Measuring depth of thin slots

[WindyParticipant @windy30762]

[WindyParticipant @windy30762]

I require to measure the depth of 0.050" wide slots that are deeper than the width.

There are blade micrometers and attachments that fit digital calipers.

Is there another way to measure without having to purchase a tool that will rarely be used.

I don't mind making a simple attachment to do the job.

Paul

[BowberParticipant @bowber]

Turn a 0.050" pin to a set length and place it in the slot then measure how much is sticking out. it'll be quite delicate but doable.

Steve

[Les Jones 1Participant @lesjones1]

Hi Paul,
You could try inserting a strip of metal into the slot and measuring the height of the strip from the surface. Then subtract this reading from the width of the strip. If the slot is not too deep the strips of stainless steel that are used to stiffen the rubber part of windscreen wiper blades might do the job, I tend to keep these when replacing wiper blades as I have found them useful. One I happen to have at the moment is 30 thou thick and 135 thou wide. They are not all the same width but they are parallel.

Les.

[John Stevenson 1Participant @johnstevenson1]

50 thou is just less than 1/16" ish, so reasonably rigid for anything that goes in the slots.

I'm also guessing that with your engines this isn't a one off and need to be done over and over ?

So how about grinding the sticky out bit at the blunt end of a set of digital verniers a tad thinner so it goes in the slot.

Good thing with the digital set is you can zero anywhere and get a direct reading.

Actually just measured the ones on my desk and they are a dead 50 thou so only need a gnats right bollock grinding off

[Jeff DaymanParticipant @jeffdayman43397]

Years ago I made a simple tool to do a similar job. Selected a piece of .040 music wire and cut to arbitrary length, say 1 1/2". Ground ends flat-ish and square-ish with a Dremel tool. Removed any burrs by a light stoning. Selected a piece of 1/4" x 1/4" square brass about 1" long. Drilled brass at centre of one face .045" dia. thru. Drilled and tapped #4-40 at centre of face 90 degrees to drilled face, so tapped hole intersects drilled .045" dia. Made a small knurled setscrew threaded #4-40. Put wire in .045" hole, installed knurled setscrew in tapped hole, and there it was, a custom mini depth gauge. No fancy finishing was done, and no high precision machining was required.

In use, the brass face is placed on adjacent face next to hole or slot to be measured, setscrew is loosened, the wire pushed to bottom of feature to be measured, setscrew tightened, then vernier caliper or electronic caliper or scale is used to measure from end of wire to face of brass for a pretty accurate depth measurement, depending on operator's "feel" for the wire to hole interface.

I've used this simple crude gizmo many thousands of times, it's surprising how often it comes in handy. JD

[jason udallParticipant @jasonudall57142]

Since your slot/grove is deeper than width you can’t use the normal “wires”

Beware any free moving blades..These can rock over and read high..or low depending on viewpoint. .but in any case read wrong.

Two possibilities. .
Mic with either jaws made for this or use extention cuffs ( available in a variety of “jaws”)…or even make your own. .
Or butcher/modify calipers which are cheap enough to sacrifice / dedicate to this goal.
But recommend digital in either case because as JS says set a falae origin then read directly. ..many have made slip ups over simple arithmetic while caught up in the moment while machining…

[WindyParticipant @windy30762]

JS I did think of your idea but you have verified it and will do that.

I'm going to make a batch of Dykes piston rings and like to make sure clearances are reasonable.

The piston part of a batch was made years ago apart from modifications and like to make sure its ring dimensions are correct.

Thanks for the suggestions.

Paul

[Paul LousickParticipant @paullousick59116]

Instead of modifying your calipers, attach a narrow blade which could be removed later. Clamp or glue the blade to the calipers. (superglue can be dissolved with acetone)

[Russell FurzerParticipant @russellfurzer50760]

If the slot is long enough then you could use a feeler gauge on its edge and measure how much sticks out

[HopperParticipant @hopper]

If you are doing a batch you could make a simple "go/no-go" type of gauge by turning both ends of a piece of round, say 1/4" dia, down to just under 50 thou diameter and make each end the max and min depth allowable for the job. Or make them a little bit over length, say 10 thou, then use feeler gauges under the fatter part of the gauge to measure exactly where the bottom of your groove is at.

[WindyParticipant @windy30762]

Have modified the caliper using a small carbide milling cutter.

It is the one I got with my mag subscription it only had to be modified slightly to do the job required and is ok for other types of measurements.

The caliper is used at my hydro meetings to measure my pumps stroke etc. it's now a dedicated tool for my steamer engine.

Paul

[mechman48Participant @mechman48]

Make a simple depth gauge for future use… I made one using a piece of ally from the scrapbinium, & an odd bit of tungsten tig welding rod ( 2mm – .040" ) that I had left from some years ago…

George.

[mechman48Participant @mechman48]

Erratum… Mea culpa, tungsten tip is 2.55 mm – .100"… but you could use a 0.032" piece of silver steel, Oh the shortcomings of the aged… grey matter doesn't function like 30 years ago, . You've got it sorted any how.

George

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