Author Topic: Mini mill kerf  (Read 724 times)

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2169
    • View Profile
Mini mill kerf
« on: November 20, 2017, 07:06:11 PM »
I have the limit switches working in the mini mill and have been able to cut some 20x20 squares with ok results.

Running at 100mm/min it seems to be limited to 0.25 mm per pass on scrap plywood with a good quality 3mm end mill. 50mm/min and 0.50mm cut chatters a lot.

Also have a plunge drill working with ok accuracy. Added code to the svg file parsing that detects small, less than 8.0mm circles, and turns them into drill operations. Because the mill collets are limited in size I will drill with 3mm bit and bore to size on manual drill press.

The spindle motor is quite weak (along with everything else being marginally crap) so I don't expect to be able to cut any type of metal but am thinking it could make nice picture frames for mirror etchings.

Questions:
   1. What tools are available for compensating for tool width (kerf)?
   2. What is the notation/procedure for setting the Z axis on a tool change.
   3. I use openscad for all my 3d design work and generate stl files for 3d printing. Looking for a utility
       that would take a stl file and slice it into a number of 2d files with user selected layer depth.
   4. What is the proper syntax and units for grbl dwell. I want to pause on every Z change.
SARCASM - Just one more service we offer here.

Administrator

  • Administrator
  • Hero Member
  • *****
  • Posts: 2742
  • Administrator
    • View Profile
Re: Mini mill kerf
« Reply #1 on: November 20, 2017, 08:24:03 PM »
George,

1. I know of no tools that will help you with this. Perhaps someone else knows of something and will jump in here.

2. I can't recall off the top of my head, but if you google g-code for cnc machines, it will list the g-code words for that. They are pretty common (although I can't recall myself at the moment).

Admin -- Ralph -- support @ BenCutLaser dot us
https://www.dropbox.com/s/qv1qee2vb65785t/SetupBenCutLaser3.2a.zip?dl=0
BCL Paid license: $49.95
via Paypal to bclpp@primemail.com

wild.bill

  • Sr. Member
  • ****
  • Posts: 474
  • Hey Laser Lips, Your mother was a snowblower
    • View Profile
Re: Mini mill kerf
« Reply #2 on: November 20, 2017, 09:10:18 PM »
I use a different mind set for working with the CNC - so here are a couple comments.

I have used OpenSCAD to design 2.5D parts that I have milled. It has lots of commends for 2D designs and when I have the part designed I use EXPORT to save a DXF or SVG files.

I then use Estlcam to create the actual Gcode. I select the mill that I am using and the data includes the diameter of the mill. There I select the speed that I want the spindle to move at and also how deep per pass I want, and you set the total depth to be cut. For Kerf - when you make a cut you need to tell the program if its a part or a hole that you are cutting. If its a hole the cut is offset the diameter of the mill inside of the cut so that actual cutting surface is traveling along the defined line, eg you end up with a hole the proper size.

If you say its a part the same happens in reverse and the cut is on the outside of the line so the outside of the part is the proper size.

The only time I touch stl files is for making 3D cuts with the CNC and again Estlcam will generate a Gcode file from the stl file and again you define speed and depth per cut.

So the short answer is look at Estlcam or something like it. My memory is that you use unix and I use windows for my control machines. Hope my rambling help at least a little.
Laser: was an A3 2.0w TTL L6 Z axis now 2'x3'
          OpenBuilds ACRO 510 w/ 2.0W TTL laser Cohesion Mini Z axis Homing switches
          K40 Cohesion Mini 60W LightObject LPS
          80W Red-Black 500x700

cool is simply a subjective state of mind

Lob0426

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1624
  • Let the Magic Blue Smoke out!
    • View Profile
    • Richards RasPi Web Server
Re: Mini mill kerf
« Reply #3 on: November 20, 2017, 10:10:12 PM »
The most common codes for tool diameter compensation are;
G40 tool compensation off
G41 tool compensation left
G42 tool compensation right

http://cnc-programming-tips.blogspot.com/2014/12/g40-g41-and-g42-cuttercompensation.html

Grbl does not support those gcodes. So the program has to take it into account.

Edit: G40 tool/cutter compensation off is supported by grbl. G41 and G42 are not supported.
« Last Edit: November 20, 2017, 10:16:31 PM by Lob0426 »
Richard
A5 2.5W w/homing switches on L7
A5 2W diode self upgraded from stock 500mw
Printrbot Play. Ext bed, integrated tablet control.
Printrbot Simple Metal
USA

Zax

  • T2Laser
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5868
    • View Profile
    • T2Laser
Re: Mini mill kerf
« Reply #4 on: November 21, 2017, 04:29:19 AM »
I have several CNC machines but have never used tool compensation on the equipment. I prefer to do it in software and have been using TurboCAD/CAM for years but as their upgrades get increasingly expensive I started looking at alternatives. Estlcam is a cheap solution although the user interface is a little awkward for me.

You can offset manually in most CAD programs, so technically you can create the same yourself but it's much easier to use a CAM program.

Lob0426

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1624
  • Let the Magic Blue Smoke out!
    • View Profile
    • Richards RasPi Web Server
Re: Mini mill kerf
« Reply #5 on: November 21, 2017, 10:04:45 AM »
Mine uses LinuxCNC which supports tool diameter and length compensation.
Richard
A5 2.5W w/homing switches on L7
A5 2W diode self upgraded from stock 500mw
Printrbot Play. Ext bed, integrated tablet control.
Printrbot Simple Metal
USA