Size/position changes when using weld or union functions

Hi guys, I’ve searched the forums and can’t find any reference to this issue at all so apologies if this is a known bug/feature!

I’ve noticed over the past year, when working on my designs, the dimensions have changed by maybe a few thousanths of a milemetre. Not a massive big deal but as I’m combining multiple shapes, these add up and I find that shapes that should have the same width can end up slightly different sizes over time which can make prototyping diffucult.

I can reproduce this. Take a 30x30mm square and a circle of diameter 30mm. Copy the circle and align both to either ends of the square. Select the left circle and the square. Width = 45 which is correct!


Join the two using union weld or boolean union (as there are only two shapes it shouldn’t matter)


Great - Width still equals 45mm as expected!

Now select the right hand circle as well and perform another join (we’re expecting 60mm right?): -

So it’s moved the shape and re-sized it along the x-axis!

Another example: -



Another quirk for this if you press undo and do the same thing, it either works correctly or distorts the dimension the other way (increasing the width rather than decreasing).

Seems minor but when you have a lot of parts and you are trying to align them exactly it can get a but tricky when all your shapes have “weird” dimensions of fractions of mm out!

I can confirm that there is a small glitch. For me it is 0.005 mm.

Okay, found a workaround for now (just by experimentation). If I draw the shape with a vertical orientation and join the shapes in a very specific order (in this case, bottom then top - yes, the other way around didn’t work!), then I can create the shape with the dimensions preserved (and can then simply rotate 90 degrees).

Still weird though, would be nice to get this fixed, I’ve been going through all my files and most of them have quirky measurements due to joins!

It’s pretty fancy.
Respect for your intermediate solution.

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