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homing for probe
« on: August 17, 2011, 05:30:45 PM »
How do I set up a limit switch to use to zero a grinding wheel?  I have set up a
limit switch onto which I want to move a grinding wheel to identify the size of the wheel.
So I would move the grinding wheel into position with the midline of the wheel aligned
with the limit switch and then move the wheel slowly toward the switch until it opened
and back it off slightly just like the axes do when they zero.  Then I can use the position
information to know where the edge of the wheel is as it gets ground away over time.
I assume there is axis zeroing code somewhere that I can easily adapt?

Also, I have mm lead screws and cant figure out how to set up these properly.  Do I put
mm in native units and figure 5mm per rotation?

Thanks

Offline Hood

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Re: homing for probe
« Reply #1 on: August 18, 2011, 02:14:24 AM »
Not really that familiar with the probing routine so probably best to wait for some of the others to help you with that.

For your leadscrews well it depends what your native units are, if you use metric as native units then calculate with the 5mm pitch, if you use Imperial then calculate by converting your 5mm pitch to inch, ie one rev would be 25.4/5 = 5.08 turns per inch So say for example you have 1.8 degree steppers, 10uS drive and no gearing the calcs would be 200 x 10 x 5.08 = 10160 steps per inch
Hood

Offline RICH

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Re: homing for probe
« Reply #2 on: August 18, 2011, 05:01:49 AM »
Quote
How do I set up a limit switch to use to zero a grinding wheel?


Have never done what you are asking. I always dress my grinding wheel before using it ....don't you?
I have a Sanford bench top surface grinder which is totaly manual so you measure as work progress.
It would seem that the tip or high point of the diamond would be a better reference  relative to the face / bottom / side of the wheel.
That can be used to trip a switch or whatever. Since you only grind in tenths ( .0001") at a time you will need a very accurate and repeatable
switch. What the surface being ground relative to the wheel or wheel wear rate is as your grinding is another story.

I only remember one thread  on a grinding machine trying to use Mach a long time ago.

Someone who does surface grinding at the comercial level can probably be of more assistance.
FWIW,
RICH

Offline BR549

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Re: homing for probe
« Reply #3 on: August 18, 2011, 09:47:48 AM »
 Are you looking to just reset the Zero point of the wheel or actual measure the radius of the wheel.  Setting Zero is very easy use the refhome axxis routine.  Measuring the Wheel radius and Keeping track of wheel wear is not so easy. It requires a MASTER set point of a known distance as a reference. Then you compare each touchoff of the wheel to the known setpoint value.

Just a thought(;-) TP

Re: homing for probe
« Reply #4 on: August 18, 2011, 01:29:47 PM »
Thanks guys, I did figure out the lead screw calculations and it works great now using the 25.4 conversion.

I only need to reset zero rather than come up with the actual radius of the wheel.  It seems that the switch has to be accurate but the axis zeroing process uses the same type switch and that has to be accurate as well. 

How do I do a refhome axis routine for that axis.  It has to be done as a separate command and the axis must move in the opposite direction to the normal
homing routing that I use to ref axes.  Thanks

Offline BR549

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Re: homing for probe
« Reply #5 on: August 18, 2011, 05:01:31 PM »
HUM that is not going to work well as there is no easy way to Refhome in both directions. IF you are using the refhome to set Zero you would not need to ref the other direction. The same as we do with plasma machines.

You could use the G31 probing function and set your switch up as a probe input.  You will have to create a macro to run the function.  Not really hard to do just different and has some quirks to it.

Just some thoughts, (;-) TP
Re: homing for probe
« Reply #6 on: August 18, 2011, 08:10:06 PM »
I will have to figure out how to set up a probe input...  thanks
Re: homing for probe
« Reply #7 on: August 18, 2011, 08:27:22 PM »
I just realized that the way to solve the problem might be to position the wheel near the diamond and then
manually advancing the diamond until it touches the wheel and dressing the wheel and calling that zero and
offsetting from there but a switch would be easier...

Offline BR549

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Re: homing for probe
« Reply #8 on: August 18, 2011, 09:08:03 PM »
IF you make the diamond a stationary point THEN it will be a known reference point each time you dress the wheel. Most reference the height of the stationary point above the top of the table. THAT IS if we are talking surface grinder.

It will depend on your method of reference

Just a thought, (;-) TP