Multiple cuts for same piece?

Hi,
I need to perform two separate operations on a single piece:
(1) Engrave the name of the piece
(2) Cut the piece

I’m not sure how to do this.

Anyone care to assist?

Duncan

That’ll require an endmill change. Do you have endstops?

Hi,
No, I don’t. Yet. So how does it work? What’s the workflow?

Duncan

The process will depend on your setup. Personally I have a very manual approach and separate each bit use into a separate GCode files. This way you can treat a bit change like a new “job” with the “only” issue being how to determine the new home position. If you leave the steppers engaged during the bit change, the home X and Y of the previous GCode file will be preserved and can be reused. For most cutting I like to use the spoil board and the CAM defined stock height to define by ‘Z’ home position. This way any cuts through the stock just kiss the spoil board. But for V cutting I like to use the top of the physical stock as reference since the depth of the cut into the material makes a big difference in the engraving.

4 Likes

Can you engrave with an endmill instead of a v bit? That way you don’t have to do a tool change.

You can certainly run an engraving tool path with a normal bit, but you will not get the result. Most engraving tool paths move the bit up and down to vary the width of the cut. With a straight end mill you would get this funky look where the bit would cut deeper and shallower but the width would not vary. Take a look at this heart:


Notice how the lines vary in width as the bit is moved up and down. If you used a normal bit, it would look totally different. You could pocket out the design with a normal bit, but you need a tiny bit that would take a really long time in order to preserve the detail. If it is just text, there are “special” stick fonts that can be cut using a flat end mill. In my brief web search, I did not find much in the way of free stick fonts. They tended to run about $12 per font face.

For sure a v-bit is perfect for engraving. Just throwing it out as an option not knowing what Duncan was trying to achieve. This example was done with one bit.

My was response was instigated by your use of “engrave,” which means something specific to me on the CNC. From my understanding, what you’ve done here is pocketing. Nice clean lines and a nice looking piece BTW.

1 Like

I don’t know about you but I’d be likely to accidently move the gantry during a bit change which would throw off your indexing.

You could do something like this:

  1. Before powering on your cnc (gently) push x & y axis to their zero positions, I’m assuming these are against the physical limits of those axes.
  2. Place your work piece on the bed
  3. Power the machine and jog to where you want your work’s origin to be
  4. BEFORE executing a G92 or running your script take note of the exact x and y position you’ve jogged to. Write it down.
  5. zero your axes and run your engraving gcode program
  6. jog your machine back to somewhere close to the “home” position or machine origin
  7. Turn off the machine and change your bit
  8. Repeat step 1
  9. Turn the machine back on and run a gcode command to return to the workpiece origin using the coordinates you wrote down in step 4. Something like G0 X###.## Y###.##
  10. Run your profile path’s gcode file

While I do have some (but not a lot) of experience with tool changes this is the only way I’ve been able to work it out in my head that makes sense to me. I do have the dual endstops so my process is “slightly” different but essentially the same

I find that if I leave the steppers engaged and am not violent with the bit change, the previous home X and & position is still accurate for the new bit. If I disengage the steppers, I always move the gantry.

Locating home on a work piece, relocating that home after a bit change or other operation, finding relative positions on a work piece for some operations, getting/keeping stock square with the coordinates , etc. is the greatest area of frustration and errors I have using the MPCNC. I’ve tried several approaches and have more ideas to try…and this frustration was the driving force for me upgrading to dual endstops with my Primo upgrade. I didn’t care about squareness but wanted the ability to return to a precise location after the electronics were powered down. Recently I’ve found a low-tech solution that has been helpful.

It is just a 3D printed sleeve with the head of a T-pin inserted to create a precise point. I created it so that I could make accurate cuts in stock that had been cut to size on my table saw. I found being off by even 1mm was noticeable, and this solved the problem. But I’m also using it for other operations. I use it to mark my fixtures so they can re-positioned and used after they have been removed from the spoil board. And I can use it to create a local “origin” by either marking a point on the stock that will not be cut or even the spoil board. Knowing the relative position of this point to the home position used in cutting the stock allows me to return to the same position regardless of what happens with the electronics.

Dont do step 7 keep the steppers energized it keeps x and y zerro you do have to zeroth a axis on a bit change

These little steppers don’t have the holding power to guarantee I wont move something, that was the point of the routine.

Not all steppers have the same holding power, so your situation may be different. but my setup has plenty of holding power to preserve the position through a routine bit change. Put a V bit in your router, move some on X and Y to engage the steppers, without the turning the router on, move the router down and kiss the waste board with the bit to leave a mark and then raise your router a tiny amount. With this mark as a reference, push your router around to see how much force it takes for it to lose its position. I purchased my steppers from Ryan, and it takes a significant amount of force to move them to a new position when they are engaged…far more than I would apply during any routine bit change. Plus I cannot move them just a small amount that will go unnoticed. When I overcome the stepper, I get a noticeable amount of movement and a noticeable sound.

Note I still like to have some reference that I can use to return the router to the home cutting position if I lose power or if I lose steps during the cut.

1 Like

This is how I do it on my machine. Still don’t have dual endstops set up. Just single stop with a hard stop on the other side. Should give you a rough idea.

1 Like

This is the same process that I use. I like the Z sharpie endstop! I need to do the same thing to mine.

Hi guys,
Well, I’m happy to report that my hand-written gcode to level my top is working beautifully. I’m on my second cut at the moment, having taken off all the high sports in run #1. 1mm lower, and most of the top is being cut. Centre section still a mm or so lower.

Decreasing rectangles starting from the outer perimeter. 25mm bit, 50mm/sec feedrate, 1mm DOC. 54min for a full 2480 x 1230 table.

YEE-HA!

Duncan

1 Like

My way of doing this. Run your vbit tool path, when the job finishes, i use manual control on repetier to move 50-500mm to get the router in a good spot. Pop the height adjustment lever, and pull the whole router out of its base. Swap bits, and reinstall router. I screw the height adjustment out an inch or so to make sure I’m above the work peice.
Execute a g1 x0 y0 f2500.
Execute a g1 z0 f300.
Run height to workpiece.
Run a g92 z0
Run my second program. Touch plate will be en route shortly (that v1 first gen collectors peice).

1 Like

Hi Jeff,
Thanks for the method above. I was thinking that I don’t actually NEED to etch the pieces before cutting them - all I need is to be able to identify which parts are which, because many of them are very similar, and they come in LHS and RHS variants also. So I think I may have two options. (1) Before removing the parts from the sheet, manually write their names on them (not a very high-tech way of doing things, messy and prone to errors. (2) Fit a slide-on sleeve to the router bit with a pencil/ballpoint in the end, and run the etching gcode. Remove the sleeve, and run the cutting gcode.

Only problem is - I will have to design the sleeve myself (do-able, I guess), but I’m stumped when it comes to what to use for the scribing. There needs to be some give in the drawing, but it needs to be absolutely in the same position as the bit itself.

A third option (but this requires a tool change) is to fit a sharpie holder like I’ve seen on thingiverse which replaces the router but is perfectly centred. I’ve tried to print this three time, but it is just too flimsy. I might cut something out of 3mm plywood and see if that is stronger.

Regards,
Duncan

The bit and the pen don’t actually have to align. As long as the pen is firmly attached everything will be fine. If you use the same point on the workpiece as the beginning point (origin) then both will be correct. You can run the pen and bit as 2 jobs. After you power on, move the bit/pen to the beginning point on the workpiece and tell the machine this is the new 0,0,0 (origin) by sending the gcode G92 X0 Y0 Z0.