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  1. #61
    3mm wide tabs? But how thick?

    I set 2mm wide x 0.4mm thick but due to my z running low for some as yet unknown reason, they came out at 0.15 mm thick.

    Sawing these parts out is going to bugger the finish, is there another way?

    If not then I might have to revert to sending them out for laser cutting again but i really, really do not want to have to do that.

  2. #62
    Sorry typo
    3mm high and ~12mm long
    Careful filing and sanding then scouring pad gives a reasonable finish. If you want a mirror finish with no sign of tabs then you are back to fixing the part down in the middle using any holes that are available instead of using tabs.

    On occasion I've also put the raw tabbed part in a vice edge up and used the machine to skim it down 0.05mm at a time and remove the last but if the tab. You can get a very good finish but you ideally need a parallel edge on the lower side to reference to sitting in the vice. But this takes time and is best for simple shapes.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #63
    Wow! 3x12mm thats a serious tab, really doubt it would go on these parts IMHO.

    One idea I just had was to split the job into two overlapping parts and use solid clamps with a pause in the job to allow two new clamps to be set over the cut part and the other clamps to be removed. It would mean double the tooling changes but might work?

    There are no holes for fixings internally.

    I was using 1300mm/min and 2.5DOC for the 5mm single-flute tool.

  4. #64
    Is it not possible to leave 2 or 3 decent tabs 12mm x 3mm on straight edges and remove tabs as final cut after clamping the parts?

  5. #65
    Possibly, I'm working on it now in CAD and will post when i've got to sheet cam to see if i'm barking up the wrong tree.

  6. #66
    Ok, lets run this up the flagpole...

    This is the job - two parts. Outer line is the base metal - 5mm Aluminium, the three point down the centre are M6 screws for fixing to the bed.

    Looking at it now I can pretty much see why it failed - once the last pass of the roughing cut is made down the centres there is bugger all holding the two parts to the central stub - just the centre holding tabs which were way too thin to stand up to the cut.

    This is my next plan - place some full-depth tabs maybe 10mm wide where the red dots are, make all the cuts, including the finish passes, then using the 2mm finish tool add some cuts to nibble away at the tabs after maybe fixing a couple of clamps - as suggested.
    Click image for larger version. 

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    Doomed to failure or possible plan ?

  7. #67
    Onion Skin will work better has it holds all round and can be lot thinner.

    To be honest Dave and no disrepect meant here and I know you have some experience with milling but think your kind of trying run before can walk with this.? By that I mean you haven't had much time using this machine so don't know it's capabiltys and your part isn't exactly new user friendly with those smaller cutters.

    You may be better stepping back a little and work upto this part.

    Also the Water cooled spindles above 12000rpm do have resonable amount of torque and shouldn't struggle with 5mm carbide tool while ramping only 0.5mm so are you sure you have the VFD parmaeters set correctly.?

  8. #68
    That's the point - there is no all-round, which is why it failed. The base metal is only just over-size for the whole job, once the perimeter is roughed the only fixture it has is the middle strut and that only had the tiny tabs or possibly onion skin - just not enough meat.

    No offence taken JAZZ, speak your mind ;) There is a long story with these parts, not for here but suffice to say I have customers waiting and really wanted to get them done myself instead of farming them out - this has applied some undue pressure but I think I can win still.

    My experience is all manual - I'm used to throwing in a 1/2" cutter, clamping the metal down and diving in at full depth and adjusting the feed to suit as I'm twiddling the handles. The learning curve here is staggering, my presumptions were originally to use a feed and speed guide - set those parameters and have at it - this was wrong by a long-shot and I realise that now. It probably explains why 90% of the videos i have seen on youtube are all running very light cuts.

    There is a slim chance that the loss of power on the spindle is connected with my odd VFD issue - maybe it really is a duff VFD after all - the new one should arrive tomorrow and i'll be fitting that before running any more tests - another good thing with a UK supplier is that help is only a call away and they are very helpful ;)

    I will get that set up, check my Z axis calibration, then run some simple tests on scrap before diving in again. The new cutters will be here for the weekend and I will switch to a more softly-softly approach to feed rates as it seems most others do.

  9. #69
    Quote Originally Posted by Davek0974 View Post
    The new cutters will be here for the weekend and I will switch to a more softly-softly approach to feed rates as it seems most others do.
    Not too softly and most do cut too slow or too shallow but it's good idea to find your feet first before gunning it. When your settled you'll be surprised how much you can push the limits with right tooling and feeds etc.

    If part has decent area to it then Double sided tape can work well if your not using cutting fluid or light amount of fluid.

  10. #70
    Will try the DS tape, good point.

    Would you agree with the "few heavy tabs and remove last" idea??

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