| Author | Message | ||
     Colin Shannon New member Username: Colin Post Number: 12 Registered: 02-2007 Rating: N/A |
I know I aksed this question before but it must have been on the old forum, so at the risk of being flamed, here goes. Stan, I also lost the email you sent with some info on it as well, now I have the need to use them! How do I connect limit switches? I've read through the other posts on here, but need something more specific to my set up. My system comprises of the break out board, then individual driver boards for each axis. Basically I need to know where to connect the remaining wire from the limit switch, and how to configure the program. Please keep this simple. I've atatched a pic (gotta love Paintbrush) of my break out board.  Any help appreciated. | ||
| Stan Gray Moderator Username: Stan Post Number: 109 Registered: 01-2007 Rating: N/A |
Hey Colin, It's been awhile. I don't see a port ground on your break out board. You need to tie the open end in your drawing to pins 18-25, the port ground pins.  | ||
| Colin Shannon New member Username: Colin Post Number: 13 Registered: 02-2007 Rating: N/A |
Hey Stan, Thanks, you are right, there are no 18 to 25 pins on my board (no wonder I was getting confused). The pins do solder directly to the board though so I will just tap onto those. Having read in the other posts, do I need a resistor (10k) inline here? Thanks. Colin P.S saving up for Maxstepper, can't wait. | ||
| Stan Gray Moderator Username: Stan Post Number: 110 Registered: 01-2007 Rating: N/A |
Hey Colin, you should be fine sinking to ground without resistors, that's what the port is set up to do, it's just when you bring in outside power to the port that you want to limit current to protect. | ||
| Colin Shannon New member Username: Colin Post Number: 14 Registered: 02-2007 Rating: N/A |
Hi Stan, Thanks for the help! Yippeee, I got it working (que little victory dance). After I spent 10 minutes just pressing the switch to see the pretty red light come on the CNC control panel I made efforts to mount them to the machine....that's a mission in itself but still happy. I just tapped into the 18 to 25 pins on the BOB. I also played around with some resistors before I read your second post, and they actually caused the relays on the BOB to trigger - weird, but without them it functions perfectly. A question about directions, how does Kcam know specifically which limit switch has been triggered? Is it a combination of the system knowing the direction of travel in the code, then using this info combined with the relevant axis limit switch being triggered? I've got another question as well (probably belongs in a new post) - feel free to move it if you see fit... I'm setting up the axis's on the lathe to be more accurate (ie: when my code says to move 10mm it moves 10mm!). What is a generally acceptable variance in measurement? I can get repeatability down to .03 of a mm (eg: it may go to 9.99 mm on one pass, then 10.01 mm on the next) - I personally think this is not too bad (I'm not making weapons grade parts here). Any thoughs on improving the accuracy further or should I just be happy with that. My leadscrews are the factory intalled ones on the lathe - no mods. Thanks again Stan for the help. Colin | ||
| Kelly Ullrich Moderator Username: Kellyu Post Number: 89 Registered: 02-2007 Rating: N/A |
KCam can determine which switch tripped by knowing the current direction during the parallel port stepping process. If you trip a limit switch manually (not stepping the motor), KCam may be wrong which one it is. There is a parameter called Backlash. That may be the adjustment you need for improving your accuracy. | ||
| Colin Shannon New member Username: Colin Post Number: 15 Registered: 02-2007 Rating: N/A |
Hi Kelly, Thanks for the info on the limit switches - thought that's how they worked. With my measurements, I have not looked at backlash yet - will do after I get the initial settings right. Basically what I do is run the x axis past the point to be measured from, then back a cm or so in the direction to be measured, then go from there - so the axis is 'under tension' when measured. Once I have that sorted working out the backlash amount should be easy. I actually mount a digital caliper in the lathe chuck and have the tool post move it to get the measured distance. Thanks again. Colin | ||
| Colin Shannon New member Username: Colin Post Number: 16 Registered: 02-2007 Rating: N/A |
Hey Kelly & Stan, What ype of limit switches are people using or is recommended? I've got a number of mini pushbuttons and some lever type micro switches laying around, are these the best option, or how about using a magnetic (reed) type switch - I see benefits to this type as there needs to be no physical contact to activate it (if a bit of swarf accidentally gets between a 'mechanical' type switch it could possibly give in inaccurate reading), or are these, by their nature, inaccurate as far as 'switching' at the same point every time? How are the mechanical switches for repeatability? Thanks. Colin | ||
| Stan Gray Moderator Username: Stan Post Number: 112 Registered: 01-2007 Rating: N/A |
Hey Colin, I've used reed and magnets with no problems. I think they are just as good as a micro switch, maybe better. The reed switches are sealed and not subject to moisture or coolants. The mini pushbuttons might get crushed unless you use a lever configuration to activate. When it comes to micro switches I prefer Cherry's, I've seen more Micro Switch brand fail. You should always when possible mount your switchs so they don't get crushed if you over run the switch. | ||
| Fred Mueller New member Username: Freddie Post Number: 8 Registered: 03-2007 Rating: N/A |
Hi Colin, I have been using miniature pushbutton microswitches with very good results. I get repeatability of less than .0002 inch. I thought about reed switches but when I tested them, I could not get the accuracy that I wanted. Also since I sometimes cut steel, I don't like to have any magnets the attract the chips! I built a small mounting system that uses a spring loaded plunger(make sure the spring force is greater than the switch actuation force)that will provide about 1/4 inch of overtravel. If by chance the system does not stop, then the overtravel runs out and I get a hard mechanical stop that will stall the steppers. | ||
| Kelly Ullrich Moderator Username: Kellyu Post Number: 90 Registered: 02-2007 Rating: N/A |
I haven't used any yet, but I always felt Optical sensors would prove to have the most accuracy and repeatability. Any thoughts? | ||
| Colin Shannon New member Username: Colin Post Number: 17 Registered: 02-2007 Rating: N/A |
Hmmmm, Fred, good point on the magnet attracting chips. I only machine alloy at the moment but who's to say I don't do the odd bit of steel later. Lots of good (and different ideas). I've thought about the optical sensor. You would need to have some kind of 'bar' to break the beam - easy enough - the sensor would obviously need to be protected to prevent spurious triggering by falling swarf (I've always wanted to use the word spurious!). Any ideas on a cheap circuit to build for this - would be great to test, and I'm sure it could only cost a few $ to make, and would give perfect repeatability every time. I've actually got a handful of photo sensors (the 2 part one with the infrared led and sensor in one package)laying around here as well. I connected up a couple of the microswitches last night, but feel it's only a matter of time to replace them due to coolant getting in there, even with a protective shroud, that stuff gets everywhere - nice oily residue! | ||
| Herb Michael New member Username: Dnaman Post Number: 18 Registered: 02-2007 Rating: N/A |
I did my limit switches with microswitches. You can get them with actuator arms that have a projection on them which you hit with a "wiping" motion as you travel past. If the switch doesn't cut out due to a failure somewhere, you don't crush the switch, you just keep going right past. It's easy enough to build a solid "if all else fails" stop past the microswitch (like a locomotive buffer) ... no point in screwing up the switch because of a failure somewhere (like it wasn't plugged in). If I were doing an optical switch, I'd look at a reflective sensor. The slot type might get filled with swarf and give all kind of trouble. A reflective sensor/target strip could be mounted way in the open. An IR source/receiver pair wouldn't be affected by room lights. Either kind might be affected by coolent spray ... perhaps some kind of splash guard if it proves to be a nuisance (again, I would think the reflective setup would be easier to keep clean if it comes to wiping it off occasionally. (Decent microswitches by the way should be hermetically sealed and should be unaffected by coolant). Either setup (chopped beam or reflective) has been described for homebrew tachometer use for minilathes and the like complete with drive circuits. Google around and you should find something. | ||
| Kelly Ullrich Moderator Username: Kellyu Post Number: 92 Registered: 02-2007 Rating: N/A |
Sometime (long) ago, while disassembling a tape recorder or printer, I came across an interesting sensor. It was an IR receiver/transmitter assembly with a lever arm that broke the beam. It had and extremely light spring force(gravity on the plastic). It may have been used for sensing paper. That is what I would like to try some time. I think it would be improved if it was covered with a rubber baffle to keep out metal and liquids. |
