Is having 4 bed leveling adjustment points rather than 3 problematic?

Question

My Ender 3, and I think lots of printers, have 4 bed leveling adjusstments, one at each corner. It seems to me that having 4 points produces an over-determined system, making it confusing to get the leveling right - adjusting one of the four may have little or no effect, but then cause a later adjustment elsewhere to have effects that violate a least-surprise principle.

Would it be better to have only three points? Or is the fourth necessary/useful with non-completely-rigid bed structures to add rigidity?

@КонстантинВан: Three points determine a plane. Four points, unless you ensure the fourth one is on the plane determined by the first three, determine a warping of the plane into a saddle-shaped object. — R.. GitHub STOP HELPING ICE, Apr 02 '23 at 01:49

0scar · Answer 1 · 2023-04-01T13:46:42.093

4

Similar reasoning as for question "3 vs 4 bearings for y axis travel"" holds. If you introduce a fourth point, it is more difficult to make a flat plane.

Provided that your bed is stiff, e.g. a flat piece of glass, or a thick metal plate is used, you do not need more than 3 screws. Both my custom built printers use pieces of glass on aluminium heated beds that use three screws for levelling, the third screw is located in the middle of 2 corner points.

If your bed is thin (e.g. thin heated bed with tape, so no glass) and flexible or warped, an extra screw might be handy to deform the bed to a more flat plane, but it is more difficult to level.

edited Apr 01 '23 at 13:46

answered Jun 28 '19 at 15:38

0scar

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I'm in agreement with 0scar. I have a monoprice mini IIIP with a four point "leveling" system. I've added a piece of glass atop a silicone thermal transfer pad. The four-point system warps the thin aluminum bed very badly. I've since drilled a hole in the front to create a three-point level. No more bed warping! – fred_dot_u Jun 28 '19 at 18:13

Константин Ван · Answer 2 · 2023-04-01T16:23:18.387

Synchronization failure when having more than three points in an axis

If the movements of those points for an axis are perfectly synchronized, there shouldn’t be a problem. However, in the physical world, inertia and elasticity come into play and hinder synchronization of such points. One of the points could move earlier than the others if they are not properly synchronized. In a 4-points-for-an-axis system, that means bending.

I guess that’s why printers that have a 4-point Z axis usually have a dedicated motor for each point to synchronize electronically, rather than trying to synchronizing them with a single motor and a timing belt.

Despite the difficulty in synchronization, having 4 points for an axis has an advantage over having three: it adds rigidity.

Is having 4 bed leveling adjustment points rather than 3 problematic?

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