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Thread: Roughing pass or no roughing pass for 3D project

  1. #1
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    Roughing pass or no roughing pass for 3D project

    Hi, I purchased a CAMaster Stinger 1 2x4 (1.7kw spindle) a couple months ago and just completed my first 3D project (10"x10") in walnut shown below. Abstract artsy-fartsy piece.

    IMG_0866.jpg
    As you can see there are some rather deep cuts (up to .86 in deep). I did two roughing cuts. First with a 1/2" end mill (30 min) and a second with a 1/4 ballnose (1-1/2 hrs).

    First roughing pass (1/4" steps):
    IMG_0840 3.jpg

    Second roughing pass (max depth 0.6"):
    IMG_0841 2.jpg

    Finally I did the finishing pass with an 1/8" tapered ballnose with a 1" cutting height (9 hrs). The finishing pass was with a 5% step over. The final finish was beautiful with only a couple of places with some torn grain that needed sanding (320 grit).

    IMG_0861 2.jpg

    Now to my question. Given the small stepover, is it possible to avoid the roughing passes and go directly to the finishing pass? Would save a couple of hours and bit changeover. I'm guessing the concern would be stress on the bit. However, I am assuming these bits are capable of cutting full height, but is it advisable for 9 hours? Any advice would be appreciated. Cheers, bob

  2. #2
    First off, your first/last image is pretty sweet. Beautiful. Killing or reducing the roughing passes is going to do to two things, increase your number of finish passes, and depending on final finish pass reduce your final surface quality. Its a balance you you have to find that speaks to material, tool and machine rigidity, speed, and depth of cut. I would personally ditch the two roughing passes for a single roughing pass using the largest ball nose cutter you can run that will get into the detail and run as fast as possible ignoring your surface finish. Then hopefully you can have a single finish pass that will leave you with acceptable result. Second scenario would be two roughing passes with a large tool firs and the second tool only doing the final deep cleanup it can reach. You can fudge both of these in a program like VCarve Pro or you can do it with Aspire/Fusion and rest machining.

    The answer with these to me is to rip off the roughing wide open as fast as your machine will run with the biggest tool possible leaving only what you absolutely need then get to your painfully slow finish pass.

  3. #3
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    Quote Originally Posted by Mark Bolton View Post
    First off, your first/last image is pretty sweet. Beautiful. Killing or reducing the roughing passes is going to do to two things, increase your number of finish passes, and depending on final finish pass reduce your final surface quality. Its a balance you you have to find that speaks to material, tool and machine rigidity, speed, and depth of cut. I would personally ditch the two roughing passes for a single roughing pass using the largest ball nose cutter you can run that will get into the detail and run as fast as possible ignoring your surface finish. Then hopefully you can have a single finish pass that will leave you with acceptable result. Second scenario would be two roughing passes with a large tool firs and the second tool only doing the final deep cleanup it can reach. You can fudge both of these in a program like VCarve Pro or you can do it with Aspire/Fusion and rest machining.

    The answer with these to me is to rip off the roughing wide open as fast as your machine will run with the biggest tool possible leaving only what you absolutely need then get to your painfully slow finish pass.

    Makes sense Mark. I am hesitant to push my machine too hard without knowing the consequences.

  4. #4
    Quote Originally Posted by Bob Falk View Post
    Makes sense Mark. I am hesitant to push my machine too hard without knowing the consequences.
    In my opinion in an operation like this there really arent any devastating consequences. Your either going to borderline stall your spindle (likely never happen) or break a tool (again likely never happen). Your machine can likely withstand 10X what your throwing at it. The end result will likley not be a machine issue but rather a finished product issue (bad finish).

    The hard part with these textures is the finish pass is always painful and you have to do the math on post processing cleanup vs machine run time. Its very easy (for me especially) to want to speed up, increase stepover, get the part off the machine faster, only to result in a lot of painstaking hand work to clean it up. Flip side, machining the part like its a optical surface (slow, ultra tight stepover) makes a part that is unsaleable (whether that matters or not).

    Your 9.5 hours seems a little steep. I 'd think your gains are in the roughing and cutting your finish by 2/3 and its still a long run-time part.

    Youve got a stout machine. Dont be afraid of pushing it. They are thoroughbreds. They want to run. They protect themselves as well.

  5. #5
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    Beautiful “artsy-fartsy” piece Bob, and congrats on the Stinger. I’m still loving mine. I will generally run one roughing pass with a .25 end mill on a piece like that. My main motivator is to reduce the wear & tear on the pricey tapered ball mill.
    I’m retired and tend to baby my Stinger but you can push it pretty hard providing you have a solid work holding setup.
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  6. #6
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    I agree with Mark's advice. There are certainly sometimes when roughing passes can be skipped, but those are usually situations where the nature of the design doesn't put a lot of lateral load on the cutter. For most work that is complex and/or includes a lot of deeper plunges, roughing is essential to allow the finishing tool(s) to be able to work efficiently without extra load and resulting deflection. While this means a lot more time machining, the end result is always what's most important. My first major 3D job for a client included the "pleasure" of nearly 8 hour cut times. Per piece. Two required. Plus multiple test pieces because I was very new to it! That was a LONG, LONG week. Plus.
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  7. #7
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    Great looking piece Bob. It's a learning curve certainly. I keep thinking I will get to the curve but not yet. So my suggestion would be to try more aggressive step over rates. I'm assuming you are using Vectric because I believe it comes with the Camaster. I believe it gives you an estimated run time when you calculate tool paths. See what more aggressive stepover rates do for the time and ultimately the finish. I'm nowhere near an expert here. Just an amateur still experimenting and learning as time permits. Following with interest.

  8. #8
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    Stepover does need to be considered. Roughing is often done with the typical 41% stepover that's default for many tools. Finishing cuts are typically done with stepover between 5% for really critical surfaces up to about 11%, depending on the tool and the design. It can go completely the other way for special effects...Roger MacMunn's textured background technique for signs, etc., gets a 91% stepover and a different, smaller one for a more linen like effect. Stepover is your friend.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  9. #9
    There are some great responses above.
    If you omit a coarse roughing pass, and try and do everything with a tapered ballnose cutter,
    Your first pass into the material will need to be VERY SLOWLY done.

    It's cutting 100% of the cutter diameter in that first pass, even if the return path is only 5% to 10% stepover.
    Watch you don't break the cutter if it plunges full depth in that first pass outwards.

    If necessary set it superslow,cut out & cut back, and then restart the file with a faster pass for the rest of the job.

    There are times in certain 3D jobs when a vertical edge does need to be vertical.
    That's not going to happen with a tapered cutter.

    Ive found for some jobs a 1/16" ballnose cutter with straight or parallel sides gave a far better finished job than the tapered cutter- but beware the cutter has to be long enough to be able to get into the bottom of some 3D pockets too, without the chuck scraping the keepable surface.

    Onloy expereince will teach you where there are efficiencies to be made cutting corners, and where the long way might be better.
    Last edited by Ian Stewart-Koster; 11-15-2020 at 8:36 AM. Reason: typo
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  10. #10
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    Thank you all for the thoughtful and informative responses. Ian, I think you convinced me not to try to do this in one finishing pass. I am going to do some experimentation with stepover vs. finish quality.....I am hesitant to push the boundary on finish quality to much as I would rather the machine produce a nice finish rather than having to sand. Cheers, bob

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    Quote Originally Posted by Jim Becker View Post
    Stepover does need to be considered. Roughing is often done with the typical 41% stepover that's default for many tools. Finishing cuts are typically done with stepover between 5% for really critical surfaces up to about 11%, depending on the tool and the design. It can go completely the other way for special effects...Roger MacMunn's textured background technique for signs, etc., gets a 91% stepover and a different, smaller one for a more linen like effect. Stepover is your friend.

    Jim, I’m interested in the textured background technique. I looked up Roger (Rodger?) MacMunn and saw some nice sign work, but not many details on the textured backgrounds. Any links you know of?

  12. #12
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    The hot setup, IMO, for this sort of thing is an 'extended reach' ball endmill. Not a long flute. They have standard length flutes, or maybe even stub, and a solid relieved shank above them for clearance. Much more rigid, much less prone to chatter and making your ears bleed from the screeching.

  13. #13
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    Quote Originally Posted by Ben Grefe View Post
    Jim, I’m interested in the textured background technique. I looked up Roger (Rodger?) MacMunn and saw some nice sign work, but not many details on the textured backgrounds. Any links you know of?
    It's actually relatively simple and just uses a pocketing tool path...actually two of them. The basic setup uses a ball nose cutter with the stepover raised to 91% and the raster angle set to 35º on the first pass and then to -35º for the second pass. The perimeter last pass only is used on the second toolpath. The resultant background is a cross-hatch type texture that paints up well or is nice even on oiled wood. Here's an example on a sign:



    A modification of this is to decrease the stepover and use a finer cutter (especially on small things), such as a very thin tapered ball nose...same technique otherwise. This gives a more linen-like texture. Example on this pet urn top:

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  14. #14
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    Quote Originally Posted by Bob Falk View Post
    Thank you all for the thoughtful and informative responses. Ian, I think you convinced me not to try to do this in one finishing pass. I am going to do some experimentation with stepover vs. finish quality.....I am hesitant to push the boundary on finish quality to much as I would rather the machine produce a nice finish rather than having to sand. Cheers, bob
    After looking at those photos, there's no way I'd try and do that with just a finishing pass unless it was something like HDU and even then, that particular piece of art would be pushing things. I "might" do it with one roughing and one finish, but I'd have to look at it a lot more in detail. I think you are being wise in realizing that getting a really good finish off the tool is a good thing with something like this because it's extremely difficult to sand out tool marks with all those nooks and crannies.
    --

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  15. #15
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    Okay, feed my ignorance please at the risk of hijacking the thread which I don't want to do. What is the "raster"? I saw that in the settings on Vectric and avoided it because well I didn't want to let Pandora out of her box. IF I need to do a separate thread say so.

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