Using indicators for limit switches.

[wmcghee]

I had posted a question a couple weeks ago about setting X and Y with a probe. After some very helpful info I was able to modify a program and the probe did the task fine. It was, as some of you guys told me, putting my $350.00 probe in danger of damage and adding extra steps in the set up. Well, I realized you guys were right. I didn't like the extra steps and the thought of busting the probe was more than I wanted to bear.

Anyway, to make a long post short, I was trying to come up with something for proximity switches. I was planning on doing like someone else in a previous post and use a bolt and spring. As I was looking for springs in one of my old toolboxes I ran across an old indicator. They are spring loaded so I thought I would give it a shot. Its not the best looking setup out there and probably not the most durable but it seems to work very well.

I attached the indicators to magnets with the regular screws. Then I attached the magnets to the table with Gorilla glue. It was kinda tricky getting them right where they were about 7/8" or so from the hard stops so I would not lose any travel.

I will try to upload some pictures of the setup so you all can understand better.

[Brady Watson]

Wayne,
If you shop around you can buy real proximity switches for around $10-25 ea.

-Brady

[wmcghee]

Here is the one for X axis. I had to add a copper plate to give the indicator something to make contact with
5350

[wmcghee]

This is the one for Y axis
5351

[gerald_d]

Hi Wayne, that is a smart, economical, reliable way to see where your SB really stops! Killing 2 birds with one stone - stopping + measuring.

*bookmark thread*

[wmcghee]

FYI, when I run the home.SBT program to set the home position on initial contact the indicators will move about.030 off of zero. When it moves away and makes contact at a slower speed the needle moves less than half a thou. I had a smaller wire running to the control box when I first hooked them up and the indicator would move about .003.

[earld]

I've been considering making an offset fixture for setting the Z offset with a dial indicator and a flat tip. Rather than reinvent the wheel, has anyone tried this?
I'm in the wrong thread for this, but, does the Shopbot aluminum offset tool hold very accutate offsets?
Earl

[Brady Watson]

Duane,
The Z-zero plate works very well and is very accurate.

-Brady

[bleeth]

I have noticed that when I intentionally hit limit switches using keyboard or remote the first contact usually reads slightly different than successive ones made by backing off and hitting again.
This has been puzzling me for a while. I always do this starting only a couple of inches from the switches. If it were a person absorbing a punch I would say that on the second and third jab it was set and ready.
Dave

[Brady Watson]

Dave,
One thing that can increase the repeatability of your limit switch is if you take the target bolts out and grind the heads down totally flat. I believe that most of them have 'nubs' that stick up on the bolt head. This can cause the limit switch to trigger off of the nub, instead of the surface of the bolt head. Sounds trivial...but it really does increase repeatability.

-Brady

[rjguinn@optonline.net]

I agree with Brady. I've used the prox switches since they were 1st offered by Shopbot using flat ground bolt heads.Never had a problem with close tolerence repeatability.
Jeff

[dingwall]

I'll try grinding the heads of my proximity bolts. I've been toying with the idea of mounting dial indicators at the home point.

[bleeth]

Thanks for the tip-I'll be grinding bolts tomorrow.
Dave

[R. Thomas (Unregistered Guest)]

Hi all,
I have a friend who is willing to give me a couple of prox switches and help me hook them up (he knows a bit about electronics/robotics). Does anyone know where I can find info on the connections to be made in the Shopbot control box?

Thanks

[paco]

http://www.shopbottools.com/files/SBD135_040714Prox%20Switches,%20PRTalpha.pdf (http://www.shopbottools.com/files/SBD135_040714Prox%20Switches%2C%20PRTalpha.pdf)

..page 5; that's about the Alpha though... should look similar for "ancient" PRT! 8-D

[R. Thomas (Unregistered Guest)]

Thanks for the info,

I went back and looked in my manual and I do have that page for my "ancient" PRT96. I guess I hadn't looked closely enough. I'm not sure if the switches I get will have the same color wires, but I guess my friend should be able to figure it out what wires go where.

Thanks again.

[stickman]

I have discovered a problem with my proxy switches. It will locate the X and Y home, however when the carriage is in a move or jog during normal operation, the switches WILL NOT stop the operation and it bangs at the stops. They light up, after I hit the stop button, I have to move the carriage from the limit switches, in order to get it to work.

Can anyone tell me what I need to change in order to get this to work.

[paco]

Hi Jay!

You need to set the Input switch #3 Mode to Limit switch...


5352

... or it just be a simple input switch rather than a limiting one. This way, it will stay like you know 'em to be but will limit movement when triggered. You might want to enable File limit checking too (SF,1); this will prevent most (depends on good table base coordinate location) non-wanted movement IF the Limit for table are correctly set (VL settings; you can set SF there too).