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Bad finish on one side.

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by imnoto, Aug 30, 2017.

  1. imnoto

    imnoto United States Iron Registered Member

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    Just learning 360 and made a little part to figure things out.

    One side looks ok considering I stopped and started this job over and over.
    OkSide.jpg
    The second side tho is really bad looking.
    I did 2D adaptive to clear the bulk came back to finish the last .020. I split the .020 into 3 passes at full depth climb milling so probably stepover of about .007 on .375 endmill.
    OuchSide.jpg
    Ideas?
     
  2. TomS

    TomS Active User H-M Supporter-Premium

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    I had a similar problem where the X and Y linear cuts were smooth but arc and circular cuts were rough. Turns out it was bad AC ball screw bearings. Here's my thread and how I reached that conclusion, http://www.hobby-machinist.com/threads/need-help-to-improve-surface-finish.61229/. Could be several other things though, e.g. gib adjustment, spindle bearings, recutting chips, etc. If you give us some background information on your machine and setup we can help you narrow down the source of your problem.
     
  3. imnoto

    imnoto United States Iron Registered Member

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    Thanks for the reply Tom, I'm sure I have a few issues with my machine but I have cleared up this issue was a problem I think I was cutting more than I thought on finishing pass. Sorted that in 360 and here are some pics after.
    I will be reading your thread anyway to maybe help narrow down some of my other issues.
     

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  4. TomS

    TomS Active User H-M Supporter-Premium

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    Yes, much better finish. How much were you trying to remove on the finishing pass? Lot's of things can affect surface finish and it can be a bit daunting wading through it all. You may already know this but Fusion has a feature where you can repeat the finish pass by clicking on the appropriate box. I do this on all finishing cuts.
     
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  5. imnoto

    imnoto United States Iron Registered Member

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    I'm a bit confused on how 360 handles the multiple finishing passes but somewhere between .010 and .020.
    I did not have the repeat finishing pass on, I will do from now on.

    My Confusion..?
    I need to cleanup .020 from the previous adaptive cut so...

    If I put .003 step over and 1 finishing pass it looks like its going to slam through the last .020 thinking its taking .003 off. Correct?

    So I guess I have to calculate what is left to take off? Like .020 left div .003 = 6.6 round up to 7 passes of .003 step over providing I want to take the last .020 in .003 cuts.
    I guess I thought that Fusion would figure that stuff out and I could just say take .003 till you get there.
     
  6. TomS

    TomS Active User H-M Supporter-Premium

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    I am no expert on Fusion 360 but this is how I set up to do 2D contour finishing passes, which I assume is what you are doing. For your roughing passes you tell Fusion how much radial stock to leave. In your case you are leaving .020". When setting up your finish contour click on the "Passes" icon at the top of the 2D Contour dialogue box. Scroll down the list of setup options and click on "Multiple Finishing Passes". The next two options on the list are "Multiple Finishing Passes" and "Stepover". Click on "Multiple Finishing Passes" and setup option "Number of Finishing Passes" will appear. If you want to take a .010" width of cut then enter "2" in the box, i.e. two passes at .010" each equals .020". You can also enter .010" in the "Stepover" option box but in this case it is redundant. On the other hand say you have .020" of stock to remove and you want to take a .015" WOC on the first pass then follow up with a .005" WOC pass. You would click on "Multiple Finishing Passes", enter "2" in the "Number of Finishing Passes", and enter .015" as your "Stepover". Fusion knows you left .020" of radial stock so it does the math for you and produces a .015" first pass and a .005" second pass. For repeating the final machining pass scroll down a few more set up options and click on "Repeat Finishing Pass". Someone please correct me if I'm wrong.

    BTW - I would suggest a finishing pass of at least .005" width of cut. Too light of a cut and you are just wearing out your cutter.

    Hope this helps.
     
  7. imnoto

    imnoto United States Iron Registered Member

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    Thanks Tom yes this totally helps, I will play with it and test the options now that I have a better understanding of how they should work.

    Noted on the finishing pass WOC. I'm kind of a noob as you can see.
     
  8. TomS

    TomS Active User H-M Supporter-Premium

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    I'm learning too. Spent my entire career (40+ years) in the machining/manufacturing industry but only ran manual machines. Been playing around with CNC for about three years so it's still new.
     
  9. imnoto

    imnoto United States Iron Registered Member

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    What CNC machine do you have? I'm trying to figure out speeds and feeds and how much my machine can take.
     
  10. TomS

    TomS Active User H-M Supporter-Premium

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    I converted a PM-932 square column mill drill. I can run up to 8650 rpm. Being a hobbyist I run it on the conservative side. Just finished up the
    CNC machining on a 6061 T6 aluminum tool setter this afternoon. Roughed the periphery at 3000 rpm, 1.30" DOC, and .050" WOC using a 5/8" 4 flute HSS rougher. Probably could have pushed it further but why? As you said you have to get a feel for what your machine can handle. The only way to find out is push it a little further until you hear it say "no more". Then back off a little.
     
  11. imnoto

    imnoto United States Iron Registered Member

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    Oh Cool, I have a PM-940 on order :) Plan on CNCing it once I get it in and figure out how I'm going to move the thing around to my shop.
     
  12. TomS

    TomS Active User H-M Supporter-Premium

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    You are going to like the 940's extra Y travel and weight. Should make a great CNC machine. By the way Davd Flowers CNC'd a 940. Do a search on the Precision Mathews forum on this site.
     
  13. imnoto

    imnoto United States Iron Registered Member

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    Well considering I have a HF 44991 mini mill this thing is going to be a monster compared to my 3 inch Y travel I have now lol.

    I know David, too bad he hasn't finished his conversion yet, offered to buy a kit from him if he gets it done before I start :)
    I can't find anyone that's making a kit for the 940.
     
  14. TomS

    TomS Active User H-M Supporter-Premium

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    The 940 is definetly a step up! I don't know of anyone that is making motor mounts or ball screw & ball nut mounts for the 932 or 940. Making your own can be a rewarding experience, at least it was for me, and when done you will know your machine inside and out.
     
  15. imnoto

    imnoto United States Iron Registered Member

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    Thanks for all your help Tom maybe will see you in my Build thread when the machine finally comes in :)
     

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