Feed rate for cnc
  • David,

    The reason I ask. The Sextus kit I bought from you was beautiful. The plywood sheets cut by your cnc were perfect. The parts I cut out for the Secundus aren't bad but I don't think they hold up to the level of your work.

    I just finished cutting out the plywood parts for the Secundus. Would you please share what bit, bit rpm and feed speed you use for the Secundus when milling the 5 and 8mm parts?

    Did you sand the sheets after the cutout before you shipped them?

    Oh and BTW, The very best quality Finnish Birch Plywood I can get here in the States is junk compared to what you provide. Fewer number of plys and B/B grade is the best I can find.

    Thank you!
  • Feed rates, cut depth, number of flutes etc. etc. etc. is all a bit like witchcraft, well sort of.

    The thing is that good results depend on a great number of factors, of which the 2 most important as far as I am concerned are one the machine and second the router/spindle being used, everything else is just a question of cut path tweaking.

    The more rigid the machine the better, flex and slop are going to reduce the quality of anything you cut.

    The router/spindle is just as important, I use a HF spindle from Elte LINK. Which is a great piece of kit and has not let me down once in all the years and I do an incredible amount of cutting.

    Okay I realise not everyone has the money, need or inclination to spend great amounts on a CNC router, so lets look at what can be changed.

    I use for all the cogs/sheets a finishing bit with 7 spiral flutes LINK and I run at about 22,000 RPM and if the bit starts to show discolouration I replace it, although a blunting bit can also be recognised by an increase in the little hairs that stand off the wood where the cutter has travelled.
    Travelling speed of 20 mm/sec, although that is very much a theoretical speed as it decreases around corners etc.

    I never go above 3.5mm depth for one pass, so for a 4mm sheet I do 2 x 2.5mm, 6mm sheet 2 x 3.5mm.

    And as you mentioned yourself, one big factor is the quality of the material being cut, the aviation grade ply I use is as far as I am concerned the best for the job, not cheap, but then I was not going for cheap but for quality.
  • Thank you Dave, I'm new to the cnc router having had one for just a couple of months. I really appreciate the info. I will increase the number of flutes and the RPM's. I currently am running a high quality 2 flute bit at 12000 which has worked very well on 2.5D and profiling of hard woods but it resulted in a lot of hairs where the bit has travelled and frankly not as clean as your work.

  • I have a shopbot and cutting is not a problem but I always have tool marks no matter what speed I cut.Plus I make living on my machine so it is hard sometimes to cut clocks. I rather get the full kit from dave just to make life easy. but I built the primus from scratch and parts of the sextus and made the secundus and tetras parts. but I have to sand more. I usually only use downcut bits in the smaller bits I can have fuzz on the bottom of the cut if the sheet is not held down tight enough. but usually no tearout. but tool-marks that have to be sanded out more then what dave has. my spindle only goes to 18k
    I rather cut clock gears they are pretty easy overall. Had to cut small letters out of 1.5" mdf and man what a pain to cut them without tabs.