Author Topic: A Different Approach  (Read 5530 times)

Offline 75Plus

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A Different Approach
« on: August 27, 2011, 01:07:46 PM »
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.






Offline nearnexus

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Re: A Different Approach
« Reply #1 on: August 27, 2011, 09:13:13 PM »

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


Offline 75Plus

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Re: A Different Approach
« Reply #2 on: August 28, 2011, 09:38:22 PM »
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.

Offline John-Som

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Re: A Different Approach
« Reply #3 on: August 28, 2011, 11:20:24 PM »
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

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Offline nearnexus

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Re: A Different Approach
« Reply #4 on: August 28, 2011, 11:30:51 PM »
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
« Last Edit: August 29, 2011, 06:34:03 AM by nearnexus »

Offline 75Plus

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Re: A Different Approach
« Reply #5 on: August 29, 2011, 03:43:19 PM »
Over the weekend I made this into a "system". I can now use the gauge on either side of the carriage, depending on the job at hand, as well as measure the cross slide movement. When using the gauge on the gearbox side I see no need for the swing away mentioned earlier so I just use a clamp block on the ways and attach the gauge. For cross slide use I made a mounting block and embedded 4 rare earth magnets. I found two holes drilled in the cross slide for some unknown (to me) purpose which were just the right size to tap a 3/8-24 thread to secure a block for the plunger to bear against.

Here are some pictures of the results.

Here it is mounted on the left of the carriage.



Here is the setup for measuring the cross slide travel.



A view of the mounting block for the cross slide.



And the gauge with all the mounts.



For those who like to look inside here is a couple of shots.






Offline nearnexus

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Re: A Different Approach
« Reply #6 on: August 29, 2011, 07:13:01 PM »
Thanks for posting those.

Interesting to see a close up of the mount which enables the gauge to be attached to a magnetic dial indicator base and used as a digital probe indicator.

I was pretty impressed with the twin functionality of that little gauge and tracked down an Ebay seller who will ship world wide at reasonable rates, so I ordered one.

If anyone else outside of the USA is interested, here is the current Ebay link.

http://www.ebay.com.au/itm/DEPTH-GAUGE-DIGITAL-INDICATOR-2-1-DEPTH-GAGE-0-4-/190562940188?pt=LH_DefaultDomain_0&hash=item2c5e6fb51c

I don't intend to modify this one, as I already have the elcheapo one that works fine for the original concept.

But for the money the Igaging one is also well worth having in the drawer, especially when you consider how the price compares to a dedicated digital probe - and my sheet of spare batteries that I bought off Ebay for peanuts fits both units.

Rob


« Last Edit: August 30, 2011, 12:08:04 AM by nearnexus »

Offline nearnexus

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Re: A Different Approach
« Reply #7 on: September 19, 2011, 03:55:02 AM »
I got my little Igaging depth gauge today as used by Joe, and I must say it really is a nice unit.

Very smooth and the repeatability is excellent (100%).  

Sideways deflection on the Igaging is also not an issue, as it is intended to be used as a digital indicator, as well as a depth gauge.

The original little elcheapo DRO is the way to go to modify into a Micro DRO, and you've got nothing much to lose if you screw up.  I use mine a lot.  I see the price has come back to under $6 AU again.

But for anyone looking to get a really nice depth, come digital indicator, the Igaging is highly recommended - and not expensive if you shop around.


Rob