home / limit vs home and limit switch

[fozzyber]

quick question, I looked but could not find a straight answer.
I know you can have one switch to act as a home and limit switch, ( no problem here I understand)
but if you use 2 switches one as home and one as limit, which one should trip first?
ie you start your homing routine y starts to move negative, your limit switch should trip but be ignored then home is tripped and zero is set.?
is this how it should work. or is it home is tripped then limit ?

Thanks.

Jerry

[cnckeith]

yes, home switch always trips first..
suggestion... Use HomeAll for all the home switches and software travel limits to take care of the other side and/or LimitAll

[Gary Campbell]

Jerry...
Not sure I understand your logic, or even the question. That said based on machine logic for 2 switches, one home, one limit. You may get the machine to "drive" by a homing switch to hit a limit, but I doubt you will ever get it to drive by a limit to hit a home. Make sense?

I use 2 switches (in the + direction) on my lathe. One set as home, the other set as limit. The limit is set to sense a tailstock collision and can trigger before the home is hit. In this scenario, I must rely on soft or envelope limits to stop the machine in the positive direction as the home set switch will not.

[fozzyber]

Got it that did answer my question.
thank you,
I was thinking of using 2 switch per axis, home + limit but I see what you are saying,
ditch the second switch and let the software handle the rest.

The reason I was asking is i have my prox (home) switch set in line with my target, so if it over runs it would hit the prox switch.
I was thinking to have a limit switch set to the side about 1 inch to stop it from over running.

Side note / question : are hall effect prox switches more accurate with the target coming straight at it or the target passing by it (perpendicular)
my old machine has them coming straight and has worked well, but never really tested anything different

jerry

[slodat]

This sheet has some good info on proximity switches.

[cncman172]

fozzyber,

I actually use optical sensors for home switches, and mechanical limit switches for limits. My though was sometimes optical or proximity sensor can fail and I did not want my machine to crash into an end stop and damage something. I learned that the hard way once, so after that episode I decided to install the limits to protect the ballscrews. I had gear heads on servo motors which are extremely strong.

Russ

[tblough]

Home can be anywhere within your machine limits. Home is just where machine coordinates are set to 0,0. You can travel + or - from home up to either your hard or soft limits.

[Tapburrbit]

On the topic of home/limit switch vs homeall and limitall I noticed this.

This is my second Acorn retrofit to a Bridgeport boss 5 . The first machine has a very early Acorn Maybe version 1. I wired each home/ limit switch to it's own input 1, 2 and 3. It's been working fine and the single switch on each axis works both as a home switch and a limit switch.

This second machine I'm just about finished with has the new ver4 acorn. I followed the suggest HOME/ALL wiring in series. The single switches only work as home switches. I tried jumping them over to the limit/all input also but of course that didn't work because the limit took priority and the machine did not home.

Should I just wire the switches to individual inputs like my first retrofit to get the single switches to act as both home and limit switches ?

Is the purpose of Home all and Limit all just save inputs? only 1 if it's a 3 axis machine. But you need six switches instead of 3.

David

[slodat]

The purpose is to save input. Personally, I use an expansion board and run plus and minus switches on all axis on my machines.

[tblough]

+1 to slodat.