Profiling an outline: Bit doesn't plunge deep enough into the material.

Here's the place for discussion related to CAM/CNC and the development of the Path module.
Forum rules
Be nice to others! Respect the FreeCAD code of conduct!
Post Reply
blank
Posts: 10
Joined: Sat Oct 22, 2022 12:22 pm

Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by blank »

Hello,

the following problem could be related to FreeCAD, as well as the CNC controller or the actual cnc machine. I suspect a misunderstanding on my part in the FreeCAD settings, so I try it here first.

I'm trying to mill the attached adapter plate using a simple profile operation. The material will be a 2mm carbon fiber plate, so I skeched the plate, padded it to 2mm height and created a path job. For the job's stock, I set z height to 0 on both sides. In the profile operation, I now set the start and final depth to 0, because I want to mill the plate in one go. The attached file contains all the described operations.
I now export the attached gcode file and load it into Candle. I position the bit over the cf plate so the tip touches the surface and zero the position. When I now run the operation, the bit only plunges halfway into the material and basically "engraves" it instead of cutting it. I tried to set start and final position to -0.5, hoping that this would fix the problem, but it still only went about halfway through the material.

Does anybody know why this is happening?

My system:

Code: Select all

OS: Ubuntu 22.04.1 LTS (ubuntu:GNOME/ubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.1.29410 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 0.20.1)
Hash: f5d13554ecc7a456fb6e970568ae5c74ba727563
Python 3.10.5, Qt 5.15.4, Coin 4.0.0, Vtk 9.1.0, OCC 7.6.2
Locale: English/United States (en_US)
Im using a Genmitsu ProVerXL 4030 and Candle 1.1.7.
Attachments
adapter_plate.txt
(4.72 KiB) Downloaded 14 times
adapter_plate.FCStd
(91.09 KiB) Downloaded 17 times
User avatar
sliptonic
Veteran
Posts: 3457
Joined: Tue Oct 25, 2011 10:46 pm
Location: Columbia, Missouri
Contact:

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by sliptonic »

Because your start and end depth are both 0.
Set your start depth at 2 and make sure you step-down at least 2mm to cut it in one pass.
GeneFC
Veteran
Posts: 5373
Joined: Sat Mar 19, 2016 3:36 pm
Location: Punta Gorda, FL

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by GeneFC »

blank wrote: Sat Nov 26, 2022 5:54 pm Does anybody know why this is happening?
The biggest problem is that you mis-typed the depth entries. Your file shows 0.2 mm instead of 2.0 mm.

The best thing is to just accept the defaults. They should work fine in this case.

Gene
blank
Posts: 10
Joined: Sat Oct 22, 2022 12:22 pm

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by blank »

sliptonic wrote: Sat Nov 26, 2022 6:24 pm Because your start and end depth are both 0.
Set your start depth at 2 and make sure you step-down at least 2mm to cut it in one pass.
Now I'm confused. Here is how I understand these function:

If you have a plate of 2mm thickness with a stock of 0mm in z direction and set the start depth to 2mm, the end depth to 0 and the step down to 1, then the router should make three runs. The first one is right over the pate's surface and therefore has no effect, the second one goes 1mm deep into the plate and the last one cuts through the complete 2mm of the plate. All of this requires that I set the router's zero point with the bit exactly above the surface of the plate before cutting.
So my settings of 0mm for start and end depth should make the router cut the whole plate in one go, shouldn't they? Where's the error in my understanding?
blank
Posts: 10
Joined: Sat Oct 22, 2022 12:22 pm

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by blank »

GeneFC wrote: Sun Nov 27, 2022 1:01 am
blank wrote: Sat Nov 26, 2022 5:54 pm Does anybody know why this is happening?
The biggest problem is that you mis-typed the depth entries. Your file shows 0.2 mm instead of 2.0 mm.
I set the end depth to -0.2mm to ensure that it goes completely through the material, even if the bit isn't correctly positioned with submilimeter accuracy. I used the blue tape method to attach the workpiece, so there is a little extra space between workpiece and spoilboard.
User avatar
sliptonic
Veteran
Posts: 3457
Joined: Tue Oct 25, 2011 10:46 pm
Location: Columbia, Missouri
Contact:

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by sliptonic »

blank wrote: Sun Nov 27, 2022 12:48 pm So my settings of 0mm for start and end depth should make the router cut the whole plate in one go, shouldn't they? Where's the error in my understanding?
If you start at 0mm and proceed to 0mm, there's nothing to do. The algorithm subtracts the start point from the end point to figure out how much distance needs to be covered. It then uses the step distance to figure out where each intermediate step should be.

Also, the start-depth isn't the height position of the first cut. It's the top of the material as documented here:

https://wiki.freecadweb.org/Path_Profile
jescombe
Posts: 90
Joined: Tue Mar 09, 2021 4:19 pm

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by jescombe »

blank wrote: Sat Nov 26, 2022 5:54 pm I now set the start and final depth to 0, because I want to mill the plate in one go.

I position the bit over the cf plate so the tip touches the surface and zero the position.
I think these statements highlight another issue. Sounds like you are setting Z0 on the top of your stock, and then also setting a final depth of 0 (or 0.2). That is not going to cut much!

Your attached file shows Z0 at the bottom of the stock. Simplest option would be to touch off on whatever your 2mm plate is sitting on, and then (leaving all the depth settings at default), a profile op would have a start height of 2mm, and a finish depth of 0mm (which it would cut in one pass given the default step down of the tool diameter).

Another option would be to set Z0 at the top of the stock, and then the path would be generated from 0 to -2mm. (Touching off on the top of the stock is generally what I do, so I tend to pad my sketches in a negative Z direction - to avoid adjusting Z0 in the job properties).
GeneFC
Veteran
Posts: 5373
Joined: Sat Mar 19, 2016 3:36 pm
Location: Punta Gorda, FL

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by GeneFC »

blank wrote: Sun Nov 27, 2022 12:48 pm Where's the error in my understanding?
First of all, you must use the correct terms or everyone will be confused.

The three depths in the Profile operation are

Start Depth
Final Depth
Step Down

There is no "End Depth".

But the biggest problem is your understanding of the measurement scheme.

Both the Start Depth and the Final Depth are referenced to the exact same location, namely the Z=0 height for the Model as it exists in the Job (not in the base model in the Body). It sounds like you are trying to measure down for the Start Depth and measure up for the Final Depth.

Any way you slice it the difference between Start Depth and Final Depth needs to be the entire distance you want to cut, probably 2.2 mm in this case.

Gene
blank
Posts: 10
Joined: Sat Oct 22, 2022 12:22 pm

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by blank »

jescombe wrote: Sun Nov 27, 2022 2:09 pm Your attached file shows Z0 at the bottom of the stock. Simplest option would be to touch off on whatever your 2mm plate is sitting on, and then (leaving all the depth settings at default), a profile op would have a start height of 2mm, and a finish depth of 0mm (which it would cut in one pass given the default step down of the tool diameter).
Thanks, that's problably it. I just concentrated on the software side of depth calculation and forgot to take the actual hardware into account. If you position the tool right above the material and zero it, then the tool position equals the zero depth position of the path operation. After all, the tool cannot know the absolute dimensions of my model. Now this all makes sense.
Stupid mistake, and now it will be on the internet forever... ;)
jescombe
Posts: 90
Joined: Tue Mar 09, 2021 4:19 pm

Re: Profiling an outline: Bit doesn't plunge deep enough into the material.

Post by jescombe »

blank wrote: Thu Dec 01, 2022 9:14 pm Stupid mistake, and now it will be on the internet forever... ;)
Am sure we've all done similar :) - and given a choice of mistakes, I would take a "too shallow" tool path every time!
Post Reply