Screwdrivers and removing early Avo movements

[SeanMcK]

Is there a non magnetic material screwdriver out there, if so who makes it?
So far I have tried sheet brass in a pin-vice like aluminium scalpel/craft-knife handle, no luck. My lastest attempt is cutting up the barrel a B&Q garden label marker pen to form a tube to guide the screw driver, just by chance its a snug fit around some of the screw heads and can actually be used to lift and lower those screws etc. Other thoughts were a drilled out piece of dowelling or a piece of bamboo/cane.

If there are no non magnetic material screwdrivers how then do the 'pro's' do it?

Ta

[Station X]

Goggling shows up several suppliers of non-magnetic screwdrivers including this one:-

http://www.cousinsuk.com/catalog/6/1101/1297.aspx

Item 5 in the list.

[SeanMcK]

Blimey that comes as quite a surprise really, I was expecting these to be antique tools only but when you look at the applications mentioned understandable. You live and learn

[Leon Crampin]

I have removed AVO movements several times using a steel bladed screwdriver. I think problems arise when the steel blade is attracted to a pole piece and is then pulled off. This is likely to result in a degree of demagnetisation although alcomax magnets would be less affected by this maltreatment than the earlier cobolt steel types.

My technique is to use a secure non magnetic spacer so that there is no chance of the screwdriver blade moving off axis. I seem to remember the last time I did this, I used a small piece of expanded polystyrene - wrapped in a plastic bag to keep bits out of the magnet gap.

Testing the basic sensitivity on the 50uA range before and after movement removal by this method revealed no significant change. When replacing the movement, remember the screws are fitted to holes tapped directly in the bakelite front panel and should therefore not be overtightened.

I would be interested to hear the views of the AVO experts on this topic.

Leon.

[Mike-repairman]

I've taken the movements out of two panel AVO valve testers (similar meters) many times with a normal screwdriver with no problems.

[pmmunro]

SeanmMck,

The two readily obtainable non-magnetic materials which I would suggest are brass and austenitic stainless steel.

Of these, the easiest to find is probably brass which can be found at most tips in the form of the rod used for ball valves. The flat which forms the arm which slots into the piston valve can even be cut back and help anchor the rod in a file handle (which will of course have to be sanded and varnished to show due respect to an Avo movement).

If you prefer material free of pre-ownership, model engineering suppliers can probably help, but carraiage costs are a deterent.

Leon's method of placing a non-magnetic shield between the screwdriver and the magnet is another possibility but I woulds suggest that a material less likely to disintegrate might be better - even a piece of corrugated cardboard.

The important point is that there is a risk of a steel screwdriver being drawn against the magnet with sufficient force for the impact to reduce the field strength of the magnet or to cause other damage. The method chosen to avoid this will depend on how often you are likely to want to remove movements and how well you can trust yourself to follow the discipline of following the method chosen as you may find it necessary to remove the movement several times during any one repair process.

I'm probably telling you something you know as well as I do (apologies if I am) but even some tool manufacturers supply screwdrivers with blades wrongly ground - please see attachment - regrinding a screwdriver tip to the correct shape can transform a very unpleasant tool into something amazingly effective.

PMM.

[David Simpson]

Sean, If you live near the coast & know a friendly marine engineer - try & get hold of some small dia. bronze stud bar or rod, & file your own screwdrivers to size. Bronze will be strong enough to handle all the BA sizes of wee brass bolts used in electronics & most of the smaller mild steel ones. As pmmunro intimated - the shape & tip dimentions are important. ie Screwdrivers used for slotted head woodscrews & general purpose work are not really suitable for instrumentation work.

Regards, David

[SeanMcK]

Good stuff in these posts, thanks folks.