DIY edge finder
Touching off easily
I had a request to cut and engrave high pressure laminates. These are a lasagna of compressed paper and phenolic resin, coated in a thin layer of (colored) melamine resin. HPL is really so durable that it’s even taken for facade planking. It is dishwasher safe and some variants can be heated to 200°C without taking any damage. You can find HPL as boards on playgrounds, garden tables, as panels in the tram etc. So I was like “cool stuff, let’s get started!”
I used the cutting data recommended by a couple of websites with values for “hard wood”.
2-flute upcut wood carbide endmill, speed of cut
450m/min
, 6mm
, Z+ 6,5mm
, S24000rpm
, F3500mm/min
, full slot, climb milling.
And I was alarmed by the way the cut looked when I was done. Here are the symptoms:
First, I checked the spindle. No overheating, still tightly clamped to the portal milling machine, no bearing clearance, endmill securely fastened. Then I thought “Maybe something is wrong with the portal? Can I bend it?” No, I couldn’t. Then I looked at the endmill.
It didn’t look good at all. The cutting edges were practically gone where they had touched the material. Strange. It was brand-new when I started the job and it didn’t even run for 20 minutes.
I did some more research on the internet. HPL is incredibly hard and tough. To compare some values (Brinell-hardness):
I have found some recommendations for cutting HPL like “Carbide endmills should have a cutting speed of up to 150m/min
” and “Use diamond-hardened cutters or 1-flute ones that are optimized for Aluminium”.
To correct things, I just did all cutouts again at finishing settings in CAM. With a fresh endmill and less aggressive feed rates of
F2500mm/min
and an updated depth per pass of Z+1,5mm
.
The result looks much better now.
Still, let’s recalculate cutting data to take material differences to hard wood into account. I’ll choose a 4mm
single flute (z=1
) coated carbide cutter for aluminium and assume a cutting speed vc = 150m/min
for HPL at a feedrate per tooth fTooth = 0,025
similar to cutting mild steel.
Target RPM: \(n=\frac{v_c}{\pi d}=\frac{150000\frac{mm}{min}}{\pi \cdot 4mm}=12000\frac{1}{min}\)
Target feedrate: \(F=n \cdot f_{Tooth} \cdot z = 12000\frac{1}{min} \cdot 0,025mm \cdot min \cdot 1= 300\frac{mm}{min}\)
I chose a 4mm endmill because my router motor torque diminishes over-proportionally when I reduce RPM. With larger endmills, this effect would probably lead to insufficient cutting power. If you have a spindle with an asynchronous machine, your torque curve is essentially flat so that shouldn’t be a problem of yours then.
The feedrate seems so slow - I hope that this wouldn’t heat up the material so much that it degrades (it won’t melt according to Wikipedia…)
For your reference: Here is the related thread in the forum that I am visiting regularly (all in German).
I have made some parts with the bespoke endmill and settings. I optimized the settings a little for reduced cycle time and ended up with the following values:
ftooth = 0.04mm
and vc = 130m/min
. For the 4mm endmill, this resulted in
S = 10300RPM
F = 410mm/min
Z+ = 3mm
vc = 1%
This endmill lived for about 1h. Not much still. Cutting with this kind of bit would never become economical. The HPL I am using has two material properties that will kill carbide cutters quickly. First, it is abrasive so the thin cutter edge is being beaten up. Second, the chips do not carry enough heat away from the cutter edge in time so that their sharpness deteriorates even more quickly.
A more economic solution with 40 times (manufacturer statement) more lifetime might be to take a carbide bit with thick diamond blades (e.g. like this one). The downside is that it’s almost ten times as expensive. If I have to cut this material more often in the future, I might buy one and share my experience - in the meantime, I’ll rather have the cutters sharpened to save money.
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