Straitening the needle on an analog display? - Page 1
Forum section: electronics / testgear

author: ftransform
author_rank: Frequent Contributor
timestamp: April 02, 2013, 03:40:28 am
content: So I have a nice triplet meter. Unfortunately when I was removing the visor (in order to buff out scratches on a wheel) I accidentally bent the needle by pressing the case up on it.The needle looks like it consisted of a very light hollow tube, which was clamped flat, so it is like this ===-------------------- originallyThe flat part bent like 30 degrees.What is the proper way to straiten this thing out? I got it in the ball-park using tweezers but I do not think that I will ever get it into spec by doing hand manipulations, and I am also afraid that it has been weakened and that it will snap, so I think I need some kind of jig. It is off on certain measurements by several millimeters currently. I have trouble thinking of a jig that begins cylindrical and then gets flat.Can any watch makers (robrenz?) figure out a solution to this problem? Is replacement the only option?Am I correct in assuming that it was blackened with a carbide lamp btw?

author: amspire
author_rank: Super Contributor
timestamp: April 02, 2013, 03:49:34 am
content: Usually you can straighten it out with your fingers. If it was a sharp bend, then yes, it could break.I am not sure why you are worried about "getting it in spec".If you get it fairly straight, then you zero the meter, and the measurements will be as accurate as usual.Check for meter movement balance. Lie the meter on its back on a flat surface, zero the meter. Then hold it upright - is it still zero?Rotate it 90 degrees on its side. Is it still zero?It the meter is still balanced, it will probably work great even if the pointer is not immaculate.

author: ftransform
author_rank: Frequent Contributor
timestamp: April 02, 2013, 04:04:52 am
content: Quote from: amspire on April 02, 2013, 03:49:34 amI thought that the needle was supposed to be in the same place if you hold the meter with any corner pointed towards ground. I cannot get it in this condition. I think we are describing the same procedure but I am not 100% sure.I read this on some website which I cannot find again (long time ago).I never tried finger tips, perhaps they will work well... it did not even occur to me to not use tools. I was trying to press it up against a flat piece of metal but this was frustrating to say the least. It is bent on 3 axis, not only to the side, so I guess there is some torsional damage near the tubular part.

author: amspire
author_rank: Super Contributor
timestamp: April 02, 2013, 04:37:34 am
content: Obviously you have to avoid pressure on the bearing. If the bend is far enough out from the bearing, then rest your fingertips on the meter display panel and squeeze you fingers to grip the pointer. Avoid any other movement.Then try and push the rest of the pointer back to the proper position.A quality meter movement will stay at zero at any position, but if it doesn't, any meter can be rebalanced. It is just a matter of adjusting the weight on the other three short meter arms near the bearings. The adjustments are ridiculously sensitive. Just see how it was done originally, and try and use the same method.

author: smashedProton
author_rank: Frequent Contributor
timestamp: April 02, 2013, 05:40:23 am
content: If it is really bad, you may have to anneal the needle to prevent breakage. .. my two cents

author: robrenz
author_rank: Super Contributor
timestamp: April 02, 2013, 01:44:00 pm
content: Give us some good close up pictures so we can all have a better idea of what condition it is in now.

author: ftransform
author_rank: Frequent Contributor
timestamp: April 02, 2013, 05:37:58 pm
content: Quote from: robrenz on April 02, 2013, 01:44:00 pmI will have the pictures up in a few days (not around it right now).Is annealing it really ok? I thought they were made of aircraft aluminum, I thought that was a process for steels. I noticed usually when I heat aluminum it gets brittle.IIRC it was balanced with little loops of wire.It is a triplet 310, type 2, made for IBM. Interestingly it has a 0-6, 0-12, 0-30 and0 0-60 scale. I believe it was for telecommunications work.Usually the triplets did not have a 0-60 or 0-30 scale.

author: smashedProton
author_rank: Frequent Contributor
timestamp: April 03, 2013, 05:18:44 am
content: Annealing is kinda funky for non ferrous metals. But the basic idea is the same. That is that you should try to remove the work hardening before you try to bend it back