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Indi-cal Bore/groove Gauge

BGHansen

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#1
I picked up an Indi-Cal (called and Indicator caliper in the manual) off eBay for around $25. It’s used to measure inside bore diameters and ‘O’ ring groove diameters. Measuring range is 0.200” to 6.000”. They sell new for around $200 but can be had on eBay for $25 or less (be patient and don't pay too much). If you’re shopping on eBay, look for one with most/all of the parts or you might be making some pieces.

There should be an instruction sheet, 8 extension rods in varying lengths, 6 different points similar to dial indicator points, a pair of thumb screws and jam nuts that thread into the Indi-cal, and a small sheet metal clamp/screw for mounting a test dial indicator. I attached a scan of my 1957 unit instructions for reference.

The Indi-cal has two arms that are pinned and pivot in the middle like external snap-ring pliers. The indicator points and extension rods are screwed to one end per the instructions to about 1/8” larger than the size to check. A TDI is mounted to the top; it must have a dovetail base to attach to the Indi-cal. They sell/sold adapters to mount Gem and Last Word indicators as an accessory.

The unit is calibrated with a separate micrometers which are adjusted to 0.015”, or half of the indicator travel range, larger than the dimension to check. Then an “anvil” or contact point for the TDI is run up into the TDI indicator point and up to its full travel. Turn the TDI dial to match the appropriate thousandths of an inch, and you’re good to go for checking ‘O’ ring grooves and bores.

The indicator points going into the bore are 3.000” from the pivot point as is the “anvil” that the TDI indicator point touches, so the readings on the TDI are one for one to the bore. Well, as accurate as a TDI is . . .

In the photos attached, I used a Mitutoyo TDI on the Indi-cal to check a 1.000” standard ring for an inside micrometer. I calibrated the Indi-cal to 1.015” or 0.015” over the bore and adjusted the anvil that contacts the TDI point up until it just reached the end of travel. Then turned the TDI to 15. Seemed to work OK, I checked the bore a number of times and was within 0.001” each time.

Is the Indi-cal now my “go to” measuring tool for checking bores or ‘O’ ring grooves? Probably not. It has its place, but I prefer to use inside mic’s for checking bores and an internal dial caliper gauge for grooves. The inside dial calipers like the one pictured below go for $55 on eBay but have a limited range of about 1”, so I’d need a bunch of them to match the Indi-cal’s 6” measuring range. Plus the caliper’s points aren’t as fine as the Indi-cal so I’ll go to the later for a narrow groove. Each tool has its place, nice to have options in the tool arsenal.

I suspect based on the prices for used Indi-cal’s on eBay that they are not extensively used. Like I mentioned, they are still sold new for around $200, but used ones can be had for under $25. I usually expect to pay about two-third’s new price for good used items; that’s about what the internal dial calipers usually go for on eBay ($30-$40).

By the way, expect to do some fine threading if you need to make some of the parts. The thumbscrews, jam nuts, extension rods and points are all threaded 2-56! Mine was missing one of the points and one of the jam nuts was stripped; isn’t it great to have the tools to fix your tools!

Bruce

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Bob Korves

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#2
TDI? I think that is a Volkswagen thing -- turbo, diesel, intercooler... Dial Test Indicator (DTI)? 8^)
Nice tool review, Bruce!
 

BGHansen

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#5
TDI? I think that is a Volkswagen thing -- turbo, diesel, intercooler... Dial Test Indicator (DTI)? 8^)
Nice tool review, Bruce!
Hi Bob,

Thanks! Yeah, I think they are called dial test indicators . . . I see them listed both ways on eBay, must be too much on-line shopping, now my terminology is all screwed up!

Bruce

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Last edited:

4gsr

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Staff member
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#6
Bruce,

Had a bad experience with one of these several years ago. QC rejected a bunch of parts for the O-Ring grooves being out of tolerance. We traced it down to this instrument. It was giving inaccurate readings on every other part. The instrument had been "monkeyed" with by many who thought they knew what they were doing. At the joints of movement, they either had worn to where they were loose or some one "reamed" to holes so it would go together easier from taking it apart. Well anyways, this slop caused the instrument to give inaccurate readings. We were getting about .008" variation in readings on the same O-Ring groove!

So be careful and watch the measurements you get. I know you have the expertise to watch for stuff like this, but for others whom may not. Ken

BTW- I prefer the Starrett Groove gun myself. Just can't afford one yet!