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A Different Approach

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75Plus:
I have been following the thread on adapting a Tire Tread Gauge as a mini DRO. I often have the need for measuring the length of cut on some of the items I make. I have been making do with a 0 ~ 1" dial indicator but have found that the length of travel can be somewhat constraining. As a "work around" I came up with this design.

Thumbing through a tool catalog I ran across a digital depth gauge by iGaging. It is also 0 ~ 1" but it comes with extensions to allow measuring a hole up to 4" deep. It also has in internal return spring. It cost me $17.50 including shipping.

My approach was to mount the gauge in such a manner that it could be swung away to allow the carriage to move away from the chuck with jamming the device. It also had to be repeatable. My testing showed that I could repeat with no more than .0005" error over 10 raising and lowering cycles. Actually 2 of the 10 showed the error. the other 8 were spot on.

I started by making 2 identical clamping blocks that fit vee rail on my lathe. Only one of the blocks actually clamped onto the ways. The other one was fastened to the gauge to ensure accurate locating after moving. I decided on a 6" bar between the two clamp blocks. I used 3/4 X 1/4" aluminum bar. To ensure the maximum repeatability I used a precision ball bearing liberated from an old hard drive for the hinge.

These pictures should help explain the project.

Here is the various parts before assembly.



Here it is mounted on the lathe. With no extensions I have approx. .850" usable measurement.



With an extension added I can get a total travel of 1.056". With both extensions in use I can move the carriage approx. 9" from the normal work location with the gauge raised.



Here the gauge is swung away to allow the carriage to move away from the chuck.



I am very pleased with the results of this project and am planning to adapt the gauge to measure the cross feed travel also. I will post this when I have all the details worked out.

nearnexus:

I saw those gauges when looking on Ebay, and they seem good quality, unfortunately they cost too much to ship to Australia and no one here seems to have them.

Is the inbuilt spring low tension (easy to compress) ?

Rob

75Plus:
Yes Rob, the return spring tension is very light. There is no gib strip so it does not take much pressure to move the bar.

John-Som:
75Plus

That is a very professional looking adaptation of the digital tyre gauge and it is interesting to see the ingenuity of members in modifying the digital tyre gauge for use in the workshop.

Whilst there are benefits of using a tension spring rather than a compression spring it is even better without any spring at all. As my friend Aussie Jim suggested simply fix a small diameter rare earth magnet on the tip of the probe. this will ensure the probe follows the movement of the carriage or cross slide.

Apart from making the modification more straightforward to carry out there is less danger of movement of the read head when pushing (or pulling) against the probe.

John-Som

nearnexus:
I suspected that the spring would be suitably light, as I saw a kit for that gauge which also included various probe extensions AND a mount to allow it to be used as a digital probe indicator.  Nice.

It wasn't cheap (about $65 US from memory) but was comparable in price and function to a regular digital probe.

I wouldn't try to use the cheaper ABS plastic $10 ones as a digital indicator, as the probe could flex when checking run out.

To use a magnet on the probe tip should work, but I would consider milling a recess into the face of the black ABS plastic so that the face of the magnet can come flush with the edge.

That way you can still attach it to the smallest possible area as in the case of the mark 2 version with the concealed spring.

Whichever way you choose to do it, they are a super handy little gauge and I wouldn't be without it. 

Rob

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