Cutting Depth & Z-Axis

This topic contains 6 replies, has 4 voices, and was last updated by  Chad Youngblut 7 months ago.

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  • #10862

    alex555
    Participant

    I’m a new KNK Force user. I’ve read the manual and several support webpages, but I’m still having some trouble understanding how the Cutting Depth relates to the Z-Axis, and how to best use the machine. I’m cutting dense materials that need several passes at gradually lower depths in order to cut cleanly.

    I’ve read that each Cutting Depth increment represents 0.02mm of downward Z-Axis travel. The manual states that during tool loading, the blade should be referenced against the mat. But this means that the blade will always try to go all the way through the material on the first pass (or at least as much as the blade holder spring tension allows). And then every increment of Cutting Depth would try to drive the blade farther below the mat! Why would I ever want to allow the blade to go past the mat?

    Alternatively, I can reference the blade against the top of the material, as is recommended when using the rotary tool. The downside with this approach is that I have to guess how low a Cutting Depth I can use before the blade hits the mat. This is the issue that all solenoid cutters have — and I bought the KNK Force specifically to avoid this issue!

    If I were to build a cutter, I would assume that the lowest Z-axis point should be set during the tool loading stage. If I were to reference the lowest Z-Axis point against the mat surface, I would never be able to cut through the mat. To cut through dense materials, I would start with the cutter at a high point in the Z-axis, and gradually lower it with each pass until it reaches the lowest point (i.e. the mat). Assuming each pass cuts the material effectively, the spring in the blade holder would never be overwhelmed, and thus the spring would never prevent the blade from reaching its lowest Z point (i.e. the mat).

    I’m confused about why the KNK Force is designed different than this. Can someone fill me in?

    Also, what exactly does the Surface Height represent? When loading the tool, it seems that each increment of 100 on the Surface Height increases the distance between the tool bracket and the base of the machine by 1mm. Based on a spreadsheet I found online, it seems like a surface height of 0 just decreases the granularity of the Cutting Depth (i.e. SH=0 means that each increment of CD will lower the blade by a larger distance than when SH=300). What’s the point of this? Why not eliminate the Surface Height and just increase the granularity of the CD (i.e. make it 1-1000 instead of 1-370)

    Finally, I seem to remember reading a while ago that the machine can sense the top of the material somehow (by lowering the head until resistance is felt?). Is this true, or am I thinking of something else?

    The more details anyone can provide regarding my questions, the better! I come from an engineering background, and I really like the openness and technicality of the documentation, and the build quality of the machine.

    Thank you!

    Alex

    #10892

    Sandy
    Moderator

    Hi Alex,

    Sorry for the delay. I assumed someone else would respond, but I can go ahead and handle these questions for you.

    (1) Regarding: I’ve read that each Cutting Depth increment represents 0.02mm of downward Z-Axis travel.

    The change in CD is not linear along the Z Axis. At the top of the axis (Surface Height of 0), the change is ~ 0.012 mm. At the bottom (Surface Height of 670), the change is ~0.002 mm.  At a Surface Height of 300, it’s ~ 0.009 mm.

    (2) Regarding: The manual states that during tool loading, the blade should be referenced against the mat.

    As you mention later on, the spring inside the blade holder prevents that from happening. You always need to use a CD higher than 0 to cut any material with the blade. You’ll also note in the table in Section 2.06.3, we only recommend using the mat as the reference point in two situations. During the original testing, we tried always setting the Z origin with the blade tip on top of the material but we found it led to less consistent results. The reasons for this are presented in Appendix B2.

    (3) Regarding: If I were to build a cutter, I would assume that the lowest Z-axis point should be set during the tool loading stage. If I were to reference the lowest Z-Axis point against the mat surface, I would never be able to cut through the mat. To cut through dense materials, I would start with the cutter at a high point in the Z-axis, and gradually lower it with each pass until it reaches the lowest point (i.e. the mat). Assuming each pass cuts the material effectively, the spring in the blade holder would never be overwhelmed, and thus the spring would never prevent the blade from reaching its lowest Z point (i.e. the mat). I’m confused about why the KNK Force is designed different than this. Can someone fill me in?

    This is basically how the KNK Force is designed. And given enough passes, the blade should eventually reach the mat. But that’s not how our customers want to cut most of their products with the blade holder. In fact, if we were to say cut your cardstock in, for example, 6 passes at a CD of 1, then most would respond with things like, “Why did I buy this cutter if it has so little force that it takes 6 passes?”  Or “I’m running a business here!  I can’t waste that much time on a cut.”

    Personally, I do use more than one pass when cutting cardstock that will easily cut in a single pass. I will use 2 passes (SD 30, ED 40) versus a CD of 75 because I get nice cuts on small intricate designs by not forcing the blade so much.  I do encourage that approach with a lot of the Force owners, but beyond 2 passes, the paper crafters are not going to want to use more.

    For the rotary tool, we don’t use the mat for the Z origin because it’s simply too easy to cut all the way through the mat if it’s bowing just the tiniest amount. However, if our customers would be careful enough to make sure their CD is set to 1 AND then have a thicker protective layer over the mat that can act as a buffer zone, then one should be able to cut that way.  But since the customers also often want to engrave with the rotary tool, then the Z origin MUST be set on top of the material, because you cannot enter negative values for CD.

    (4) Regarding: Also, what exactly does the Surface Height represent?

    Surface Height is defined in Section 7.04.2. It’s like an adjustable baseline for the Z origin.  The default is 300.  However, if you then try to engrave or cut a material that is 1/8″ thick, you cannot get the tool high enough to insert the material for cutting and set the Z origin on top.

    (5) Regarding: Finally, I seem to remember reading a while ago that the machine can sense the top of the material somehow (by lowering the head until resistance is felt?). Is this true, or am I thinking of something else?

    No, this is not a feature on the Force.

    In summary, I want to emphasize that typically there are multiple ways to  accomplish the same result on KNK machines. However, presenting ALL of the possibilities, along with the pros and cons of each one would make an already-long user manual much longer and, most likely, overly complicated for the majority of our customers.  So, we test and test and try to come up with the best option to get the job done.   But when customers tell me that they did something entirely differently and got a great result, I applaud them.  I never argue with success!   And if it a different way DOES make things easier for all, then I will gladly rewrite that section of the UM and post at our most active forums (right now, Facebook groups) about the findings. : )

    Feel free to ask more questions!  Also, feel free to present some of your own successes and recommendations. They are very much welcomed and appreciated.

     

     

     

    #11023

    alex555
    Participant

    Thank you very much for your thorough reply, Sandy! I’ve been able to fill in a few of the gaps in my understanding, with the help of your reply, rereading the manual sections you mentioned, and playing around a bit with the machine.

    I’ve been cutting some pieces by referencing against the top of the material, using calipers to get a maximum material thickness, and then setting the ED to be significantly larger than the material thickness. Using maximum blade spring tension helps a lot. Finding the right ED takes a lot of trial-and-error, and is especially frustrating when the material isn’t uniformly thick. This also results in cutting into the mat — although my mitigation is to use a 1.8mm thick piece of plastic as my mat, with thick double-sided tape as the adhesive (tape that has a substrate, so it adds some amount of waste area for the blade to drive into, past the material).

    As I mentioned, my ideal case is to just determine an appropriate SD that’s near the top of the material, and not have to worry about the ED — knowing that the machine will never drive the blade past the mat, and not having to do a bunch of test cuts to ensure the material is fully cut.

    I tried using the API to accomplish what I want. It works, but I don’t want to have to re-implement all the cutting logic (e.g. the initial pre-cut movement that aligns the blade in the right direction) if I can avoid it.

    As an aside, I also found that I couldn’t share API access with the web GUI: if I connect to the cutter, issue a command, and disconnect, then the GUI no longer works until I reboot the cutter.

    I also briefly played around with referencing the knife against the mat, then reducing the surface height afterwards. If I understand correctly, this effectively lets me use negative cutting depth values (i.e. above the referenced surface). For example, I’d reference the tool against the mat with SH=300, reduce SH to 200, then take multiple passes with SD=1 and ED=100 (as long as  CD + new_SH <= old_SH  then I will not cut through the mat). This only worked with the blade tension set to maximum — and even then, it may even require no spring in the blade holder. I still have to experiment more to see if this works and is better than the normal “guess the ED” method.

    I know my use case is not the general case, but I’m still not 100% clear on why the SH is needed in the first place. Why doesn’t the machine just represent everything to the user as X,Y,Z coordinates? To me it seems like it would be simpler.

    Two small features that would be nice to have in the web GUI:

    1. The ability to see the current X & Y position of the cutter when doing the X-Y origin placement in the “Prepare the cutting job” stage. This way I can place my cuts efficiently, minimizing material waste. Even cooler would be to optionally use the camera to help choose an X-Y origin. Even cooler than that would be to have a laser projection of the cut onto the work surface (as is done on industrial fabric cutting machines) — but that’s just wishful thinking.
    2. Ability to use negative CD values, to avoid having to do the SH juggling that I mentioned above. This could be an advanced option, so as to not confuse people who wouldn’t care about it.

     

    #11062

    Sandy
    Moderator

    Being able to use the camera to set the XY origin is on the To Do list.  That’s a much-needed function, especially for those trying to engrave onto existing objects.

    #30765

    jonasah
    Participant

    I am trying to cut E flute corrugated cardboard (sneaker/ shoe box material) is about 1.5-2mm in diameter/ thickness but not at all solid. Also maybe emboss or crease it too.  I am experiencing similar issues.  I am used to using slightly more robust drag knives on CNC gantries but am hoping to make the KNK an open use tool for students.  But we need to be able to cut cardstock, chipboard and corrugated in a modest number of passes (2 or 3 max).

    If anyone can help or tell me this will never work I am all ears.  I am at this point looking into a deeper blade (I cannot find anting)and rigging the spring to be even stronger than designed–adding a doubled up compressed spring or a sleave to give it less range).  I agree the entire point of a z axis is to use it for ovious numerical control. Top of table is great if you know you are working downward from there in absalute coordantes.  A spring makes this nearly impossible to understand in a clear way, but it is even harder when the interface is obtuse with how this particular feature works.   the UI could use some little thumbnails like CAM software like this.

     

    https://drive.google.com/file/d/1BGELHCnBTkeGok1N6Fj24F-Gg91E5Ukd/view?usp=sharing

     

     

    #30766

    jonasah
    Participant

    also, I have wondered if we could rig up a way to carry a larger knife holder for soft material:

     

    http://cosmos-industrial.com/index.php?main_page=product_info&cPath=3&products_id=20

     

    or if maybe the KNK can be hacked and turned into a small router:

     

     

     

     

    #30796

    Chad Youngblut
    Keymaster

    Something like this “should” work. I’ve checked in SCAL and offset control isn’t an issue (I tested by entering a value of 10mm).  This would require some experimentation, but I like the idea behind it!

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