Burn marks along z-axis

[Nash]

Hello Maslow Community,

This my first post. I just finished to mount my Maslow a few weeks ago and started to print a few objects. I am really happy with the outputs but I have a recurring issue:

• Along the z-axis (and also where tabs are created) the plywood gets burn marks,
• The shape gets a bump/dents everywhere the z-axis moves.

Here a few pictures of a printed wheel (which should be a perfect circle):

Anyone getting the same issue ?

Could it be:

1. Router shaking?
2. Wrong calibration?
3. Wrong spindle rotation (currently CW direction)?
4. Normal, I’m just being too picky…

[Gero]

Are you on the lowest RPM with the router and highest feedrate for Z in the g-code?
Is it an up-cut bit?

[MeticulousMaynard]

I see that kind of burning frequently on Z moves. The tool is rubbing on the material from too high of a spindle RPM for too low of a feedrate. That rubbing is also going to overheat and subsequently dull your tool. @Gero’s suggestions are the best way to mitigate the issue. Not sure what style of cutter you’re using, but another way to help reduce this issue is to lower your flute count. I tend to use single flute tooling when possible for that reason.

If your primary concern is the burn marks on your part, you can use a lead-in and lead-out on your tool-paths:

This keep that dark spot away from the edge of the part, in the scrap area. Not sure what CAM you’re using but I’m sure most programs have that ability.

[Dag83]

I found that using triangular tabs mostly solves this problem.

[Gero]

What are the General Machining Strategies used in CNC Programming

Old, but not only 3.1.3 is interesting. Ramping could help if your cam software can do it.

[Nash]

Thanks you all. I’ll experiment with triangular tabs and ramping in the following weeks and post my feedback. I’m using FreeCAD at the moment and I’m not sure it can create lead-in/lead-out path.

[Gero]

I’m using FreeCAD at the moment and I’m not sure it can create lead-in/lead-out path

You seem to have all options mentioned above (v0.17). I haven’t tested them though.
The ‘RampEntry Dress-up’ look promising on the screen.

Double-clicking on the ramp operation and changing settings there did not work for me, but changing angle and method in the Property panel seems to work.

A trapezoid holding tab is achieved by changing the angle in the Holding Tags Dress-up.

[UNUS_TRESQUATRO]

Greetings! I also ran into this problem along the z axis, but not only, as in the photo you can see that the black stripes are venerated when the machine moves on the other axis, the machine jerks visually, because of this there are black serifs, who faced this? Why does the router twitch and leave black lines?

[Gero]

Can not tell you what it is, but perhaps give some hints, where to look.

• CAD/CAM
  Check your software if you have allot of ‘segments’ that make this curves/‘splines’.
  Depending on your software you might have an option to increase the size that a curve is segmented to, to get a lower amount of segments.
  

  
  
  I could imagine that if you have hundreds of segments (-> puts in g-code to thousands of lines), the software stops for a millisecond with each line. This will increase if you have a lot of “large radius are replaced by straight line to improve accuracy” in the log file.
  If you have a chance, replace splines with arcs. They run smother.

• Do a test if you get better results with ->climb or with -> Conventional cutting https://www.youtube.com/watch?v=meBT2758pik

• You router speed could be to high for your feed-rate. Lower RPM and increase the feed.

• After this hours of running and the heat that the bit went through (if it was the same bit), I would retire it. It’s likely very dull.

Just a few thoughts.
Regards, Gero

[gersus]

I’m new to this but maybe your sled isn’t sliding smoothly along your substrate?