BL(3D) touch woes... Any ideas?

Veti · 13 Nov 2018, 09:27

i bought and tested one of those clones and found them to be far to inaccurate. (+/- 0.05mm)

what i did in the end is build a BFPTouch from thingiverse. It uses an optical endstop and is far more accurate. Marlins M48 gave me a SD of 0.002. It is not susceptible to heating being on compared to the bltouch.

Mangy_Dog · 13 Nov 2018, 09:46

Thanks for the trouble shoot... But I think I have all points covered. It did give me th link to buy genuine a BL touch, so ordered one...

As for the hump... Yeah maybe the gantry is sagging not sure what to do about it. I honestly thought 2 10mm hardened steel with spaced out bearings would stop any sag like that.... Any ideas there?

T3P3Tony · 13 Nov 2018, 18:17

@mangy_dog well, that's also what the mesh bed compensation is there to some extent. Once you have the BL touch working repeatability then try the printer with the compensation.

Phaedrux · 13 Nov 2018, 18:28

Have you tried printing a first layer calibration print to see if the bulge is actually there or not?

0_1542133661353_bedlevel_nozzle_0.4_200x200-0.3-0.8.stl

If you print that scaled to your bed size first without compensation active, and then again with it on you should be able to tell if the heightmap is correct or not.

bot · 13 Nov 2018, 19:17

Approximately how much does the gantry weigh? Including the bearings, the carriage, hotend, etc. excluding the rails?

Mangy_Dog · 14 Nov 2018, 09:58

@bot I don't know, but It has 2 mini turbo fans, 4030 I think... A chimera with volcano blocks. A small but not pancake stepper for direct drive extrusion, a titan like setup (custom design) and the BL touch. 4 ln10uu ball bearings and a slightly wide design thanks to the fans layout. All printed in cf petg.

Honestly wouldn't have thought that be enough to make the gantry sag.

The span is 500mm..... Maybe that is just enough to make this sag.

Oh and the sag is real. Did a paper grip test and the hot end pinched the paper very tightly in that jumped area

Phaedrux · 14 Nov 2018, 16:51

@mangy_dog Sometimes the sag can also be a result of the rods getting bent during a head crash.

bot · 14 Nov 2018, 17:19

@mangy_dog I did some quick and dirty FEA in fusion 360, and I was able to elicit 100 microns of displacement with 2 kg on one pair of rails. Steel rails with ABS plastic mounts, over a ~500 mm span

Stack two of these on top of each other, and I could understand the displacement you're seeing in reality.

Phaedrux · 14 Nov 2018, 17:49

Have you done a test print with mesh compensation active? It should have no problem taking care of the distortion.

Kenny66 · 15 Nov 2018, 01:10

From the mesh image it looks like it's bowing UP not down.
What do you have on top of the cast aluminum bed?
My guess is your bed sheet is flexed either from the binder clips or from natural flex when it's heated and being held at the corners.

Truth be told though I wouldn't worry about it. The bed mesh will compensate for that and your mean error is < 0.1mm. I wish mine was that close.

I am also having the same issue that the probe doesn't always deploy when doing a G30 S-1. Mine does complete a bed mesh with no issues though.

phantomix · 15 Nov 2018, 11:11

@kenny66 said in BL(3D) touch woes... Any ideas?:

From the mesh image it looks like it's bowing UP not down.

Exactly. When the X axis bows down, the probe will trigger earlier which results in an elevated point
I would have expected a more "cylindrical" shape of the probing result, though.

Edit: As it seems to be a CoreXY, there would be bowing on the X and on the Y axis, which explains the result.

Kenny66 · 15 Nov 2018, 17:54

Could always take the bed sheet off and probe the aluminum directly and see what you get.

Mangy_Dog · 16 Nov 2018, 01:27

Hi all sorry for not replying sooner, the probing is direct on the 6mm thick cast aluminium. The machine is still in early testing and as such the beds not even been heated up... I've not even fitted the heat matt yet

Yeah its core xy, and the rods are alined vertically, with a 6cm space and 6cm separation of 4 bearings, I has thought that the spread load would negate downward stress.

Anyway, I'm now designing a rail xy that I will fit, replacing the rods... The y will be a 12mm rail bolted to 2020 aluminium. If that ends up sagging I'll cry.... A lot...

Using mesh compensation might correct the hump to some degree, but I would still know it's off. And it would never be perfect...

My print carriage I'm certain is under 2kg, heck I think it's under 1... It didn't feel as heavy as a bag of sugar...