Size of cuts not accurate

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MidCitySlim
Posts: 39
Joined: Sun Nov 01, 2015 9:49 pm

Size of cuts not accurate

Post by MidCitySlim » Fri Jun 09, 2017 3:52 pm

FYI I am using Fusion 360 software into UGS. I am trying to cut out some letters via a contour cut and then inlay them into a corresponding pocket. Here's what I'm starting with...
Screenshot 2017-06-09 08.25.23.png
Screenshot 2017-06-09 08.25.23.png (6.6 KiB) Viewed 816 times
Here's what I get...
Screenshot 2017-06-09 08.45.50.png
Screenshot 2017-06-09 08.45.50.png (98.8 KiB) Viewed 816 times
The problem is, my contour cut is too big (this particular measurement ends in about 0.275") and my pocket is too small (this measurement ends up being 0.235").
Screenshot 2017-06-09 08.27.29.png
Screenshot 2017-06-09 08.27.29.png (21.36 KiB) Viewed 816 times
In Fusion 360, I don't leave any stock. I'm not sure if there is another setting I'm missing, but it seems like the toolpath is staying away from the edge by about 0.01".

I also have discrepancies between the vertical and horizontal measurements across the entire piece. The horizontal measurements are closer to the expected (0.27" vs 0.265"), but across the whole piece there seems to be an error of +/- 0.005. Is this expected?

I don't know if there is a better way to inlay letters (Vcarve maybe), but I haven't learned that yet. I do have a 60 degree v bit, if anyone has a good tutorial in Fusion 360, that would be amazing.

Thanks!

WillAdams
Posts: 8556
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Size of cuts not accurate

Post by WillAdams » Fri Jun 09, 2017 5:55 pm

You should start by ensuring that the machine is mechanically sound and running well.

Then, ensure that your spindle is plumb and square. https://www.shapeoko.com/wiki/index.php ... he_Spindle

Then, determine your endmill runout for an actual diameter to enter into your CAM app.

Then, calibrate for belt stretch: http://docs.carbide3d.com/article/42-ho ... lt-stretch

For Fusion 360, what I have is:

- http://carbide3d.com/docs/fusion360/

and from: https://www.shapeoko.com/wiki/index.php ... are#3D_CAD
Available under an annual license w/ pricing ranging from zero to $300 to $1200 annually.[18] http://www.autodesk.com/products/fusion-360/try-buy Knowledgebase article on activating startup or educational licensing[19]
CAM tutorial[20]

http://community.carbide3d.com/t/so3-fu ... oints/2142

There is now a Carbide3D post-processor: http://fusion360.autodesk.com/learning/ ... 06B36D160D [21] Notes on post-processor for associated CAM: http://www.shapeoko.com/forum/viewtopic ... 28&p=52650 https://forums.autodesk.com/autodesk/at ... bide3d.cps [22]

http://carbide3d.com/docs/fusion360/

http://help.autodesk.com/view/fusion360/ENU/ [23]

http://www.restrictedayerspace.net/cnc/ ... -shapeoko/ [24]

shapeoko post processor.zip[25]
https://github.com/Strooom/GRBL-Post-Processor [26] --- free / opensource / documented Post-Processor which translates RPM values into dial-settings for Dewalt and Makita trim routers, and will alert you and recommend solutions for some errors in a design. Modified version: C3D-SO3-DEWALT.cps.zip[27]

http://cam.autodesk.com/posts/ [28]

Note that some users have found it necessary to increase the precision for metric files so as to avoid Invalid Gcode Error 33: http://community.carbide3d.com/t/grbl-e ... 33/1204/10 with Carbide Motion 4 and Grbl 1.1, there is a setting which may need to be changed to avoid a similar error: http://community.carbide3d.com/t/fusion ... =willadams

Free license available to hobbyists and startups making less than $100,000 annually (must be renewed each year, details: http://www.autodesk.com/company/legal-n ... titlements ): http://knowledge.autodesk.com/support/f ... n-360.html

Engrave/V-carving added as a feature.[29][30]

Adding tabs when cutting 2D feature: http://www.shapeoko.com/forum/viewtopic ... 749#p63749

Job setup

Step and repeat is termed a "Pattern".[31]

Notes on scaling of SVG files: http://community.carbide3d.com/t/how-to ... ack/1419/9

Discussion of limitations: http://www.shapeoko.com/forum/viewtopic ... 303#p55303

Has problems when model is defined in Imperial and CAM is done in metric.[32] Metric should be used to avoid Grbl Invald G-code #33 error.[33]

Criticism on Reddit: https://www.reddit.com/r/cad/comments/4 ... st/d2xfdv3

FEA and interference analysis (complex FEA can be performed via AutoDesk's servers for an additional cost). Uses a joint based system to limit degrees of freedom and a top down (as opposed to bottom up) assembly system.[34]

Cribbage board: http://a360.co/1sbSWTO

http://community.carbide3d.com/t/fusion ... flow/88/21

Useful plugins [35][36]:
https://github.com/hanskellner/Fusion360Image2Surface46 --- Fusion360 plugin for converting an image (height map) to a surface. Has a neat example with a penny.
https://github.com/hanskellner/Fusion360SoftJaws22 --- Creates soft jaws automatically.
https://github.com/tapnair/NESTER --- Flattens a 3D design specifically for use with a CNC router....
https://github.com/CrypticRage/BossJoints --- for CNC joints
https://github.com/benbreen/Cycloidal --- for generating gears and pinions.
https://github.com/visualapproach/WeirdGears --- non-round gears

Tutorials:
https://www.7thdensity.com/single-post/ ... Fusion-360 [37]
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

cgallery
Posts: 26
Joined: Sat Apr 01, 2017 9:43 pm

Re: Size of cuts not accurate

Post by cgallery » Sat Jun 10, 2017 1:08 am

Is it possible your bit is smaller than you think? That would be one way to have a profile that is too big and pocket that is too small.

MidCitySlim
Posts: 39
Joined: Sun Nov 01, 2015 9:49 pm

Re: Size of cuts not accurate

Post by MidCitySlim » Mon Jun 19, 2017 7:25 pm

Thanks for the advice.

I confirmed:
Frame is square.
Gantry runs within 0.003 on y-axis on both sides.
Spindle is square to 0.003 inch to a freshly-faced board.
Drill bit measures exactly 0.0625".

Here's the latest test:
- I left no stock on either cut.
F on F.PNG
F on F.PNG (36.92 KiB) Viewed 750 times
Result:
FonF.PNG
FonF.PNG (194.29 KiB) Viewed 750 times
And the resulting measurements:
Stats.PNG
Stats.PNG (20.5 KiB) Viewed 750 times
Curious what you guys think about programming the calibration offsets for each axis considering the ratios. And whether that will help right now with some of my problems...

WillAdams
Posts: 8556
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
Contact:

Re: Size of cuts not accurate

Post by WillAdams » Mon Jun 19, 2017 8:29 pm

You need to:

- cut a slot and measure it to determine effective endmill diameter (actual endmill diameter plus runout)
- cut a pattern and measure it so as to calibrate for belt stretch: http://docs.carbide3d.com/article/42-ho ... lt-stretch

Then you can try a standard pattern such as the diamond-circle-square and see where you stand: https://www.shapeoko.com/wiki/index.php ... quare_Test --- for such a narrow endmill you may also need to leave a roughing clearance and then work out whether a climb or conventional finishing pass is more accurate: https://www.shapeoko.com/wiki/index.php ... al_Milling
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

MidCitySlim
Posts: 39
Joined: Sun Nov 01, 2015 9:49 pm

Re: Size of cuts not accurate

Post by MidCitySlim » Mon Jun 19, 2017 9:25 pm

The measured 'slots' that cuts the F Contour above read weirdly. The slots are 0.25" deep with 0.130 stepdowns.

The horizontal lines are almost all 0.063" wide, while the vertical slot measures from 0.062" to 0.070".

Also, I'm curious which offsets I use since the ratios go either way depending on the cut.
Stats.PNG
Stats.PNG (25.03 KiB) Viewed 741 times

WillAdams
Posts: 8556
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
Contact:

Re: Size of cuts not accurate

Post by WillAdams » Tue Jun 20, 2017 12:26 pm

Also, I'm curious which offsets I use since the ratios go either way depending on the cut.
Please see: https://www.shapeoko.com/wiki/index.php ... al_Milling

Or consider:
An interesting technique which would also calculate runout would be to, "Mill multiple sizes and graph the results as actual/expected. Linear regression will reveal that there is a constant error (cut size not exactly equal to nominal cutter diameter) and a proportional error..."


(from: http://www.shapeoko.com/forum/viewtopic ... 908#p41862 )
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

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