How To: Using Dial/Digital Calipers

When I started machining a few years ago, I immediately purchased a set of dial calipers- they're probably the single most useful tool for use in machining, aside from the lathe or mill themselves. I quickly realised that calipers were just as useful for scale modeling. Since then, my workbench hasn't been without a set.

Simply put, it's a precision measuring tool. Used with a simple calculator, it's the best scale conversion tool I've ever found.

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Digital and dial models. The digital is pretty obvious to read. The dial is easy also, it just takes a moment to learn to use it:

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This caliper reads 0.750 inches, or 3/4". The scale that runs the length of the beam shows that it's open just over 7/10 of an inch, and the dial shows how much more. 0.700 + 0.050 = 0.750. Quick and easy when you've learned how.

Dial calipers are availible in either decimal inch or metric- or you can just multipy/ivide by 25.4 to convert between. Digital calipers, you just push a button to convert.


Either set can be used for very small measurements.

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This enamel wire is 0.011" in diameter- just over one one hundreth of an inch. Multiply this by 24, and in 1/24 scale, it would be 0.264" - perfect for 7mm spark plug wire.


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The wheels in the Dragon BMW M3 kit measure 0.780" in dia. Times 24 = 18.72". A bit large for the 17" they're supposed to be- but that's kit accuracy for you.


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Pressing the inch/mm button quickly tells you that they're 19.82mm- for those of you who enjoy the metric scale.


Inside measurements can also easily be done-

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The rims are 0.683" wide on the inside, or 16.4" in 1/24. Minus a little bit for the brake calipers, and that's the largest size Brembo disk I can fit into this wheel.


It also works just as well in reverse:

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The seat belts on a full size M3 are 1.860" wide. Divide by 24, and in 1/24, the seat belts should be 0.077".

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A very nice set of calipers (like Mitutoyo) can run over $100 USD- however, there are many less expensive ones availible. I've used both, top of the line and 'generic import', and honestly haven't been able to tell a difference. The two that I have each cost about $20-25 USD, and they can be found on Amazon for less than $16 USD.

I wouldn't model without a set!

nice how to!

Glad to see you covered both metric and imperial/standard measuring systems to prevent confusion.

Il agree digital calipers are the most amazing thing to have in machining. Depending on how accurate things have to be such as performance parts say an alignment dowel for a s/c. We had 2 pairs of mitutoyo calipers in the shop one has been there for over 4 years and the other set is like 2 years old the older set was off from the newer one by .035". But they have been handled pretty badly, no depth gauge dropped several times still worked pretty good but not good enough for accuracy. Nice idea for car modeling though.

WOW! Who would have thought! All the time I've been using one of those 1/64" scales, this never crossed my mind. :p

Good stuff! I've always prefered the analog caliper over the digital one, for some reason I can use it a lot better. I think it's because that's the one I was first introduced to, and also the lack of batteries :D.

Glad to see you covered both metric and imperial/standard measuring systems to prevent confusion.
What's the difference???? Same principle whether you are working with metric or imperial calipers.

With regard conversion IMHO, I don't think a caliper "How to" is the right place to post a metric to imperial to metric or 1:24/1:25/1:12 etc conversion tables for every dimension from 1" to 6 feet. Everyone canm work that out for themselves



Thanks MPWR for a useful guide. I've got to get myself some more accurate calipers - mine just show mm divisions :(

I'd love a pair of these, will have to be on the lookout. Added to the how to index.

I bought one of the digital ones on ebay for about $20. I can honestly says its one if the best tools I own. It came in very handy for my civic build.

I just ordered a 6" digital caliper from http://www.harborfreight.com/. I got it for $19 shipped by using a coupon for $5 off and some free tin snips! Yea! Now just awaiting its arrival.....

Great how to. I can't make models without my caliper. But one correction. You forgot to take the flange into account when measuring your M3 wheel.
http://www.automotiveforums.com/vbulletin/showpost.php?p=1275993&postcount=14

I bought a cheapo dial caliper from MSC Direct for about $15, they're a machine shop supplier and I have an account with them. As long as you keep it clean and put it back in the box once in a while, it'll last a long time.

Check our eBay for them, I'm sure you can get one for less than $20.

Bob