The 'ol LR Core rubbing on Braces Issue

Hi all.

I have my LR3 up and running (mostly).

I initially had issues with the LR Core rubbing against the braces, and this was fixed by loosening off the bearing nuts as suggested in the doco, however, the rub is back.

At the top of the LR core, there is a nice amount of clearance, not so much on the lower.

I’ve read some posts already and have checked the various related items with calipers i.e. the tubes are 25.4mm (well, about 25.49mm-ish), the braces I printed are the 25.4mm ones, and the bearings are dead on 22mm.

All printed on a Prusa MK3S+ 0.6mm nozzle. Last time I printed a calibration cube, it was all pretty spot on for accuracy.

I’ve also tried a variety of combinations of loosening and tightening the bearing bolts at both the top and bottom or the LR core.

Any other suggestions/tips/help?

Unfortunately the last time we saw this I believe it was a printer that was crooked. So instead of printing a square it printed slight parallelograms.

A test cube is too small to test very well but any large square model that you can print to take up most of your bed. Then measure the diagonals. They need to be fairly equal. If not your braces or even your core could be significantly under/oversized.

Hey, that’s my cue: Der Froschkönig - Lowrider 3 in Oldenburg, Germany - #181 by Tokoloshe

You can find all about it here. It’s quite a lot to read, but looking at the pictures is enough. :smile:

Judging by your pictures, the top is also rubbing against the strut plates sightly (you can see colour on the edge being slightly rubbed off). Was the same with mine. Top rubbing slightly, bottom not fitting.

Thank you, Ryan and Philipp,

I had a think about the situation; the Core “used” to be OK and was now not, so I think the issue was not so much a square printer, but perhaps the material I printed with (PLA) and where the LR is located.

My LR3 is in a Shed, and gets direct sunlight (through “laserlite”, brand name sorry, but I’ve always known it as this).

My theory is this:

On hot days, the PLA is getting warm enough to become more “elastic” and over time with the weight of the router attached to it, the Core has distorted causing the bottom to move and eventually rub against the braces.

Whilst waiting for your replies, I printed a new LR Core using PETG and 50% infill (21 hours later…) and “hey presto”… seems OK now;

(Had to print in black, I ran out of Red PETG)

To quote a site resulting from a Google search of “PLA vs PETG”:

“PETG is best known for its durability and strength, and the plastic is resistant to high temperatures, UV rays, water, chemical solvents, and more. All of this makes PETG an ideal filament material option for printing parts that will exist in harsh environments or have to undergo a lot of physical stress.”

Sounds like what I need.

I’ll give this new Core a try and see how it goes.

Again, thanks for the support and tips!

Oh, and Ryan, I’ve enjoyed the heck out of building this machine, thanks for sharing.


I printed mine in petg. vastly superior imo. it does have flex unless you bump up the infill.

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Have you tested that? At what point are they equal?

I was pretty sure with the already high infill we use in PLA there was no equivalent rigidity breakeven point in PETG.

So I printed everything with PETG at the exact infill you specified, however, if I had to do it again i would up the infill on:

  1. y drive and z drive
  2. braces (from 30 to 50 as there was some torsion possible although I did LOVE the flex in making it super easy to clamp down to the rods)
  3. xz leadscrew stub… i did mine at 90% vs 70%