I just found this triple edge finding device to help automate axis setting and I was wondering how zero is set today on the LR2? This seems like a brilliant approach but not sure how one would integrate such a thing? https://www.youtube.com/watch?v=19VrS3hn0MA
-Jeff
I know they seem neat but that is just locating one point. It is not giving you a reference edge. So you know where the exact corner is, but not how the material is skewed/rotated. Beyond locating a surface and endmill tip during a tool change I don’t see much use for homing. You will usually leave stock on the edge to clamp to so a super precise zero corner seems to be a waste of time to me.
Yes, as I thought more about it I came to the same conclusion you did overall but it still has a use for at least one scenario I encounter with the ShopBot at the Makerspace anyway.
While it won’t guarantee that you can re-load and precisely reposition a piece of stock (for example if you share the CNC and have to remove a partially finished project and resume another day), it will at least help you if your machine crashes mid-job and loses it’s XYZ. That being said if I align the stock to the same short edge of the spoilboard (assuming it hasn’t been moved) and then use this, wouldn’t that ensure I could reload it and find zero consistently on a given piece of stock?
The more regular scenario where it does help is: If you home it with the tool before starting a multi-hour, multi-file job and then the machine loses it’s home position, you can be assured you can re-set it if the stock hasn’t been moved.
Maybe this isn’t applicable to the LR2, but on the Shopbot it seems to crash with alarming regularity, and it is non-obvious whether or not it will lose it’s home position. It is definitely painful to try and re-find it if you’re doing high precision work like I was recently. I did think to lightly plunge the tip of a brad bit in to zero when I started and that saved me when a job ran long and I had to unload it mid-way, but it didn’t save me from skew. I dealt with that by marking vertically across the stock and spoilboard with a sharp pencil and then hand aligning.
-Jeff
Just thinking about this a little bit more for the unload and reload a sheet scenario. Would it be viable to zero against your regular origin and then read x,y at the other three corners and correct for skew? I guess to do so would require taking base readings the first time you use the stock so it has something to reference to as well. If skew correction is even viable, of course. 
-Jeff
Exactly. You can do it in software…if you can afford it.
That is the beauty of the dual endstops. Home with regard to the machine, If it crashes mid job and doesn’t destroy the job (which it does99% of the time) You can re home and go. Using teh block you are just doing a sort of work offset.
There are a thousand ways to do things. It really is best to fix a problem you actually encounter. Trying to plan for failure will result in it failing in a different way.
If my job fails, typically the work piece is ruined so I don’t care where home is.
With that tool changes can get messed up as they rely on you leaving a corner to use it off of. The less “you” (me/us) are actually involved the more accurate the job will be.
True, that.
I hear you.
There is a practical reason I anticipate needing it, and that the LR2 partially enables this scenario, which is awesome.
Like many, my workshop is the garage and with a very rainy 5 months here during the winter, available shop space shrinks from two bays to one, as my wife insists on being able to park in the garage. As well, we have some fairly aggressive noise bylaws in the area that I recently became aware of that can really limit cutting time (and even which days you can).
Since the LR2 can easily be removed and stored, it is feasible to take on an ambitious project that will take many hours to cut. By breaking it down in to individual toolpaths or groups of toolpaths it can be cut in on different days. Or different weekends. But in between I am likely to need to use the space for other things. Being able to reposition the stock accurately within the table and continue an in-progress job is helpful in this kind of situation. I think I found a low-tech solution that should work for me.
If I cut a line of 3/4" dog holes in the spoil board straight across the Y axis at the top of my X-axis travel and position the Y-axis of my stock against the dogs (like these: Adaptive Cutting System Versa Stops | KregTool.com Official Store ), it should always ensure I’m in the right place on Y. Using a triple edge detect it would set everything and I believe that would achieve the ability to continue jobs between removing stock and storing the LR2. The caveat being, as you said, it won’t work if you cut your Y-axis to the point where it isn’t stable to use it to re-align, but that can be planned for.
Bench dogs have the advantage of being affordable, easily removed if not needed for a job, and slide right out after the stock is screwed down.
Similarly, if I put a few X axis spoil board dog holes perpendicular to the zero edge for the Y-axis then it is easy to re-load the stock to the same square location on the table. Especially if I use a lateral clamp from a third side to apply pressure. Kreg make a cheap plastic one of those but it does require more dog holes in the table, thankfully the CNC will make adding them easy.
There would still be the challenge of getting the bit over the same 0,0 position without a sensor though. Does the LR2 calibrate itself to the endstops as an absolute reference we can use?
Would it be feasible to play around and determine as an end user where a comfortable 0,0 would be over that stock corner near the dog holes and note that offset so it can be manually input consistently to continue jobs in the future after the machine was off-line for awhile and maybe needs to be set-up again?
-Jeff
That all really comes down to what you think is accurate enough. Breaking it down and setting it back up is next to impossible to get good accuracy without really good locating skills, and CAM. Breaking down the machine requires re-calibrating it every time.
What you are asking for would benefit from a software solution more than a hardware one. What you are asking is going to be difficult even with software unless accuracy isn’t that big of a deal.
Hi @vicious, sorry my ignorance but I am relatively new in CNC, your project was the one who brought me to this new world, exciting and many times frustrating.
I have the dual ends tops since the beginning, all working great, I am trying to cut and engrave panels with little cuts and engraving letters of 3mm size, and I can tell you, almost gave up many times… So as you said above, “You will usually leave stock on the edge to clamp to so a super precise zero corner seems to be a waste of time to me”.
Would you please explain to me how could I make it more efficient? I have to cut an acrylic panel, then I have to paint it and after I have to engrave the letters in the exact position in the panel I just painted and cut before. So how should I position the panel for the engraving? How can I make sure the panel is level in the X & Y? there is always some millimeters difference which ruin the project.
I download STLcam as per your suggestion, they have the edge finder on the application but does not work with Marlin, can I change the firmware to have the edge finder?
Thanks for any input you can give me.
I would design a little corner L bracket, with 3-4 dowels to jeep it in place and then also cut the dowel holes in my spoil board. After that, I would have a good reference origin, but I could remove it if it wasn’t needed.
Doing the corner probe thing is going to be a huge amount of work, and I don’t see the benefit.
Hard word to use around here. What does exact mean to you? How far off is okay?
If you are good to have it under a 1mm just use a some sort of corner block to realign it each time you move it (the most basic of production jigs). If you need something along much more precise you will need to use alignment pins like Jeff is referring to.
You have endstops so your machine is already starting in the “exact” same place, you just need to position your work in the same place. A corner finder doe not typically do this as well as you would think, it still allows for rotational errors unless you probe multiple places on each edge.
Depending on the length of the piece, I would consider a second alignment piece an appropriate distance down one (long) edge of the piece, also with locating pins into the spoilboard.
Manolo, from my square testing on dual endstops, if they are really well positioned and you move your gantry to whatever coordinates from home position you should have very accurate results…just have a look at the drawing I did to test it…(drawn twice)…drew it once from home position to xxxx on X axis and xxxx on Y axis, once finished sent the machine home, called it back to the same X and Y position and re-drew it…it looks like only done once…make sure you position your workpiece exactly where it was …so take your time to square your machine right and she’ll pay you back with very nice precision.
Hope it helps you, give it a try and tell us.
Enjoy it !!!
