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thomashomer1986
28-08-2015, 03:46 PM
Hello all, I have a basic question on wiring up my limit switches.

The leadshine MX3660 has 4 inputs which are suitable for limit switches, but that tells me that i can basically only have 4 limit switches total? ie X-, X+, Y-, Y+. So how do I set up limit switches for Z- and Z+?

Clive did mention on my my other thread that he just uses 1 limit switch per axis (ie X-, Y- and Z-) and uses them to home the machine, then rely on the soft limits to prevent crashing at the other end. Im happy to do that if I have to, but i would have thought a limit switch at each end would always be the safer option?

Thanks.

njhussey
28-08-2015, 04:22 PM
I believe you can wire all your limit switches in series (if you're using mechanical) and just use one input for limits. Then use one home switch for each axis.

Clive S
28-08-2015, 04:33 PM
I believe you can wire all your limit switches in series (if you're using mechanical) and just use one input for limits. Then use one home switch for each axis.
Yes but you can do it with sensors as well but mechanical are mush easier to deal with I thought it showed you how to connect them in the manual.

njhussey
28-08-2015, 04:55 PM
Yes but you can do it with sensors as well but mechanical are mush easier to deal with I thought it showed you how to connect them in the manual.

It does,

15969

I just though I'd specify mechanical to stop people chiming in that you couldn't do it with sensors....you can it just adds a few ms on to the time it takes to sense the limit.

thomashomer1986
28-08-2015, 05:41 PM
I didn't see anything in the manual about wiring up in series. I'll have another look tho because I often do miss things!

Thanks for the image Neil, however what does NPN and PNP mean?

Am I right in thinking then, that input 1 can be X home, input 2 is Y home, and input 3 is Z home. Then use input 4 for all the other limit switches in series?

Thanks everyone

cropwell
28-08-2015, 11:31 PM
If you are using Mach3 you can wire every homing switch in series, as Mach3 moves the axis until the switch is tripped and then back it to the untripped status. It Homes each axis separately in the order Z, Y, X (Z first to get the tool high and out of the way). Other CNC software may do similar, but I have only used Mach3.

Have a look at this article http://www.learningaboutelectronics.com/Articles/Difference-between-a-NPN-and-a-PNP-transistor . I presume that you are asking about limit switches, which can be regarded as transistor switches, although I am being a bit simplistic about it.

Cheers,

Rob

thomashomer1986
30-08-2015, 09:41 PM
I am using LinuxCNC but I've only just started out with it so I am unsure yet as to how it homes itself etc... It's all new to me tbh.

Clive S
30-08-2015, 11:35 PM
I am using LinuxCNC but I've only just started out with it so I am unsure yet as to how it homes itself etc... It's all new to me tbh.Ok start with the basics are you using mechanical switches? Tell us in as much details where you are at and if you are using a mill or a router ..Clive

thomashomer1986
31-08-2015, 01:18 PM
I'm using mechanical switches, it's a small router that I'm using them on. Only a small working envelope (approx 250mm x 250mm x 75mm).

Clive S
31-08-2015, 10:12 PM
I'm using mechanical switches, it's a small router that I'm using them on. Only a small working envelope (approx 250mm x 250mm x 75mm).Ok been busy all day. have you got the switches mounted on the machine if so a picture would help. Is it that you don't know how to set them up in Linux I am trying to get the gist of what you need to know. ..Clive

thomashomer1986
01-09-2015, 06:53 PM
Sorry I admit I have been a bit vague.

My main issue was how to wire up 6 limit switches to only 4 inputs but after a bit more research I now realise there are multiple ways I can do it. Now I know that I can do multiple switches in a series I think I should be ok.

I should be ok with the linux bit as the stepconf wizard is nice and easy when setting up the parallel port pin id's. However if I'm wiring X+, Y+ and Z- in series then what option would I choose for that input?

The switches I'm using a only basic, in fact they probably aren't the best for my machine as they aren't lever type ones, just a small plunger. But they are all I could get my hands on for free!

The images show the limits mounted in x and y, I haven't yet mounted the z as I need to make a suitable bracket first.

cropwell
01-09-2015, 07:26 PM
My MD machine came with inductive home switches and they were mounted axial to the travel, so it was possible (and too damn easy !) to jog onto them and crush the sensor coil. So my first mod was to move 'em round 90degrees and make them bypass sensing (if that makes sense).
I notice you say 6 limit switches. It is not usual to have a Z--, so why 6 ?

Clive S
01-09-2015, 07:33 PM
Sorry I admit I have been a bit vague.

My main issue was how to wire up 6 limit switches to only 4 inputs but after a bit more research I now realise there are multiple ways I can do it. Now I know that I can do multiple switches in a series I think I should be ok.

I should be ok with the linux bit as the stepconf wizard is nice and easy when setting up the parallel port pin id's. However if I'm wiring X+, Y+ and Z- in series then what option would I choose for that input?

The switches I'm using a only basic, in fact they probably aren't the best for my machine as they aren't lever type ones, just a small plunger. But they are all I could get my hands on for free!

The images show the limits mounted in x and y, I haven't yet mounted the z as I need to make a suitable bracket first.Ok I would not use a limit switch on Z- just the home switch z+ at the top because there generally is no defined position because of tool length etc.
Also be aware that if you do it in stepconfig and then edit the .ini file the file will be overwritten the next time you use stepconfig. hope this helps.

thomashomer1986
02-09-2015, 04:53 PM
Ah right I understand about the Z- limit switch, of course that's not really needed then. And mounting the limit switches at 90 is a good idea too, think i may try that.

I think i know what i'm doing now, thanks very much for your help.

malgazz
07-01-2016, 09:40 AM
I have limits on all my axes, using mechanical ones without levers. I find the levers bend over time and can give slight variances to ones' home position and the work start position. This can be a problem, if doing repetitive cutting after etc.
Depending on how one sets up the material in the cam programme and how you zero the Z axis on the table, can in the beginning, can result in having the Z dive into the spoilboard, if not paying attention to what one is doing.
Putting on the limit for the Z axis can help in stopping it dive right through the spoilboard.
I am using leadshines' mx 4660 with Mach3 and all limits wired in series.
Most people seem to zero the Z to the top of their material. Easiest, especially when not cutting the full depth of the material.
I started to zero to the spoilboard and mic the material each time before cutting to ensure that I do not cut into the spoilboard, adjusting the cam toolpath if needed. This way I have set the limit of the Z to 0.1/0.2 mm below the surface of the spoilboard.

Clive S
07-01-2016, 09:58 AM
This way I have set the limit of the Z to 0.1/0.2 mm below the surface of the spoilboard. Not understanding what you are saying here. If you are saying that you use a Z- limit switch set to -Z .1 then how do you account for different tool lengths and still use the limit switch?

malgazz
07-01-2016, 10:07 AM
I do not have an automatic tool changer and therefore have to zero the z each time a different bit is used. Zero-ing the z to the spoilboard each time. This effectively changes the amount of travel the z can make. The longer the bit the shorter the travel distance etc. I have approx. 150 mm of travel on the Z.

Clive S
07-01-2016, 11:03 AM
I do not have an automatic tool changer and therefore have to zero the z each time a different bit is used. Zero-ing the z to the spoilboard each time. This effectively changes the amount of travel the z can make. The longer the bit the shorter the travel distance etc. I have approx. 150 mm of travel on the Z.Yes exactly. So how are you using a Z- limit switch to stop you from diving in to the spoil board?

malgazz
07-01-2016, 11:37 AM
It does not prevent one diving into the spoilboard, just limits the amount of damage. I have found that sometimes care is not taken in setting up the toolpath on how the machine zero's on the Z axis. When setting up the material in the cam software, persons sometimes overlook where the Z is zeroing (top of material, or top of the spoilboard).
It is some times confusing to some who are just starting out, that the Z homes reverse to the other axes and incorrectly apply how the machine zero's in their toolpath can inadvertly cause them to cut into the spoilboard.
I sure helped me in the beginning. Subsequently have just left the limit in place, just in case.

JAZZCNC
07-01-2016, 08:05 PM
It's just a Spoil board so what's the issue.? Spoil board is meant to cut into it's no big deal.

To Limit the end of travel makes sense if you can run the bearings or ballscrew off the end but just running a little deep into spoil board doesn't warrant limit switches and they can be more trouble than there worth on low end of Z axis.