How to Measure Tapping Depth

How about grinding a bolts lead thread off, zero your vernier on the length of the bolt, insert bold and measure the bit sticking out. That will give you your tapping depth! (Forget about the minus sign, that only indicates the thread is sub surface!)

I want an instrument for checking the depth, I know the methods that how i can measure this alternatively,But moreover i want instrument

You will need to use the sharp end of the calipers - or if your calipers have an RS232 connection you could read on a display http://www.compendiumarcana.com/caliper/ - or you could buy

Isn't this a micrometer?

How about one of these available locally from here?

Why would a normal standard depth gauge from Mitotoyo not suffice? Hole too tiny for a caliper or too large? I remember looking at a depth micrometer with a range of tool end sizes for measuring smaller than 6 mm hole diameter. Since I was into engine rebuilding at the time I did not bother to get the others.

Do you not have access to a regular catalog of measruing instruments?

Hey ELNAV,

You can not reliably tell where a thread stops by bottoming out a measurement in the hole. Even if it is threaded with a bottoming tap, you will still have a variance in screw insertion. A non-bottoming style tap is even worse!

Chinese digital calipers are so cheap nowadays if the hole to be measured are smaller than the width of the calipers depth probe it is simple to grind down the width to suit. also it does not spoil the ability to alter the width again even if it is shortened as the calipers can be zeroed at any position.

Buy two or thee if you need to measure a lot of holes of different diameters.

U can calculate by how many round of the thd you had engage. example 5 round X1.5 pitch=7.5 mm depth

If you want to measure tap depth instead of hole depth, you need to measure the depth of the point where the thread reaches a critical diameter or percentage of thread depth. Inserting standard threaded body like a gage screw or sectioning the hole are 2 ways to do this. If you work for the manufacturer of the threaded holes, it might be fruitful to qualify the process instead of inspect all of the output.

If you just need the depth of the hole, get a depth micrometer. Use a point on the end of the measuring rod if the bottom of the hole is not flat.

Hello Rajesh verma;

Please we need method of tapping, type machinery used and depth dimention etc. to give informed reply, thanks.

I'm not sure how accurately you need to check the tapping depth - that will depend upon circumstances. But I've seen a shop-made device used; it used two half-balls, each with a diameter of maybe twice the pitch [or = crest-to-crest-to-crest]. They were on the end of a long U-shaped wire spring, with an outside width just less than the hole diameter. The round surfaces faced outward, and when the two halves were squeezed together to form a full sphere, the device was pushed down the hole. It was then lifted until a "click click click" sound a feel indicated that it had been raised to where the threads started. A reading at this position was used as reason to accept or reject; the first three or so threads were assumed to be incomplete.

It is easy to adjust the number of threads to ignore, assuming that the same type of tap was used for a series of holes. A simple mark on the legs of the spring will say whether adequate depth is seen. If this will be used for several sizes, a small block higher up the U, with a hole parallel to the legs and holding a straight wire with smooth end, can provide an adjustment (set screw on the wire leg for position).

It is a very simple thing to assess depth of thread when tapping.

Using a starting seven and one half threads are lost due the lead angle.

Using a plug tap three and one half threads are lost due the lead angle

Using a bottoming tap 1 and one half threads are lost.

Sounds like a good rule of thumb - thanks! - but my ancient Machinery's Handbook gives a wider variation. The "American Standard Straight Shank Tapper Taps - Fractional Sizes" table calls for 11 -12 chamfered threads for NC [National Coarse], and 15 -17 for NF. Nut and pulley taps are chamfered over as much as half of the thread length, which could easily mean 10 threads. Of course, none of these would be appropriate for use in blind holes, so Plug or Bottoming should be used. Because this is an old copy of the book, it doesn't mention metric taps, and there may be newer standards for the ones it does contain. I would never count on a purchased tap meeting a particular standard, unless the manufacturer explicitly claims compliance.

In any case, if a few holes are measured by counting turns when installing a bolt, and the same holes checked using the simple push-in / pull-out device I tried to describe, the total number of crests found by the device, minus the number of turns the bolt will go in, will say how many to ignore.

We generally figure by number of threads x pitch