Australian Facetors' Guild Limited

B & W Depth of cut meter

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  • 28 Jan 2020 10:47 PM
    Message # 8697082


    I am looking at putting a depth of cut meter on my Halls Xtra. I'm just wondering if anyone else has done this and have and photos or tips. I've seen someone install one on a ultra tec using a Simpson multimeter using a buzzer to give a audio as well as an analog visual.

  • 29 Jan 2020 7:38 AM
    Reply # 8698899 on 8697082

    I looked at fitting one of those on my machine years ago, but could not find enough info on how to fit it. So I fitted a digital height gauge instead, I put an article in facet talk 228 page 5 about it.

    It was something I was already familiar with anyway, as there was one fitted to a milling machine at work.

  • 30 Jan 2020 7:34 AM
    Reply # 8701271 on 8697082

    The version of the depth of cut meter I have seen is just a spring contact like that found on a relay mounted so that it majes an electrical contact with an arm on the head as the hard stop is reached.

    The -ve wire on the battery is wired to the body of the machine.  The +ve wire goes to a light bulb or LED (with resistor) then to the contact.  An analog multimetre on the Ohm scale can replace the light bulb and battery, or it can measure the voltage drop across the light bulb.

    As depth of cut is reached, the contact makes progressively longer contact with the body of the mast, resulting in the light progressively turning harder on or the multimeter needle swinging towards its maximum swing for the circuit.  It is pretty much an all or nothing equation.

    A dial indicator gives a better indication of how cutting is progressing.  It also gives an idea of the state of your lap, eg whether it is dished or flat.

    Frank, I have a linear scale like yours on order for my concave cutter's horizontal alignment.

    But I saw on Youtube where a chap mounted digital calipers to the tail stock of his lathe.  If you could position a pair of calipers on the body of the cutting head so they didn't get in the way of the mast height adjustment, they would be cheaper than the linear scale.

  • 30 Jan 2020 5:59 PM
    Reply # 8702032 on 8697082

    Lathe tail stock movement is horizontal where as the faceting machine head is vertical. So the remote readout helps a lot.

    Another thing I would have liked to fit to my machine is a Digital Angle Encoder like Ultra Tec have on theirs.

    I read on another forum that Tom Herbst had wrote about how to fit one in his volume two faceting book. So I bought that book just for that info and he had dedicated 26 pages to the subject, but it was over my head so I didn’t attempt fitting one. Plus, the top end encoders that I would want to get the 0.01deg increments were about $300US.

  • 30 Jan 2020 6:30 PM
    Reply # 8702052 on 8697082

    Hi Frank,

    Makky Brown (Andrew Brown) on the Aussie Lapidary Forum has a string of posts on that forum relating to fitting a digital encoder to his GemMaster.  You may pick up some pointers there.  I think he uses an Arduino programmable micro controller to count the pulses and convert them to a digital angle readout.

    If you have access to a good mill, you could always make a cranked hard stop calibrated to 0.01 degrees.  It would take the creation of 2 matched 1/4 (quadrant)  worm drive gears to set the hard stop.  The two gears would need to be bolted together and the gear cut, then made so the offest between them can be adjusted so they operate as a backlash eliminator. 

    If cut with a 6mm thread, each turn of the handle will rotate the gear 1mm of radius.  Set the radius right and one turn = 1 degree change in angle of stop.  Thus 3.6 degrees rotation of the thread 0.01 degree change in stop angle. 

    You may need to bolt two disks together to cut the screw thread, then cut away 3 quadrants leaving say a 95 degree quadrant to drive the adjustment.

    Add an odometer and you have a faceting head that works like a Facetron facetor's head.

    Of course you could go for smaller gears with 1 turn = 3.6 degrees stop change, then 1 degrees rotation of screw = 0.01 degrees adjustment of the hard stop.

    It might be easier to Implement than learning to programme.  



  • 30 Jan 2020 10:12 PM
    Reply # 8702177 on 8697082
    Anonymous member (Administrator)

    I’m using one on my Gemmasta faceting machine. The quill pivot housing is insulated internally but with a bit of fiddling it can be adapted to any machine. Pretty basic, just looks hard but is easy to construct. It's basically an analogue voltmeter panel meter (not an ammeter though) with a 9Vdc plug pack power supply and a variable resister all in series, to act as an Ohmmeter. I had all the bits lying around in my junk box, but they are readily available from any electronics store like Jaycar or Altronics. The variable resister should be a wire wound type. I'm using a very old meter and pot from an old CO2 machine for measuring exhaust emissions in the days of carburettors.  1.8Kohms but anything close to that value should work.

    Once you've manufactured all the hardware into a housing, to set the FSD (Full Scale Deflection) just connect the two leads together power it up and turn the potentiometer till the needle reaches the last mark at full scale on the right hand end of the meter scale. You will have to watch this carefully depending on where the potentiometer is when you first turn it on, you may have to turn it one way or the other. If the meter goes in the opposite direction, just swap the wires on the back of the meter. The numbers on the scale don't mean anything as we're just using it for the needle movement.

    As the photo shows it's connected into the little hole in the quill housing and grounded on the back plate. I found it wasn't reliable if I grounded the ground wire anywhere else as there was too much resistance through all the bearings & joints, so I mounted the ground wire directly on the protractor back plate. When the back end of the quill touches the angle stop, where the angle cheater is, a circuit is created and the needle deflects. I find the needle starts to flicker just as it comes into contact with the stop and if you keep cutting the needle moves to full scale.

    The circuit revolves around the contact resistance at the stop, less resistance will cause the needle to move further. There is more resistance just as it reaches the stop and if you keep cutting the resistance gets less, hence more needle movement.

    I stop cutting just as the needle flickers then look with my loupe. I've cut my cutting time in half because I’m not looking as much and I'm finding the target meet is more accurate. I wouldn't rely on it for final polishing or getting accurate meets but it's great for the first rough cut.

    I gave up on dial gauges, any slight ripple in the lap and the needle went berserk and ultimately wore the internal bearings out, Dial gauges aren’t designed for that type of use.

    I've attached a couple of photos & a wiring diagram

    Good luck in adapting yours


    3 files
  • 31 Jan 2020 8:55 PM
    Reply # 8703920 on 8697082

    Thanks for that info Gordon, I do recall getting an offer from Makky Brown on the Aussie Lapidary Forum to help me fit an encoder.

    I also spent a lot of time looking through his thread on concave faceting attachments. Thinking about making one of them, not realising they are more complex than making the basic machine itself.

    I’ve never bought a machine but always made my own. The latest change to this one being to make a new quill block with the index lever on the bottom and ditch the protractor. So I could use a magnetic protractor on the top of the block. Not a cheap one from Mitre10 but a good one with a claimed accuracy of 0.05deg. Using the dial gauge as a stop after setting the angle on the finer cutting laps like 600 and 1200. Though did spend a lot of time finding out how those laps had to sit on the master lap and shimming them, to prevent needle flutter.

    Lots of great info here on fitting an electric depth of cut metre, may have a go at fitting one sometime.


    1 file
  • 31 Jan 2020 8:58 PM
    Reply # 8703922 on 8697082

    What's the file size for pictures? Used to be able to post good size pictures.

  • 31 Jan 2020 9:44 PM
    Reply # 8703970 on 8697082

    It seems to be something to do with the site not converting jpeg picture to png. As I have in the past posted 200kb jpeg pictures and they have converted to 20kb png and show up as full size pictures.

    For example Pauls picture in (Pushing the boundaries in competitions) is a 18.7kb png file that fills the screen when you look at it.  My recent picture is a 24kb jpeg that is minute when opened.

  • 01 Feb 2020 7:26 AM
    Reply # 8705189 on 8697082

    Hi Frank,

    I have some design notes on concave cutters in Facet Talk 228 starting at page 23.

    I've found the Acme thread used for CNC cutters is too course as it moves 8mm per turn.  I've since bought a length of 6mm threaded stainless steel rod from Bunnings and am going to make an anti-backlash block to replace the existing Acme thread.  This will give 1mm adjustment per turn making it easier to adjust the horizontal positioning of the mechanism.  

    I also have the type of guage you fitted to the mast of your machine on order.  This will make it easier to position the cutter accurately.  I found that you need to be able to adjust  the position of the cutter in 0.01mm increments to accurately position concave facets, and the  Acme thread and dial indicator I have are too fiddly.

    Vibration at the cutter head is still an issue, but using the dial indicator I can fiddle with the rotation of the collet to minimise vibration.  If I had  lathe I would be making my own collet and collet holder.  I an going to try the ER11 extension holder again using brass bearings with graphite dots instead of pillow block bearings to see if I can improve the cutter.  I think my last attempt failed because of play in the bearings, and they were noisy.  As a result I think pre-loaded tapered bearings or oiled brass bearings may be the way to go.

    I see that Polymetric use a collet with straight sides instead of the tapered collets used in the ER series form China.  Clarry Trevena also uses a straight sided collet that is used for high speed ait tools.  But I don't have the equipment to fit the collet housing to a shaft with sufficient accuracy to keep the cutter from wobbling.  



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