# Indi-cal Bore/groove Gauge



## BGHansen (Nov 8, 2016)

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 (Nov 8, 2016)

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


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## Ed ke6bnl (Nov 8, 2016)

Turbo diesel injection I think


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## Bob Korves (Nov 8, 2016)

*Turbocharged direct injection*
https://en.wikipedia.org/wiki/Turbocharged_direct_injection

We were all wrong...


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## BGHansen (Nov 8, 2016)

Bob Korves said:


> 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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## 4GSR (Nov 8, 2016)

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!


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## Bob Korves (Nov 8, 2016)

Dial test indicator.  They are not all digital, including the one in your post...
https://www.bing.com/images/search?...+indicator&qpvt=dial+test+indicator&FORM=IGRE


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## BGHansen (Nov 9, 2016)

Bob Korves said:


> Dial test indicator.  They are not all digital, including the one in your post...
> https://www.bing.com/images/search?...+indicator&qpvt=dial+test+indicator&FORM=IGRE


Hi Bob,

Yup, corrected my post to change "digital" to "dial".

Thanks, Bruce


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## Uglydog (Mar 17, 2018)

BG,
Spent a little time sorting stuff again today. Found one of these in the piles. No tips.... 
Perhaps I'll find one as I continue to dig. Perhaps not. 
You mentioned making tips in your initial post. 
Looks like PennTool and MSC have the points/tips for sale. However, I might want the challenge of attempting to make my own, as I've not threaded anything this small. 
Looks like 2x56. Can you confirm?
Did you make tips? Did you turn them on a lathe or use a die?
Suggestions welcome!!

Daryl
MN


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## mmcmdl (Mar 17, 2018)

Here is my set used with a Bestest indicator . This is a very handy little tool . I used to have to make special tips for this on many projects . Many of our grooves were impossible to measure with conventional tools .


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## Uglydog (Mar 17, 2018)

mmcmdl said:


> Here is my set used with a Bestest indicator . This is a very handy little tool . I used to have to make special tips for this on many projects . Many of our grooves were impossible to measure with conventional tools .


Mmcmdl,
Any tips on making tips?
I've not threaded this small. Based on my measurements she is a coarse 2x56tpi. 
I need to check if my 15" Colcester will even do a 56tpi....

Daryl 
MN

Sent from my SAMSUNG-SM-J727A using Tapatalk


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## mmcmdl (Mar 17, 2018)

Uglydog said:


> Mmcmdl,
> Any tips on making tips?
> I've not threaded this small. Based on my measurements she is a coarse 2x56tpi.
> I need to check if my 15" Colcester will even do a 56tpi....
> ...



Daryl , I use to turn down a bunch of blanks and pop the threads off with my small die head . I still have the head and I could most likely find my chasers . I don't have a lathe at the moment but I'm in the process of buying a machine shop once again . I'm downsizing and going back into my original basement setting . Tired of fighting mother nature in the garage . If I find those chasers , I'll lend them to you along with the head and you can pop them out !


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## Tony Wells (Mar 17, 2018)

I've got one of those, and never had an issue like Ken mentioned. The only caveat I would point out is that in the setting of them, if all the travel limits aren't within the indicator limits, it can move the point position on a friction held point, or knock the LW ratchet to the next notch and mess up your zero.

I also have a Starrett groove gun, but sometimes I like the lighter touch of the Indical. Seems like I am missing one of the extension rods, from loaning it out. I think the threads got broken off so it "disappeared". I also like the wire contacts for narrow grooves like retaining ring grooves. Overal, a handy tool to have in the arsenal.


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## mmcmdl (Mar 17, 2018)

Yes , they are cumbersome to set and use , but they are lifesavers sometimes . We actually made tips and bent them in 2 places at 90 degrees to get around some tight spots . We actually sleeved a few where the tips would go thru small bores and then slid the sleeves up and measured much larger grooves . LOL , government work . Proximity fuses and projectiles . We finally convinced the engineers to make them in 2 pieces in production  ! 

Daryl , I'll post a pic in one minute to help you out .


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## mmcmdl (Mar 17, 2018)

If you have one of these .......

a releasing tap holder or die holder . Make up a quick die holder that holds the 2-56 die and slip it into this . Feed that Colchester to a set stop at a slower feed than the pitch of the die . When your machine hits your stop , the holder pulls out and spins with the material . Reverse the spindle and it backs off the thread . Pretty simple but effective .


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## BGHansen (Mar 18, 2018)

Uglydog said:


> BG,
> Spent a little time sorting stuff again today. Found one of these in the piles. No tips....
> Perhaps I'll find one as I continue to dig. Perhaps not.
> You mentioned making tips in your initial post.
> ...


Hi Daryl,

Yup, 2-56 thread. I made a tip for mine so it's complete. Nothing super critical on the dimensions as the Indi-cal is calibrated on each set up. Recall using 303 or 304 for the tip I made.

Bruce


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## Uglydog (Mar 18, 2018)

mmcmdl said:


> If you have one of these .......
> 
> a releasing tap holder or die holder . Make up a quick die holder that holds the 2-56 die and slip it into this . Feed that Colchester to a set stop at a slower feed than the pitch of the die . When your machine hits your stop , the holder pulls out and spins with the material . Reverse the spindle and it backs off the thread . Pretty simple but effective .





BGHansen said:


> Hi Daryl,
> 
> Yup, 2-56 thread. I made a tip for mine so it's complete. Nothing super critical on the dimensions as the Indi-cal is calibrated on each set up. Recall using 303 or 304 for the tip I made.
> 
> Bruce



Thanks mmcmdl and BG for confirming the 2x56. Had to get out the old biology microscope I keep in the shop to count the threads.
Somewhere there is a small die head I'll look today to learn the size of the head and if there might be any chasers with it. If I find/buy chasers then I may need additional coaching on putting her to work! But, mms coaching above is a great start.

Daryl
MN


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## BGHansen (Mar 18, 2018)

Hi Daryl,

Here's a POTD link to an indicator point I made for the Indi-cal.  Probably not the best way to do it but it worked for me.

Bruce

https://www.hobby-machinist.com/thr...in-your-shop-today.14637/page-288#post-433858


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## Uglydog (Mar 18, 2018)

Found a Geometric die head I'm not sure if it works or if it's precision scrap.
Never used one.
Have several die heads in the pile, and a couple dozen chasers. None 2-56. Not sure which fits what or how to know if these vintage tools work.
I'm also finding 2-56 hand dies online, hoping to look for a 2-56 in the stacks here before I purchase anything. 
It might  be a couple weeks until I get back to this..... 
Thanks all for the assist!!

Daryl
MN


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## Tony Wells (Mar 18, 2018)

You don't have to cut the male 2-56 thread unless you just want the challenge. Drill and tap a 2-56 hole in the extension or tip and loctite a set screw in the tapped hole. No one will be the wiser.


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