Looking for good CNC routing reference


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    Default Looking for good CNC routing reference

    So now that I have built my first CNC router system, I find myself on a pretty steep learning curve to figure out how to get the most out of it. Making sawdust is pretty easy, but having a really nice useful part at the end is a little tougher. There is alot of really great information on CNCZone, but there was also alot of confusion. Its difficult to separate the good from the bad sometimes.

    I have a ton of questions that range from very basic (What sort of things should go on a "checklist" before I press the START button for routing a new part? What operations should I perform on the CNC vs. traditional woodworking machines) to more nuanced (What are the differences between different tool path strategies and when should I choose different ones? How do I determine the trade-off between tool path time and surface finish?). I could probably list twenty questions that have come up as I am starting to work on some of my first projects.

    I don't mind making mistakes. In many ways it is the fastest way to learn, but I like to avoid "stupid" mistakes...the things that everybody knows are stupid or that could cause significant damage or injury. Is there a general reference guide to CNC routing anywhere where I can learn "how its really done?"

    Thanks,
    Robert

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    Default Re: Looking for good CNC routing reference

    I could probably list twenty questions that have come up as I am starting to work on some of my first projects.
    Go ahead and list them, and we'll answer them.

    I don't think I've ever seen a comprehensive reference, as there are two many variables. You almost need to take them at a case by case basis.

    Gerry

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


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    Default Re: Looking for good CNC routing reference

    Alright, you asked for it.

    First, in general, I am looking to do alot of 3D work...guitar necks and carved hollow-bodies, asymmetric bowls, other strange shapes. Some of this work will require good accuracy. Alot of my questions come from this perspective. I currently have only used Fusion360 for CAM so that has shaped some of these questions.

    Basic questions:

    1) What are the sorts of things that people do to avoid stupid setup mistakes? I have already have a couple of instances where I have set my zero point incorrectly and that has resulted in either crashes or machining errors. Any sort of checklist for this? I would like to avoid these sorts of mistakes in the future, and I have a feeling that I haven't made all of the common mistakes, yet.

    2) Related to (1) above, what methods do people use for setting the zero point for a job? Clearly the centerline of the spindle needs to be calibrated to the workpiece in order to machine in the right position, but a router bit is a really weird shape and hard to get centered on anything. I have been using a 1/4" steel pin to find X and Y, but that requires that I remember to offset by 0.125" before I set the zero. I've already forgotten that once. I also have been using a piece of paper to determine when the pin is getting close to the workpiece, (i.e. it pinches the paper) then I offset by 0.003" to account for the paper thickness. This is not a new problem...there have to be tried and true ways of doing this.

    3) Do people generally mill their workpiece to size using conventional woodworking tools or use the CNC? I can already see that this will depend on stock size, clamping methods on the CNC, what conventional tools are available, etc. so I'm sure there is no single answer here.

    4) What work holding methods do people use and for what reasons? I've seen hold-down clamps, edge clamps, screwing right to the spoil board, vacuum. This may be something I just have to work with until I get more experience. Edge clamps make me a little nervous because they don't seem to have a good way to push the stock down into the spoil board. Do they work?

    5) What sorts of tricks are out there to make setups easier and more accurate in general?


    More complex questions:

    6) What are the real-world differences between various tool path strategies? Fusion 360 (like other CAM packages, I'm sure) has a variety of strategies for creating tool paths, and many seem to have similar purposes. It is clear to me that some of these were developed simply to accommodate the geometry being machined. Others were created to reduce the time needed to machine or to somehow improve the quality of the machining. I am also confident that the best way to learn is to try different things, so maybe that is the real answer.

    7) Is it generally better to try to complete machining geometry with fewer, more complex programs or with more, simpler programs? An example of this would be carving out the inside of a shallow bowl. I can understand wanting to rough out the shape with a fairly large flat end bit, leaving some material behind for a finishing pass with a ball-end bit. This requires two programs and re-zeroing the bit in the Z direction for the second program. The alternative would be to program the roughing and the finish pass with one program using the ball end bit. Maybe the CAM software doesn't really provide good options for this, so the first option might be the real answer. Are there standard ways of figuring out this sort of stuff, or should I just learn the different schemes and start being creative with how I use them?

    8) There seem to be many ways to control certain aspects of machine operation. Specifically, to minimize the jarring motion that the machine can produce when it changes direction, the accelerations can be adjusted either in the motion controller or the G-code (via the CAM package). I have also seen settings in both that relate to how accurately the machine will follow the ideal path. Where is the best place to control these sorts of things, the motion controller or the G-code? Maybe this depends on what CAM package and motion control software is being used (among other things).

    9) I've seen alot of discussion about feeds, speeds and depth of cut. I am familiar with concept of chip load and how to calculate it. There still seems to be a certain amount of intuition that goes into this, however. My system is probably powerful and stiff enough to run a 1/2" 2-flute bit through hard maple at 600 IPM with a 15000 RPM spindle speed with a 1/2" depth of cut. The real question is whether that would actually produce a good cut and whether the bit will break. This is just an example, but I don't have a good way to know if I should program my machine to do this. From my experience with manual routing, I would NEVER attempt this, but the CNC holds the spindle much more rigidly than I could, and I couldn't move accurately at 600 IPM anyway. Do you really have to rely on experience to figure this out? I'm not looking forward to seeing a 1/2" bit breaking off, so I have limited my feed rates and depth of cut to reasonable limits so far. Is there any better guidance for depth of cut and step-over distance? Is there a rule of thumb related to the cross section of the bit?

    10) Am I just over-thinking all of this? ;-)


    Thanks,
    Robert



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    Default Re: Looking for good CNC routing reference

    Quote Originally Posted by DDgitfiddle View Post
    Alright, you asked for it.

    First, in general, I am looking to do alot of 3D work...guitar necks and carved hollow-bodies, asymmetric bowls, other strange shapes. Some of this work will require good accuracy. Alot of my questions come from this perspective. I currently have only used Fusion360 for CAM so that has shaped some of these questions.

    Basic questions:

    1) What are the sorts of things that people do to avoid stupid setup mistakes? I have already have a couple of instances where I have set my zero point incorrectly and that has resulted in either crashes or machining errors. Any sort of checklist for this? I would like to avoid these sorts of mistakes in the future, and I have a feeling that I haven't made all of the common mistakes, yet.

    [Sure, make a checklist. Is the material securely held down? Are the zero points accurate? Is the tool tight in the collet? Is the dust collection running? I could go on, but you can do this yourself.]

    2) Related to (1) above, what methods do people use for setting the zero point for a job? Clearly the centerline of the spindle needs to be calibrated to the workpiece in order to machine in the right position, but a router bit is a really weird shape and hard to get centered on anything. I have been using a 1/4" steel pin to find X and Y, but that requires that I remember to offset by 0.125" before I set the zero. I've already forgotten that once. I also have been using a piece of paper to determine when the pin is getting close to the workpiece, (i.e. it pinches the paper) then I offset by 0.003" to account for the paper thickness. This is not a new problem...there have to be tried and true ways of doing this.

    [If you need to be accurate, use an edge finder to set X and Y. This goes in the spindle instead of the tool, and gives you a reference that won't break if it overshoots the mark. You do have to remember to offset by half the diameter (put that on your checklist).]

    3) Do people generally mill their workpiece to size using conventional woodworking tools or use the CNC? I can already see that this will depend on stock size, clamping methods on the CNC, what conventional tools are available, etc. so I'm sure there is no single answer here.

    [Right; it usually helps to have a little excess material to hold onto that won't be hit by the tool. But it depends on what you're doing, and how you're holding things.]

    4) What work holding methods do people use and for what reasons? I've seen hold-down clamps, edge clamps, screwing right to the spoil board, vacuum. This may be something I just have to work with until I get more experience. Edge clamps make me a little nervous because they don't seem to have a good way to push the stock down into the spoil board. Do they work?

    [They can, but it depends - on thin stock, they can bow the material upwards. Vacuum works better for things like that, if you've got it. But if there are lots of little pieces, or a lot gets removed in the cutting process, then it can start to be overwhelmed. ]

    5) What sorts of tricks are out there to make setups easier and more accurate in general?

    [You're right, someone should write a book...]


    More complex questions:

    6) What are the real-world differences between various tool path strategies? Fusion 360 (like other CAM packages, I'm sure) has a variety of strategies for creating tool paths, and many seem to have similar purposes. It is clear to me that some of these were developed simply to accommodate the geometry being machined. Others were created to reduce the time needed to machine or to somehow improve the quality of the machining. I am also confident that the best way to learn is to try different things, so maybe that is the real answer.

    [You've answered your own question. But if you think about it, some of the logic behind using one or another strategy will become evident.]

    7) Is it generally better to try to complete machining geometry with fewer, more complex programs or with more, simpler programs? An example of this would be carving out the inside of a shallow bowl. I can understand wanting to rough out the shape with a fairly large flat end bit, leaving some material behind for a finishing pass with a ball-end bit. This requires two programs and re-zeroing the bit in the Z direction for the second program. The alternative would be to program the roughing and the finish pass with one program using the ball end bit. Maybe the CAM software doesn't really provide good options for this, so the first option might be the real answer. Are there standard ways of figuring out this sort of stuff, or should I just learn the different schemes and start being creative with how I use them?

    [There's no particular reason to rough out 3D shapes with a flat end bit. A big ball-nose will work just as well, without creating "stairsteps" that don't machine away as smoothly as cusps in the final pass. If there isn't too much detail, you can use the same bit to finish as you did to rough out; results will be smoother than if you used a smaller bit.]

    8) There seem to be many ways to control certain aspects of machine operation. Specifically, to minimize the jarring motion that the machine can produce when it changes direction, the accelerations can be adjusted either in the motion controller or the G-code (via the CAM package). I have also seen settings in both that relate to how accurately the machine will follow the ideal path. Where is the best place to control these sorts of things, the motion controller or the G-code? Maybe this depends on what CAM package and motion control software is being used (among other things).

    [You tune the motors in the control software; that's where the acceleration is set, which determines how fast a move is at the outset. Velocity, which is the eventual speed that's achieved, is addressed in the CAM software, but the G-code can't vary the acceleration on the fly. You can also program the machine to do "continuous contouring", which makes things smoother at the expense of absolute accuracy, since it tends to cut corners. "Exact stop" will be more accurate, but a lot jerkier.]

    9) I've seen alot of discussion about feeds, speeds and depth of cut. I am familiar with concept of chip load and how to calculate it. There still seems to be a certain amount of intuition that goes into this, however. My system is probably powerful and stiff enough to run a 1/2" 2-flute bit through hard maple at 600 IPM with a 15000 RPM spindle speed with a 1/2" depth of cut. The real question is whether that would actually produce a good cut and whether the bit will break. This is just an example, but I don't have a good way to know if I should program my machine to do this. From my experience with manual routing, I would NEVER attempt this, but the CNC holds the spindle much more rigidly than I could, and I couldn't move accurately at 600 IPM anyway. Do you really have to rely on experience to figure this out? I'm not looking forward to seeing a 1/2" bit breaking off, so I have limited my feed rates and depth of cut to reasonable limits so far. Is there any better guidance for depth of cut and step-over distance? Is there a rule of thumb related to the cross section of the bit?

    [These things vary with different machines. A large commercial router in the $100k range might be stiff and powerful enough to do a cut like that - a DIY machine made with skateboard wheels running on plumbing pipe not so much. It sounds like yours is somewhere in between. It's usually best to start out with a reasonable speed (not so slow the material's showing dwell marks) and a shallow depth of cut, and if it seems to be working fine, trying a slightly more aggressive cut next time - until something breaks or grinds to a halt, at which point you back off...]

    10) Am I just over-thinking all of this? ;-)


    Thanks,
    Robert
    [Not really; these things are worth thinking about, but you're still going to have to experiment to find answers that work for you.]

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Default Re: Looking for good CNC routing reference

    Somewhere on these forums there is a macro for mach3 that helps with edge finding. Basically what it does, is you have two wires connected to your BOB and when electrical contact is made, it stops the machine, and then you can set your zero for that axis.

    For example, if cutting something out of wood, I would put a piece of metal with one of the wires attached on the surface, the one I use is 0.375" thick. The other wire is attached to the bit. When you set the Z zero, the Z axis moves slowly down until electrical contact is made, and then the machine automatically stops. Then I set the Z zero, and jog the z axis up and over so it's not overtop of the work piece and then down 0.375" past the zero, then rezero. Now I have set the zero for the top of the work piece.

    For edges, you can do something similar to set x and y zeros. Typically I would jog the bit over by half of it's width in X and Y before setting each respective zero and use the corner point of the raw material as the zero point when generating G code in CAM. When you change tools perhaps to go from a roughing to a finishing operation, you only need to reset the Z zero, X and Y are still set.

    Make a checklist and print it out if it helps you to avoid crashes.

    I may have missed it, but I didn't see what kind of machine this is? Spindle power and machine rigidity will vary significantly between each machine design, especially for DIY designs. No one can really answer what DOC and stepover your machine can handle, although they may be able to answer in relation to what the bit can handle on a rigid machine. I think a better question would be to ask what kinds of bits you should use on different materials and what feedrates have worked well for others. Then you need to do some experimentation to find out how far you can push your specific machine as far as DOC and stepover.



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    Default Re: Looking for good CNC routing reference

    1) Everybody makes mistakes. I guess that practice makes perfect. The more you do things, the fewer mistakes you make.
    If there's a mistake that you make repeatedly, then perhaps a checklist would be a good idea.
    I would think that the most common mistakes would be in zeroing the axis. And again, once you get into the habit, it should beco0me second nature.

    2) A lot of people use probing routines to find their XY (and Z (zero positions). A device like the Triple Edge Finder makes it easy to quickly find a corner.

    I work a bit differently than most, in that I rarely zero my X and Y axis. I do the majority of my work in machine coordinates. I have X and Y axis fences on my machine at X zero and Y zero. I program my parts relative to this origin, and just place the stock against the fences, and lock it in place with CAM clamps.
    I also have a grid of T Nuts in my table, and will sometimes bolt my parts to the table. Again, I program the parts relative to my fixed origin, so I don't need to zero the X and Y axis. I just home the machine, place the parts, zero the Z, and start.

    On the rare occasion that I do need to zero the X and Y axis, I do it by probing.

    I zero my Z axis with auto zero probing routines and a touch plate.


    Some people use a laser crosshair to find their X and Y zero, if it's not that critical. Just jog the machine until the laser crosshairs are where you want, and set the zero position. This is usually done with a simple macro that automatically sets the offset.


    3) Lot's of variables here. It depends on what you are doing, and what tools you have available.

    If I needed a piece of wood already cut to size, I'd typically use my table saw, and jointer and planer if required.
    Remember, a CNC Router is just another tool. Use the tool that does the job the best.

    4) Lots of different ways, as you mentioned. It depends in part in how your machine is set up, and also in what you are doing. Personal preference also plays a part. Some people like doing things a certain way.

    As I mentioned, I generally use CAM clamps. I'd prefer vacuum, if I had it available, but I find the CAM clamps to be the next best thing. Vacuum also has it's limitations. But it's very fast, and especially good for production work.

    I don't have an issues with my DIY CAM clamps lifting the stock.. But I know it can be an issue with some edge clamps.

    I've never used any type of clamping that sticks up above the part. Too easy to run into.

    When I machine aluminum, I always bolt it to my table.

    5) This is a pretty general question. I guess you would say jigs or fixtures, or the fences that I use. I really have no setup. Just place the part on the table, clamp and go. Jigs and fixtures, or even a vise, would be similar. Anything that lets you position your stock in a repeatable place.

    6) I've never used the CAM in Fusion, but I just loaded it up and took a look.
    Let's start with 2D.
    I'm assuming that you are working mostly with wood? In that case, you're mainly going to be using pocketing, and contour toolpaths.
    Contour (also known as profile) toolpaths are generally used when cutting out shapes. The tool follows a path, and is usually offset to one side of the path.
    Pocketing is used to remove areas of material.
    Fusion has an Adaptive Clearing toolpath, which I've never used. This would be used in a similar way to pocketing, to remove a lot of material.

    If you need to clean up the top surface of your boards, you can use the facing toolpath. Many people also use a pocketing toolpath for this, in CAM programs that don't have facing toolpaths.

    All of the 2D toolpaths in Fusion generally have specific applications.

    3D.
    With wood, in many cases, you simple do a roughing pass, and a finish pass. This is most often done with parallel, or spiral toolpaths. Fusion gives you a large variety of other options, mostly to cover specific situations, but parallel or spiral will go a long way when working with wood.

    What's really important, IMO, is to understand when to use 2D toolpaths vs 3D toolpaths. Many people will create a simple geometric 3D model, and trry to use a 3D parallel toolpath on it. In many cases, 2D toolpaths like pocketing and contour will do the job better, and faster.

    Personally, I think that Fusion's CAM is overkill for CNC Router users cutting wood, and it greatly complicates the learning curve for beginners. Having said that, it's free, so it's hard to pass up. And if you master Fusion's CAM, you'll have learned a lot. But for some applications, a much simpler approach can be much faster. All my 2D programming is done with simple 2D CAD drawings, and fairly basic CAM. My day job for the last 20 years is programming and running big industrial routers, and everything I do is done with quick 2D drawings, and basic contour or profile toolpaths, with the occasional pocket.

    7) It's better to use the appropriate tool for the job. If this means multiple tools, than use multiple tools. I wouldn't try to avoid changing tools, unless it's a production job, where the tool change would take more time..
    For some 3D work, like shallow relief carvings, it's often possible to skip the roughing pass, and just do a single finish pass. This is usually done with a tapered ballnose tool, and works best if the cutting starts at a shallow depth.

    My machine uses an auto zero macro that automatically measures the tool after a tool change. So if I have a program with multiple tools, the machine moves to a specified tool change position, and stops. I change the tool, and click a button, and the machine measures the new tool, and continues with the g-code for the new tool.

    8) The CAM really has very little control over this. Or should I say, these are really two different issues.

    Violent direction changes are in part due to the nature of most inexpensive controls, which use a linear acceleration and deceleration. Ideally, you'd use a control with S Curve acceleration, which can be much smoother. UCCNC has future plans to implement this, but I wouldn't expect to see it for at least a year.
    Most controls also have some type of Constant Velocity mode, which can make things much smoother. However, this comes at the expense (in some cases) of decreased accuracy. In order to smooth out the motion, the control needs to round offthe corners of the toopaths, to make s smoother transition from one direction to another, while trying to maintain a certain velocity.
    Higher acceleration settings can allow the control to follow the path more accurately, at more consistent speeds, but comes at the expense of more violent transitions. The rigidity of your machine plays a part here as well. If your machine shakes and vibrates with direction changes, then you may need to reduce the acceleration settings to smooth things out. The downside is that you won't be able to follow the path as accurately, unless you slow down more when changing directions.

    Note that S Curve accel isn't perfect. While it can make the machine much smoother, and more accurate, in some cases it can increase cycle times, because the machine will run a bit slower in the corners.

    Error tolerance settings in Fusion can have a big affect on the quality of the toolpath. Again, I don't have much experience with Fusion. What happens is that you can end up with toolpaths that won't run as smoothly on your control as others do. So it's not that the toolpaths make your machine run smoother, but rather, different toolpaths affect how smoothly the control can move the machine. There's a lot of info out there on setting the toolpath tolerances in Fusion.

    9) Your typical 2.2KW spindle is probably not powerful enough to make that cut. Depending on how sharp the bit is, I would expect the spindle to stall. You shouldn't be able to break a 1/2" carbide bit, unless a) the spindle stalls, or b) you try cutting through metal at those speeds. At work, I have a 15HP spindle, and I've broken one 1/2" bit in the last 8 years. A typo had me attempting a cut at 1200ipm and 1500rpm.

    With any bits over 3/8" diameter, I'd expect the spindle to be the limiting factor in how fast and deep you can cut.
    Other factors come into play, however.
    One is workholding. You'll find that holding parts still while making deep, fast cuts can put a lot of force on the parts, often causing them to move.
    Another is machine rigidity. If the machine is vibrating, or flexing, it'll affect cut quality. You'll need to keep the chip load within the machines capabilities.
    The other factor is cut quality. You'll most likely be looking for optimal cut quality, which may require you to greatly reduce speeds.

    If you want the best possible tool life, you want to cut with the highest feedrate possible, with the lowest rpm possible. If you want the best possible finish, you might be at the other end of the spectrum.

    Tool geometry can also come into play here. Different types of tools have different chip load ratings, meaning some tools can cut much faster than others.

    If you want to cut at higher speeds, I'd recommend 3/8" bits rather than 1/2". They're much cheaper, and the cutting forces are a fair bit lower. And they are still capable of cutting nearly as fast as 1/2" bits.

    Unfortunately, it's very much a trial and error game, if you have no experience. Your machine has a lot to do with what you can actually do

    If I had to guess, for a starting point, I'd make that 1/2" deep cut in maple at about 300ipm, and 14,000 rpm. Assuming you're using a good quality spiral bit. But I'd also dial the FRO down to about 60%-70%, and slowly increase it as you go.

    You don't want to stall your chinese spindle, as they aren't too tolerant of stalling.

    Hope this helps.
    Keep in mind that these are fairly general answers. Feel free to ask more specific questions, which will likely result in more specific answers.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

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


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    Default Re: Looking for good CNC routing reference

    Sorry, I should have let everyone know what machine I am running. I have a FineLine Automation Saturn 2x4 using Teknic ClearPath motors (NEMA 34 SDSK series). I am running UCCNC with a UC300ETH controller on an MB2 BOB. For those not familiar with the Saturn machines, it uses an 80mm welded steel frame and a 3"x6" 8020 extrusion for the gantry. It has a rack and pinion drive for the horizontal axes and a ball screw for the vertical. The system is pretty stiff. As an example, I find that I am not able to square up the gantry by homing the two motors independently to two sensors. The gantry will not flex enough to allow this to happen, so I had to square the gantry by adjusting it mechanically. I have a 2.2kW Air-cooled Chinese spindle run by a Hitachi WJ200 VFD.

    So with this system, I am pretty confident I COULD run the profile I mention in question (9) above, except for knowing if the bit could handle it, and what the wood would look like afterwards.

    awerby, thanks for the responses. I probably do need to write up a checklist at least until it becomes second nature. I have a habit of working in the shop in the evenings after my day job, when I am a little more prone to mistakes. A checklist would help. It sounds like I'm going to have to do a little experimentation before I really try some more "important" work with expensive materials. I appreciate the thoughts on using a ball end instead of a flat end bit for roughing. I haven't really tried either yet, so I will start with the ball end and see how it goes.

    I have used an edge finder on a Bridgeport, but all the ones I know of are really limited on speed. My spindle only goes down to 9000 RPM, and most edge finders wouldn't survive that. My replacement has been a precision ground steel pin and trying to be careful with the jog button stepping in 0.001" increments. I suppose I could use an edge finder without turning on the spindle, but maybe not the most accurate way to do it.

    On machine control, I guess you have pointed out the real issue...I need to play with the accelerations until I am happy with how the machine "sounds. Approximating motions with continuous contouring is probably not what I am after.


    NIC 77, I am familiar with the technique of zeroing the bit with an electrically conductive plate. I haven't implemented this yet, but may consider it if it really simplifies things.

    Is there anywhere to find out what DOC and stepover a bit can really handle when running at the recommended chip load? I would think that this is limited by the strength of the bit. I realize that wood is an inconsistent material, but a de-rated value should be available. How many $30-$60 bits does any one person really want to break?

    Thanks,
    Robert



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    Default Re: Looking for good CNC routing reference

    Gerry,

    Thank you for the detailed answers. Alot to think about and work through. Based on everything, it looks like what I really need to do is make some chips. I'm struggling a little with Fusion right now (all day today!!) trying to get it to do what I want. I can definitely see your point about being overly complicated. The 2D stuff is going pretty well, but the 3D doesn't seem to want to work the way I was hoping. I've got alot of experience in 3D CAD, but not much in CAM.

    Thanks,
    Robert



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    Default Re: Looking for good CNC routing reference

    So with this system, I am pretty confident I COULD run the profile I mention in question (9) above, except for knowing if the bit could handle it, and what the wood would look like afterwards.
    As I mentioned above, I don't think your spindle will be up to it.


    Is there anywhere to find out what DOC and stepover a bit can really handle when running at the recommended chip load? I would think that this is limited by the strength of the bit. I realize that wood is an inconsistent material, but a de-rated value should be available. How many $30-$60 bits does any one person really want to break?
    Solid carbide spiral bits are far stronger than you think. If you look at the chip load charts from Onsrud, they specify the chip load when DOC = diameter. As depth of cut increases, you should decrease the chip load.

    You won't break bits from pushing them too hard. I've cut 3/4" sheet goods (plywood, particle board and MDF) at ±800ipm and 17,000rpm with 3/8" bits, one full depth pass.
    Chip load will be limited by your spindle power, hold down method, and cut quality. Not the tools, provided they are quality tools.

    My rule of thumb for DOC? for 1/8" & 1/4" bits, I limit my DOC to the tool diameter. With 1/4" bits, I'll cut at speeds up to 450ipm, at 18,000 rpm, depending on material. For hardwoods, I usually do a roughing pass at 300-350ipm, and a full depth finishing pass at about 150-200ipm.

    For 3/8" and larger bits, you can cut up to 3/4" in one pass, with no fear of breaking bits.

    One thing that can break bits, is poor workholding. If a board is vibrating while cutting, or moving, your chance of breaking a bit goes up a LOT.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

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


  10. #10
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    Default Re: Looking for good CNC routing reference

    How about a real-life test with a wood guitar body i have ready to go.?
    Nothing like making real parts.........
    Ready for any cutter, any depth of cut any feed and RPM.
    I have material and cutters, Smallest is s1/8" up to 1/2"

    Attached Thumbnails Attached Thumbnails Looking for good CNC routing reference-bottom-half-hybrid-1-jpg  
    Been doing this too long


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    Default Re: Looking for good CNC routing reference

    Looks a little familiar.



    Actually, I agree with you...the best way to learn is with real parts. I posted my latest experience on my build log. Short story...still having trouble, but I have learned alot.

    http://www.cnczone.com/forums/fineli...ml#post2120226

    Thanks,
    Robert

    Attached Thumbnails Attached Thumbnails Looking for good CNC routing reference-guitar-1-jpg  


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    Default Re: Looking for good CNC routing reference

    Just carve them out, wood or aluminum
    Sorry about the bowl...

    Attached Thumbnails Attached Thumbnails Looking for good CNC routing reference-lp-jpg  
    Been doing this too long


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    Default Re: Looking for good CNC routing reference

    Never played an aluminum guitar. Aluminum neck, also? How much will that weigh?



  14. #14
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    Default Re: Looking for good CNC routing reference

    This will be a 1 pound 3 oz billet top after machining, and wood bottom.
    The necks are the same weight as hard maple,



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Looking for good CNC routing reference

Looking for good CNC routing reference