Telescopic Gauges - Technique?

A bit of a personal history for starters:

My sandwich course, 1954-1958, included twelve months factory attachment of which the first few months were spent in the Trainee Modelshop. (Question #1: why was it called a 'modelshop' ? ) I made some BA spanners and a Browne & Sharpe toolpost spanner, some toolmakers' clamps and a scriber and centre punch or two. They can't have turned out too badly - one of the toolmakers' clamps was nicked!

Subsequently, such workshop skills as I have, have been built up, patchwork fashion, relying on books, live examples and, recently, YouTube videos and lots of trial and error along the way.

One blank area in the patchwork has been hands-on experience with using the telescopic gauge to measure bores. I've never tried it.

I've watched the famous YouTube gurus inserting the telescopic gauge into the bore with a forward lean, pulling it past 'top dead centre' and then measuring it with a micrometer. I presume that the gauge is set with just sufficient tightness to hold the moving arm still but not too much to prevent the arm moving within its mate to adopt the diameter of the bore.

But, question #2, do they then tighten the handle to prevent the closing force of the micrometer from altering the reading?

Question #3, how is tthe technique altered if the depth of the bore is, say, only just sufficient to admit the head of the gauge?

I know that attaining this sort of skill is best achieved with the hands-on aid of a mentor; mentor performs operation, learner performs operation, sequence repeats until both achieve the same reading. I don't have that opportunity but I do have to machine a spigot to fit a recess (think chuck + backplate) and there'll be no second chance. I have mounted chucks on backplates in the past by just very carefully taking off less and less until they fit. I'd like to have a bit more control this time.

I look forward to members' comments. How do you do it?

Bestt regards,

Swarf, Mostly!

P.S.: I do have a digital caliper gauge.

I find they are fairly accurate, +-0.001" mostly, but they vary in quality which can affect their "feel". If I can, I use the Moore & Wright ones, they are smoother than my cheap set. They can be dismantled and the 45 degree ends made smoother, many people have done this mod.

My standard method is to compress and lock the gauge before putting it in the hole. Then unlock with the gauge handle tilted relative to the axis of the bore and then lock just enough to hold the setting. Then rock the gauge (I prefer having the ends in a vertical plane if possible) past the tightest point and remove. Careful measuring without changing the size last. Repeat for critical measurements to prove matching figures.

Practice on known bore sizes if possible, I have a ring gauge, but with care a locked micrometer can be used, but you need to be square each time with parallel faces.

Old Mart is correct in action but I do a few extra bits in my measuring action.

Wipe the bore to be checked firstly. Next check the gauge is free and springy with no sticking and smooth action. Put in the bore at a slight angle with the gauge unlocked and tighten to lock. Next move the stem of the gauge perpendicular to the axis once only over center till you feel the gauge us free. Remove from measured item and carefully measure the gauge with a micromiter with care to not to over pressure the gauge and move it. Repeat all actions and compare sizes with first try.

I hope this helps.

David

I tell people to get a ball bearing. Measure the ID with your gauges, and keep trying until you get the same diameter as the bearing. Use the Outside of the bearing to practice the feel for the correct diameter of the bearing outer. Eventually you will figure it out and then be able to measure with confidence with both the outside mic and with the tele gauge.

I do as others have said rocking the lightly nipped up gauge across the diameter once to set the guage. I always tighten it slightly before measuring.

When measuring I support one end of the gauge on the micrometer anvil then rock the gauge slightly as the mic is closed to feel for contact as it passes over centre so to speak. Always repeat several times to get a mean but never rock across the bore and back to set it - just the once only

Neil's tip of using a bearing is a good one - not heard that before - but a good way to establish to yourself you are getting the right kind of feel and measurement skills from an exact known source.

Tug

Takes practice, and plenty of it. Just like anything else really.

And on holes 1/2" and under you are better off using ball gauges. Much easier to set, giving more reliable result for the inexperienced (and the out-of-practice experienced too!).

I usually rock T gauges in two planes. First -- with the T at an angle -- side to side to make sure the T gauge is sitting dead centre in the circle of the hole, then carefully rock it over centre lengthways once to get the size. Same technique in the mike to get careful measurement without moving the plunger of the T gauge.

It does take practice and "feel" and if you are not doing it all the time, you do get rusty. These days, proper inside mikes and dedicated bore gauges are not that expensive so are worth looking into.

Edited By Hopper on 29/08/2022 10:13:09

I insert the gauge in the bore and lightly nip, straighten the gauge to close it down to size. The gauge should not be able to rock side to side, if it does it is undersize. I then tighten and check it does find a point where it touches without excess force, if you need too much force then it is probably oversize and if there is no sweet spot then you are undersize. Definitely a tool that developing a feel for will help with accuracy, some care with the mic is also required and using the ratchet should avoid compressing the gauge.

Mike

I find that using a micrometer stand makes it a lot easier when measuring bore gauges.

Steve

Ask ten 'Engineers' the same question and you'll get ten different answers, the same applies to 'Feel'. Some rely on a certain number of clicks of the ratchet stop but that doesn't allow for the speed of spinning the spindle closed. Doubt with his skills Ramon would really need the extra 'nip' to ensure not pushing the bar back. Wonder what the blind machinists (NO slight OR pun) comparison measurements are using a Braille mic? The ability to get a 25mm measurement on a 25.1mm block is extremely easy for some and especially winding the toolroom foreman up "Can i borrow the 1-2" adjustable spanner.

Feel is an acquired thing that applies when fitting parts together and don't even start to introduce tolerances.

Regards Ian.

How many people use calipers these days. When I started my apprenticeship in 1950 I was expected to have inside and outside calipers, a square and a six inch rule, and know how to use them. We were expected to have our own tools because it taught us to respect them. You never borrowed tools off another workman. Tools could be bought at the works shop, at a discount and paid for weekly.

Good afternoon, Ian,

Thank you for your post. (Thank you to all other posters as well but I want to reply particularly to Ian. )

I started this thread with some trepidation because I do appreciate that 'feel' is not easy to communicate using the written word. For that reason, I am grateful to everyone who has bravely made a contribution.

However, my opening post does contain three specific questions. #1 is a matter of interest but is a side issue from my main enquiry. Several contributors have answered #2 but nobody has addressed #3. The task I have before me does involve a recess that is too shallow to permit 'rocking ' of the telescopic gauge.

Thank you again to everyone who has commented and I look forward to still more contributions.

Best regards,

Swarf, Mostly!

I don't know the answer, as I never use telescopic gauges. Up to 1/2" I use ball gauges, as suggested by Hopper. From 1" to 32" I use internal micrometers. For the awkward 1/2" to 1" range I use test pieces, either from stock material or ground to a specific size as needed.

Andrew

Hi Swarfy, For test pieces to practice on, pop round to your local bearing supplier and ask for a few old bearings - they will normally have plenty and be glad to give you some. Noel

The bores of old bearings do make useful practice pieces for measuring as they are made very close to the exact size. I have a collection of mostly new bearing races up to 6" bore which can also be used for milling parallels. Not only testing telescopic gauges, but also to see how close the inside ears of calipers are. My Mitutoyo's and Tesa can measure inside to 0.001" reliably, but I would have to try out the cheap digitals before trusting them.

Regarding your backplates, nothing wrong with that method, it,s the way I made mine, teeny bit at a time.

Result---snug fit !

Regarding your backplates, nothing wrong with that method, it,s the way I made mine, teeny bit at a time.

Result---snug fit !

I do have a set of those gauges [how good they are is another question ] but I dont remember the last time I used them, never really got the hang of them.

Sorry for the omission SM.

Shallow depth bores are difficult at best. When boring out the bearing housings on the IC engines that very situation arises Though I 'size' the hole with a accurately turned plug gauge I do use the tele-gauges to get me close.

In this case I try to hold the gauge as carefully as possible across the diameter of the bore with it just loose then gently nip up. i.e. no rocking though centre. This can sometimes give a false reading due to potential movement, albeit very slight, on the tightening action but several readings will get you pretty close.

I had a set of Moore and Wright gauges and later bought the double sided versions - Draper I think. They were as someone said a bit hit and miss and 'draggy' but an hour or so taking them apart and stoning all sliding surfaces transformed their use. I sold the M&W ones on.

Best - Tug

Swarf Mostly, re your #3

I'm not sure what you mean by Digital Calipers on your p.s. in the first post.

I always struggle a bit with smaller internal measurements, up to a couple of inches or so; or at least I always think I do, so resort to trying to take measurements by two different methods and comparing them.

I'm fortunate in having all sorts of measuring instruments that I've picked up cheaply over the last 30-40 years, several of which are intended for internal distances.

If your Digital Calipers, are of the sliding 6" scale type, like vernier calipers, but digital, then yes I have them in vernier, digital and dial varieties, as well as conventional internal micrometers, and a 3 point bore gauge.

By far the easiest instrument I have for bore/internal measurements are a couple of sets of MPJ dial calipers, which came via ebay: I most commonly use a set which covers about ½" to 1¼"
I think I paid about £20 delivered, but they regularly show up in the £30-40 price range.

They are similar in style to these eye wateringly expensive Mitutoyo ones from Machine DRO
https://www.machine-dro.co.uk/mitutoyo-internal-dial-caliper-0-4-1-2-0-0005-209-352

Even though mine are old, they are easy to use and repeatable to less than a thou with care, and ideal for shallow bores, short linear steps etc.

Bill

Sorry for the omission SM. My induction/enslavement was only a couple of years after yours and was instructed/directed by quite a few sexagenarians - thankfully, boy, those guys knew their onions.

As Ramon has stated, in anticipation of a shallow bore measurement , first job would be to turn a plug gauge, the diameter of which can be easily checked and then 'Creeping up' to the required bore.

Regards Ian..