reprap.org]

Yes, the only 'rule' is the minimum angle for a given reachable diameter, you cannot use a percentage of the machine dimension as the position on the articulation relative to clearance diameter varies a lot depending the belts and fans installation.

Compared to 'Kossels', 'Rostock' like machines will have longer arms and larger reachable diameters because belts are within the columns, so proportions and angle while effector is at center cannot be the same.

If you raise the minimum angle, that will give longer arms and the 60° 'standard' angle at center will increase to 63/64° or more.

Some have complained about arms bending/vibrating with longer arms, but longer arms improves print quality and reduce banding.

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Pierre

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The pivot point is at the center of the ball.

ive managed to figure out the arm lengths thankyou very much for your help much appreciative

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Check my rubbish blog for my prusa i3

up and running
[3dimetech.blogspot.co.uk]