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A Tale of Two Indicators

The ultimate denouement of my busted coaxial indicator

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Martyn Nutland 114/01/2022 09:48:14
18 forum posts

A few of you may remember that last July members were good enough to comment on the cheapo coaxial dial indicator I had bought. It had a dangly probe and as such was quite useless. You might further recall that I compounded its uselessness by snapping the probe holder.

Having recovered it from the bin I managed to get it working by machining a new holder that was sufficiently thick to be gripped by the instrument's beam (See 'Limp Probe' if you're interested.) But to be honest, my replacement was not as elegant or accurately shaped as the original.

It was then that Jason, on this forum (16/7/21) suggested that if I had shortened the clamping screw on the beam (to modify the point where it 'topped out', or fitted shims on either side of the holder, all might have been well. But, of course, I had already broken the holder!

As it happens, MSC Industrial in the US stock the holder that fits all these Chinese(?) indicators at $9 (I wonder whay!), but rather unhelpfully they won't send them to Europe. However, through great generosity, Tom Lipton of Ox Tool video fame, bought me one and sent it to France.

Lesson number one: The spare is no better than the original. PLEASE NOTE IF YOU CONTEMPLATE BUYING THESE INSTRUMENTS.

I now implemented Jason's shimming idea - I baulked at the screw-shortening as a bit fiddly. Fiddly! F-i-d-d-l-y! Try shimming the holder in the beam to discover what fiddly really is. It took me about two hours but with a 0.016" shim you can get sufficient tension - a bit too much, actually - to pre-load the probe i.e. it ceases to dangle uselessly. I subsequently got a flicker through about 0.01" on the needle when sweeping round an Austin Seven cylinder bore with the mill running at 100 rpm. (Thanks again to the forum on the advice on coaxial speed). This was about the same accuracy I achieved with the holder I made used around the inside of an A7 piston skirt.

ALL THIS SAID, I bit the bullet, as I suggested I might, and bought off ebay a used Blake Economy (god knows how old). It cost $200 plus taxes etcetera. What a difference! Straight-out-the-(patinated)-box, conspicuouslly smoother action and very slight flicker of the needle between two 0.005" graduations. Only two probes mind you, as opposed to about eight with its chinese cousin! And no special (crappy) spanners....or gibberish instructions or pedigree from someone who'd probably never seen it.

Lesson number two: You do get what you pay for; so pay the money.

Tip: Might be worth setting up on a cheapo and fine tuning on a decent instrument.

Best from Martyn for a peaceful and healthy 2022.

Neil Lickfold14/01/2022 10:19:43
753 forum posts
129 photos

What a great read. You can make your own other probes for the Blake indicator. I would suspect that the 8 spares may still work. I made some for specific jobs, and the one I use the most is about 1/2 the length of the standard supplied probe. It works really well when height is restricted, and when only doing small diameter bores.

I turn it round by hand until it is less than 1 turn out, and then start the mill. Mine is the ht for a long time it was 1metric 0.01mm per division and got it in 1987.

Clive Foster14/01/2022 10:33:28
2988 forum posts
105 photos


Nice to hear that you got sorted out in the end.

My cheapo works pretty well but clearly isn't up to the standard of the real thing. Realistically its as good as I could expect for the price and does the deed, with care.

Guy Lautard published drawings for a Blake style unit that appear to be well thought ot and should work well.Clockmaker standards needed in some places tho'. Its pretty obvious where slack clearances canr unin you day!


bernard towers14/01/2022 14:41:00
390 forum posts
102 photos

sorry Clive but clockmaker fits fall way short of good engineering and toolmaker fits. i say this from the viewpoint of having made two coaxial finders and the fit of the parts has to be a minimum of reamed holes and polished shafts? plungers. short article for MEW awaiting printing.

Martyn Nutland 115/01/2022 07:42:03
18 forum posts

Glad you were interested! I too thought the probes would be interchangeable.


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