Cheap Idea for a DRO

[irving2008]

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?

[1113562]

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?

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.

[irving2008]

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.

Good point about the reverse of the PCB. It definitely is some form of ground plane.... might go look in Aldi/Lidl whatever for some cheap ones...

[BillTodd]

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

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?