Thread: Cheap Idea for a DRO
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11-05-2010 #1
Hi Bill,
Thanks for this. I obviously did not look too hard at your diagrams did I?
The web site has been up and down over the past few days and I kind of gave up last night. I'll try to get a bit more time on it looking at your stuff.
I like the idea of using a PC or laptop for the readout's and controls. I've never really got into VB programming but I'm quite happy with PIC assembler (not C though...that scares me). I was told that VB interface to RS232 Com Port is not that well documented and is a bit tricky? Have you thought of a USB version seeing that RS232 com ports seem to be disspearing off the modern PC's (especially laptops)?
Did you have any thoughts on producing longer bar's/PCB for the read head to slide on? All the cheap Chinese calipers seem to come with a short 150 mm bar.
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10-05-2010 #2
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*** NEWB ALERT*** 1st post***
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I'm in the process of putting a DRO on my X3. Given that a Yorkshireman has been defined as a Scot deprived of his generosity it prob'ly comes as no surprise that the reading heads for the scales will be these, at £2.99 a pop:
http://www.virtualvillage.co.uk/150m...01481-065.html
I've gutted 3 of these to get just the reading heads (ie no case, no readout, no battery) and replaced the batteries with pairs of capacitors to reduce jitter. They talk nicely to the capacitive scale strips I'm using (ex Wixey tablesaw DRO) so it looks all good to go. Readout is a Shumatech DRO550.
Please understand that all this is written with the unshakeable confidence of the totally ignorant. I know nothing about machining but I'm having enormous fun learning.
Regards, John
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10-05-2010 #3
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10-05-2010 #4
There are the same ones I bought ($US8) and seem to work OK with the scales I bought from Shars
They're spares for when I gut the original heads on the scales prior to mounting on my X2 mill.
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11-05-2010 #5
i reckon the combs should be easy to mill out on a CNC PCB mill. They are 0.6mm thick PCB double sided but the reverse is plain. On the top side is the T-comb structure and a ground strip. Since the mechnaism is a capacitive vernier it would seem perectly reasonable to manufacture this in say 150 or 200mm approx lengths where the end is exacly halfway through a 'T' and then end butt them together ensuring electrical conductivity across the join with a solder infil. getting positional accuracy on the second or subsequent 'comb' is the critical factor (as well as the basic accuracy of the comb). Some sort of jig might do the job.
Alternately, buy 3 cheap ones and look to join the PCB together as per above. Milling a new channel from stainless might be tricky, but aluminium might do just as well.
It worth an experiment don't you think?
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11-05-2010 #6
Yes I fully agree an experiment is worthwhile.
For proof of principle it seems least effort to try butting two PCB's from two existing gauges together to see if this gives good results across the transition. The infill with solder may be tricky and may cause delamination and a nasty lump. Would it not be better to join down the gaps between T and comb in an L shape machining in the end of each strip.
Re the channel, is it essential to have a channel at all? Providing the reader is in close proximity with the PCB I can't see why it can't work. 0.8 mm (1/32") Shims on the reader half can be used to raise it off the bar.
Another question I have is "is it essential to use double sided pcb"? If the reverse is just plain copper the same capacitance would be achieved by bonding a single sided PCB to a SS bar or Aluminium or a brass bar if you prefer. I'm not sure if the design relies on the reverse plane of the PCB floating electrically from the bar in which case this may explain the need for a double sided PCB.
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11-05-2010 #7
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27-02-2011 #8
Irving,
If you're still interested, the sensor PCB is available as a spare part for the Wixey saw bench
two 31" lengths for $35 :)
http://www.wixey.com/fence/spareparts/index.html
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11-05-2010 #9
I have just buzzed my PCB and the comb fingers are all linked together by the thin strip of copper that runs along the bottom so this would need to be joined across the strips
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11-05-2010 #10I like the idea of using a PC or laptop for the readout's and controls. I've never really got into VB programming but I'm quite happy with PIC assembler (not C though...that scares me).
I was told that VB interface to RS232 Com Port is not that well documented and is a bit tricky?
Have you thought of a USB version seeing that RS232 com ports seem to be disspearing off the modern PC's (especially laptops)?
Did you have any thoughts on producing longer bar's/PCB for the read head to slide on? All the cheap Chinese calipers seem to come with a short 150 mm bar.
Since there seems to be some interest here, I've attached the PC app and PIC files to this post. The VB app has a sort of demo mode that'll allow you to add scales and adjust the value by dragging the mouse over a button. The current version is a fixed 640x480 window to suit my panel-pc, but I have a part finished MDI (multiple document - so I could add hole layout and utility functions) version that I would like to finish ... sometime.Last edited by BillTodd; 11-05-2010 at 11:50 AM.
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