What did you do Today 2018

Don't get rid of those magnets!

Wrap each in some foam rubber, with insulation tape around, ie, make a sort of tennis ball size foam ball, wound stiffly with tape. Place a largish Sandwich type plastic bag into another, and place the ball within. Wrap the outer bag over, as you would a sandwich, and place the ball in the Swarf Tray..For steel swarf, it works a treat - just unwrap the outer bag, stretching it inside out, keeping all swarf within, and empty in the Swarf Bucket, and refit the bag, or replace if it has big holes..

The foam keeps the swarf from direct magnet contact, which makes it difficult to remove the swarf otherwise..

On the subject of the rubber gumming up..I have similar issues here at home - I suspect it is salt/humidity due to the proximity to the sea - 50meters from the ocean's edge, but not sure.

All the 'tactile' feel ( maybe a silicon based ) covering on the knobs of my oscilloscope have become sticky and can be squeezed off of the knob, between ones fingers. Ditto the rubberised coating on my Wine Corkscrew, and some pens, as well as the rubberised handle of my Bosch battery drill.....Very odd. First I thought it was maybe my sweaty hands ( can't be oily hands, least not on the 'scope and corkscrew!) , but parts of the drill body that are not in hand contact are even muckier..

Joe

edit - spelling..

Edited By Joseph Noci 1 on 17/02/2018 14:17:40

Edit - Sheesh! more spelling...personal note - engage spell checker before brain in neutral..

Edited By Joseph Noci 1 on 17/02/2018 14:18:54

The actual position and accuracy of your home switch plays no significant part in the accuracy of your machine operation unless you plan to remove and replace your part between operations. Bottom line is - if you machine a reference part (start with a circular profile perhaps), how does it measure up? For various reasons, you are unlikely to do very well with a hobby machine conversion (or an old industrial machine, for that matter), no matter what limit switch you fit (lipstick and pigs?). I'd be happy indeed if I managed 10um.

Martin - look at suppliers like Omron for "proper" switches.

Murray

Murray and John,

These are the type of switches I was looking for, used in industrial robot applications for homing, overrun and positioning. They are operated by linear cams, **LINK**

Martin P

This seems a bit like more money than sense, not that I can't see the attraction, but wouldn't it be much more cost effective to get a Schmitt trigger photo interrupter and make your own switch?

Hi there, Joe,

Thank you for your response.

Since I posted my earlier message, I've encountered another pair of perished sleeves. These were on the two spacer pillars each end of a pair of magnets. They were far worse than 'gummy', more like the consistency of thixotropic bituminous paint. But my vodka is safe - I found that liquid 'soap' is good for cleaning the stuff off my fingers.

I seem to remember that I had a similar problem with some sleeves that were blue, rather than black - they perished after I'd removed them from the hard drives but I'd put them in the same container as the screws I'd salvaged from the drives.

Thank you for your suggestion regarding the magnets. Some time ago, we listed some on ebay. They were bought by a motorcyclist to replace the magnets in his 'tank-bag'. He came back later full of thanks and praise and said the magnets were very good - his tank-bag stayed on the tank at over 100 MPH! In view of our 780 MPH speed limit, I didn't risk becoming an accessory after the fact by asking him how he knew!!!!!

Best regards,

Swarf, Mostly!

In my earlier post - for '780 MPH', please read '70 MPH'.

Best regards,

Swarf, Mostly!

Darn it, you just wrecked my daydream about a ‘Thrust’ sports Car variant!😢

Edited By V8Eng on 17/02/2018 17:32:48

On that note:

**LINK**

I purchased a few of these - they have a '10 pack' for $35.00 - and they work very well - about a 2micron hysteresis.

Joe

Hysteresis looks good, but how is the repeatability? Some good information and recommendation here on measured repeatability for opto switch.

But really I'm being lazy, easier to re-use something I have which works well for height setting on the mill for a similar application on the lathe. Unlike either the microswitches or one of those opto boards it has already got its own housing. Also very easy to interface, just one wire to an input on the BoB (which already has a pull-up). It's a bit awkward having to move it between machines, so I'm planning a simplified version for the lathe.

Murray, the reason for wanting an accurate home switch is to be able to home the machine once at the start of a machining session and then use any tool for which I have set up an offset to turn to reasonably accurate diameter without having to take a test cut with every tool. I've spent most of the afternoon working out how to do this and it looks fairly straightforward and works fairly well, will work better when I've set up all the offsets with more care.

Repeatability is second to none, I installed a washing machine fed and emptied by two robots using these switches on all three axis and for the last ten years none have needed replacement, adjustment yes when the screws come loose.

Martin P

2um hysteresis is slightly OTT, it could ring like a bell, which is why you want that Schmitt trigger.

For accuracy it's very own Voltage regulator would be a good idea and a dust/light proof housing.

3D printer uses ordinary microswitches. The z-axis is very sensitive to small changes in the start point but it seems be very repeatable, I'll do a simple test.

OK, over several (i.e.>>5) runs the 'skull pointer' on top of the Z-axis lead screw finishes pointing to 'four o'clock' with a consistency that is better than +/- 1 minute. So that's within 2/60 of a rotation. The screw pitch is 0.8mm and 0.8/30 = 0.027mm

As the stop screw is bearing on a level with an advantage of about 3:1, the microswitch must have a repeatability no worse than and probably better than 0.01mm. That's pretty impressive for a bog-standard sub-miniature microswitch, to be honest I am pretty boggle by the consistency of it! - I just repeated a few runs to check it wasn't just wishful thinking!

Neil

Hi Robin, please provide details of what you are proposing in place of limit switch for position ID.

Emgee

Here's a nice one, £1.50 from RS, will a link to the RS data sheet work?

https://docs-emea.rs-online.com/webdocs/0d1b/0900766b80d1bd95.pdf

The Schmitt trigger gives it a natural hysteresis. It would need some way to keep a steady current through the LED which is why a separate Voltage regulator would be extra nice.

I'd guess he's recommending a switch with less hysteresis one with 2um could suffer jitter/repeat triggering under the vibration of ordinary machining.

Greater hysterisis won't make a switch less repeatable or accurate, but it does make sure that once triggered it will stay switched until positively released.

No different from the Banggood item I referenced , which HAS a Schmitt trigger formed by an LM211 . If you wish you can by changing the value of one resistor, make the hysteresis 'anything' you would like - not so with the integrated jobby..Feed it with regulated 3.3V to 5V.

Neil, there should not be much vibration while doing position sensing, I would hope..Not sure how these are being employed in the applications on this forum? During a heavy interrupted cut on a mill? Where would sensing take place during such?

Joe

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Yes, if you post it as a link

**LINK**

https://docs-emea.rs-online.com/webdocs/0d1b/0900766b80d1bd95.pdf

MichaelG.

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Aha! So the picture of planet Earth rising over the Lunar horizon is for posting Links

Here's a thought, microswitches may have great hysteresis but they also bounce

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If the icon was shown in better resolution, it would be a little more self-explanatory

... It allegedly depicts the Earth, with a Chain [world-wide-web link]

... The adjacent one is to break the link.

MichaelG.

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P.S. Norman [NJH] once asserted that it was actually a picture of a bubblecar.

Small point: any input on a CNC controller worth its salt will be triggered by the first edge it sees and apply a debounce timer.