Limit switches sold with the Shapeoko now ?

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AlainTernet
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Limit switches sold with the Shapeoko now ?

Post by AlainTernet » Wed Dec 16, 2015 6:10 pm

I checked today the Shapeoko website and I discover a new option (I think it's new, I don't see it before)
when you buy, you can buy the standard kit or the standard kit with limit switches.

I don't find any info about this limit switches.
Anyone have more info about ? Is it usable to make homing procedure?

I am near to buy my Shapeoko and I considered buying a limit sensor kit From Kevin H. Patterson
https://www.tindie.com/products/kevpatt ... sor-343rt/
See it in this video: http://youtu.be/vqU_5wZAX3s

Anyone have a experience or advise with Kevin H. Patterson limit sensor ?

With one is the best, the carbide one that come with the Shapeoko or the Kevin one ?

WillAdams
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Re: Limit switches sold with the Shapeoko now ?

Post by WillAdams » Wed Dec 16, 2015 6:58 pm

Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
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Fablicator
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Re: Limit switches sold with the Shapeoko now ?

Post by Fablicator » Wed Dec 16, 2015 7:06 pm

I would go with a simple switch based kit from either Carbide motion or any of the 3rd party vendors on this forum. Nothing fancy is needed.

The carbide kit is a homing only kit, which allows a repeatable zero. It is not a true limit kit which halts the machine if you exceed the maximum travel.

A true limit kit has switches which trigger at both the Max and Min XY travel (for a total of 5 switches)

RoguePirin
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Re: Limit switches sold with the Shapeoko now ?

Post by RoguePirin » Wed Dec 16, 2015 7:59 pm

AlainTernet wrote:I don't find any info about this limit switches.
Anyone have more info about ? Is it usable to make homing procedure?
Limit switches are a physical/non-software means to tell the CNC controller when the machine exceeds your desired boundaries. Usually, you would define these boundaries at the full extent of each axis, for a total of 6 switches (2 per axis). However, many people who go this route do not bother to put limit switches on the bottom of the Z-axis, as the length of tool changes between bits and it would be hard to have a distinct extent. Know that if you go this route, you will need to recompile GRBL to indicate that multiple limit switches are on a single limit switch input (not hard to do; there are plenty of guides out there).

When you perform a homing cycle, the system uses 3 of this switches (1 per Axis). This allows the system to return to a known start position every time the system is powered back on, as it loses its known position when you turn off the power. Both the Shapeoko sensor pack, and buying 3 from Patterson would give you the ability to home.
AlainTernet wrote:Anyone have a experience or advise with Kevin H. Patterson limit sensor ?
With one is the best, the carbide one that come with the Shapeoko or the Kevin one ?
I don't have any experience with either sensor, though I see the following differences:
  • You can buy any number of Patterson sensors (5 if you want to use hard limits), but you get exactly 3 with the Shapeoko kit
  • The Patterson switches use Hall-Effect sensors (solid-state, extremely repeatable) while the Shapeoko use cherry switches (mechanical - can wear out over a long time [probably not a concern for this CNC machine])
  • The Patterson switches don't come with any way to connect to the Carbide Motion controller (you need to provide your own connections) while the Shapeoko has both connectors and mounting hardware.
I am partial to the Hall-Effect sensors (I am in the middle of building my own right now), due to the solid state nature (no moving parts to wear out, not susceptible to dust, extreme repeatability, etc.). However, it is definitely not a turn key solution. I still have to figure out how to mount everything. Don't be fooled by the low cost of the Patterson sensors; you will have to pay more for wiring, connectors, mounts, etc. There is something to be said about having the Shapeoko kit just be plug-and-play and you are done.
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veng1
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Re: Limit switches sold with the Shapeoko now ?

Post by veng1 » Wed Dec 16, 2015 9:25 pm

The kits sold by vendors on this forum are also plug and play.

twforeman
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Re: Limit switches sold with the Shapeoko now ?

Post by twforeman » Thu Dec 17, 2015 2:27 pm

The kit that I sell has switches on both ends of the X and Y axes and is plug and play. (And is cheaper than the Carbide 3D kit. :) )
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twforeman
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Re: Limit switches sold with the Shapeoko now ?

Post by twforeman » Thu Dec 17, 2015 3:11 pm

RoguePirin wrote:Know that if you go this route, you will need to recompile GRBL to indicate that multiple limit switches are on a single limit switch input (not hard to do; there are plenty of guides out there).
Actually you don't need to do anything to Grbl if you have limit switches on both ends of your axes. You just wire them in parallel (or series if you are using NC switches) and when the machine trips a switch Grbl E-Stops.

It doesn't matter which switch trips, and Grbl doesn't care which end of the axis trips. Once it's tripped you have to reset and re-home anyway.
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RoguePirin
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Re: Limit switches sold with the Shapeoko now ?

Post by RoguePirin » Thu Dec 17, 2015 3:16 pm

twforeman wrote:Actually you don't need to do anything to Grbl if you have limit switches on both ends of your axes. You just wire them in parallel (or series if you are using NC switches) and when the machine trips a switch Grbl E-Stops.

It doesn't matter which switch trips, and Grbl doesn't care which end of the axis trips. Once it's tripped you have to reset and re-home anyway.
Are you sure? I was just going off of the Grbl source code. In config.h, there is the following section:

Code: Select all

// If your machine has two limits switches wired in parallel to one axis, you will need to enable
// this feature. Since the two switches are sharing a single pin, there is no way for Grbl to tell
// which one is enabled. This option only effects homing, where if a limit is engaged, Grbl will 
// alarm out and force the user to manually disengage the limit switch. Otherwise, if you have one
// limit switch for each axis, don't enable this option. By keeping it disabled, you can perform a
// homing cycle while on the limit switch and not have to move the machine off of it.
//#define LIMITS_TWO_SWITCHES_ON_AXES
I am sure it will work without enabling this feature, but it sounds like a good practice to enable it as a safety feature???
Shapeoko 3 #677, Nyloc nuts, ¾" HDPE base with t-nuts, Dewalt 611 w/Super PIDv2

twforeman
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Re: Limit switches sold with the Shapeoko now ?

Post by twforeman » Thu Dec 17, 2015 3:21 pm

Huh. I've never seen that before.

I'm not sure how that would work for homing. Since the switches are on the same pins Grbl has no idea which end the machine is on. So if you start the homing cycle when the machine is already on the 'home position' switch it will just drive the machine through the switch. It's my impression that when a switch is tripped and Grbl goes into alarm state it loses all position, but I could be wrong.

I just manually move the machine off the switch (by unlocking the alarm state and jogging) and then home.

That setting doesn't make any sense to me as to how it would work.
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RoguePirin
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Re: Limit switches sold with the Shapeoko now ?

Post by RoguePirin » Thu Dec 17, 2015 3:32 pm

I was confused by this when I first read it to. However, after reading it for about the twentieth time now, this is how I interpret it:

It clearly states that the feature only impacts the homing cycle, not the e-stop functionality of the switches. Therefore, I think it is a purely a convenience feature.

If you only have 3 limit switches, and your machine is already homed when powering on the board, then it won't alarm and you can run a *very* short homing cycle. If you have 5 switches (more than 1 per axis), and you start up with a switch triggered, the controller doesn't know which axis extent it is at. It requires human intervention to move the machine inside the work area and then run the homing cycle.

As long as you start the machine with it not engaging any limit switches, then you don't need to enable this feature.
Shapeoko 3 #677, Nyloc nuts, ¾" HDPE base with t-nuts, Dewalt 611 w/Super PIDv2

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