Thread depth measurement gauge requirement

Use a thread gauge caliper that has a go and a no-go! The suppliers of your thread gauges may have them in stock!

Plug gages are great. They are NIST traceable.

But there are other methods. There is the thread micrometer. Very useful and easy.

There is the three wire method. Not as easy but very accurate, and often the preferred method for accuracy.

There is the optical comparator/molding.

But as you see, these are all for external threads.

So? I would use an NIST traceable/certified thread plug gage of proper fit class etc.

Now as I re-read you are asking thread depth. Sorry bout that give me a second. There is a very simple and very accurate formula based on revolutions. So let me look it up and I will re-post proper response.

Be right back.

cr3

Now you have said that, It has got me thinking about the question! He is on about the depth the thread goes in! So my caliper suggestion is rubbish! (oops!) So we have an M8*1 or an M8*1.25 which is 10.4/10.6 dp? I think if you use number of turns, the problem is your tolerance is a bit tight to allow this style of checking! ie M8*1 is 10.5 revolutions plus or minus 0.1 revolution which in itself not too easy or M8*1.25, which is 8.4 revolutions plus or minus 0.08 revolutions! some how I don't think this will be good for you!

Best method is the thread plug end not in its holder, set your vernier to zero on the length of the thread plug end, stick it in the thread and measure what sticks out without resetting the vernier!

<M8 X 10.5 ±0.1> SURE?

Look up http://www.auto-met.com/gage/metric_thread_gage.htm

for all specs+prices.

mm

I've used plug gauges in the past that had a flat ground on them so that the shoulder of the flat indicated the limit for the thread depth. From memory I think that the depth tolerances than were wider than ±0.1 so a visual check was ok. I guess that if the shoulder was 10.5mm from the end of the plug gauge you could clock from the part face to the shoulder to check it.

±0.1 seems a very tight tolerance for a thread depth, does it really need to be that tight?

If you are looking to do this check inline, and would like to do it on 100% of the parts take a look at smac actuators. A std. actuator used for thread checking has a 5um linear encoder, so it is not a problem to detect the tolerance you are talking about. The SMAC can be set-up to do a wide variety of checks.

SMAC has been used for this type of check.
www.smac-mca.com

Here is a link to a thread check on a thru hole appliciaton.
http://smac-mca.com/swf/threadvideo.swf

It would be helpful if we could use correct terminology so that one has a better chance of answering questions correctly.

With vee form screw threads, they are represented as e.g. M8 x 1 or M8 x 1,25, where M8 is the Major Diameter and 1 or 1,25 is the pitch of the thread and thread depth is measured at right angles to the thread axis and is the distance from the root of the thread (minor diameter) and the crest of the thread (major diameter).

The length of the thread can either be shown as a liinear dimension or e.g. M8x1,25x12 where 12 represents 12 mm as all dimensions on engineering drawings are in millinetres.

Yes, the terminology got me too.

Thread depth, threaded depth, threaded hole depth, length of thread.

Extra thread never hurts anything and every manufacturing engineer will tell you, they will not tap beyond where they have to (costly).

Extra thread depth, if not controlled to some degree of accuracy, could affect the tesile stess of the bolt, as it will alter the root or minor diameter of the thread. This would be of more concern in smaller diameter threads.

Could you try with Linear Height gauge. Use 2 mm probe.

Thank you.