I’m sure this is a simple fix but I haven’t figured it out yet. I’m cutting a 3/4 " piece of plywood. I’ve zeroed the bit on the z axis. I got to the last layer or next to last layer in a cut and the screw mount heads from the router hit the work piece and threw off the router.
What is the best way to set the axis on Z where it doesn’t hit but can cut through a 3/4" piece or whatever thickness piece that is on the CNC.
Thanks in advance
Not sure I understand correctly but wouldn’t a longer bit work (or mounting the bit a little bit lower into the chuck) ?
I’ve seen collet extensions for sale in various places (e.g. https://www.rockler.com/rockler-router-collet-extension-for-1-4-in-shank-bits). It will definitely negatively impact runout/rigidity, but depending on what you’re working on it might be a tradeoff worth making.
This on the LR2. ok, so the challenge to explain this.
I set the bit at zero on the table while the CNC is off. This allows that if it drops it doesn’t plunge the bit through the table. I could make the bit go deeper I guess and have a hole that it sets into on the HOME position. However, I was thinking more along the lines of a 3d printer where the tip sits at zero to start.
Because the LR2 automatically drops to the table, there isn’t an adjustment to keep it up a few mm’s so getting the actual x plate to not hit the work item (3/4 ply at this point). I’m thinking probably this is a g-code starting issue or something.
More than likely, it’s my perspective on the CNC vs 3d printer and something I’m missing.
On mine I can get the collet almost all the way past the carriage, though my base plate is only about a quarter inch.
I wanted to use countersunk screws, but I don’t have enough material for that, you might be able to do that. If you’re getting that close, be careful with dust collection, it doesn’t take much for it to stick itself to the workpiece with a shop vac running. Usually before a cut I run the carriage off to the side of whatever I’m going to cut and crank the router down so the end mill goes past the piece, then I lock the router in the base. So in the picture above I’d move off to the left side and make sure the end mill could at least touch the mdf spoil board. I was testing an engraving on the foam in that pic.
When my machine is off, I have the router up enough so the bit doesn’t stick out the bottom. Then I turn the machine on (in a square position), move to the workpiece origin, then up enough to account for the thickness of the work, and I adjust the router base so the bit is touching the top surface and I set the origin position. When cutting 3/4" ply, I might be cutting 19-21mm deep (I cut deeper on larger items, because there will be more error), with a few mms into the spoil board just to make sure the piece gets cut out. When it’s done, it will rise up to the clearance plane, and since I’m always standing right there (never leave your running CNC alone), I will turn off the router, raise the bit by adjusting the router base again, remove my work and usually power off there, but sometimes I will jog over to the starting position first. The router isn’t ever dropping with the bit out (at least not on purpose) and the router is off before dropping. I have a LR1, but I think it’s similar.
If your machine is dropping before you want it to, there are settings for that, and there is a gcode (M84, IIRC) that is sometimes in closing gcode that will disable steppers, which you have to remove.
Bottom line, your bit needs to be sticking out further. Moving the router down is probably the easiest. I’ve also had to remove those little plastic rings on the bits for it to go down the full 21mm. They are just press fit and I can remove them with some pliers.
OK so trying to get this in my head -
I have the cnc program set to 3/4" for thickness. Should I take that down a bit more in this case? Say 7/8 to insure it cuts through?
Appreciate the help!
ok, so bear with me if you might.
the distance between the plate when Z = 0 is 1/8th of an inch between the bottom of the plate and the top of a 3/4" board. The screws that mount the hardware slides and the router come down about 1/4"
With that said, I’m trying to figure out how to come from a Z=zero to a position on the controller (say z = 30) to lift up the z axis, then drop the router bit long enough to cut through the material, but at the same time make sure that the plate doesn’t touch the work piece when it cuts through the entire 3/4" .
So my guess is I need to do some g-code settings (estlcam) that would allow this to happen. I am thinking that I should have a zero position set and initial code would allow me to come up say Z=30, change tool which is really lowering the bit, then start the cut.
Does this make any sense now?
I hope that explains it better.
Yes to all of the above. I know it seems wonky but after the first good cut it makes sense.
#4 (as long as your are sure your bit is out as far as you need to go deep plus a mm or two).
Try it a different way, might help to get the hang of it. Set the stick out to be slightly longer than your depth before you start. I have a hole at my table 0,0,0 for the bit to hang through it necessary. That way when you drive to the work piece corner and set the Z you know you have enough tool to do it, the gcode should rest all axis to zero and off you go.
Ughhhhh, this is not easy to put into words.
Raise up the z axis before you start to measure the stickout, minding the screw heads as a Zero.
You know what they say, “a picture is worth a thousand words, but video takes 200 times the bandwidth”. I think we’re all saying mostly the same things, here’s how I do it. Not sure it’s right, but have only started one fire so far… 
Barry that helped a tremendous amount. So once you move the router bit into position over the piece to cut, which menu items are you using to set the Z axis. Would the cad program maintain the regular thickness (.75) settings for the thickness of the cut?
Ryan - it is really hard to describe. That is what I was struggling with- how to ask the question and get a sequence going properly. When I move the router bit above the work piece and then select the SD Print I want, it returns to it’s former zero position and then hits the x plate again on the bottom of the 3/4 piece.
So, I’m missing a nuance somewhere. Once I get this it will be eternally embedded into my plastic memory…
When you have the router in the right position to start, you either reset the board or issue a G92 X0 Y0 Z0 command. I prefer the latter. After you have sent the G92 command the firmware “knows” you are at 0, 0, 0 and you can start the program.
The CAM program should know the thickness of your workpiece and the depth of cut you want that matches your movement speed and the RPMs of the tool. Those three factors combine to remove the maximum amount of material without either recutting chips or bogging down by trying for too big of a bite. Tuning those three are the toughest part to get perfect, but you can get it good enough pretty easily.
Usually we cad the cut out a touch deeper than it’s thickness, but yea, the cad will keep that thickness. For milling we start at zero, and work into negative numbers, opposite of 3d printing. I use repetier to run everything, and almost never use the display, so I have one of repetier’s macro buttons send a G92 X0 Y0 Z0 to set the system’s new 0 point after I get the endmill where I want it. I’m not sure if there’s a similar button press with the lcd module. If you look back through my videos I have one on how I use single end stops on my smaller cnc, but also show the macro setup.
And if you want to send the G92 command, there are a few ways to do it easily, depending on how its setup. If you control from a Host software, there is probably a way to crate a “G92 X0 Y0 Z0” macro. If you work from the LCD/SDCard, you can create a special GCode program with tha single line. Or you can update Marlin with an updated version with a custom menu entry (see configuration_adv.h)…
Hey everyone- Thank you so much for the help and the info. Got it working and understand clearly how to make this work now on that particular point!
I made it easy and just threw a gcode file on the sd card. Simple enough to execute right from the controller.
Thanks,
Allison
Barry’s video reminded me of a simple tip for getting an accurate Z origin: put a piece of paper between the end mill and the workpiece, and slowly lower your Z while wiggling the paper. When the paper gets stuck, start to really slowly raise the paper until it is barely stuck — you’re now within 0.1mm of the top of the workpiece. It’s a lot easier than trying to visually check when the endmill is touching.
At the tail end of the instructions there should be a little blip about adding the G92 into the starting gcode for all your cuts. That is how I do it for the LowRider (not the mpcnc).
If you like how you are doing it do not read the following.
There are two other ways to do it.
1- Since you know the depth you set in CAM you can raise the Z axis that amount (plus a mm or two), and drop the router and bit until it touches the spoil board. Then move to material zero, have g92 in your GCode, done.
2-Work from the spoil board into the positive, but we’ll leave that for another day.
