Limit switches & auto tool height setter?

Discussion of tinyG control platform
pastprimitive
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Limit switches & auto tool height setter?

Post by pastprimitive » Mon Aug 18, 2014 3:44 pm

So i'll continue to search for an answer, but I thought i'd post in case anyone has already done this (I'm sure someone has).

I want to put limit switches on both ends of all 3 axises on my Shapeoko 2. I assume I would just double up limit switches to their respective axis terminals on the TinyG board?

I just want to have extra catastrophic failure protection from catastrophically stupid tool paths if you get what I mean. I had a CNC Shark Pro Plus with 0 limit switches, and once or twice it was an issue, and I just don't want to even give it the slightest chance to happen.

Second question. I want to add an auto-tool height setter to my machine. Had a guy come over and buy my 3-d printer, he happened to manufacture DROs and CNC scanning probes, and auto tool height setters. The tool height setter was just a limit switch. So I figured the hardware is no problem for me to add to my machine. But how to implement software side. I don't want to use mach3. At least for now because I don't own a copy. I mean I assume I could use the 4th axis limit switch on my Tiny G as the input for it.

So any thoughts on how to implement this software side. Is the Gcode already in place so I can just add to the beginning of each job? Or do I need to create a custom Gcode for this. Essentially the workflow is this: Change your tool bit, send auto-tool height setter gcode, machine travels to a specific location that you have installed your limit switch, z axis advances down until limit switch engaged, off set to your z-zero is sent to adjust.

Thoughts?
ShapeOko 2 6095. Double Y-Axis Nema 23s (140oz/in), X & Z Nema 23 (262oz/in), TinyG, 500W DC Brushless Spindle w/ 48VDC 10A Supply, Acme Lead Screw, 24VDC 10A Supply, Threaded Inserts Table, Auto-tool height setter.

secretspy711
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Re: Limit switches & auto tool height setter?

Post by secretspy711 » Mon Aug 18, 2014 4:37 pm

yes, if you're using normally open switches, just wire each axis' 2 limit switches in parallel, so that hitting either one pulls that pin to ground.

Grbl 0.9 supports the G38.2 straight probe function with a pin dedicated to it, as well as G43.1 tool length offset. I have not used these yet, but I have a connector on my control box going to the probe pin for future use. Hopefully that points you in the right direction.
Shapeoko 2 #5510: 1200 x 500 mm, Makita RT0701

pastprimitive
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Re: Limit switches & auto tool height setter?

Post by pastprimitive » Mon Aug 18, 2014 6:00 pm

Thanks!
ShapeOko 2 6095. Double Y-Axis Nema 23s (140oz/in), X & Z Nema 23 (262oz/in), TinyG, 500W DC Brushless Spindle w/ 48VDC 10A Supply, Acme Lead Screw, 24VDC 10A Supply, Threaded Inserts Table, Auto-tool height setter.

SniperTeamTango
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Re: Limit switches & auto tool height setter?

Post by SniperTeamTango » Tue Aug 19, 2014 1:38 am

pastprimitive wrote:So i'll continue to search for an answer, but I thought i'd post in case anyone has already done this (I'm sure someone has).

I want to put limit switches on both ends of all 3 axises on my Shapeoko 2. I assume I would just double up limit switches to their respective axis terminals on the TinyG board?

I just want to have extra catastrophic failure protection from catastrophically stupid tool paths if you get what I mean. I had a CNC Shark Pro Plus with 0 limit switches, and once or twice it was an issue, and I just don't want to even give it the slightest chance to happen.

Second question. I want to add an auto-tool height setter to my machine. Had a guy come over and buy my 3-d printer, he happened to manufacture DROs and CNC scanning probes, and auto tool height setters. The tool height setter was just a limit switch. So I figured the hardware is no problem for me to add to my machine. But how to implement software side. I don't want to use mach3. At least for now because I don't own a copy. I mean I assume I could use the 4th axis limit switch on my Tiny G as the input for it.

So any thoughts on how to implement this software side. Is the Gcode already in place so I can just add to the beginning of each job? Or do I need to create a custom Gcode for this. Essentially the workflow is this: Change your tool bit, send auto-tool height setter gcode, machine travels to a specific location that you have installed your limit switch, z axis advances down until limit switch engaged, off set to your z-zero is sent to adjust.

Thoughts?
They TinyG has a total of 8 limit switch ports, even if you wanted to put two per side of the y axis, and on every other axis, you have enough ports. You can then even set the switches up with homing, so the machine will return to a set location every, single, time.

I'm not sure about the tool setter, I presume its possible. I'll look into it.

pastprimitive
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Re: Limit switches & auto tool height setter?

Post by pastprimitive » Tue Aug 19, 2014 8:46 pm

I confirmed that you can indeed do a tool height setter with the G38.2 command. Just setup a limit switch and run the command and it will send the z axis down until it hits the limit switch. Then simply have it set that as zero minus the height of your switch. Or in my case I am going to mount it on the front of the machine and just have it set precisely to my table height, and set my home point at the bottom of the engraving material I am using.
ShapeOko 2 6095. Double Y-Axis Nema 23s (140oz/in), X & Z Nema 23 (262oz/in), TinyG, 500W DC Brushless Spindle w/ 48VDC 10A Supply, Acme Lead Screw, 24VDC 10A Supply, Threaded Inserts Table, Auto-tool height setter.

dataway
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Re: Limit switches & auto tool height setter?

Post by dataway » Wed Aug 27, 2014 2:56 pm

For my tinyg I setup a tool height setter using the Z-axis homing switch and a thin aluminum plate which is 1 mm thick, placed on the material. I have the switch set as normally open, attach a alligator clip to the bit and one to the aluminum plate and when I hit home all axis in tGFX the Z Axis goes down to set the height to +2mm as I have it back off 1mm to clear material for homing process. After the system is in home position i just issue the gcode command to send the z-axis down 2mm and zero all axis and my machine is set to run.
Shapeoko 2, Dewalt DW660 1/4" shaft/ 1/8" shaft, 3D printed Dust Shoe,Dual Y Axis.

sraney
Posts: 43
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Re: Limit switches & auto tool height setter?

Post by sraney » Fri Aug 29, 2014 7:42 pm

Sounds like a great idea. Is it possible to get a video of this ?

dataway wrote:For my tinyg I setup a tool height setter using the Z-axis homing switch and a thin aluminum plate which is 1 mm thick, placed on the material. I have the switch set as normally open, attach a alligator clip to the bit and one to the aluminum plate and when I hit home all axis in tGFX the Z Axis goes down to set the height to +2mm as I have it back off 1mm to clear material for homing process. After the system is in home position i just issue the gcode command to send the z-axis down 2mm and zero all axis and my machine is set to run.
-- sraney
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dataway
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Re: Limit switches & auto tool height setter?

Post by dataway » Fri Aug 29, 2014 8:10 pm

Sure here is a quick video I put together going through my homing sequence

https://vimeo.com/104751920

Hope this helps
Shapeoko 2, Dewalt DW660 1/4" shaft/ 1/8" shaft, 3D printed Dust Shoe,Dual Y Axis.

chmedly
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Re: Limit switches & auto tool height setter?

Post by chmedly » Fri Sep 05, 2014 5:15 pm

Dataway,
So, correct me if I'm wrong. I think you have your aluminum plate electrically connected to a tinyG limit switch input? That sounds incredibly simple. The only thing that I wonder about is static electricity protection for that input port.

cvoinescu
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Re: Limit switches & auto tool height setter?

Post by cvoinescu » Fri Sep 05, 2014 5:24 pm

330 Ω pull-up (between plate and VDD), 1 kΩ in series (between plate and pin), and 1 nF to ground (between input pin and GND) should take care of that.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

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