Messages

281

General Mach Discussion / Re: Bridgeport Mill

« on: March 04, 2008, 08:38:09 AM »

I vote for Quill as it's the least astonishing idea - but both is an intreguing prospect. Could you get mach3 to understand the idea of two Zs working togther?

282

General Mach Discussion / Re: Hall effect home switches - Nonsense and bother

« on: February 29, 2008, 05:37:07 PM »

The  laser with its well-collimated beam should provide the potential for great  accuracy. I did have an idea for using a laser for homing - if a laser mounted at 90 degrees to (say) X shines upward  onto a black pad to prevent is  going into anyone's eyes. As X approaches it brings with it a highly polished peg of round bar which interrupts the beam. Reflecting off the round bar causes the beam to sweep downwards  rapidly  and  hit a sensor.  It's the  high sweep speed  that should allow very rapid triggering, especially if the sensor is mounted a distance from the peg.

283

General Mach Discussion / Re: PCI port card addressing woes

« on: February 29, 2008, 05:26:20 PM »

Normally  this  is what  happens.  The old (triangular)  card did not prompt WXP to display a Resources tab, and  no  resources   info could be found  by other means.

The MosChip item worked ideally, just  as it should.

284

General Mach Discussion / Re: So n00b it hurts! Help please...

« on: February 29, 2008, 05:14:52 PM »

Hmm. If your customers are screaming for parts, satisfying them may be your #1 priority... sub  the work out, take a bit of a loss, clear your mind of panic and set to getting your machine going? at least that way your customers won't think of you as someone who delivers  late or not at all. It  depends how loud they're screaming really. just a possibility.

285

General Mach Discussion / Re: So noob it hurts! Help please...

« on: February 26, 2008, 04:17:30 PM »

Hello n00b, welcome aboard. I'm still learning myself but soft limits can be turned off - can't remember what screen it's on but it mihgt be Settings. Possibly too easy but just as easy to overlook.

286

General Mach Discussion / Re: Hall effect home switches - Nonsense and bother

« on: February 26, 2008, 04:12:38 PM »

I'm still very interested by the optical solution. I took a scientific approach to the problem today and plotted all the values of the three axes on 20 re-homing moves from a zeroed homing move. X and Z deviated by +/- 3 or 4 microns  while Y was sometimes as much as 90 microns out. I tried winding Y's sensor out a bit until the vane only just missed the front of the sensor, doing the same for Z as it was a bit further out than I liked the look of.
The second test run showed a marked improvement on Y with a slight improvement on Z, at this time I had around +/-3 microns on each axis according to the DRO. Certainly good enough for most work but there's room for improvement.

Ideally if I can get dead-zero rehoming I should have it - I am, after all, worth it. I'll prototype one with some RS clobber, screw it to the bed and wire it into a home switch input to test its repeatability. It sounds like a safer bet than the old hall effect sensors anyway.

The next step is to test the positioning accuracy of the machine and its steppers, drivers and software, and try out the leadscrews for backlash. more as it arrives.

Oddly enough, i asked our workshop manager about this lot and he reckoned that Y was always a bit dicky... Took five minutes to fix. That, and the brake contactor with the fried coil. and, of course, the control system that gave up its ghost, well that took a bit longer...   time aside, it's fun, isn't it? 

287

Tangent Corner / Re: Materials suggestion......

« on: February 26, 2008, 03:58:32 AM »

good point, FRP is very strong.

There's the added advantage that metal parts like pins, hinges, cable clips etc. can be moulded directly in without screwing or bolting.

288

General Mach Discussion / Re: Hall effect home switches - Nonsense and bother

« on: February 25, 2008, 08:00:21 PM »

Grand. Will look into trying one of these out. Thanks

289

General Mach Discussion / Re: Hall effect home switches - Nonsense and bother

« on: February 25, 2008, 07:19:03 PM »

thanks Hood - making waterproof boxes will be no problem. Have a look at RSwww, part number 304-560, a nice optical gate with a built in schmidt triger and logic output. Is this the sort of thing you're using? It''s only £5 and very neat - and would run off my 9V setup.

no encoders, sadly, I'm running three hefty steppers. Encoders would be nice.

290

General Mach Discussion / Hall effect home switches - Nonsense and bother

« on: February 25, 2008, 05:33:39 PM »

Well, I'm annoyed again.

My machine has three hall-effect proximity switches for homing. These have inbuilt magnets and react to plain steel vanes on the slides, or the leadscrew nut in the case of Z. They trigger a logic  pin on my second port with an arrangement that uses a 2k2 resistor in series with the sensor, and the whole lot across a 9V supply (these sensors originally had a 9v line). Across the resistor is the input side of a darlington-output optoisolator in series with a common LED to give a combined junction voltage of around 2.2 volts (plus a current limiting resistor). Effectively when the sensor is triggered its resistance rises from around 300 ohms to 13K; the voltage across the 2k2 resistor drops sharply to below 2.2 volts and the opto shuts off, allowing the logic pin on its output side to float high.

All this is very fine and well, but when I reference the axes, zero all, turn off the automatic zeroing and move all the axes -10mm, then re-home them all, they end up in slightly different places to where they started.. not usually much, 1-2 microns usually, with the exception of Y which can be much further out.

A few questions:

 - Do hall proximity sensors work best if the vane passes very close by it, or does a bit of separation help?
 - Can i expect day-to-day drift due to temperature and age affecting the interface circuit?
 - Is it really reasonable to expect a machine to home accurately to EXACTLY the same position 24 hours after it last did it?
 - if so, how?

I can find precision switches giving 1 micron repeatability on RS, but if I'm to have three of them they'll be around £500, and I won't be popular with the bean-countress.

Suggestions? I did consider that of "buy a new one from Haas" as very favourable, but... see above  Thanks in advance.