Coaxial Indicator Problem

My apologies I have been down at the boat for the morning thank you for continuing this thread.
It appears that in my ignorance my assumption that if I was down to one division on the indicator the job was within.ooo5" is totally wrong and that figure is only obtainable when the indicator reads zero movement, So if I cannot get to zero movement I must look for some other reason why .
Brian.
 
Good one Brian. You are absolutely correct. Now, lets see what other possibilities there are.

"Billy G"
 
A Co-Ax Indicator in itself measures nothing. It is for centering the work to the spindle, that's all. It matters not where the reading is as long as the needle is in the same place and not moving for 360 degrees. It's probably one of the easiest ways to center a spindle and work.

"Billy G"
 
Yes, you are correct. The CO-AX is only for centering, BUT, the question now is how well can it center? The dial on my Blake says 0.0005” OFFSET. The manufacture claims this is offset deviation from true position/div. So, at first glance, you are thinking this tool has a very good sensitivity or resolution and can find center within a few tenths. NOT TURE, with a 2” feeler you would be hard pressed to see tenths. And with a longer feeler in place, you would be hard pressed to see deviations of a thousandth on the dial. Or am I MISSING SOMETHING? Somebody please chime in. I can’t believe the Blake manufacture has been advertising this for all these years and nobody corrected them. What am I missing?...Dave
 
I have no clue what you are missing. I see your Blake the same as I see the two I have. I am having no trouble centering with either of them. The Graduation values that Blake give you are spot on. I have centered stock up to 8 inches with no trouble.

"Billy G"
 
Blake Specifications:
Feeler ball diameter: 1/8 inch
  • Measuring range: 1/4 inch axis offset
  • Capacity: 5/32 to 4.25 inches internal; 0 to 4.25" external. Optional feelers extend these capacities to 12 inches. See accessories list below.
  • Speed: spindle rotation up to 800 rpm
  • Locating accuracy: .0002" of true center
  • Initial positioning: within 7/16 inch diameter of true location
  • Graduations: .0005" or 0,01mm
  • The entire gage will just fit into a 2.2" diameter cylindrical space
  • Overall length of gage, without the feeler is roughly 5.2", with the shortest (standard) feeler installed, the overall length is about 6-3/4 inches. When the upper shaft is inserted into a chuck, the overall length is about 5-3/4 inches.
  • The spindle diameter is 3/8" on the inch model, 10 mm on the metric model.
 
Bill Gruby said:
I have no clue what you are missing. I see your Blake the same as I see the two I have. I am having no trouble centering with either of them. The Graduation values that Blake give you are spot on. I have centered stock up to 8 inches with no trouble.

"Billy G"
Click to expand...
Just to clarify please. Did you actually set-up your Blake like Brian did in a lathe? And did you find the graduation values accurate on your Blake? Did you put in a 2” feeler and move it say 0.001” and then get a 0.001” reading on the dial? Or what reading?
 
I have to rely on what you guys are doing. I have a broken ankle and cannot navigate the stairs to the shop. We tested the Blake years ago when GM bought them for the Bearing Plant here in Bristol. We found them to be the most accurate available. Ours were Lab tested. I was not on the test crew so I would guess that anything I had to say now would be meaningless to you. You guys have fun.

"Billy G"
 
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This may ruffle some feathers .... but ..oh well..... the way I see it , the co-ax indicator is correct. it will not measure accurate movement and wasn't intended to. it was intended to find a center point. the divisions vary widely in the distance they represent depending on the length of the stylus. I'm sure there is a stylus length that may work out to .0005" , but I bet it is really short. It is merely an expensive center finder using a dial gage to read center. MY opinion....I could be wrong....
 
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