Had a thought: is there a small version of a co-ax indicator for small mills?

I use a top face Interapid and I like it far better than my Blake Coaxial. I've considered selling my Blake but it's not pretty and wouldn't bring much.
 
RaisedByWolves said:
You can, but it changes the accuracy somewhat.

How much I don't know, but I made a 6" probe that is "Perfect" in concentricity, shape and rigidity, but the result was less than spectacular.

I have it, Im proud of it, its "pretty" (Grey case coloring), but a sundial is nearly as accurate for Tool&Die work as the Blake is with this thing installed.

Ill post a pic tomorrow if I think of it.
Click to expand...

The Blake is a comparator. Sure, the probes are sized, but think about it- there are very very few points (mathematical limits, like sin pi/2 = 0) where the gauge works as a 1:1 gauge. It is sensitive and accurate, so it is a comparator, not a measuring tool. You're centering, there's no dimension to measure. Just relative deflection.
 
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You really don't need a special attachment to use a DTI for locating a hole. The stem on the DTI, typically 3/16 in, can be chucked up in the spindle directly and then you just turn the spindle by hand.

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pontiac428 said:
The Blake is a comparator. Sure, the probes are sized, but think about it- there are very very few points (mathematical limits, like sin 0 = 1) where the gauge works as a 1:1 gauge. It is sensitive and accurate, so it is a comparator, not a measuring tool. You're centering, there's no dimension to measure. Just relative deflection.
Click to expand...
Right, it’s just that it takes .0003 and turns it into .0016 with something this long.

Here’s the culprit. Been sleeping in the bottom of the box for decades so the got a bit rusty looking.

IMG_3174.jpeg


And down in the basement where it lives.

On top is the rod that goes in the holder on the B-port, then the fiber rod that comes with the kit, then the long probe.

IMG_3176.jpeg


Pic are sideways but you get the idea.


The real problem I had with the exponential on these was due to the cylinder I was trying to pick the center of was out of round.

For a truly round or roundish cylinder it’s not as big a deal, but an egg shaped cylinder made my head spin.
 
All of the Coaxial Indicators are knock-offs of the original Blake design

Blake Coaxial.png


Here are a few alternatives that work with "vertically challenged" mills, including a link to one of Stefan's videos where he shows how you can mount a DTI so the face is always visible.

A vertical DTI (dial on the back) mounted in a jig-border style holder also works well:

Vertical DTI.jpeg
 
I have typically used my edge finder to locate the center of a round feature and it is accurate to +/-.0001" However, it is also more time consuming as I have to locate four edges on the four quadrants.

I purchased a miniature magnetic test indicator holder some time ago and it has been my go-to method of checking runout, tramming a face, etc. The magnetic base will mount to the spindle but it isn't very stable. This morning, I made an adapter for the holder that will fit in the 3/4" collets that I use for my TTS tooling system which will mount the indicator directly in the spindle. It requires only about 3" of quill clearance and can indicate holes from .1" to 16" in diameter or bosses essentially to zero diameter.

To make the adapter, I drilled and tapped a hole for the M5 thread in a short length of 3/4" rod. That was it. The indicator holders can be found at a very reasonable cost. In fact, I ordered one on Amazon for less than $10 this morning. Aside from the adapter, the only thing missing is the test indicator itself. Most of us have one or more in the shop and it can easily be moved for this when needed or a dedicated test indicator can be purchase for reasonable cost.
Test Indicator 3.JPG

Here, it is mounted in the Tormach spindle. Centering agrees with edge finder centering to .0001"
Test Indicator 2.JPG
The link to the holder on Amazon.
 
The issue I see with that jig borer scheme is that the horizontal range is directly tied to the Z axis range. It's an elegant approach but less useful for those of us who are already dealing with limits on Z.

Edit: My off-the-cuff comment is incorrect, I failed to include the adjustment range of the DTI-holder end of the jig.
 
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OK, I have my design worked out in my head, but Im struggling to find a suitably small indicator.

The STARRETT 80-134J fits the bill, but people want an arm and two legs for them.

Anyone know of a similar type indicator?

What Im really looking for is a drop type with a small 1"ish face. Quality doesn't matter at this point as this is strictly experimental.
 
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