Spring Calipers

[colin beightonParticipant @colinbeighton45883]

The tips of my old spring calipers are very rough and need grinding to a nice smooth surface. The problem is-what shape to choose. There are 4 obvious options-a flat surface,a curved or rounded surface,a knife edge or a point. I can see advantages for all 4 options. What do other people do?

Edited By colin beighton on 22/03/2011 20:33:36

[colin beightonParticipant @colinbeighton45883]

[colin beightonParticipant @colinbeighton45883]

[Dinosaur EngineerParticipant @dinosaurengineer]

A lot depends on the intended use. Are they inside calipers or outside calipers ? If the intended use is measuring/comparing inside diameters with inside calipers then rounded ends are best but but measuring outside diameters with outside calipers curved ends are probably most appropiate. Quite a few experienced machinists will have a number calipers that will have been adapted for specific uses , measuring groove diameters and recesses etc There is no need to grind caliper ends as they are generally not very hard and can be easily filed with small swiss type files and then stoned to get a very smooth surface The important thing is that there are no burrs or sharp corners on the ends. It takes a while to get the correct feel when using calipers due to the spring in the jaws as well as the spring joint . Practicing using outside micrometers with an inside pair of calipers can provide useful experience in the “feel” of calipers.

[colin beightonParticipant @colinbeighton45883]

Good morning Dinosaur. Your reply is exactly what I wanted. I shall proceed accordingly.

Thank you.

[TerrydParticipant @terryd72465]

Hi All,

 

While on this topic, I managed to rescue some M&W callipers from my garage fire. The main parts, while rusted after some cleaning and polishing seem in good condition but the spring loops holding the legs together over the spool have lost their temper. I would like to refurbish these callipers as an exercise. Can anyone suggest methods of re hardening and tempering these spring loops, I’d be grateful for any advice.

 

Thanks in anticipation,

 

Best regards

 

Terry

[John OlsenParticipant @johnolsen79199]

Hi Terry,

 

Well, this is of course advice from an amateur * and as such may be useless….but I would assume that the steel might be close enough to silver steel to be treated in the same way, eg heat to the colour of a boiled carrot, quench, temper to a rich blue colour (Probably on a bed of sand to get the even heat) and see how it goes. You could alway retemper it and retry if you get it too soft, although I would suggest that you don’t do so by burning down another workshop.

 

* (actually I am a professional, but not in the field of mechanical engineering.)

 

regards

John

[TerrydParticipant @terryd72465]

Posted by John Olsen on 24/03/2011 08:16:20:

Hi Terry,

 

……………….. although I would suggest that you don’t do so by burning down another workshop.

 

* (actually I am a professional, but not in the field of mechanical engineering.)

 

regards

John

Hi John,

 

I had to get rid of the woodworm somehow, and it made a great barbecue, even if just for a couple of hours. . The replacement is al,most finished, builders are coming in this morning to complete work on the floor (cross fingers)

 

Best Regards

 

Terry

[TerrydParticipant @terryd72465]

Hi John,

 

My new workshop is nearly up and running, fingers crossed, I’ll try your advice on the H & T and report the results.

 

Regards and thanks,

 

Terry

[mgjParticipant @mgj]

One for Colin – I’d suggest 2 1/2 pairs.

 

Ordinary springbows in a sensible medium size. 3″ or somesuch.

 

Next, the most useful are oddlegs I think – one seems to be always marking out from an edge and they are the ones I feel I use most.

 

Lastly inside, because I almost never use them, inside calipers – digital calipers and internal mike do the work that they did .

 

There is another tool one might consider along with calipers – the optical centre punch. Such an aid to accuracy and repeatability. I no longer mark out without it.

 

 

 

[colin beightonParticipant @colinbeighton45883]

Good morning mgj. Thank you for input.

Another idea to try would be to make some bolt on tips of various shape,rather like the sets of tips one can buy for vernier calipers.

That just leaves the problem of detecting when the tips make contact with the work. I know practising daily for ten years will do it, but I can’t guarantee having ten years left. So I was busy devising some clever electrical gadget when the name RENISHAW suddenly lit up and I discovered I was 40 years too late. As usual!

Simply detecting electrical continuity will probably be good enough.

Thanks again. Colin.

[Richard ParsonsParticipant @richardparsons61721]

Terryd There is a method used by clock makers. For reasons which will be obvious Do Not Do This in your New Workroom.

The clock maker would ‘let down’ the spring by heating it to red and letting it cool slowly. The spring would then be re-formed/re-set.

To harden the spring heat to bright cherry red/carrot colour and quench in brine.

To temper the spring the clock maker would ‘burn off’ the spring. It would be done in a metal pan with a lid and stand. The watch maker would put in enough oil to cover the spring in the pan which would be hearted up. The spring would be heated to cherry red and plunged into the hot boiling oil which should now be on fire. If it is not burning, then set it on fire. Leave for a short time and snuff out with the lid and leave to cool. When cold test the spring.

There is a problem one should use whale oil (spermaceti oil). I have used Tesco vegetable oil but the results were a bit variable. Bill, a clock maker from Milton Keynes, said that he used TREX but he was a professional.

You could scrounge a few bits of old clock spring and try it. If you find a good oil please do not keep it a secret.

Colin have a look at my pictures the album you want is ‘Setting up a tool’ and the forum Beginners questions, it might help.

Regards

Dick

[mgjParticipant @mgj]

Colin – being very polite, but ordinary calipers are for marking out and comparing at ruler readings. They are not precsion instruments for repeatablity. They used to be all that was available, and people got very skilled at using them because they had to.

 

We have moved on. But, if you want to go that route, of course, your choice, but do you really want to get involved in some kind of battery connection or replaceable tips? Not on things that only cost a few quid in the first place.

 

You can very quickly with a pair of digital calipers feel when you are tight on a dimension, or slack, and you can set a dia or depth or insidide dia, and mark out to within .001″. (Personally I don’t like digital calipers, I’d far rather use a mike, but in terms of value per £ of measuring flexibility they are unsurpassed)

 

Calipers are grand, they have their uses – several in fact, but nowadays there are too many other ways of gauging more accurately and more repeatably to trouble with much investment of time.

 

If I might suggest it, clean the tips up on this set, and then buy the next set at a car boot sale for a quid. Rather than getting exotic about the tips, make something interesting like bits of a model or the like!

 

Again, for me, there is no sense in going back to Victorian engineering standards. We always forget that we are where we are now because they were forwards thinking and always sought improvement. There is IMO little sense in faffing about with calipers, then having to carefully fit scrape and file every component, when you can work to drawing and digital accuracy and make something that will work better, first time every time.

Edited By mgj on 25/03/2011 11:52:48

[colin beightonParticipant @colinbeighton45883]

Hello mgj. I agree with all that you say. I’m afraid I was opening my mouth before putting brain into gear. I have read in books that people could set spring calipers very accurately and was really musing on how good they were and how to test the sensitivity required to be that good. But that will be just a bit of fun for myself to do.

Thank you Dick,I will view your pictures with interest.

May I now suggest-topic closed?

Thanks again. Colin.

[Ian S CParticipant @iansc]

This afternoon after I’d used and was putting away my M&W spring dividers I noticed that the spring is cracked to the center hole. Fortunately the local secondhand shop sells cheap tools, and M&W calipers and dividers are some of the tools they have. Don’t know how it happened, they are only 50 yr old. Ian S C

[Gordon WParticipant @gordonw]

I’ve found that the screw fixing/ tap to set calipers are more rigid than screw type. In the right hands they are a precision instrument. We had to fit a ball race to bored hole as apprentice training, about 2″ dia. not that difficult. I recently bought one of these new fangled battery calipers and find them difficult to use, especially on bores, maybe it’s the weight of them. Or maybe they need practice.

[Richard ParsonsParticipant @richardparsons61721]

Terryd –

After writing about ‘Burning Out’ method of tempering I rummaged through ‘Watch and Clock Making and Repairing’ by W.J.Gazeley –Hale (ISBN 0-7090-4995-1). In it the author describes a second way of tempering springs. Unlike the burning out method this one requites the hardened spring to be cleaned back to the bright metal and polished. The item to be tempered is packed and covered with brass filings except in one small area where the polished spring is left exposed.

The whole lot is then slowly and gently heated until the exposed part of the spring becomes dark blue. At that point you tip the lot into cold water and stir.

D

[colin beightonParticipant @colinbeighton45883]

Good evening Gordon. I gather from what you say that setting a caliper to fine limits is

A) possible

B) not impossibly difficult.

All of which is good news. As you are an expert in this type of manual dexterity,can I ask

1)How carefully do you look after and fettle your calipers

2)When you are busy working which measuring instruments do you reach for first?

Regards. Colin.

[John OlsenParticipant @johnolsen79199]

The bore measuring facility on either Vernier or digital calipers has its uses, but is not the ideal method. For one thing, you can only measure the ends of a bore, so it is hard to tell if it has gone bell mouthed. It is also quite hard to get a really good measurement, eg repeatable. I find that, lacking any really swish internal micrometers that it is better to use one of those expanding T shaped bore gauges, then measure that with the Vernier calipers (or a mike) outside the bore. The advantage is that once you have expanded the gauge inside the bore, you can try it up and down the bore and thus detect any bell mouthing, even if you can’t put a number to the amount. Of course this is similar to what you would do with a set of calipers, but I think the T shaped one is a bit easier to use for the occasional user.

 

However, I now do have an internal mike to cover the range from 50 to 100mm at least…it was on a special at the local tool shop. I haven’t tried it in anger yet, but it seems well made, so we shall see. (Incidently I would still have bought it if it had been imperial, I don’t mind doing a conversion to suit the available measuring instruments.)

 

It is of course arguable that for our purposes, the absolute size of a bore is usually not all that critical, provided we do the sensible thing ake the bore first and then make the piston or other part to fit.

 

regards

John

[TerrydParticipant @terryd72465]

Thanks Richard,

 

I’ll try those methods, mostly for the experience for future use.

 

Best regards

 

Terry

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Purely as a matter of interest :

 

(1)

Measuring a bore accurately is intrinsically more problematic than measuring an OD not just because it is more awkward to do but because there is a big difference in the geometry of the measuring setups in each case – basically measuring od’s is a convergent process and measuring id’s is a divergent process . This is all well known stuff so I’ll leave one of our great experts to explain the details .

 

(2)

Some of you may like to explore the use of plug gauges for any bores that really matter or which you have to make repeatedly . For smaller work these are easily made by turning silver steel or gauge plate to near size , hardening and then reducing to the exact dimension . They can be ground if you want but slipstoning is usually all that is needed for little ones .

[Gordon WParticipant @gordonw]

Hello Colin, I am no expert on anything. Just that that was all we had. It’s all about touch and feeling, they are comparators really, not measuring instruments. I’ll probably get a different reading on a mike than the next man, even using the evil ratchet end. The ends of the calipers are filed to a rounded ,ball end, shape, friction joint has a drop of oil about every ten years, not used often. What do I reach for first? The 6″ rule, closely followed by the Vernier calipers. But I do rough work.

[colin beightonParticipant @colinbeighton45883]

Thanks everybody for all your comments. I have learnt a lot.

Regards, Colin.

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