Gallery, Projects and General > The Design Shop
Coax indicator design
Bezalel:
a little late to jump into this thread maybe, but I've only just seen it. and must say I realy like it :clap:
--- Quote ---Bill,
I know this depends on the length of the bar, but in the configuration shown what sort of displacement of the meter do you get for say 1 thou of error?
(Nice job btw!)
ATM 10thou" of displacement caused and indicated 3 thou on the DTI (which would be doubled as run-out). I suppose a quick improvement would be to swap the cheap DTI for a tenths indicator.
--- End quote ---
I'm thinking when I build my own I will be looking at reducing or eliminating the resolution reduction of 3:1
by this I mean it seams to take 3 thou movement on the job to register 1 thou on the dial.
The length of the pickup has significant bearing on this
If the probe length is adjustable to approx half diameter of the job and rotated to be horizontal, such that it is pushed end on, the acuracy of the dial increases accordingly.
for unity resolution of the dial or better. can anyone think of any reason this couldn't be done here?
BillTodd:
--- Quote ---If the probe length is adjustable to approx half diameter of the job and rotated to be horizontal, such that it is pushed end on, the acuracy of the dial increases accordingly.
--- End quote ---
Yes, sort of. To work out the exact ratios you'll need to work out the effective lengths of the levers rather than the actual the lengths of the levers, but in principle the shorter the measuring arm the more the dial will move for a given displacement.
Another way to increase sensitivity, would be to change the angle of the taper on which the ball runs; If this were greater than 45° it would push the DTI slide further (you will need to stick with my original stepped design to ensure the ball is supported on the other side of the taper). It may even be possible to use a curved taper to compensate for the change in lever angle.
Alternatively, it would not be impossible to make a compound lever mechanism to increase sensitivity , as Richard Shute suggested earlier.
bp:
I've been a'wondering about this for a while.
"Wondering 1".... was to use a DTI rather than a Dial Gauge and run the probe on the lower face of a groove in the main shaft. The ultimate version of this used a washer from a thrust bearing, as they are ground flat etc etc
"Wondering 2".... was to use a cranked lever to activate the Dial Gauge, as has been previously mentioned. Fiddle about with the ratios to get a more favourable stylus movement/indicator movement ratio
"Wondering 3".... Bill, in your last version, the one with a ball riding in the groove, the side loads on the indicator must be considerable, or is the indicator probe well located so that it can only move in and out, if you see what I mean?
cheers
Bill Pudney
BillTodd:
--- Quote from: bp on May 03, 2011, 05:22:08 PM ---I've been a'wondering about this for a while.
"Wondering 1".... was to use a DTI rather than a Dial Gauge and run the probe on the lower face of a groove in the main shaft. The ultimate version of this used a washer from a thrust bearing, as they are ground flat etc etc
--- End quote ---
Yes, that should work well
--- Quote ---"Wondering 2".... was to use a cranked lever to activate the Dial Gauge, as has been previously mentioned. Fiddle about with the ratios to get a more favourable stylus movement/indicator movement ratio
--- End quote ---
A lever is certainly possible (the DTI above has this same lever built into the device)
--- Quote ---"Wondering 3".... Bill, in your last version, the one with a ball riding in the groove, the side loads on the indicator must be considerable, or is the indicator probe well located so that it can only move in and out, if you see what I mean?
cheers
Bill Pudney
--- End quote ---
The only side load on the indicator, that I can see, is from the friction with the ball as it spins (if it spins?) which is lubricated with a hardened point contact. I don't think it's a cause for great concern .
Bill
BillTodd:
I have decided to put my prototype indicator up for auction on ebay to raise money for the Royal British Legion's 90th anniversary appeal.
http://www.britishlegion.org.uk/support-us/how-to-give
It should be listed by Thursday (I'm just waiting for the Ronseal to dry on the wooden box - posh or what :headbang: ) all the profits will go to the charity (I'll pick-up the auction and paypal fees, the winner will pay the postage).
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