Tolerances and Smoothing - 2D Contours in Plywood

[HarrisonClassic]

Hi all,

Just trying to get my head around Tolerances and Smoothing. Just thinking about 2D Contours at the moment, when I get some time I'll do a similar post with data from my 3D Contours.

My goal is to understand how I can minimize machine time in the main by reducing acceleration/deceleration etc.

I have several 100 parts to route out of 20 or so plywood sheets so am ken to optimize as much as possible. While al the parts differ, the one below is typical ( 3mm roughing multiple depths, tabs, "dogbones" in corners and mainly straight lines or large radius arcs/splines.

All milled edges and surfaces of the plywood are glued surfaces to other similar parts so really smooth finishes are not important.

Below are the Fusion 360 Toolpath sizes for Tolerance of 0.01mm and 0.1mm, with and without smoothing the same vlues

Actual file sizes of the NC posts are smaller files shown below.

Now I'm assuming that smaller file sizes are better - ie. more can be sent to the CNC controller potentially.

Also assuming that for my plywood application 0.1mm T and smoothing at 0.1mm will give me a satisfactory finish, I'll create some parts tomorrow.

I do notice that the line of code are reduced with tolerance reduction and smoothing as expected, a good thing for sure.

Estimates for machining time in Fusion for each toolpath are identical - I'm assuming that the optimization using these two parameters doesn't affect machining time as they are not intricate splines or the part has lots of small areas to machine.

So mu conclusion I think is that dropping the tolerance to 0.1mm and adding smoothing of the same at least reduced file size and number of lines of code and that this is good???

am I missing anything?

David

[seth.madore]

Smoothing isn't going to be where you are going to see massive reduction in cycle time, it's just going to run "smoother" on your machine (to a point). If you have a dated control, smoothing "ON" will be less jerky.

What is your machine, controller and spindle capacity?

[HarrisonClassic]

Hi Seth,

All brand new kit ( Signstech 1325W ), NC Studio and Controller system, Vaccuum bed and dust extraction.

Specs here. https://www.signstech.com/product_detail.php?ProId=210&CateId=17#.Ye01F5Mza3I although I have a 5.5kW spindle

I've done some basic testing with it and goes pretty hard, no problems doing 3 to 6mm depth cuts with a 6mm end mill at 18000 rpm and 15000mm feed rate. No problem working around appropriate chip rates with plenty of power in the bag.

The newly posted NCStudio PP seems to work like a charm actually

David

[HarrisonClassic]

@seth.madore 

Hi Seth, did some testing today on 18mm MDF as it's what I had around.

Started quite conservatively with respect to 2D Contour operations and chip load and gradually worked my way up.

Certainly reducing tolerance to 0.1mm and turning on smoothing still gave a surface finish in the MDF that was exceptional. Much smoother operation along the curves.

i also changed my dogbones from 6mm, to 6mm with 0.5mm extra clearance. This way the tool didn't go into to cut the material, stop at a point and reverse out, there was a small 1mm diameter "loop" which kept things smooth.

Also changed right angled corners to having a small radius of 1mm ( for my application I could even do 2mm ), much smoother going around them.

Using triangular tabs and less of them reduced machining time as did moving from 3mm cutting depth to 6mm using a 6mm diameter 2 flute cutters ( I experimented with straight and upcut end mills). Again, much smoother motion that rectangular tabs.

I ended up with my last run routing out so efficiently still under my machines capabilities of 24000 rpm and 20000 mm/min ( 780 ipm ) feed rates.

Seemed perfect at;

Spindle 17500 rpm

6mm 2 flute carbide cutter

6mm depth of cut

Cutting feed rate of 17500 mm/min ( 688 in/min )

Results in chip load of about 0.02" which is a bit higher that the normal range of 0.013" - 0.016" for MDF.

Certainly impressed with being able to manipulate tolerance and smoothing in F360, seems very efficient.

I read a line in an arcticle somewhere that said "if in doubt, smooth it out" - seems true enough.

Now for testing of 3D Contours with the 6mm ball end mill....

David

[seth.madore]

Good to hear!