Does parallelity of arms matter?

Built my dual extruder delta machine recently and had a couple successful print and a few bad ones.

While trying to calibrate it as perfectly as I can, I noticed that the "parallel" arms of my delta are not really parallel. The distance of the joints at effector is around 0.5 - 1mm wider than the joints at the carriages.

Is this something that absolutely needs to be corrected?

The problem is that I see no good way of fine tuning the distances, the way the diagonal rods are mounted means the only "adjustment" I can make is to add washers, which is not really adjustable at all... Also as I only need less than 1mm increase of the width, which means I may only be able to add washer at one of the mounts, making it unsymmetrical, which I'm not sure may cause even bigger problem or not.

Yes.

Post your design and someone may be able to determine a solution.

You can buy shims, which are thinner than washers and so provide a finer level of adjustment of bearing spacing.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Alternatively you can print your own shims. That's what I did to customise the thickness for each pair of arms.

Or CAD up and print a new effector with the right spacing or a bit less that you could pad out with washers, much easier than printing or buying shims

I realised that the error is due to the mount screw holes have too much play, after loosen the screws all the mounts can move around a little bit.

Then I had a calliper set to correct width and use it as a guide to limit the mount movement before securing all the screws again.