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Author Topic: 3d Probing on Granite slabs  (Read 5850 times)

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Re: 3d Probing on Granite slabs
« Reply #10 on: February 26, 2019, 04:41:46 PM »
Hi,
my idea was for something simpler still. This is a good quality microswitch with plenty of overrun:

https://nz.element14.com/honeywell/bzc-2rq1-a2/switch-basic-top-pin-plunger/dp/1525197

My suggestion is to make a small carrier like that pictured with a stem that mounts in your spindle.
Fit the switch (plunger downwards obviously) to the carrier, fit the assembly to your spindle.
You might like to glue a small extension to the plunger to have the body of the switch somewhat further away
probed surface.

Craig
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #11 on: February 26, 2019, 05:00:26 PM »
Hi,
one of the problems with the more normal CNC spindle mounted probe is the lack of overtravel.

When your Z axis is descending looking for a contact there will always be a bit of overrun. Provided your descent
speed is not too fast and your controller operates both correctly and quickly (within a few tens of micro seconds)
the overrun will be small.

If however your controller does not respond quickly you risk burying your expensive ruby tipped probe into the surface.
Without overtravel its going to get broken.

The switch I linked has a minimum overtravel of 5.5mm.

Lets say you specify (in Autoleveller) the safe height above the nominal 'flat' surface of 5mm. You can also direct
Autoleveller to probe to a maximum depth. Thus if you caused Autoleveller to produce G31 commands of the type:
G31 Z -5.0  F100......then even if your controller missed the probe event the machine will stop its descent at -5.0mm hopefully
just a little short of the overtravel of the switch.

Craig
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #12 on: February 26, 2019, 05:01:00 PM »
Hi

Google high precision micro switch
https://www.google.com/search?q=high+precision+micro+switch&rlz=1C1ASUT_enAU791AU791&oq=high+precision+micro+switch&aqs=chrome..69i57.12774j0j8&sourceid=chrome&ie=UTF-8

Omron have a good range
https://www.google.com/search?q=high+precision+micro+switch&rlz=1C1ASUT_enAU791AU791&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj2wPHTsdrgAhVYb30KHV2QAjIQ_AUIDigB&biw=1174&bih=493#imgrc=e3unll0hLvCuPM:

If there is a risk of over travel damaging the switch place it in a spring loaded plunger that will allow it to move up and protect it from damage.

For the resolution you need it should cost less than $100

Regards
John
« Last Edit: February 26, 2019, 05:09:41 PM by John Mac »

Offline MN300

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Re: 3d Probing on Granite slabs
« Reply #13 on: February 26, 2019, 05:08:02 PM »
https://www.digikey.com/product-detail/en/c-k/LCS012P00WA26AY/CKN11533-ND/8536760
This switch is rated for low current, it has gold flashed contacts and is IP67 - Dust Tight, Waterproof.
Re: 3d Probing on Granite slabs
« Reply #14 on: February 26, 2019, 05:09:20 PM »
Hi,

Quote
For the resolution you need it should cost less than $100

I would hope to do way better than that. As it turns out I have several of these switches lying around surplus.
Even if I had to buy one, the price is $20.77 NZD including GST (new Zealand sales tax). That works out to
$13.90 USD. Element14 ship free if you order a minimum of $45 NZD. That's why Element14 is my favourite
supplier.

Craig
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #15 on: February 26, 2019, 05:12:04 PM »
Hi,
I can and have bought from DigiKey but they have a minimum freight charge of $35 NZD +15% GST.
So despite the switch you have linked to being cheap the freight kills it.

Craig
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #16 on: February 26, 2019, 05:21:56 PM »
Hi,
apologies for the picture I posted earlier, I didn't check it out before I posted it......its way to big.....and I hate
that, a real bunnies mistake.

Craig
My wife left with my best friend...
     and I miss him!

Offline MN300

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Re: 3d Probing on Granite slabs
« Reply #17 on: February 26, 2019, 05:30:02 PM »
There are many suitable switches, but be sure to get one rated for low current. High power appliance switches sometimes need the high current to keep the contacts clean and can fail when used on low DC current.
Switch failure is a reason to use a normally closed switch so a dirty contact or broken wire would not cause a crash.
Re: 3d Probing on Granite slabs
« Reply #18 on: February 26, 2019, 05:48:38 PM »
Hi,

Quote
There are many suitable switches, but be sure to get one rated for low current. High power appliance switches sometimes need the high current to keep the contacts clean and can fail when used on low DC current.

That is true. The Honeywell switch I linked to has silver contacts and would ideally be switching rather more current
than the gold contact one MN300 linked to. Having said that I have used these Honeywell switches (Omron make identical units)
for years at low currents without difficulty.

As MN300 comments there are any amount of switches that would work. I think however that plenty of overtravel is
the critical characteristic rather than switch current.

Either way the simple idea of a spindle mounted carrier should enable OP to make a probe for way less than buying one.

Craig
My wife left with my best friend...
     and I miss him!

Offline MN300

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Re: 3d Probing on Granite slabs
« Reply #19 on: February 26, 2019, 06:08:11 PM »
Overtravel could be accommodated by spring mounting the switch. Something on the order of a spring mounted tap follower that extends to a hard stop.

As Joeaverage says, you can often get away with using a high power switch that has never seen AC current. Higher power can mean higher mechanical operating force.