A lot of the cheap tools are sintered Tungsten carbide and they don't have the strength to hold an edge.
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I don't know how long will they stay sharp. I didn't used them a lot and are all still sharp. I used the most a 1' dia round nose bit cutting about 500-700 meters in MDF and it is still very sharp.
I was also looking at CMT tools with replaceable inserts but I think the price is justified only if you are routing MDF as a business, which would mean cutting maybe 500 mtr per day or hour.
I think all tungsten carbide in tools is sintered. Mixed with cobalt and liquid sintered, where the cobalt melts and fills the space between the carbide particles. Most likely those Chinese inserts had no tungsten carbide in the composition, they looked more like cast iron, maybe had some iron carbide inside :)
That's fair enough. If I can do my spoilboard once with it I am happy. I think one time will be all ready 200 - 300 m.
What cutting depth do you do? More than 1mm in one run?
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My spoilboard is actually my router table. I never cut through it. I am surfacing it only every few months with a depth of a few tenths of a millimeter. How have you got 300 m cut for the spoilboard surfacing? My table is 1400x1000 mm, with my 2" dia tool I take 50 mm width of cut which means 20 cuts of 1.4 m = 28 m.
As MDF is abrasive it is important to have the chipload as high as possible. It depends on the stiffness of your router, the tool dia & length, depth of cut and desired cut finish.
For example, let's say you are cutting with 24k rpm and 1000 mm/min feed and I do it at 8k rpm and 4000 mm/min with the same cutter. So for the chip thickness that I am cutting you make 12 cuts, your tool will wear 12 times faster.
You want to get out of the cut chips or shavings not dust.
Here is an example:
Attachment 25317
Attachment 25318
And here is rounding with an Arden "point cutting roundover" bit (for straight cutting I'm using the popular Chinese 6 mm dia single flute carbide bits):
Attachment 25319
Attachment 25320
Great explanation. Sadly I won't have prior information about the stiffness. But I know that I will use a 2.2kw Spindle which can handle 1/2" shanks.
My 300m comes because my table is 4 times longer(1,2m - 1m) x 4m. Because it is my first cnc I am building. I was expecting an uneven table with 3mm height difference. But that's just a guessed number. So with a 2" tool and 1mm cut depth I assumed 20 x 4m x 3 rounds -> 240m. But as you said you are going a few tenth of a milimeter it will even be more runs.