Author Topic: Micro DRO made from tyre tread depth gauge (Read 75942 times)

John-Som · « **Reply #100 on:** August 31, 2011, 04:16:31 AM »

ksor

No drilling of magnets. Made up a 6mm long tube with 3mm bore. One end slips over the probe the other takes two 3 x 1.5mm rare earth magnets. A dab of two part epoxy adhesive holds everything in place.

Full details of the construction are at http://start-model-engineering.co.uk/2011/08/mk-lll-mini-dro/

John-Som

Stilldrillin · « **Reply #101 on:** August 31, 2011, 04:31:02 AM »

Just ordered 50 off, 3mm magnets..... £4.99.

David D

nearnexus · « **Reply #102 on:** August 31, 2011, 05:07:46 AM »

I used my micro DRO again today to do some precision milling on the lathe and I can only say that it does an absolutely great job, regardless of the price. Very accurate.

This whole concept has really taken on a life of it's own, and it's good to see Madmodder kick it around to get the best possible outcome from the original idea.

Maybe one day we might even see a commercial unit with the same capabilities.

This is good discussion group with a good attitude - and it's a refreshing change.

Rob

dickda1 · « **Reply #103 on:** September 10, 2011, 10:33:58 PM »

Just note that digital thickness gauges have been showing up of late on ebay:

http://www.ebay.com/itm/0-15mm-Digital-Thickness-Gauge-Precision-0-01mm-Meter-/110730443767?pt=LH_DefaultDomain_0&hash=item19c80c7bf7#ht_3252wt_1260

It appears to have a very similar body to the thread depth gauge discussed here - and would be so if bits were milled away.

-Dick

nearnexus · « **Reply #104 on:** September 10, 2011, 11:12:59 PM »

Unfortunately it only has a 1.5 battery, so readouts will probably be slower.

Still, it has potential

John-Som · « **Reply #105 on:** September 19, 2011, 11:18:36 AM »

Life has become simpler. In providing a battery free supply for DRO systems commonly fitted to X2 mills it's worth pointing out that the need to provide both 3v (for the remote read out) and 1.5v (for the read head) power supplies can be avoided if read heads from digital tyre depth indicators can be utilised as these operate on 3v.

So, unless I am very much mistaken, all you would need is an adjustable power supply unit set at 3v feeding both the remote DRO and the read head. This would make my battery free power supply unit obsolete - such is progress.

John-Som

kd0afk · « **Reply #106 on:** October 06, 2012, 10:59:55 PM »

Anyone know what the shiny stuff is on the slider? If one had a longer piece of it it would read longer than 1 inch. Also, is the thing under the tiny cover a data port, if so with what and how do you use it?

ksor · « **Reply #107 on:** October 07, 2012, 02:37:23 AM »

>> kd0afk
Just read the thread ... the answer to ALL your Qs is there !

kd0afk · « **Reply #108 on:** October 07, 2012, 11:31:25 AM »

Quote from: ksor on October 07, 2012, 02:37:23 AM

>> kd0afk
Just read the thread ... the answer to ALL your Qs is there !

99% of this thread is "I got mine today" and "where do you get one?" but I did get the entire thread read and while it answered a lot of but not all my questions. I got the links answering the data port question but the question about the shiny layer needs closure. Is it a sticker, a textured strip of metal? Does it need a uniform texture to read accurately? Could a person have a strip of SS media blasted or etched to make it more accurate?

I can see real potential in this system with the AC power system and remote readout. Add a strip of "C" channel to keep the svarf out and I think it would be a great tool. You might be able to purchase a DRO system for the same money or less than the final cost of the project but it wouldn't have the satisfaction factor of a DIY.

PekkaNF · « **Reply #109 on:** October 07, 2012, 02:47:56 PM »

I believe this application is some kind of copy magnascale:
http://www.mgscale.com/mgs/language/english/product/Magnescale.html

Inductive or capacitive. I have worked with sony magnascales and these looks like stainless steel tape, but really should not be heated, stretched, kinkked, welded nearby or anything that stupid.

There are many same type of copies available, I know this one:
http://www.machine-dro.co.uk/digital-readout-systems/magnetic-tape-linear-encoders.html

The cheap tyrecauges and calibers probably have "sticker tape" next to read head. Probably best used as it is. Might be difficult to duplicate or improve at typical home workshop.

Pekka

kd0afk · « **Reply #110 on:** October 07, 2012, 02:51:06 PM »

my finger isn't made of magnascale, why does it work when I run my finger across the sensors?

BillTodd · « **Reply #111 on:** October 07, 2012, 04:45:14 PM »

Magnascales use a magnetic sine wave signal recorded on to a steel tape or wire. The read heads use a magneto-resistive element (the elements electrical resistance drops in the presence of a magnetic field)

Newall Spherosyn devices use magnetic (not magnetised) precision balls in a tube. Sensing is done by inducing a magnetic field with one coil while sensing the strength of the induced field with two other coils (to give a quadrature sine output)

Those cheap digital caliper devices (including the tyre depth gauges and expensive Mitutoyo etc.) use an array of capacitive sensors, that detect gaps in a conductive layer within the sticky backed tape. They will happily detect the motion of anything conductive (including fingers) if close enough to the sensing array.

kd0afk · « **Reply #112 on:** October 07, 2012, 05:42:20 PM »

I don't doubt you but it just seems a bit sophisticated for a device this cheaply made.

kd0afk · « **Reply #113 on:** October 08, 2012, 01:09:52 PM »

Wixey sells these things as a "saw fence digital readout" and they sell the strips in 31-1/2" strips for $35 and you get two of them. Here is the link:
http://www.wixey.com/fence/spareparts/index.html#wr7003

75Plus · « **Reply #114 on:** October 08, 2012, 02:15:56 PM »

Wixey resolution is .005" which is fine for wood but is a bit coarse for metal. Some of the depth gauges will register .0005".

http://www.wixey.com/fence/index.html Scroll to bottom for specs.

Joe

kd0afk · « **Reply #115 on:** October 08, 2012, 02:27:39 PM »

I think that is just the reader head. If the pcb strip is made the same way as the ones in the digital tire gauge then I think the resolution should be better if used with the cheap Chinese dro heads. I sent an email to the folks at Wixey to get the measurements.

BillTodd · « **Reply #116 on:** October 08, 2012, 02:58:14 PM »

Quote

I don't doubt you but it just seems a bit sophisticated for a device this cheaply made.

They are cheap because they use pretty standard printed circuit manufacturing techniques to form the sensor strips. Expensive (accurate) ones will have additional laser trimming and checking phase, taking extra time and hence money to make).

They all use chip-on-board bonding (i.e. rather than use a separate plastic package for the silicon chip, the chip is glued onto the PCB directly) with an elastomer (conductive rubber sandwich) connection to the LCD.

kd0afk · « **Reply #117 on:** October 08, 2012, 03:07:30 PM »

When I said PCB I am speaking of the slide. The sensors in the read head read the distance between the gaps in the copper pads on the slide pcb. If the dimentions of the strips are the same ie: copper pads are the same width and the gap is the same, you will have the same accuracy as with the caliper head or the tire depth gauges. Pretty sure the level of accuracy is established in the read head itself.

BillTodd · « **Reply #118 on:** October 08, 2012, 04:50:46 PM »

Quote

When I said PCB I am speaking of the slide.

As was I.

Quote

The sensors in the read head read the distance between the gaps in the copper pads on the slide pcb

Yes, they read the change in the capacitance at the edges - The accuracy is wrapped up in the measuring of the change in capacity, straight clean edges of all the parts contribute.

The tyre depth gauges use exactly the same heads as the cheap callipers

They're just re-purposing the heads to find a niche in a flooded market place.

I guess the Wixey devices have the same kind of accuracy (~10um) but have chosen not to display it (it's only wood after all)

[edit] interestingly the early callipers used a 24 bit binary output format that resolved to 1/20480th of an inch (~2um) but the LS bits are too noisy for any kind of use.

kd0afk · « **Reply #119 on:** October 08, 2012, 05:26:16 PM »

Just got a reply from Wixey and the pitch of the pattern and gap is the same. Should have the same accuracy as a digital caliper. Most of what I do is accurate to the hundredth and if I need to get down to the thou I use a mic.

John Rudd · « **Reply #120 on:** October 08, 2012, 05:32:04 PM »

Quote from: kd0afk on October 08, 2012, 05:26:16 PM

Just got a reply from Wixey

Nice to actually get a reply from a vendor.........

kd0afk · « **Reply #121 on:** October 12, 2012, 03:18:18 PM »

I'm putting something together for my south bend lathe. There are other sites out there dedicated to this concept and using the info from those sites I will be able to have a nice and fairly accurate dro with remote access and read out and it will be linked through a computer. I think the rail system that Wixey sells would be nice but covered with a length of aluminum c-channel would be better. Don't want svarf in the works.

BillTodd · « **Reply #122 on:** October 12, 2012, 05:42:22 PM »

Quote

I'm putting something together for my south bend lathe.

I had a set up like this on my old SB9 (even built the PC interface and DRO). It was OK, but the scales do not really have enough resolution for the cross-slide of a lathe.

Although the scales read to 0.0005 which appears OK, this is the least significant digit, so it's actually no better than 1 thou" accurate. This error gets doubled on a cross-slide because you're cutting diameter so you could be ~2thou" out.

Those cheap scales are OK on a drill/mill but you'll probably find them frustrating on a lathe.

Bill

kd0afk · « **Reply #123 on:** October 17, 2012, 12:34:56 AM »

I have looked at some of the schematics and plans for a computer interface for these gauges and part of it is increasing the frequency or something like that so that it reads quicker. Couldn't a person also increase the precision electronically?

kd0afk · « **Reply #124 on:** October 19, 2012, 01:41:46 PM »

I just got a second one in the mail. It's one of the black ones but it is nice. It holds it's reading after a power down so it has memory. I plan on getting a few more of this model on payday. Here is the link. http://www.ebay.com/itm/290703672736?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
I hope they are selling these out of a larger lot and that all of the ones they are selling are the same.

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Author Topic: Micro DRO made from tyre tread depth gauge (Read 75942 times)