Setting odd leg calipers

[WolfieParticipant @wolfie]

So far to get a line to cut or mill to I have simply set my digital vernier to a few thou over and scribed it with that.

Clearly that is never going to be exact so I need a set of odd leg calipers. Now these appear to be like any other caliper ie sprung at the top. So theres always going to be a small amount of give.Whats the correct and accurate way to set them? If you are just touching the pins of your vernier or micrometer it seems to me that theres still room for error as you generally have to account for a bit of 'springiness' when you nudge the calipers together.

Edited By Wolfie on 27/07/2012 11:42:05

[WolfieParticipant @wolfie]

[JasonBModerator @jasonb]

Odd legs are normally set against a rule, set them slightly large then tap on the bench until they close up to size while trying on the ruler.

They are unlikely to be as accurate as your digitals, what quite a few people do is buy a cheap second set of digitals and grind the blades so they run along an edge better than standard ones.

I only tend to use odd legs for rough making say to saw to then any accurate marking is done with a height guage thats if I don't just find the edge and use the DRO to position the tool.

J

[Peter G. ShawParticipant @peterg-shaw75338]

Tubal Cain recommends the following for all firm joint calipers of any variety:

To open slightly, tap the joint on the top of the vice with the legs pointing up. This will jar the legs slightly open.

To close slightly, tap a leg on the top of the vice with the other leg uppermost. This will then jar the legs together slightly.

It has never worked for me! But perhaps my one and only firm joint jenny is too firm! Or something.

Regards,

Peter G. Shaw

[David LittlewoodParticipant @davidlittlewood51847]

Wolfie,

I have never seen any odd-legs with a sprung joint; they have all been of the firm joint type. Like Peter, I find them a pain to adjust, it's very hit and miss, mostly miss.

I'm with Jason on this, previously I would use a surface plate and height gauge, now I mostly use an edge finder and DRO for milling, still use the former on things to hold in a lathe.

David

[WolfieParticipant @wolfie]

Whats an edge finder?

[Boiler BriParticipant @boilerbri]

I used odd legs for a long time and still do, but a while ago i bought a surface plate and height guage. My accuracy increased no end. Now i am on the look out for a vernier height guage.

Mine open and close easily by tapping carfully.

BRI

[Gordon WParticipant @gordonw]

Set odd legs as P Shaw said. But don't worry about accuracy, you can scribe from both edges and split the difference.

[The Merry MillerParticipant @themerrymiller]

You'll have fun doing that if your stock is 50mm wide and you want to scribe a line 10mm from the datum edge.

Len. P.

[David LittlewoodParticipant @davidlittlewood51847]

Wolfie,

At some point we will have to introduce you to the benefits of Google. About 2 seconds there threw up this extremely good video clip showing how to use both mechanical and electronic edge finders:

**LINK**

David

[Raymond AndersonParticipant @raymondanderson34407]

Wolfie,

You are correct that "it's never going to be exact" but then milling or drilling to scribed marks is never going to be exact , A DRO and edge finder will give you "exact" , scribed lines are ok for rough and ready .

Raymond.

[mickParticipant @mick65121]

Why not get a small adjustable engineers try square, where you can set the distance required by using the head of the digital caliper, you should be able to scribe a line as close to size as makes no difference, certainly a lot closer than using odd legs.

[S.D.L.Participant @s-d-l]

Posted by David Littlewood on 27/07/2012 12:43:28:

Wolfie,

I have never seen any odd-legs with a sprung joint; they have all been of the firm joint type. Like Peter, I find them a pain to adjust, it's very hit and miss, mostly miss.

Moor and wright do the spring type that you set like dividers see this link and scroll down to page 12 and see item MW56.

Fine for many quick jobs that dont need DRO, Mark and Drill when not a critical dimension

Stev

[David LittlewoodParticipant @davidlittlewood51847]

OK, not seen those before. Shame they don't have a step on the blunt leg, that makes them harder to keep at a constant attitude.

Just remembered that one of the small tools I made in my early days was a scriber, rather like a woodworkers marking gauge, which is actually far easier to mark with, but a bit more difficult to set accurately. With a screw adjuster, such a tool could be quite useful.

David

[JasonBModerator @jasonb]

I made one of those as well David, think it was in the Unimat lathe projects book and its still knocking about somewhere.

One thing the odd legs are useful for is marking a line parallel to a curved edge though parallel is not the right word I'm sure you know what I mean, something like setting out these rivits.

J

[David LittlewoodParticipant @davidlittlewood51847]

Jason,

Yes, you are correct, I remember it now! The book was quite a good introduction in its day, looks very dated now. His car models are inspiring though.

David

[Sub MandrelParticipant @submandrel]

David

Do you mean Gerald Wingrove? I was in awe of his models when I was a boy, yet I understand he's still going strong!

Neil

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Wolfie, below is a couple of examples of how to set and use callipers.

Strange how terminology seems to be different from place to place. I don't consider odd legs to be that accurate, however, they are categorised as precision tools by M&W. In Stev's link I've always known the type with the little right angle bit on the reference leg to be "Odd Leg Callipers", while the other type with the curved end as being "Jenny Calipers". But of course they can both be classed as Odd Leg or Jenny Calipers, but the one with the right angle bit are normally used on sheet metal as the other type are difficult to use on a thin edge.

Regards Nick.

[David LittlewoodParticipant @davidlittlewood51847]

Neil,

Yes, that's the chap. Glad to hear he's still going.

David

[Sub MandrelParticipant @submandrel]

Nick,

LBSC and others claim it's easy to develop the 'touch' to differentiate less than a thou using calipers. If so, and used as a comparator, not an absolute measurement tool, they are precision tools.

Neil

[Gordon WParticipant @gordonw]

Yes, Mr M Miller, you are correct, my excuse is that I'd just come from the workshop after drilling holes down the centre of some flat bars. Must engage brain before using high tech. equipment. The "touch" required to use calipers is not difficult to aquire, just a bit of practise. After all using a mike or a digital calper is just the same, or to me is more difficult.

[John CParticipant @johnc47954]

Or get high-tech here:

**LINK**

[David LittlewoodParticipant @davidlittlewood51847]

Neil,

What you say about the precision which can be achieved is true of external calipers; I doubt it is also true of internal ones as there is too much scope for misalignment (one direction reads high, the other reads low!). I certainly don't think it could be credibly said of odd-legs. My view of them is that you set them with a ruler; if that is not precise enough, then you shouldn't be using them anyway.

David

Edited By David Littlewood on 29/07/2012 13:48:06

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

(1) Have to agree with David – oddleg calipers are about as accurate in use as your ruler is .

Apart from the intrinsic limit on accuracy they are made worse by the error which comes from the very variable distance down the side of the workpiece that the bent leg can be set .

There is a useful but seldom seen variant of the oddleg caliper which has one leg fitted with scriber in the normal way and the other leg fitted with an accurate round ball .

(2) A far easier way of doing simple accurate marking out is to assemble a DIY set of thick and thin slips and just scribe over the top .

(3) Outside calipers on the other hand can be very accurate indeed when used by skilled machinists . They are still used in a few workshops doing repair work and making ' new for old ' replacement parts even today .

Michael Williams .

Edited By MICHAEL WILLIAMS on 29/07/2012 14:39:57

[NobbyParticipant @nobby]

Hi G.W & Guys
I find if you want a centre line lets say of an 1/2" flat bar . Mark with a felt tip Set odd leg by eye in the centre And the scribe = = from both sides and you may see 2 close lines centre pop between the 2 line. Pitch of spaces with dividers
Nobby

[Author]

Posts