# Which resolution is necessary to print bricks with a 3D printer?

I would like to print LEGO compatible figures. Which resolution is required for the 3D print in order to firmly fix the figures on LEGO bricks?

• Let me guess... the minimum resolution that allows 0.1 LDU accuracy? (Since there are 1 LDU offsets and also 0.3 LDU offsets) in the world of LEGO? May 15, 2013 at 15:53
• Producing affordable 10 micron 3d printers remains the single greatest engineering challenge of the last hundred years. ;) Aug 4, 2017 at 7:14
• This sounds like something that would best be achieved with a resin printer. Layer height can approach the tolerances required. May 11, 2022 at 9:15

In the manufacture of LEGO bricks the machine tolerance is as small as 10 my (0.01 mm).

For me, 3D printing resolution would need to be pretty close to that.

• Most are not. Most are 100 micrometers. Would it be sufficient? May 16, 2013 at 14:15
• The tolerance is given in the question. A child must be able to connect the bricks and they must not fall off. Which resolution is needed to achieve this? May 16, 2013 at 14:25
• Goven that all teh dimensions in en.wikipedia.org/wiki/File:Lego_dimensions.svg are in 100 micrometer increments, in theory I'd say 'yes'. In practice, I'd want to try it out on a borrowed printer before sinking large sums of money into it.
– gev
May 16, 2013 at 18:14
• I don't understand the question. TLG have done tons of research on this, and they are a business so they don't want to be wasting money. So if they settled for the tolerance of 10 micrometers, then a tolerance of 100 micrometers is obviously not enough. Simple as that. May 17, 2013 at 11:19
• @RegDwight Not as simple as that, since we're talking about commercial production vs DIY. Lego (and any other manufacturer of anything) can't afford to check each piece by hand, so their tolerances need to be much smaller than those of someone printing a couple of bricks at home. Even at 100 bricks a day, that would still allow you to check each brick and recycle any bad ones.
– SQB
Feb 23, 2014 at 20:22

According to WikiPedia:

The moulds are permitted a tolerance of up to two micrometres, to ensure the bricks remain connected.

But, as I noted in a comment, that is in an industrial environment, where great care is taken to ensure that not just a one-off piece is right, but that the entire batch of pieces is right. They probably take a six sigma approach or something similar.
In a DIY setting, that is not necessary. A certain percentage of faulty pieces can be tolerated, as a home manufacturer probably has the time to check each piece and recycle the faulty ones.

The image above shows the main dimensions of Lego pieces. Based on its source and the measurements given in this answer, we get 8.0mm per 20 LDU, or 0.4mm/LDU.

Since the smallest offset seen so far is 0.3 LDU, you would need at least a 0.12mm resolution to print that brick. But if you're printing pieces with a resolution of 1 LDU, you'd need a printer with at least a 1 LDU resolution.

So it depends on the resolution of the pieces you want to print.

I have actually tried 3d printing lego on a prusa i3 printer at I think 5 microns using PLA. I found that they worked fine initially but they quickly started to lose their grip. I think the issue was the layers grind against each other which wears them down rather than the brick walls flexing to grip. You certainly won't be getting anything close to the quality of real lego but you could print some cool custom parts.

Here is a picture of the finished result of one of my brick prints: