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DIY magnetic DRO

Building my own

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Ian P07/05/2019 20:45:02
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I would wait before your 'next step' so that you can test everything works before potting.

Are you connecting the cable screen at both ends? There is a case for connecting it only at the 'input' end of the wiring (the TouchDRO PCB connector) but you only seem to have 4 pins.

Ian

ChrisB07/05/2019 22:09:30
649 forum posts
207 photos

Not sure if I did this right, I connected the shield to the read head casing, the casing will slide and contact the lathe and mill body (which are grounded) so I'm thinking I should have a ground, did I get it right?

In reality I don't know if cable shielding will be necessary as there will be no other electrical wires routed along the read head cable, so I would think noise should not be an issue - but I might be mistaken.

Good advice re. waiting before sealing everything...hope the touchDro wont take long to arrive!

Ian P07/05/2019 22:51:48
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2535 forum posts
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Connecting the screen at both ends introduces the 'possibility' of the screen carrying current. Only connecting one end means that the screen is purely a screen. In sensitive audio or electronic measuring instrumentation it is usually only connected at the amplifier end.

Current flowing through a screen could be induced to the contained (signal) wires by capacitive coupling, in a perfect world no current would flow through a screen connected at both ends because the equipment at both ends should be at the same potential. In practice your lathe motor and lathe metalwork might be plugged into one 13A socket and the PSU for the DRO electronics might be in another socket so there might be a 'loop' of ground/earth wiring that acts as one turn of a transformer that could couple surges and spikes into the signal wires.

To be fair logic level signals in this DRO application are pretty immune to interference and there are a lot of 'could's' and 'possibly's' in my previous paragraphs, in practice grounding the sensor end will be OK. Not sealing everything up yet allows you to test and if necessary make changes.

Ian P

Beaker12/07/2019 19:32:23
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I just wanted to bump this thread back up. Chris B: This is really interesting stuff, please keep us updated. I'll definitely be doing this if you're successful. Thanks for blazing the trail!

ChrisB13/07/2019 09:56:59
649 forum posts
207 photos
Posted by Beaker on 12/07/2019 19:32:23:

I just wanted to bump this thread back up. Chris B: This is really interesting stuff, please keep us updated. I'll definitely be doing this if you're successful. Thanks for blazing the trail!

Hi Beaker, thanks. I did progress a bit further with these DROs.

I received the TouchDRO adapters from Yuriy some time ago. I downloaded the TouchDRO app on a tablet and connected via bluetooth to the adapters - it's very neat and clear and has lots of functions.

Next I hooked up the read heads to the adaptors to check if they actually work - moment of truth!

I did a temporary set up as I have not attached the read heads and magnetic tape to the lathe and mill yet, so I just slid the read head over the tape by hand on a table, surprise surprise it worked!!

I had a small hiccup as I found that one of the adapters had a defective input channel so I contacted Yuriy and did troubleshooting together. He confirmed that part of the board was defective so he sent me another one - thumbs up for his aftersales.

Next step is installing the tape and read heads on the lathe and mill and calibrate the scales, but I'm holding off for now. It's unbearingly hot in the workshop and I can't concentrate in this heat - I desperately need an airconditioner!

ChrisB14/07/2019 16:40:55
649 forum posts
207 photos

Being too hot to work in the shop I retreated to my study (thank God for the ac!) trying to figure out how to connect the read heads to the TouchDRO adapter.

I have a question regarding this connector (9 pin type). The circuit board came with these female ports - they look like a LCD/monitor type connector (don't know the name). Now I need to connect the read head cable to these ports. All cables with this type of connection I've seen (like data cables) are molded to the plug.

Does anyone know what connector I would need, or is it a case of buying some 9 pin data cables, cut the plugs off and solder them to the read head cable?

Chris

20190714_172246.jpg

Mike Poole14/07/2019 16:48:37
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3095 forum posts
72 photos

Search fo D sub or D subminiature, widely available from electronic suppliers.

Mike

ChrisB14/07/2019 18:27:43
649 forum posts
207 photos

Hi Mike, thanks for pointing me to the right direction. Something like these links should work I guess.

**LINK**

**LINK**

Mike Poole14/07/2019 18:32:53
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Yes Chris that is what you need.

Mike

ChrisB17/07/2019 10:12:11
649 forum posts
207 photos

Hi Mike thanks. I got the connectors yesterday (backshells out of stock arrgh!) and soldered all the connections - tedious job as the wires are so thin! Anyway, I hooked up the readheads and checked them one by one, and after sorting out a couple of crosswired connections, got them all working. Next step mount the heads and tape on the machines and figure out how the DRO app works!

20190717_105815.jpg

Clive Foster17/07/2019 10:53:44
2882 forum posts
104 photos

Nice work Chris.

Soldering and sleeving is indeed tedious.

For future reference crimp type push in connectors are much easier and, if you make a mistake, sorting out is a simple matter of pushing the connector out and popping it back in the right hole. Shells cost little more and crimp tools are, probably, a bit too expensive. Pro ones like mine are far too much! But frustration saved is well worth it if you are doing a few.

I got my tool set years ago from RS components when I had to do about 8 of the big ones. Not cheap but well worth it. I imagine E-Bay et al can offer much better deals now. I imagine crimp contacts could be gently squeezed and soldered rather than properly crimped or you can get solder bucket types. The insertion and extraction tools are cheap, about £5 for the combined tool from RS. Its the crimper that costs.

Clive

ChrisB17/07/2019 12:04:10
649 forum posts
207 photos

Thanks Clive. I would much prefer the crimp option rather than solder. One of the adapters I received was with crimp type pins, so much easier to remove and install pins. But for a one off project like this investing in tooling I would have no further use for would not be worthwhile. But for sure if I were making a lot of these that would be the way to go.

I now need to build an enclosure for the adapters as exposed electronics and swarf are not the best of friends. Not sure how to go about it, two options pop into my mind: fabricate a box from sheet metal, or mill a case from a block of plastic...the latter is more within my capability as I do not have a sheet metal bender.

ChrisB25/07/2019 19:17:13
649 forum posts
207 photos

I'm in the process of installing the DROs to the mill and lathe now. The plan is to stick the magnetic tape (supplied with double sided tape) directly to the machines and then fabricate the brackerty for the read heads. Started with the brackets for the mill first and that's almost sorted - I just need to install and align everything to the table and column.

The lathe on the other hand is a problem - my plan for the Z axis is to install the tape directly to the bed shown in red in the picture below. The read head I'll install under the carriage - should be protected from unwanted hits etc and excessive swarf and oil.

lathe z dro.jpg

The X axis however id proving to be a bit of a headache. Preferably I would like to install the magnetic tape directly to the cross slide aft face (tailstock side) but the gib screws are getting in the way. Most X axis installations I've seen seem to extend quite a bit back onto the tailstock area and I would like to avoid that if at all possible.

Would it be a good alternative to install the tape and head on the forward (chuck) side?

Ps the lathe is a WM280, I would like to know how owners of this type or similar lathes got around the installation of the X axis readout

Edited By ChrisB on 25/07/2019 19:19:46

JasonB25/07/2019 20:26:05
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on my 280 have thought about putting the strip on the underside of the cross slide offset slightly above the lead screw, there looks to be just about enough room to also get the read head (small emsi) in beside the screw or maybe a small extension out the back so the strip can be longer and you get more room for the head.

Is the double sided tape solvent proof? I would worry about paraffin or WD40 dripping onto the Z strip

ChrisB25/07/2019 21:29:36
649 forum posts
207 photos
Posted by JasonB on 25/07/2019 20:26:05:

on my 280 have thought about putting the strip on the underside of the cross slide offset slightly above the lead screw, there looks to be just about enough room to also get the read head (small emsi) in beside the screw or maybe a small extension out the back so the strip can be longer and you get more room for the head.

Excellent idea Jason thanks! Would have never thought of that.

I think that might just work, will have a look tomorrow morning and see if things fit in. The read head is very small it's 25mm long by 18mm high (might be smaller than the emsi ones) so it might squeeze in.

As for the Z axis, the adhesive tape looks like its quite resistant to chemicals...according to the RLS website FAQs regarding the tape. **LINK**

dro tape.jpg

old mart25/07/2019 22:04:04
3398 forum posts
210 photos

Isn't the tape for the lathe in a rather vulnerable position? Could it go at the rear of the bed underneath the overhanging part? Just below the saddle clamps.

Edited By old mart on 25/07/2019 22:05:22

Mike Poole25/07/2019 22:27:47
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3095 forum posts
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Posted by Clive Foster on 17/07/2019 10:53:44:

Nice work Chris.

Soldering and sleeving is indeed tedious.

For future reference crimp type push in connectors are much easier and, if you make a mistake, sorting out is a simple matter of pushing the connector out and popping it back in the right hole. Shells cost little more and crimp tools are, probably, a bit too expensive. Pro ones like mine are far too much! But frustration saved is well worth it if you are doing a few.

I got my tool set years ago from RS components when I had to do about 8 of the big ones. Not cheap but well worth it. I imagine E-Bay et al can offer much better deals now. I imagine crimp contacts could be gently squeezed and soldered rather than properly crimped or you can get solder bucket types. The insertion and extraction tools are cheap, about £5 for the combined tool from RS. Its the crimper that costs.

Clive

You are dead right about crimping Clive but a bit of preparation can make the solder bucket version much less painful, many years ago I made a heavy block with tapped holes for various d-sub plugs, I then tin all the holes and ends of the wires after a light twist to stop any stray strands. A quick touch with a fine point iron and a nice bright secure joint with no bridging to adjacent pins should be achieved. Getting the cable cores the right length will help, too short makes life difficult and too long will leave a lot of cable to try and stuff in the shell. I don’t usually sleeve but I try to minimise any bare cable and not use cable that is too big. It’s always worked for me.

Mike

ChrisB26/07/2019 11:09:24
649 forum posts
207 photos
Posted by JasonB on 25/07/2019 20:26:05:

on my 280 have thought about putting the strip on the underside of the cross slide offset slightly above the lead screw, there looks to be just about enough room to also get the read head (small emsi) in beside the screw or maybe a small extension out the back so the strip can be longer and you get more room for the head.

Took the cross slide off this morning to see if the read head would fit next to the lead screw. Unfortunately there's not enough space, my read head is 7mm wide and the space between the lead screw and slot in carriage is about 5.5 - 6.0mm.

There seems to be just enough space above the lead screw however, so if I mounted the read head directly to the under side of cross slide directly above the lead screw, and then installed the magnetic tape to the side of the slot in the carriage, it might just work. Will take a some pictures as it's difficult to explain with words sometimes!

Posted by old mart on 25/07/2019 22:04:04:

Isn't the tape for the lathe in a rather vulnerable position? Could it go at the rear of the bed underneath the overhanging part? Just below the saddle clamps.

Edited By old mart on 25/07/2019 22:05:22

The casting below the saddle clamp is not ideal to directly tape the magnetic strip - it's a bit uneven and the read head would not ride constantly above it. Where I plan to place it, the read head will be out of harm's way under the carriage. True the tape is exposed but I can't see it getting damaged in that area. The tailstock will mostly live there and there will be enough clearance - so I think it should be fine.

ChrisB26/07/2019 13:34:38
649 forum posts
207 photos

Photos as promised:

 

As can be seen in this photo of the carriage, there is not enough space for my read head to fit in next to the leadscrew, (7mm wide head)

20190726_132902.jpg

 

However I can install the magnetic tape to the side of the slot in the carriage where the cross slide lead screw lives. ( note: the tape is the other way round holding on as it's a magnet - still not 100% committed so did not install it permanently yet)

20190726_132649.jpg

 

The read head just fits in the space above the lead screw between the carriage and cross slide. I can install the read head in the position shown in the photo below. The head will need to be secured to the bottom of the cross slide and the head cable fixed securely out of the way of the lead screw.

20190726_132501.jpg

 

I think this might just be possible, but I would like to know what's your opinion, especially Jason's (since he came out with the original idea!)

20190726_132532.jpg

Edited By ChrisB on 26/07/2019 13:34:59

JasonB26/07/2019 14:14:34
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I think where you show the head in the last photo will clash with the nut when the cross slide is wound fully towards the operator.

Why not put it right at the back, the screw does not extend the full length so you don't have that in the way or risk catching the wire

What are the 3 dimensions of your head and I'll take a better look at mine later. This is a photo I took a while ago of where it would fit with the mag strip extended out the back by 50mm or so with the extension also serving to protect head and scale from swarf.

20190104_140738[1].jpg

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