1945 Avometer Model 7 - UK Vintage Radio Repair and Restoration Discussion Forum

Sinewave · 20th May 2019, 10:09 pm

I recently acquired my first Air Ministry Model 7.

Now, I need to open it up. However most of the screw heads have corroded away.

In typical fashion, if I had an item in the workshop which was steel cased with screws like this, I'd drill them out. However, being a bakelite case I'd rather get some advice first from some more experienced restorers.

Thanks in advance!

The Philpott · 20th May 2019, 10:31 pm

One useful set of tools i have yet to get is a set of left handed drill bits. Being brass screws it should be quite easy to centre pop them then persuade them out with a (2mm? 2.5mm?) LH bit on a slow speed. The brass tends to be quite hard in these instruments though, and the bit could start grabbing and spin the whole meter round or shear the screw. Quickly backing off on downward pressure is the best way of fighting this.

If you don't have LH drill bits heating what's left of the screw head with a soldering iron, oiling it with wd40, then tapping it round might work. (Not too much heat though; as you know at this point in history the screws probably go straight into bakelite rather than brass inserts)

Dave

Sinewave · 20th May 2019, 10:37 pm

Thanks Dave,

I think a start with the left hand drills is a good idea. I'd probably be best to use a pillar drill rather than a hand drill for this, which I don't have at home - but we have one at work.

They already think I'm mad at work, imagine being seen putting an Avometer in the pillar drill!

AndyGilham · 21st May 2019, 7:01 am

Sounds lke a bit of gentle persuasion......with a high speed roational drill and a meter clamp down hard......sounds just the job!

I have 2x model 7, a model 7 mk2 and a model 40 mk2 on my very tidy work desk at the moment, I really should move them.... i'm getting a lot of comments at either end of the scale from 'wow an Avometer, i used to own one' to 'get rid of that old rubbish'

Andy

vinrads · 21st May 2019, 7:57 am

Left handed drill bits , I didn't know about these, must look for some , I have tried looking for small thread extractors with no luck , Mick.

brunel · 21st May 2019, 9:27 am

You might find suitable screw extractors here.

https://www.ffx.co.uk/Search/Elastic...0extractor/1/7

Sinewave · 21st May 2019, 9:46 am

The trouble with extractors is you need to drill a hole first and they tend to be bigger than the the 6BA thread of the Avo.

21st May 2019, 1:57 pm

with a dremel and a grinder, destroy the head of the screw and pull out the case.

Sinewave · 21st May 2019, 4:31 pm

Quote:

Originally Posted by Aitor Eneko

with a dremel and a grinder, destroy the head of the screw and pull out the case.

That sounds as though it won't only be the screw which gets destroyed!

The Philpott · 21st May 2019, 6:42 pm

I never really considered LH drill bits until i had a couple of cordless drills with a reverse gear. They are more expensive than RH bits (You knew they would be..) A set of Imperial bits seem to be cheaper than the metric ones (suits me fine..)

Dave

Sinewave · 21st May 2019, 8:50 pm

Quote:

Originally Posted by The Philpott

I never really considered LH drill bits until i had a couple of cordless drills with a reverse gear. They are more expensive than RH bits (You knew they would be..) A set of Imperial bits seem to be cheaper than the metric ones (suits me fine..)

Dave

I'm going to see my ex Fleet Street printing press engineer friend at the weekend (who has every tool known to man), I bet he has some left hand drills - if not, then I'll just buy a small selection.

20th May 2019, 10:09 pm	#1
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	1945 Avometer Model 7 I recently acquired my first Air Ministry Model 7. Now, I need to open it up. However most of the screw heads have corroded away. In typical fashion, if I had an item in the workshop which was steel cased with screws like this, I'd drill them out. However, being a bakelite case I'd rather get some advice first from some more experienced restorers. Thanks in advance! __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

20th May 2019, 10:31 pm	#2
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,105	Re: 1945 Avometer Model 7 One useful set of tools i have yet to get is a set of left handed drill bits. Being brass screws it should be quite easy to centre pop them then persuade them out with a (2mm? 2.5mm?) LH bit on a slow speed. The brass tends to be quite hard in these instruments though, and the bit could start grabbing and spin the whole meter round or shear the screw. Quickly backing off on downward pressure is the best way of fighting this. If you don't have LH drill bits heating what's left of the screw head with a soldering iron, oiling it with wd40, then tapping it round might work. (Not too much heat though; as you know at this point in history the screws probably go straight into bakelite rather than brass inserts) Dave

20th May 2019, 10:37 pm	#3
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: 1945 Avometer Model 7 Thanks Dave, I think a start with the left hand drills is a good idea. I'd probably be best to use a pillar drill rather than a hand drill for this, which I don't have at home - but we have one at work. They already think I'm mad at work, imagine being seen putting an Avometer in the pillar drill! __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

21st May 2019, 7:01 am	#4
AndyGilham Pentode Join Date: Oct 2016 Location: Dover, Kent, UK. Posts: 235	Re: 1945 Avometer Model 7 Sounds lke a bit of gentle persuasion......with a high speed roational drill and a meter clamp down hard......sounds just the job! I have 2x model 7, a model 7 mk2 and a model 40 mk2 on my very tidy work desk at the moment, I really should move them.... i'm getting a lot of comments at either end of the scale from 'wow an Avometer, i used to own one' to 'get rid of that old rubbish' Andy

21st May 2019, 7:57 am	#5
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: 1945 Avometer Model 7 Left handed drill bits , I didn't know about these, must look for some , I have tried looking for small thread extractors with no luck , Mick.

21st May 2019, 9:27 am	#6
brunel Heptode Join Date: Sep 2005 Location: LEEDS.......North of the River Aire. Posts: 872	Re: 1945 Avometer Model 7 You might find suitable screw extractors here. https://www.ffx.co.uk/Search/Elastic...0extractor/1/7

21st May 2019, 9:46 am	#7
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: 1945 Avometer Model 7 The trouble with extractors is you need to drill a hole first and they tend to be bigger than the the 6BA thread of the Avo. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

21st May 2019, 1:57 pm	#8
Guest Guest Posts: n/a	Re: 1945 Avometer Model 7 with a dremel and a grinder, destroy the head of the screw and pull out the case.

21st May 2019, 6:42 pm	#10
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,105	Re: 1945 Avometer Model 7 I never really considered LH drill bits until i had a couple of cordless drills with a reverse gear. They are more expensive than RH bits (You knew they would be..) A set of Imperial bits seem to be cheaper than the metric ones (suits me fine..) Dave Last edited by The Philpott; 21st May 2019 at 6:56 pm.