There are a lot of 'chatter' marks in your machining.

I think you need to thoroughly check the rigidity of your machine (all axes) because something is just not right there.

My first thing to look for would be backlash / slack in the Z axis ( thrust bearing, spindle motor, etc.)

Tweakie.

Tweakie.CNC,

Thank you I will go back and check the things you are recommending. 

Steve

Ok, here are the things I did today.  Again my machine in a Legacy CNC Woodworking Arty 18" x 36"

•   Leveled the table to within .0013” over the X travel  36”
•   Leveled the table to within .0021 over the y travel  18”
•   Measured the machine travel against the actual travel for X,Y and Z
     o        X was out ?  Forgot to write it down
     o        Y was out .0529” short
     o        Z was out .0124”
   
Used the Program in Mach 3 Advanced Settings Axis Calibration to change Motor stepper values (used my 6” digital caliper clamped to bed”)  to measure travel.  Did this multiple times to get closest measures I could.

•   X Used  6” travel on digital caliper and now within .0005
•   Y Used  6” travel on digital caliper and now within .0005
•   Z Used  5” travel on digital caliper and now within .0005
•   Went over all the gears, rail teeth, motor gears to check for slop
     o        Adjusted Y rail teeth to tighten
     o        X was good
     o        Z -  I found there is .0035” slop in the Screw and Nut that moves the router up and down for the Z travel

   This is the only thing I could not adjust as I assume it is wear
   What is the tolerance on this?
   Do I need to replace these two parts (see pictures attached)

So after all of this, hours of course later I ran part of a program to V Carve the word David that is part of one of my projects I need to get done.  I would say it IS better.  Please look at the pictures, particularly the top and beginning of the D and the tops of the V and I.  These points are still not good, better but not good enough. 

Could my slop of .0035”  in the Z travel in my screw and nut cause this?  I am probably not using the right parts names, so I have also included pictures of this.

Making some progress but still not perfect.   

Thanks, Steve Hasebroock

Hi Steve,

That machining certainly looks like a great improvement on your earlier example. I think you are heading in the right direction.

A Z axis backlash of 0.0035" is not bad but V-Carving can place a lot of loading on the cutter so the whole machine really does need to be rigid. Have you tried taking a second pass at the work (same settings) ?

Tweakie.

Hi Tweakie,

I agree making good progress.  I wrote to  the manufacturer on the Z axis backlash, eager to see what they say.

I have not tried a double cut.  Will try that in the next couple of days.  Today and tomorrow are real busy so may not get to the machine before Wednesday. 

I have learned a lot about CNC fine tuning. 

Will report back

Thank you, Steve

I have my problem fixed. Fortunately the Manufacturer Legacy CNC Machine called me and signed into my machine and could see pictures of the problems.

He walked me through procedures to adjust out backlash on my X and Y axis. This machine has Rack and Pinion X and Y.

On Z I have about .0035 backlash, but he didn't think that would be my problem. My Z is nut and screw type, don't know what the right terminology is for that.

He also had me flatten a board on x travel and then another board on y travel. We were both very happy with the tram results. Never perfect, but really good and also decided this was NOT my problem.

Last after this I had good improvement, but still some problems in the quality of letters. Then found that the one 60 degree bit I was using performed great when set at 65 degree and the other when set at 67 degrees. Interesting as I ran the program suggested by CNCNutz and I would say that test showed by bits close to 60 degrees. Interesting!

Thanks to everyone that had input and ideas.

Steve

Definitely mechanical.  My take on it: if it looks good, it is good.  If you don't like the way it looks, then take steps to fix it.  If you are able, get new parts for your z axis and replace them.  The other thing you could do is adjust down your velocity and acceleration.  If these two settings are too high, they will exacerbate your machine slop.  What are your speed and velocity settings?

A couple of things to consider:
1. Z backlash  - look at the code and see how deep the V is going into the material.
    Then calc what .004" difference would make in the radius of the cut.  You have what
     you have, so live with it or fix it.
2. Material - different material will machine different so don't expect perfect results
    from an inferior  material.
3. Spindle runout - yes you have some, just a matter of degree and depending on movement
    adds some to the problem.
4. Setup and how you define the machining also affect the final results

V carve probably provides for the proper movements in the code and Mach will implement
the code properly. If you want to have near perfect lettering  your machines system must be capable of producing it and setup properly. It's that simple.
RICH