How do you use a Blake Coaxial Indicator

I have a Blake Coaxial Indicator and needed to overbore a hole today. The hole is .998" ID and needs to be bored to 1.325". Anyway, I bought this and have never used it. I put the straight feeler into the holder like the instructions said and then from there could not figure out how to keep the feeler against the wall of the bore.

The instructions say to eye ball the center of the bore and then work from there. How do you keep the feeler engaged with the bore wall if when the feeler is in the middle of the bore the feeler does not touch the bore?

I called Blake and they said I was using the right feeler and that it should go up to 4.25". The nice guy at Blake told me to put my thumb onto the feeler and push it. He then said that the feeler should be on top of the work and open to a bigger diameter than the hole. He advised to then bring up the quill and just let the feeler slip into the hole.

This is what I did and of course the feeler popped right back into the center of the bore like I expected it to and was nowhere close to touching the walls of the bore.

Can someone please tell me how to use this tool before I go crazy???

Thanks, Steve

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Reply to
Robert Swinney

Steve, did you remove the split plastic ring from the indicator body first? That plastic ring is placed on the indicator to protect it from excessive movement and damage in shipping. If you don't remove it, you will have very little indicator travel to work with.

- Michael

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If you hold the indicator in one hand and hold the rotating V against the body you should be able to move the indiator arm from a position in line with the body to about 80 degrees. If your holding the V pressed firmly the needle will not move while rotating the arm and the arm should stay at any position you leave it within the 80 degrees. The drag on the arm should be firm but not excessive and can be adjusted by the pivot screw. Now releasing the V and applying pressure on the arm towards the center you should see the needle moving.

Bernard R wrote:

Reply to
Bernard R

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You start with the *center* of the indicator approximately over the center of the bore.

You are supposed to push it far enough so the socket changes its angle (it is mounted with a friction mount to the center of the indicator). You apparently just pushed it to outside the diameter of the bore, without changing the socket's angle. If it won't move, you may need to loosen the screw on which it pivots just a little.

Push it far enough so when you relax the push, the feeler is a bit outside the hole -- then hold it far enough in so you can lower it into the bore, and start measuring.

I hope that this above helps.

Also -- if you run it under power, it *must* be at the slowest speed your mill can achieve. Too fast, and it is likely to bounce around in the bore (with no reasonable reading), or ever worse, pop out and risk bashing your hand (as well as damaging the feeler, and perhaps the workpiece).

Good Luck, DoN.

Reply to
DoN. Nichols

According to the Blake manual, the spindle speed should not exceed 700 to

800 rpm. I find that 600 rpm works pretty well for me.


Reply to
Mike Henry

could not figure out how

============================== Key to this for me understood how a coaxial indicator works.

Principal is that the feeler is always in contact with the diameter of the part, either external or internal. The feeler then causes the "T" at the bottom of the indicator housing to pivot pushing the housing up on the central shaft. The amount that the housing raises is what the indicator actually reads.

There is a joint in the connection where the feeler attaches to the t-bar that allows the feeler to pivot with when moving across the t-bar but pushing the t-bar when it is in-line. This is most important when attempting to "zero" a punch mark.

When picking up the center of a bore or boss you generally won't get the indicator to read zero. With your mill running at a slow speed you will see the hand on the indicator move as the feeler sweeps around the bore. The idea is to get it to stop moving at some reasonable value, for example .050. This does not mean that you are .050 out; just that .050 is your "zero" for that particular setting of the feeler. The TIR in this case is the difference between the max and min reading. Crank the x and y slides to minimize the movement. You will need to minimize the movement for first one and then the other axis several times. Because the ball of the feeler slides on the surface of the bore or boss, a smooth surface is important.

Your question points up an important industry/marketing problem. In almost all cases precession tools are sold with no or minimal instructions. While this *MAY* be correct for bulk sales or sales to experienced machinists, it is a huge problem for those with less experience. FWIW -- I teach machining at a local community college and many of my students are currently employed in the machining trades as machinists but lack knowledge of certain aspects/tricks of the trade such as how to quickly set a lathe tool on center using a pocket scale, how to use a "wiggler", and how to use an edge finder.

The marketers of these products appear to be making a fundamental error in assuming the purchasers of their products know how to (correctly) use them, and they would be well advised to have extensive instructional materials available. This could be printed materials, or even better a DVD/VHS video. In this age of computers, they can distribute at zero cost through their websites by providing files in pdf, avi, etc. formats for downloading.


Reply to
F. George McDuffee

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