Hello guys

I was really wondering if anyone has actually tried these pyramid tools (V bit engraving)
10pcs Carbide Steel 60 Degree 1 8" Router Pyramid Engraving Bits CNC Machinery | eBay

I have seen these tools being sold in different places and sellers
the company/sellers claim they are made from sub micron ultra fine carbide grains
most importantly they have a very narrow tip 0.1mm , probably the sharpest i have found so far to be sold
at the same time they come in 1/8" or 1/4" cutting diameter, which means that they can be used to cut with their full cutting length not only their tips
company/sellers clams they can be used normally with wood, plastic, brass, copper and even iron!!

-1st question
Is it really possible that these cutters can actually even cut anything? I dont see any sharp cutting edge,
it might make more sense if they cut only shallow depths with there tips
these cutters are amazingly cheap, 10 of them equal the price of 1 of the normal v bits if not less
like here
1 8" 1250" Carbide 2 Flute Micro Drill Mills 60 Degree Point Kyocera | eBay
I used to use this tool, after some research it seem it has a tip diameter of 0.3mm (3x the 1st one)
however it did not last long and its tip was broken in the middle of a cut, so it is almost useless now for me, as I dont need it for chamfering
I am basically looking for a 0.2 or less tip diameter cutter that can last better than the Kyocera one
I have emailed Kyocera about this issue and requested a cutting condition (in case i was using it wrong) but they never replied!

So at the end I thought if any has tried these cheep chines cutters it will be very good,
because i believe their tips should be much more difficult to break because of their different geometry at same time they have very narrow tip 0.1mm
it also has 3 edges instead of 2 for Kyocera
but I still can not imagine if they can actually cut anything, I also failed to find any video for them

-2nd question
what would be the most suitable V bit to use in Al, brass or copper (light metals) for 1 to 2mm depth of cut at most?

-3rd question
10x Bottom Carbide PCB Board 30º Engraving Bits CNC Router Tool V Shape 0 3mm | eBay
are these V bit are used only with pcb or it can be used with deeper cuts?
why they have such geometry? (just curios)

-4th question
what would be the best engraving strategy for the longest life time of the cutter and to avoid tip breakage too?
would I step down all the way to the desired depth and feed slower or have it in multi steps?
what about rpm speed ?

Hope to hear from you guys what do you think about it