# cnc router



## duncan9 (Aug 24, 2010)

I have just completed building my second cnc router and I do not have limit switches or homing switches on it . I am runnihg EMC2 for the controller software . My question is should I bother installing homing switches or not ?
Frank


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## BOOMER52 (Jun 4, 2011)

duncan9 said:


> My question is should I bother installing homing switches or not ?
> Frank


Hi Frank,

That's a fairly subjective answer you are looking for. It all depends...! Since this is your second router build... let me ask if you installed homing switches on your first? If you did... then did you find them to be useful? If you didn't... are you feeling OR reading from others... about how much you need them? Do you have a time sensitive machine use routine that could be improved by the many gadgets that incorporate HOMING? OR are you more the simple hobbyist that occasionally carves a project now and then.

I put myself in the hobbyist category and did not install limit nor homing switches. The manner in which I use my machine I've not missed having them. But that's just me... I'm certain you'll receive an opposing response... hence the 'It depends' answer above.

BOOMER52


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## duncan9 (Aug 24, 2010)

Hi Boomer52
Thanks for your reply I did not have homing switches on my first one and I am a hobbyist like yourself . I have x and y stops installed on the table to locate the blanks that I place on the table to cut so I think I will install homing switches . Do you know if the switches should be located so the machine runs into them or should they be located so the machine could go pass them ?
Frank


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## BOOMER52 (Jun 4, 2011)

There are three type of switches that are seeing usage in CNC... mechanical, inductive, and optical. There is really little difference between mechanical and inductive in this application... but the optical switch falls beyond my level of knowledge so I can't comment. In my opinion, I prefer a mechanical switch, and not the snap action variety... as long as the switch is a 'quality switch'.

What you are wanting is a switch that is 'repeatable'. Each time an axis homes, the switch is opened or closed by a ramp or blade causing switch contact depending on whether you wire yours to a NO or NC condition . It of great importance to have a switch that has a repeatable trip point at that point of contact.

Most machine homing switch installations are of the by-pass variety... where a ramp or contact blade can go past the contact button in an abnormal condition. You want to avoid the CRASH contact switch installation as these can easily be damaged with even a slight overrun.

BOOMER52


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## duncan9 (Aug 24, 2010)

thank you I am going to get to work designing the mounts for the switches. it makes sense to me , sometimes all you need is to bounce it off of someone else .
Thanx
Frank


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## rtunas (Jul 14, 2009)

The type of switch you use is dependent on the accuracy needed. Mechanical switches have what is called hysteresis which the amount of time it takes for a switch to close and make contact. In CNC if you need micron accuracy I would stay away from mechanical switches as the hysteresis is greater therefore the accuracy not as great. Theory is that once you home a machine it stays there but variables cause you to home a machine more than once. Then since a machine does not return to the same home every time your repeatability is not accurate. An optical switch has less hysteresis therefore greater accuracy and repeatability. Hopefully this does not confuse you. In a system using true CNC with scales with position feedback and not stepper motors this is critical. Using stepper motors it is entirely unnecessary. Using stepper motors is not a CNC anyway it is actually just an NC machine as the computer tells the stepper motor how many pulses and does not care if it made it or not. Ok enough of my 29 years in maintenance of CNC I will stop boring people.


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## gorbo (Jul 19, 2011)

duncan9 said:


> I have just completed building my second cnc router and I do not have limit switches or homing switches on it . I am runnihg EMC2 for the controller software . My question is should I bother installing homing switches or not ?
> Frank



When I first built mine I installed all the limit/homing switches but to be honest I have never used them, but having said that yes install them just in case!!


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## Metalhead781 (Jul 27, 2010)

The inductive switches on my 60x120 ShopBot are very accurate, +/-.0012. The way it's setup, It uses a small screw that you can adjust for gap. Very simple to setup and adjustment.


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## kolias (Dec 26, 2008)

On my 1st CNC I didn't use home / limit switches and that was ok. On my 2nd CNC I use both home and limit switches and I find them very convenient. I use my CNC for hobby.


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