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Telescopic bore gauges.

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Ron Laden30/04/2020 07:55:06
2248 forum posts
446 photos

I have been thinking of getting a set of telescopic gauges and have been reading up on them. It seems there is a bit of a love - hate relationship with them. Some swear by them, others don't plus I have read they are only good once you have developed a good technique and "feel" in using them,

Wondered what you guys think of them, love them or hate them?

Andrew Johnston30/04/2020 08:08:55
6266 forum posts
677 photos

Got a set somewhere, but can't immediately find them. Which about sums it up. I much prefer to use proper internal micrometers.


Former Member30/04/2020 08:09:02

[This posting has been removed]

David George 130/04/2020 08:20:10
1656 forum posts
497 photos

I use my telescopic gauges all the time and can get within a thou no problem I would like a set of three point internal mics but SWMBO would not be amused at the cost. Get a quality set Starrett or Mitutoyo I would recommend. There are a few places that you can get a Tele into that a mic wont fit like a recess in a tube.


Andrew Evans30/04/2020 08:20:33
342 forum posts
8 photos

Once you get the technique right with practice they are pretty accurate. I have the gauge at an angle in the bore, nip up the screw, move the gauge perpendicular which pushes it closed until I can feel no more resistance and then remove the gauge for measuring with a mike.

John Paton 130/04/2020 08:20:55
304 forum posts
17 photos

I agree with Andrew.

For non critical bores a decent external caliper is quicker and has good feel to check for ovality and taper in the bore.

To put numbers to taper I find a 3 point micrometer bore gauge quicker and more accurate but that might be because I dont use bore gauges very often. So I use the micrometer when checking bores on car engines.

For honing and final finishing bores I like to use bore gauges to check progress as it is so easy to take off a bit too much metal (measure twice cut once!).

Horses for courses in my view and for the occasional job it is cheaper to turn your own 'go / no go' plug gauges to suit the job.

Edited By John Paton 1 on 30/04/2020 08:21:54

Andrew Johnston30/04/2020 08:34:08
6266 forum posts
677 photos
Posted by Andrew Evans on 30/04/2020 08:20:33:

Once you get the technique right with practice they are pretty accurate.

Assuming one doesn't have an independent means of measuring the bore how does one know when one has the right technique?


Tony Pratt 130/04/2020 08:38:47
1692 forum posts
8 photos

'Proper internal micrometers' are obviously the best option but as they are very expensive, sometimes bargains can be had on Ebay, a decent brand of telescopic gauges are a good 2nd choice.


JasonB30/04/2020 08:48:08
21436 forum posts
2448 photos
1 articles

On the odd occasion that I get them out I tend to use them more a as comparitor when boring cylinders and cylinder liners as they are often 100mm or more long and you can only access one end while still in the machine and they can give an indication of any taper in the bore where other devices may only be able to measure a little way in..

lfoggy30/04/2020 12:19:27
169 forum posts
14 photos

I use my Mitutoyo set all the time and I certainly get very consistent measurements with them using either a micrometre or digital caliper. Measurements are reproducible to 0.01mm. As has been said above, hard to know how accurate in the absence of a reference standard but absolute measurement can't be far off. For example I recently bored a hole to a measured 25.02mm which was an excellent very close sliding fit on a 25.00mm bar.

Has anyone tested this type of gauge against standard bore setting rings to get an idea of their absolute accuracy?

mechman4830/04/2020 12:22:46
2933 forum posts
460 photos
Posted by Andrew Evans on 30/04/2020 08:20:33:

Once you get the technique right with practice they are pretty accurate. I have the gauge at an angle in the bore, nip up the screw, move the gauge perpendicular which pushes it closed until I can feel no more resistance and then remove the gauge for measuring with a mike.

Precisely what I do, & have been taught so. I have recently used my set to measure the bore of the cylinder for my beam engine project.


Rod Renshaw30/04/2020 12:33:01
329 forum posts
2 photos

I seem to remember a recent thread on these gauges which emphasised that a decent make of telescopic gauge works well, with practice, but a cheap gauge lacks the smoothly sliding action needed to get a good feel for the bore. Also, for the same reason, older gauges which have been "broken in" by much use work better than new ones. I agree with others that they may not be as easy to use as 3 point gauges, but they are much more affordable for the ocasional user.


Former Member30/04/2020 12:46:21

[This posting has been removed]

William Chitham30/04/2020 12:55:29
125 forum posts
52 photos

This Old Tony recently posted a video showing how he dismantled and fine tuned bore gauges to make them work smoothly: **LINK** . I suppose he is shortcutting the natural "break in " process that makes old tools feel nicer.


Steve Crow30/04/2020 13:26:51
283 forum posts
166 photos

I only needed the 2 smallest sizes so I got a couple of Mitutyo rather than a set.

Lovely and smooth with loads of "feel", so much better than a no-name brand I have. Consistent readings too.

Using a micrometer stand makes all the difference as well (unless you've got 3 arms).


IanT30/04/2020 15:21:08
1895 forum posts
184 photos

I've got the two sets from Arc - and have used several of the larger ones for jobs recently.

They may not be the best quality but they do work although I suspect personal technique is a more important factor. Not having his masters touch, I've tended to take several readings to see if measurements are consistent - mostly as a way to see if I'm doing it well enough.

I used to use calipers to do this but the bore gauges are slightly easier I feel - and my calipers are fairly long - so access to bores was a bit more of a problem ( I don't have a swing-back boring tool holder - some way down the TUIT list I'm afraid).

So whilst not essential, they are nice to have but do need practice would be my summary.



Former Member30/04/2020 17:23:20

[This posting has been removed]

Ron Laden30/04/2020 17:44:46
2248 forum posts
446 photos

Thanks guys for your thoughts on the gauges and a big thank you to Barrie for the tests, thats made my mind up I am going to get a set of the gauges.

That sort of accuracy is probably more than I will ever need but good to know what can be achieved, though I appreciate it will need some practice on my part in using them. I cant afford a three point micrometer so I think the gauges will do me fine for my type of work.


Martin Rock-Evans30/04/2020 18:03:24
23 forum posts
14 photos

Just a thought on getting practice measuring a bore, someone much wizer than me suggested practicing with a known bore such as the bore of a ball bearing. these tend to be hard and fairly accurately ground to a size, with published limits. Much cheaper than a standard, available in a range of sizes and probably good enough for beginners

Edited By Martin Rock-Evans on 30/04/2020 18:04:13

Former Member30/04/2020 18:18:36

[This posting has been removed]

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