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  1. #1
    How long is a piece of string?! Iím after some rough guide feeds and speeds because I find myself just making stuff up. These feed and speed calculators seem to throw up some strange figures to me. To be honest I donít think Iím wildly out there as Iíve had no broken bits and they all feel cool or just slightly warm after operations.

    So here are a few specs just for a ball park figure. ďListen tool the toolĒ is commonly used. Mine all sound fine bar the long 4mm compression EM which always squeals.

    I tend to cut at tool diameter depth. Pretty much hardwood. Always pick 18000 rpm and usually somewhere between 1500mm/min and 2500mm/min. The lower end is for smaller tools of 2mm and very fine v bits and the higher end for the 6mm bits. God knows why!

    My machine is from JazzCNC (in machine discussion thread) so although not industrial, itís a solid lump that could take a bit of stick.

    So Iím after just a rough guess. 2mm, 4mm, 6mm in hardwood feeds and speeds. I can fill in the gaps! Find myself feeling less and less knowledgeable.

  2. #2
    I agree this is a confusing subject especially as you have to convert others suggestions from inch to mm most of the time. I'll tell you what I think I have deducted, though this is theoretical till my machine (same as yours) arrives.

    1. Cutting wood is way less critical on F&S than metal or even plastic. So simple rules of thumb will be fine.

    2. Cutter manufacturers chip load data are for industrial production machines so a red herring for hobby machines. However cutting too slow seems to be a common pitfall. Somewhere saw recommendation to always keep a minimum chip load in mind (theirs was 1 thou or 0.025mm). As recommended chipload can be 50x that there is plenty of head room.

    3. With a small machine and small jobs, speeds are a whole lot less important than you would think as the machine never gets to that set speed. Acceleration settings will have a far greater influence on cutting times.

    4. Limiting depth of cut to D seems to be another rule of thumb, but I have also seem 2D used in wood so again this keeps thing conservative (and slow).

    4. So either stick with conservative values as cutting times are small compared to set up, or test the machine to find its limits. The result will be a broken bit for small dia or a stalled drive error (the advantage of having closed loop steppers).

    5. Feed and speed overrides mean you can programme a safe starting point then ramp them up and watch the results. I suspect Jazz's machines are more capable than I will feel comfortable running a new job at with a hand over the estop. So operator nerve will be the biggest factor on most jobs!

    Any of this right?

  3. #3
    All of your observations sound sensible. I may in the near future push it a bit further.

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