Small curves are not accurate

[Paul_Langard]

Hello everyone
After succeeding to make the maslow ready to cut, I tried to cut a 18cm circle yesterday,it’s not perfect, it’s slightly skewed (±1.5mm) but i was happy with it!

I started to cut pieces for my first project: making a solar dehydrator, the design is based on the omy solar brother and is basically:

• a box, with a system to generate heat using a mirror and a black surface
• over which you can stack trays. The stacking system uses little round notches.
  
  

I made the design of the trays in inkscape:

And produced the gcode with Krabzcam with those parameters:

• 6mm two spirals compression bit (don’t have smaller for now, the 1/8" are coming later)
• feed rate: 1400mm/min
• plunge rate: 300mm/min
• step down: 3.5mm

the height of the trays is accurate, the width is also accurate

the curves on the short sides are somehow accurate

but those little round curves on the long sides are not

the top of the curve is off centered, i don’t understand how to debug this
I made the path using a circular arc ( the resultinig curve should have a 27mm width, and 6.5mm height, centered)

is this a problem with the diameter of the tool (6mm) being comparable to the height of the curve?

thank you very much all, have a nice day!

[Allen1]

Do you have a picture of the cutout orientation. I’m wondering if maybe some curves in the y direction and some curves are in the x direction - might explain why some are good and some others are not.

So far for me, I found that the Maslow does not do fine adjustments well in a very small area. For instance, if I am cutting box joints and it needs to cut the overcuts in the joints, it struggles.

For instance, when it is cutting this box joint you can see it probably cuts the left side fine because it’s traveling from left to right so it goes down and in to make the cut out and then back up around for the top of the joint, but as it gets to the other side for some reason as it’s coming down to make the other side of the joint it never really pulls back in, maybe this is backlash or slack or something but it’s pretty consistent on most the joints.

[Paul_Langard]

@Allen1

For instance, when it is cutting this box joint you can see it probably cuts the left side fine because it’s traveling from left to right so it goes down and in to make the cut out and then back up around for the top of the joint, but as it gets to the other side for some reason as it’s coming down to make the other side of the joint it never really pulls back in, maybe this is backlash or slack or something but it’s pretty consistent on most the joints.

Hi, thank you for the reply and sorry for the delay in my answer!
The cutout is similar to the svg I shared, all curves are on the same axis. I finally noticed that the top curve is off centered, but the bottom ones are far better… Which really throw me off!

after my first project on this wooden frame, I decided to try concrete anchors, a 4400x3300mm frame, hoping for better results. I used those dimensions in my yaml file, accurate enough to get the maslow ready to cut.
(about -5mm of center point deviation on both bottom anchors)

I ran two test on this new setup:
a 2mm square grid (1x1mm)
3mm router bit, drill operation, 3mm depth target with 3mm step, 1400mm/min feed rate and 300mm/min plunge rate

in the upper left of the board: simply awful

in the center of the board: slightly better but not quite good

a 25mm square
3mm router bit, 1mm depth target with 1mm step
1400mm/min feed rate and 300mm/min plunge rate

accurate, indeed 25mm from corner to corner BUT see those lines…
They are not straight which is a nightmare if you need pieces that are perfectly flush
I will keep investigating on my side, but I would appreciate any input you might provide regarding such issues.
Is this an expected result? Can it do better?

Thank you very much, have a nice weekend you all!