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  1. #1

    4th axis carving questions

    Hobbyist level, I have built 3D printers and refurbished an old Epilog Laser, Now I am looking at building a task specific 4 axis router for gun stocks.

    I have seen what appears to be 2 distinct styles of carving a gun stock on a 4 axis router.

    one has the 4th axis just "indexing" the stock and the tool carving Longitudinal as shown in this video: https://www.youtube.com/watch?v=P5_nT1hsQf8

    The other is where the stock continually rotates on the 4th axis as it is carved "Radially" https://www.youtube.com/watch?v=Ik_UKwVTMv8


    Is one method better than the other?
    Does it require different CAM packages to perform one or the other?
    What would be a good "Hobbyist" CAM package to perform one, the other, or both?

    It looks like they are using a Ball end bit for their carving, for the final cut it would seem the point of contact/cut would be infinitely small, requiring the passes to be in the millions for a smooth finish without ridges?

    I have found books and articles explaining generic CNC router theories, but nothing in depth dealing with 4th axis, bit choice and carve paths for desired results,, Does anyone have a good source for reading material for these subjects,

    Many Thanks,

  2. #2
    Gold Member
    Join Date
    Apr 2004

    Re: 4th axis carving questions

    The choice of which 4th axis carving strategy to use - indexing or continuous - depends on the configuration of your part and your expectations for it. To use your rifle stock as an example, if that slot in the top of it needs to be square on the sides, then an indexing strategy would be best. If you carved it using a routine where the tool moves down the X axis, increments in A, then moves back up to X zero, etc. then your slot would be wider at the bottom than at the top. But if your primary concern was smoothness on the outside, you could use the continuous strategy and put in the slot later, as a separate operation. Indexing usually will show a little discontinuity where the various toolpaths meet.

    For jobs like this where you need a smooth contoured surface, a ball-end tool is always used. Otherwise you'd have gouging from the edges of a flat endmill. It does remove less material at a time, though. 3D carving is always going to be slower than 2.5D. The cusps where the passes of the tool adjoin are smallest when the diameter of the tool are largest and more noticeable when the diameter is smaller. To counter that tendency, you need to space the step-over tighter with smaller tools. But it's not in the millions even then; an approximately flat surface can be achieved without infinitely small step-overs. Since your rifle stock has a generally smooth surface without tight spaces that need to be reached by the tool, it looks like you could do the whole thing with a fairly large-diameter ball-end cutter, like about half an inch.

    I'd suggest using DeskProto as your CAM package; it can do both types of 4th axis carving - indexed ("n-sided") and continuous (along X or along Y), and has a lot of other handy features as well. We sell the multi-axis edition at a significant discount to hobbyists. I don't know of any books that talk about 4-axis carving in any depth, but there's a lot of instructional material on the DeskProto site: DeskProto offers CNC machining for non-machinists
    Andrew Werby

  3. #3

    Re: 4th axis carving questions

    Thank you for your in depth response.
    The inlay would be a separate operation, most likely with a bit change to an end mill bit.

    I will look into Deskproto and the associated literature.

  4. #4
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003

    Re: 4th axis carving questions

    You may find that you get a better finish machining along the stock, with the grain of the wood. But you may also finds that it's more susceptible to tearout that way, depending on the roughing strategy.

    There are very few CAM programs that support continuous 4th axis. The "Radial" method. I think Fusion 360 offers it in it's machining extension, for an additional $1600/year.

    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CNC Dovetails & Box Joints

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5

    Re: 4th axis carving questions

    Thank you for the response, 90% of what I use would be laminated plywood.
    What is odd is both videos are from the same machine supplier,, unsure of why they used different techniques.
    I may give them a call and see if they will give a "Hobbyist" 10 minutes on the phone.


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