[TINAM]

Hello!

I'm new to hobby cnc'ing. The question is about optimal feedrate, step depth and rpm for cutting out details from plywood.

Situation:
Birch plywood 18mm thick (~700kg/m3)
Kess 1050 FME 10000..32000 RPM
Cutter- cutter d=3mm, shank d=3mm, cutlength=20mm, overall length=38, no. of flutes=3, VHM, upward chip ejection (a "noname" from ebay)
Max speed for machine (that stepper motors feel comfortable ) as I have set it up in Mach3 is 50mm/sec.

The job consists of cutouts, there are only few small pockets, 5mm in depth.

What would be Your suggestions on those parameters? Primary I don't search for "fastest" approach, but the most "correct" one. The thing that worries me is the "composite" nature of plywood (this one is bonded with a phenol resin adhesive (EN 314 / 3 rd class; BS 1203 / H4 (previously WBP); DIN 68705 Part 3 / type BFU 100)).

Thank You so much in advance!

[Dropout]

What is the chip load of the bit? Onsrud shows anything from .003 to 0.013 for their 1/8 bits in laminated ply.

Once you know that, it's easy math.

[tazzydean]

any type of ply I would use a compression cutter Onsrud does sell a bit thats an 1/8" cutter 60-102 were you planing on cutting in one pass or several. 18mm ply with a 1/8 cutter make sure you buy a handful i'm sure you will break a few. i would try cutting about 85 IPM, 18,000 rpm and 3 passes of 1/4" good luck cutting that.

[TINAM]

Thanks for pointing in chipload direction!
That is a value I don't know.

..a "noname" from ebay..

As I understand, not knowing this parameter makes the whole calculation pointless. I googled up some manufacturer sites, and from what I saw- lets consider chip load 0.006" = 0.1524 mm

feedrate = RPM * No. of flutes * chipload
feedrate = RPM * 3 * 0.1524
feedrate = RPM * 0.4572
feedrate=0..3000mm/min
RPM=10000..32000

When setting maximum feedrate and minimum RPM the chipload still isn't reached, is it?
chipload=feedratemax/(rpmmin*flutes)=3000/(10000*3)=0.1

In how many steps do I have to cut those 18mm- where does step depth go in this formula? Or do I have a fundamental misunderstanding here?

[ger21]

at your max speed of 3m/min, Id guess to make 6 passes, 3mm deep at 18000-20000 rpm. If it cuts good, increase the depth of cut 1mm at a time.

And the bits will probably get dull very quickly.

[TINAM]

Your answers are starting to come faster than I can process them.

85 IPM, 18,000 rpm and 3 passes of 1/4" good luck cutting that

I just cannot force me thinking in imperial units
So 2159 mm/min, 18k RPM and 3x6mm passes.
Sounds great and those are +/- the speeds I'm using now to do testcutting. But in context of tazzydean post- where does the chipload comes in, meaning, the parameters You gave seems not to take advantage of the near-maximum stress the machine can take. Or in real life situations the formula is for... And where did the 3x6mm came from? Experience, experience, experience?

6 passes, 3mm deep at 18000-20000 rpm

Sounds safe.

I do know that 3mm cutter in 18mm thick plywood does sound "breaking those cutters". Anyways, that is what I have now, a min of 3mm collet; no cutter that has 3mm shank diameter, a smaller cutter diameter AND cutter part length >18mm. I need those cuts as thin as possible/ balanced with not breaking them in every turn, so right now I draw all details taking 3mm cutwidth in mind.

[tazzydean]

experience experience experience lol and alot of oops well b4 I ever heard of a forum. The chipload chart for me is just a mild referance I seem to always run at 18,000 rpm. so use that as a starting point, the way I see it the scale runs like this..... fine powder like dust ( too slow of feed rate) broken bit ( way too fast of feed rate ) anywhere in between is what your looking for. BTW what kind of parts are you cutting out of 18mm ply??

[TINAM]

The parts are for a chair that I design- doing a 1:1 prototype as I need also to do a real scale test (tension, compression, bending, shear stress... dipl.arch. talking here ) I'm trying to go with 18mm instead of 21. The urge for searching theoretical max speed is simple- if the design is a success I will have to produce some for exhibit.
Thanks for answers, I will turn to experimentation now. But if anyone has something to add, please!