Alternatives for a DRO display change

[John HinkleyParticipant @johnhinkley26699]

Today’s update.

Evri added an extra day to the display delivery schedule, but at least it arrived.  Had to wait an extra day or two for the plugs and sockets, though they eventually turned up, too.  Managed to wire up suitable connections and ….. Nothing happened!  Well, not strictly true, the display lit up, performed its self check and just sat there. I have a couple of pre-used glass scales which I plugged into the vacant X- and Y-axis sockets, leaving the Z-axis connected to the magnetic scale on my mill.  Changing the position of the various scale readers merely made the last digit flicker and not record any movement on any of the scales.  Somewhat stumped, I decided to consult the manual and diligently went through all the set up parameters that I considered relevant, with no success. A little dejected, I then made a decision to purchase some 5micron magnetic scale read heads to see if they would clear the problem.  Uncle Ali came up trumps again, less than £70 for three, postage free!   They are due in 8 days.  In the meantime, Machine-DRO got a bit of my pension for two metres of magnetic tape, just in case I need to replace the fitted scale tape with known “good” stuff.   You’ll  have to wait to hear how this next part of the adventure goes. I promise, if it works, or not, you’ll be the second to know. Everything will be TTL protocol so I don’t envisage any problems.

(And, I’ll say what you’re all thinking – “this idiot has got more money that sense!”.)

Quite right, but if it works as expected, I’ll have a 3-axis DRO with all the bells and whistles for less than £125, which is what I set out to achieve. I don’t intend stuffing my coffin with money and the children are well catered for – so why not?

Counting down the days ……….

John

 

[NealebParticipant @nealeb]

If the last digit flickers between two values – my own scales and DRO read to 5micron so the last digit switches between 0 and 5 – then there is a good chance that only one of the A and B channels is connected. The DRO relies on two pulse streams 90deg out of phase to detect both motion and direction of motion; if one pulse stream is missing then it quite literally does not know if it is coming or going!

My own system started doing this when one channel in the read head failed. It might be that there is a pin mismatch between your scale and the DRO such that only one channel is connected correctly?

[John HinkleyParticipant @johnhinkley26699]

Nealeb,

I have absolutely no reason to doubt your logic and I thank you for trying to help, but the digits weren’t just flicking between two values – they were just flickering.  Not only was it the display which was connected to the magnetic scale already fitted to the mill but also the displays for both glass scales connected to the X-axis and Y-axis ports.  I tried all the different resolution settings for the Z-axis, to no avail.  At least I know that the scale readers that I have ordered are 5 micron units, so that will remove one variable from the equation.

John

 

[NealebParticipant @nealeb]

OK – understood. Always difficult to second-guess someone else’s problems. Good luck and hope it all works when the new scales arrive.

[John HinkleyParticipant @johnhinkley26699]

Thanks. I hope so, too. Maybe it’ll help someone else on a similar mission in the future.

I’ll post the follow up in due course.

John

 

[John HinkleyParticipant @johnhinkley26699]

How time flies when you’re waiting for a package from China.  Well, two packages, actually. And sequentially at that!

First, though, a brief recap as it’s been so long since I posted on this thread.  I last said that I was waiting for the delivery of the display.  That duly arrived and there’s little to say about it other than it looks just like a multitude of other displays available from similar sources.  While waiting for its arrival, I ordered three 9-pin D plugs from eBay and stripped out an old Ethernet cable for some short lengths of wire.  I wired these plugs as per the pinout diagram in the display manual and hard wired it to the innards of the existing four pin aviation-style plugs on the mill readers.  Switched the display on and ran the reader up and down the Z-axis magnetic strip, hoping to see the display move.  It didn’t! Instant deflation.  Some experimentation with the settings of the display and still no improvement.  So I then decided that the mismatch must be the read head to magnetic tape interface.  Mindful of the poor reputation of Far East goods, I ordered a length of 5µm tape from M-DRO.  Took nearly a week to reach me and when I opened the package, it was 200mm long and not the 2 length I was expecting!  My fault, entirely, but an expensive mistake on my part.  However, I had a length of known, good quality tape to play with.  Eagerly shot out to the workshop and set up a test run.  What a disappointment.  No movement of the display, just random flickering of the digits. Damn! I said, or words to that effect.  Another re-think.  Being into this upgrade to the tune of around £120, I thought that I might as well go the whole hog and get some tape to replace that which is on the mill.  This time I searched Aliexpress and found a source with an “introductory offer to new customers”.  I ordered 4m (yes, four metres!) for the princely sum of £21.89 – hardly more that I’d paid for the 200mm length!  If it turns out to be useless, it serves me right and I’m that much out of pocket.

Long story slightly shorter, it arrived yesterday evening and this morning I had a little play with it.  I have to say, I’m extremely chuffed that it is not only supplied with separate stainless steel strip, but initial teats on a short length show that the display responds correctly and I have high hopes that the combined collection of disparate parts will together give me the display that I set out to achieve. I have made a short video on YouTube, to be published later today, summarising the sequence of events.  I have a current project ongoing which is occupying the mill at the moment, but when that is finished, I willbe getting on with modifying the mill DRO to the new system.

John

 

[Michael GilliganParticipant @michaelgilligan61133]

Keep up the good work, John

Sounds like you are onto a winner !

MichaelG.

[John HinkleyParticipant @johnhinkley26699]

Well Michael, I’m certainly encouraged by the latest developments.

For anyone who is interested, the YouTube video is here.

John

 

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for sharing that, John … it looks very encouraging

I shall be following your adventure with great interest.

MichaelG.

[John HinkleyParticipant @johnhinkley26699]

Failing to raise much enthusiasm for continued work on my present project, I turned my mind to the DRO set up.  I should say that the current system relies, at least on the Z-axis, on magnetic tape stuck directly to the mill column and the read head passes over it of course.  I didn’t like that idea much, specifically for aesthetic reasons, so I considered my options with regard to mounting the tape in a more pleasing manner.  I was hoping to mimic the commercially available scales, but in a lower profile due to the diminutive size of the mill. Casting my Google net far and wide, I happened upon some LED strip light aluminium extrusions which seemed to fit the bill.  They came with mounting clips, end caps and translucent clip-in covers.  I could only obtain them in in multiples of 6six, each 1 metre in length, but at £8.49 including P&P, who was I to complain?

I’ve made up a test piece approximating to the length of that required for the Z-axis:

Fitting the ned caps supplied wasn’t very satisfactory , so I’ve designed my own version and 3D printed them in black ABS-GF as seen in the photo above.  They have a hole on them to secure the extrusion to the mill.  (In the background you can see the test scale.  This was put together before I decided to make my own end caps, so the gap at the end of the magnetic strip is too small and this will be remedied in the final version.  I noted that when I’d stuck the tape and stainless cover in, my alignment was, shall we say, less than satisfactory.  Alibre Atom and 3-D printer to the rescue again and a suitable tool was made to (hopefully) ensure that the tape and steel cover remain central to the extrusion.

Not a very well composed shot, regrettably, but the better one was out of focus!  David Bailey I am not! The idea is that the tool has a Y shaped cross-section, with thin (0.8mm) wide legs which straddle the tape as it is laid down in the channel.  That’s the theory, anyway,  Whether it will work in practice, only time will tell.

That’s as far as I’ve got today, so I’m off to get my ‘flu and Covid booster injections.  I’ll add more progress reports here, as and when.  Unless people beg me to stop!

John

 

[andy198712Participant @andy198712]

I’m really keen to see how you get on!

is that tool for the head or to stick the strip down centrally ?

[John HinkleyParticipant @johnhinkley26699]

Sorry, I thought that I’d replied earlier this afternoon.  I must have forgotten to press the “submit” button . . .

Yes, the Y-shaped tool is to try to ensure that the magnetic tape and subsequently the stainless steel strip sit centrally within the aluminium extrusion.  I haven’t tried it out yet and before I do, I’m going to reprint it in plain PLA instead of ABS-GF, which can be a little rough to the touch.

John

 

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