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IndustryArena Forum > CAM Software > BobCad-Cam > Grooves in Walls in Pockets
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  1. #1

    Grooves in Walls in Pockets

    I have a project that requires a groove inside a round hole or pocket, attached is a file which approximates the part I'm struggling with along with a screenshot with detail of the part.
    I have 3-Axis Pro so the right cutters for the job are available to me but I've looked through all the tutorials and Video Professor material and can't for the life of me work out how to even start to approach this one. I've tried extracting edges for the groove to a new layer but from there I'm a bit stumped!
    Any ideas would be much appreciated,
    Thanks,
    - Nick

  2. #2
    Join Date
    Sep 2012
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    I think the easy way is to do it as a 2d profile and keep the clearance issues in mind manually. I would extract the inside arc geometry from the slot, then extend it to create a longer arc. You can do this for the top and the bottom just to make it easier to get the specific coordinates of the Z axis so you know exactly what the opening size is. I would use only the bottom arc to run the profile from, but if you select both arcs and then right click/(select)Entities Summary, you can get the specific max and min Z value of the two arcs, which will allow you to figure out the Z depth for a profile. You then create a profile of a single depth of cut to the bottom of the slot, then create more as appropriate moving upward until the full slot height is achieved. If the bottom of the slot is at Z=-35mm and the top is at Z=-25mm and you are using a 5mm tall T cutter, you would make the first cut with the depth set to -35mm and then perhaps a second cut at a depth of -32.5mm and a third cut at -30mm. The third cut would be cutting at Z-25 at the top of the cutter, so you would be done. It's important to extend the arcs in order to prevent the cutter from gouging the material on the way up or down. Not sure is there is really a faster way to do it, though there might be a way to use the solid geometry (I use V24, so I don't have T cutters anyways). Either way, I would prefer to do this type of toolpath in a more manual fashion via 2d profile. Sounds complicated, but once you do it a few times, you can do it in minutes. Here's roughly what it would look like:


  3. #3
    Thanks for that, it looks like an option.
    I'm hoping that as some 3D features in V25 give T cutters as an option that there will be one feature that will do this.
    I've managed to get partway to a solution with Equidistant Offset, I can't work out why it's generating the toolpath quite the way it is though - image attached - I'll keep beating my forehead against the problem and see if it will give in ;-)
    Regards & Thanks,
    Nick

  4. #4
    OK, I think I'm getting somewhere, by limiting the stock Z dimesion to the cutter thickness I've forced a 2D path, potentially I can duplicate the 2D path at several depths to do the job.
    If set to take two cuts the path is generated to take the deepest cut first, then a lighter cut (should be the first) of thin air
    Deep Joy!

  5. #5
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    Apr 2009
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    mmoe way is the way I would approach it.
    Is this groove for grease or a key or do you know ?

  6. #6
    Join Date
    Sep 2012
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    The problem with any 3d toolpath is that it's not going to match the top and bottom of the slot unless you go through more trouble than you would doing it as a 2d toolpath. If the cutter is 5mm tall, as my previous example, and the slot is 10mm, if the first time that the 3d toolpath encounters the slot is 1mm below the top of the slot, it won't cut the top of the slot and probably won't cut the bottom of the slot either depending on your spacing. The toolpath step-over or step-down would have to match the top of the slot and then the bottom of the slot exactly from the initial point of reference. This can be done, but you'd already be finished generating the toolpath in 2d in my opinion. In 2d, it does what you tell it whether that cuts into the solid too much or not because it doesn't take the solid into account (for better or worse depending on what exactly you tell it). But in 3d it will calculate the movements based on the solid, and if there is even a .005mm interference it will machine the outside of the slot instead of going into it.

    I'm not sure about V25, but the V26 demo allows for T-cutters in 2d profiles as well (might have been a new feature). In V24, I don't have T cutters at all and just specify the tool as an endmill, keeping mental track of the fact that it's got a smaller shank than it's actual diameter. The only issue with this is that it won't simulate correctly if you're into simulating parts. V26 would probably allow it to simulate correctly by selecting the T cutter (again, can't remember in V25).

  7. #7
    That all makes sense, it seemed logical that if BC included T Cutters they should be properly functional, at least I now have the option of two workarounds within BC, Endmill or T-Cutter.
    Thanks for taking the time to reply and explain, it's much appreciated.

    The posted part is just a representation of the actual part, in the actual part the tube wall is interrupted and the slot accepts a locking lug from a sleeve which pushes in & turns to lock,
    Regards & Thanks,
    Nick

  8. #8
    Thanks to mmoe & jrmach for pointing me in the right direction to force BobCad to do what I'd like it to do, attached is a solution using Equidistant Offset with a T Cutter, I've left all the layers in I used while fiddling but in the end I only used the slot base plane and the boundary, it's really quite quick to configure,
    Each pass is defined in Z using the Parameters - Top of Job and Bottom of Job,
    I had to select Bottom to Top under Patterns - Cut Pattern to get the paths to run from centre outwards.
    ATB,
    Nick
    Attached Files Attached Files

  9. #9
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    "Thanks to mmoe & jrmach for pointing me in the right direction to force BobCad to do what I'd like it to do, "


    your welcome ? ?

  10. #10
    Quote Originally Posted by jrmach View Post
    your welcome
    Very Kind

  11. #11
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    Sep 2012
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    Nick,
    I think that the T cutter in Equidistant Offset is functioning normally, even though it may seem like you are doing a lot of work to get the result you want. Let's say that you cut the part in half along the vertical so that it's a semi-circular vertical wall, and then rotated it so the inside of the tube is facing up, then ran an endmill in Planar Slice along the surface. The same problems would come up. The tool always steps over the same distance and if that step doesn't coincide precisely with the start of the opening, the tool will not cut the slot to the correct size. It's a function of how toolpaths are generated off of 3d solids, so the T cutter is working in the exact same way as an endmill would or any other tool would. From that perspective, the tool is fully functional in the operations where it is available, it's just not automatic that it will do quite what you hope. No matter what tool you use, when the surface is not uniform, you often have to find a way to set the tool up to cut along the surface as you intend.

    I think the only thing with using Equidistant Offset is that you end up machining against the wall of the part in addition to the slot itself. By using a 2d profile, you can restrict the cut to only the slot. If the finish quality of the inside of the part doesn't matter, then either way is fine, but if you need a high quality finish to the inside of the part, I'd be concerned that you might end up with a ring of marred material where the cutter runs outside of the slot. It may also be that it's a whisker smaller than the hole it's running in, in which case it's not an issue. Using 2d geometry that is extended to bring the cutter away from the inside diameter of the part on entry and exit ensures that it won't cut (maybe more like scratch) the surface where you don't want it to. 2d geometry will always offer the advantage of engaging the material only where you want to, while 3d geometry is a bit trickier to get the toolpath restricted through the use of boundaries. While it can be done, that is where I think 3d toolpaths are slower than 2d toolpaths for this specific task.

    I checked back on V25 and found that there was not a T cutter in anything but the Pro strategies. That does look to be one of the upgrades that were added to V26, which allows those tools in all toolpath strategies including both 3d and 2d (at least where it would make sense to have it). If you only do this from time to time, as I think most of us do, it's no big deal to use an endmill in 2d instead. If you do this a lot, you might consider upgrading to V26 as it would be a useful addition for those who use it. Even if I had V26 where the T cutter is available in any toolpath strategy, I'd probably still chose to do it as a 2d profile routine just to keep the cut confined specifically to the slot alone. It will always be the fastest way to achieve that for the foreseeable future.

  12. #12
    Join Date
    Mar 2012
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    1570
    A 2d profile is the way to go here.... you can use side roughing to step in if you want. The only other option to create an undercut and have the software offset/comp for tool geometry is to be a multi axis user. Kinda extreme for this example, but provides 7addition tool paths for 3 axis cutting that supports under cutting and more!
    Al DePoalo
    Partner Product Manager BobCAD CAM, Inc. 866-408-3226 X147

  13. #13
    Quote Originally Posted by mmoe View Post
    Nick,
    I think that the T cutter in Equidistant Offset is functioning normally
    Yes, I guess it's probably working "Normally", trouble is that it's hard to know because the documentation is so sketchy, there's actually no entry in Help for T-Cutter!

    Quote Originally Posted by mmoe View Post
    it may seem like you are doing a lot of work to get the result you want.
    It's not much work, it was very quite quick once I found which settings affected the path in what ways, it does give control over horizontal depth of cut in multiple passes. Having no prior Cad/Cam/CNC experience I only started halfway through this year and still often like to have the "hand-holding" of simulation prior to cutting air or metal, it's nice to see some use from my upgrade to "Full Simulation" too ;-)

    Quote Originally Posted by mmoe View Post
    I'd be concerned that you might end up with a ring of marred material where the cutter runs outside of the slot.
    Thanks mmoe,
    that's a very good point, I think that's very likely in the test file I posted. I wasn't considering that when generating the boundary at exactly the ID less 1/2 tool OD, my main concern was to generate functional cutting paths I'm sure a small tweak to the boundary would sort it out.

    Living in the UK I'm relying on the Video Professor Series, Al's excellent tutorials and the very kind input on BobCad Support Forum(s), as with many technical subjects such as SQL and VB programming, a good technical reference can make life far simpler,
    Regards,
    Nick

  14. #14
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    Apr 2009
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    This is what appears a typical woodruff key slot.Feed in,feed out,Done.Fiddle Farting don't pay well.

  15. #15
    I cut typical Woodruff Key slots in shafts on my manual mill and in pulleys on my shaper, Fiddle Farting with CNC when you don't need it don't pay well, I am genuinely interested in the capabilities and limitations of the software I've licensed, I know curiosity and interest aren't for everyone though,
    Regards,
    Nick

  16. #16
    Join Date
    Apr 2009
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    Why ask questions when you already have the answer you want?Never mind.

  17. #17
    Because this isn't a motor pulley or anything else to key to a rotating shaft and so it it isn't a Woodruff Key slot that I want to cut, unless someone's making some newfangled, curved Woodruff Keys??
    Never Mind!

  18. #18
    Join Date
    Apr 2008
    Posts
    1577
    What about an Advanced Rough? Kind of dependent on this file but a much better result.

    Edit, I noticed that your T-Cutter was only 1mm thick but if you change the cutter height to 1mm it will do two passes (I think). I orginally set it up as an Endmill but forgot I could use a T-Cutter, doh!

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