More plastic milling wisdom from Fred Schultheis at North Bay Technical

I spent several hours using my vertical fluted end mill with HDPE over the weekend. I reported on the builder's blog that I was having trouble with the swarf fouling the end mill and eventually ruining the job. This happened whether or not I widened the cut.

At that point I started sifting amongst the very sparse information on milling HDPE on the web and ran across this...

[www.youtube.com]

What jumped out at me was they were using a very different end mill than I was. I looked at Fred's Schultheis website at North Bay Technical and he had the fish-tailed, 2 flute spiral end mill that they were using in sizes that I can use.

[www.northbaytechnical.com]

Fred, as usual, was a treasure trove of information on milling plastic and I got information on the spindle speeds, feed rates and cut depths that I need.

Briefly, we're looking at feed rates of 5-8 mm/sec with a max of 17. Cut depths looks like always less than the diameter of the end mill. The videoclip recommended 0.8 x end mill diameter for the cut depth.

Also, if melting is a problem, use a coolant. Duh! :-s Good job Zach and Adrian have been working on peristalic pumps. I'll have use for one very soon, it looks like. :-)

---

-------------------------------------------------------

Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

I avoid coolant by taking a very shallow cut (0.1mm) and moving relatively quickly (15mm/s). That way the heat generated is spread so sparsely that the plastic does not melt. I have milled 3mm HDPE / aluminium laminate, POM, Acrylic and polystyrene that way.

It is probably not the most time efficient way of milling plastic but I don't have any problem with swarf build up because it is very fine dust that gets taken away by a vacuum. I would rather wait a bit longer than have the hassle and mess of coolant. I suppose it depends on how much milling you want to do. I only did enough to make an extruder and prefer to use FFF because it is far less hassle and mess.

---

[www.hydraraptor.blogspot.com]

Apparently, if you use Fred's settings you don't get melting and can take cuts to the side of about 1 mm for the 1.27 mm end mill at 8 mm/sec, which means that you can remove about 3 cm^3/min cutting at a depth of 6 mm. That is fairly efficient.

---

-------------------------------------------------------

Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

I first tried cutting sideways but that produced too much melting so I ended up doing all the cutting with the bottom 0.1mm of my end mill. There is no way the drill I am using would be ably to take a 1mm slice 6mm deep at a feed rate fast enough to avoid melting. Also, I can see why swarf removal would be a problem.

I remove a max of about 0.1mm * 3.175 * 15 * 60 = 0.29 cm^3/min so an order of magnitude less.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
>
> I remove a max of about 0.1mm * 3.175 * 15 * 60 =
> 0.29 cm^3/min so an order of magnitude less.
>
I currently get about (0.1 mm * 1.59 mm * 8 mm/sec* 60 sec/min)/1000 mm^3/cm^3 = 0.076 cm^3/min with the 1/16" diameter end mill. I hope to do a LOT better, because I'm really interested in doing some fluidics control circuits.

---

-------------------------------------------------------

Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Hi Forrest,

... in the first video i've seen the very long shavings winding around the mill and forming a ball of thread, what will make ugly traces on the surface.

For avoiding this i use a 'deep-drilling'-strategy, where the mill go down stepwise 1mm, then returns to the safe-position (1mm above the plate), then drill one 1mm-step deeper, and so on ...

I'm milling in POM/Delrin with nearly 18000 rpm and maybe 12mm/s feedrate with cut-dephts of the mill-diameter without any coolant.

With plastics that tend to melt i use coolant (car-shield-washer fluid, it's a mixture of tensides and alcohol in water) or try to rise the feeding speed.

Viktor

VDX Wrote:
-------------------------------------------------------
> Hi Forrest,
>
> For avoiding this i use a
> 'deep-drilling'-strategy, where the mill go down
> stepwise 1mm, then returns to the safe-position
> (1mm above the plate), then drill one 1mm-step
> deeper, and so on ...
>
That's the "pecking" technique that the narrator in the videoclip was talking about.

---

-------------------------------------------------------

Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Hi Forest,

... OK, i don't have sound at my daywork-PC, so viewed it only.

By the way: - another hint for milling difficult materials (resins, PU-foams, ...) is to put them over night into the froster (e.g. -18