Lash – What's the theory behind the numbers?

Hi,

I was having trouble getting my circles to come out of circles. Once I'd rechecked all my steps/mm and sorted out an eccentric X axis pulley, I turned my attention to lash (using Skeinforge Lash plug-in)

I've used a lash calibration object from Thingiverse (Here: [www.thingiverse.com], and also here: [www.thingiverse.com]) and I've now got good results. I'm finding my circles are correct within approx 1 mm (over a diameter of 40mm) but I'd like to try and really tie it down.

The problem I have is that both the lash calibration objects involve quite small measurements. Instead of a 20mm cuboid with hole I'd like to be measuring, say, a 80 mm cuboid so my measuring error isn't so important. However, I don't really understand the theory involved, so can't work out the new lash figures.

The 20mm cuboid calculations require this:
- x-backlash = (measured object width + measured hole width - 30) / 4
(30 is the what the object width and hole width add up to be in a perfectly printed object)

But if I just scale everything up by 4 (80mm cubiod, 40 mm hole in centre) is my new calculation this?:
- x-backlash = (measured object width + measured hole width - 120) / 16
??

It's the "4" and "16" I don’t understand.
- Why was "4" the correct number for the 20mm cuboid?
- Is just scaling up to "16" correct for a 80mm cuboid?

Any illumination would be a great help

Thanks

Pete

Lash would be a constant regardless of object size. So if the circle was supposed to be 20mm in X and was instead 21mm, the lash is 1mm. If the circle was supposed to be 100mm and it is 101mm, there is 1mm lash. It's that simple.

The absolute positively last thing you ever want to do to fix lash is use the skeinforge lash settings. There are almost always hardware causes which can be fixed.

The lash plugin can never make a really good compensation due to the dynamic nature of 3d printing. It is meant more for milling applications.

---

www.Fablicator.com