Setting odd leg calipers

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

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

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

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

Whats an edge finder?

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

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

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.

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

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.

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.

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

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

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

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

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

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.

Neil,

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

David

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

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.