Need Help!- Placement of Limit Switches

[dpgoldberg]

How close to the physical end of travel should a limit stop switch be placed? They will be adjustable but I'd like to get in the ballpark. My machine will have a top speed of around 200 inches per minute. I'm planning to install six switches, two per axis. The limit switches on one end will also function as home switches as is possible using Mach 3. I know I could use soft limits for the other end but I just feel better about having limit switches at both ends of travel.

[mlabruyere]

Originally Posted by dpgoldberg How close to the physical end of travel should a limit stop switch be placed? They will be adjustable but I'd like to get in the ballpark. My machine will have a top speed of around 200 inches per minute. I'm planning to install six switches, two per axis. The limit switches on one end will also function as home switches as is possible using Mach 3. I know I could use soft limits for the other end but I just feel better about having limit switches at both ends of travel.

I only use 3 homing/limit switches, soft limits (min and max), and hard stops on mine. My travel is: X=42.5", Y=43", Z=3.5" and my rapids are 500IPM.

The limit switches are very near the hard stops to give maximum travel. The great thing with the soft limits is I program the software to slow the movement when within 2" of min or max. This helps prevent those bone rattling hard stops....

[Dorsal]

Yep! 3 switches only, and my soft-limits are set at 1 inch with 300 ipm rapids.

[Fastest1]

Originally Posted by dpgoldberg How close to the physical end of travel should a limit stop switch be placed? They will be adjustable but I'd like to get in the ballpark. My machine will have a top speed of around 200 inches per minute. I'm planning to install six switches, two per axis. The limit switches on one end will also function as home switches as is possible using Mach 3. I know I could use soft limits for the other end but I just feel better about having limit switches at both ends of travel.

I dont think a limit switch can be used for a home also. Double check on that. I think the machine can not pass a limit but can pass a home. It takes 2 different pins. 1 for limits 1 for home. I personally use a distance off my limit as home. I also only run 1 switch per axis all sharing the same pin. I do have a ramp at each end so it emulates 2 switches.

[dpgoldberg]

Originally Posted by Fastest1 I dont think a limit switch can be used for a home also. Double check on that. I think the machine can not pass a limit but can pass a home. It takes 2 different pins. 1 for limits 1 for home. I personally use a distance off my limit as home. I also only run 1 switch per axis all sharing the same pin. I do have a ramp at each end so it emulates 2 switches.

According to the video tutorial on the Mach 3 site the same switch can be used for both home and limit. The program knows how to interpret the signal. Supposedly, they can also all be on the same circuit, and depending on the axis movement and position the software will know which axis had been triggered.

[hemsworthlad]

Yes you can use home and limits on same switch, mach knows to treat the switch signals differantly when homing.
How far off the hard stop's is totally up to you and how comfortable you feel running close to the hard stops if you have any.?

[M250cnc]

Originally Posted by Fastest1 I dont think a limit switch can be used for a home also. Double check on that. I think the machine can not pass a limit but can pass a home. It takes 2 different pins. 1 for limits 1 for home. I personally use a distance off my limit as home. I also only run 1 switch per axis all sharing the same pin. I do have a ramp at each end so it emulates 2 switches.

Fastest1 why do you keep repeating wrong information, as you were informed in this thread http://www.cnczone.com/forums/diy-cn...iguration.html

I am sure you wouldn't appreciate people replying to your cries of help on the Mach3 forum if they were giving you wrong information.

MACH CAN USE LIMIT SWITCHES AS HOME AS WELL, ALL ON THE SAME PIN

Do you not read the replies

[Fastest1]

Yeah I did read it. I didnt understand it then either. I have watched the videos too and still get confused. Mine works now, all on 1 pin and 3 switches but no home switch as stated. That is exactly why I said double check. I sure dont mean to mislead anyone. There are plenty of challenges here without any misguidance, sorry. All of my learning disabilities shine thru here!

[brtech]

The manual does a better job of explaining how it works than the videos do.

The key to understanding it is that when Mach isn't homing, tripping the switch is E-Stop.

When Mach is homing, first of all, it always travels TOWARDs the limit switch by assuming it's somewhere in the middle.

Then, it DOES NOT E-stop when it trips the switch. Instead, it moves back until the switch deactivates. Then it's home and it will zero the DRO.

It homes each axis separately (including A if it is slaved to another Axis).

[ger21]

Originally Posted by brtech When Mach is homing, first of all, it always travels TOWARDs the limit switch by assuming it's somewhere in the middle.

Actually, it doesn't assume anything. It either moves in the + direction, or the - direction, which is set by the user in the Config>Homing screen. If you happen to be on the wrong side of the switch, it won't find it.

[johnmac]

brtech is correct. I would like to add that you can if you want the home position to be farther away from the limit switch you can specify an offset amount in the homing dialog. Then your home position can be anywhere you want.

John

[M250cnc]

Originally Posted by dpgoldberg How close to the physical end of travel should a limit stop switch be placed? They will be adjustable but I'd like to get in the ballpark.

The most accurate way of using a limit switch as a home is to use a micro switch with a lever with a roller on the end, when it is travelling towards the limit it will run up a ramp then activate.

You could set the limit a safe distance (Measured) then run the axis full speed to the limit you will then know how far the table overshoots you can then decide the amount of tolerance.

Originally Posted by Fastest1 Yeah I did read it. I didnt understand it then either. I have watched the videos too and still get confused.

Then please ask why it's not working for you. This site is for helping each other out.

Originally Posted by ger21 Actually, it doesn't assume anything. It either moves in the + direction, or the - direction, which is set by the user in the Config>Homing screen.

Gerry is correct, after you have set the hard limits then you set the homing axis direction using the method he describes.

Originally Posted by ger21 If you happen to be on the wrong side of the switch, it won't find it.

This statement is only true IF YOU HAVE A SEPARATE HOME SWITCH using a separate input pin.

Not only that but Mach will ignore a limit switch while looking for a home and just travel to the machines end travel and crash/stall your motor.

So for a beginner using the same switch for home and a limit this can't happen