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Telescopic bore gauges.

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Ron Laden30/04/2020 07:55:06
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1969 forum posts
390 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
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5553 forum posts
650 photos

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

Andrew

Barrie Lever30/04/2020 08:09:02
645 forum posts
76 photos

Ron

They are a useful addition to the war chest in my opinion, they take a little bit of getting used to but are a cost effective way to measure a wide range of bores.

No substitute for a 3 point bore mic but they are horribly expensive.

B.

David George 130/04/2020 08:20:10
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1257 forum posts
438 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.

David

Andrew Evans30/04/2020 08:20:33
321 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
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274 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
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5553 forum posts
650 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?

Andrew

Tony Pratt 130/04/2020 08:38:47
1147 forum posts
5 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.

Tony

JasonB30/04/2020 08:48:08
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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
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146 forum posts
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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
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2689 forum posts
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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.

George.

Rod Renshaw30/04/2020 12:33:01
114 forum posts

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.

Rod

Barrie Lever30/04/2020 12:46:21
645 forum posts
76 photos
Posted by lfoggy on 30/04/2020 12:19:27:

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?

Ifoggy

OK I have just done a quick test as you describe, the only caveat that I would add is that my Bowyers reference standard and all the instruments are a bit cold.

On a 3/4" ring reference standard, I got on the first try 0.74965" so 3/10's of a thou down, the three point bore mic also read slightly low at 1 and 1/2 tenths down.

The telescopic gauge is a brand new Desqua from Chronos, I will try a Moore and Wright.

I will repeat all the tests when the instruments are up to temp.

B.

William Chitham30/04/2020 12:55:29
44 forum posts
14 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.

William.

Steve Crow30/04/2020 13:26:51
220 forum posts
70 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).

Steve

IanT30/04/2020 15:21:08
1547 forum posts
144 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.

Regards,

IanT

Barrie Lever30/04/2020 17:23:20
645 forum posts
76 photos

I have had a chance in the last half hour to have a good opportunity to test measuring an internal diameter with telescopic bore gauges and a three point micrometer, I have to say I surprised myself with the results.

I will layout a few ground rules first, I have a pretty sensitive feel for this type of measurement, I think the secret with using telescopic bore gauges is that the feel in the bore has to be the same feel/resistance when in the micrometer's anvils, not by using the micrometer's ratchet as that is too course against the relatively elastic telescopic gauge.

So what was the test equipment?

From the left

dsc_1063.jpg

  • Powerfix IR non contact thermometer, the weak link in the test equipment.
  • Bowers 0.7500" ring standard
  • Mitutoyo 1" micrometer standard
  • 20 and 5mm Tesa RSD tungsten carbide class 2 slip gauges.
  • Starret 229 telescopic gauge.
  • Moor and Wright 900/0.5-0.75 telescopic gauge
  • Dasqua dual telescopic gauge
  • Bowers 0.75" to 1.00" 3 point internal micrometer
  • Mitutoyo Digimatic 293-766-30 (very good condition, no hard use)

All equipment had been in the workshop for 3 hours and the equipment all measured between 19.5 c and 20.5 c with the IR non contact thermometer.

I checked the Mitutoyo micrometer against the Mitutoyo 1" standard and it read perfectly.

dsc_1064.jpg

I then checked the same Micrometer against a 20mm tungsten carbide slip gauge as this was close to the 3/4" area that the tests would be conducted in.

dsc_1066.jpg

0.78740 = 19.99996mm (lets call that 20mm)

So this had established the baseline of the micrometer that we would use to measure the telescopic gauges with, as you would expect from an un-abused Mitutoyo Digimatic it gave pretty well perfect readings.

So I measured the ring standard with the Bowers 3 point internal micrometer and it gave a perfect reading, the lines on the barrel and the shaft lined up perfectly at 0.75" this was an improvement on an early reading when the instruments were colder that showed a just discernible indication of slightly less than 0.75".

The three point micrometer is beautiful to use in a bore like this and gives very confident readings with little feel required.

So then I carefully went through the telescopic gauges and got the following readings

  • Starret 0.74990"
  • Moore & Wright 0.74995"
  • Dasqua 0.74995"

I did not hold the ring standard in my hand rather left it on the bench and the entry for the telescopic gauge's was perfect, the above readings are not the best of a set of readings rather they are the first reading that I took, I was very careful with the feel of the gauge in the ring and matching that feel to between the anvils of the micrometer.

I will be honest and say that I am staggered at how good the readings are and are repeatable although the readings require a lot more dexterity than the three point bore micrometer.

I hope this helps answer some of the earlier questions.

B.

Edited By Barrie Lever on 30/04/2020 17:24:32

Ron Laden30/04/2020 17:44:46
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1969 forum posts
390 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.

Ron

Martin Rock-Evans30/04/2020 18:03:24
17 forum posts
10 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

Barrie Lever30/04/2020 18:18:36
645 forum posts
76 photos

Martin

The ID of a bearing is a good idea to practise on,

Basically you have to feel the merest contact in the bore and apply that same feel when between the micrometer's anvil's, not repeat not by using the micrometer's ratchet, otherwise you are not comparing like with like.

B.

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