Michael G
12th Dec 2015, 07:04 PM
One of my favourite bits of measuring equipment is my IRA2 as it makes measuring bores easy - you put the arms into the bore, wind them out until the scale reads zero, remove and then wind the arms in with a micrometer in until the scale reads zero again. The used one I bought some years ago was complete with little extensions that allowed it to be set with ring gauges and used to measure variations from a set size. Not having ring gauges, that bit is beyond me though. I've always wondered how they work but never been game to disassemble mine as to replace it would cost around US$2,500.
359938
Recently on ebay I put in a silly bid for one that had been seriously abused. A few days later for US$60 I was the owner of a rather beat up version - but if nothing else I could see how it worked. Strangely, the seller's photos and description did not mention anything about green paint everywhere...
359934 359937
As you can see, someone had given it an Dulux overhaul. The arms were also a bit loose and the crystal had been cleaned with abrasive. To repaint I had to strip it right down. Lots of tiny parts - the width of the unit is 60mm, and most of the screws were in the 1 to 2mm diameter range. Green paint had gotten in everywhere -
359940
I carefully masked up and resprayed. It has a hammer tone finish and to get something close to the original colour, I actually bought 3 different cans and tried them out to get the best match.
After painting came reassembly. The photo shows how it works - the arms have quadrants on them and are wound in and out using the worm on the main shaft. That is spring loaded so that if the arms encounter resistance (a bore) the worm travels down the shaft. The dial movement (fitted in the second photo) has a pin that rides on the collar above the worm in the first photo. If the worm moves, the collar does. If the collar moves, the needle does. Simple really.
359939 359943
Also in that first photo you can see the pivots for the arms. The pivot is a pin with conical ends and seated in conical seats. As part of the reassembly process I managed to adjust the slack out - I suspect that it may have sprung the frame when dropped
A couple of interesting things I found while taking it apart - the movement is dated July 1961. That makes it over 50 years old. The 'good' one that I have is a whippersnapper by comparison, as it's build date is only 1982.
359941
The black half round knob next to the display can skew the scale across a thou either way. How? the top of the scale is mounted with springs in slots so that it can move. Those cunning Swiss!
359942
The crystal needed to be replaced, so I cut another out from poly carb sheet. The first I used the old crystal for a template but I think it was also a replacement as it turned out not to fit. The second go was made from measurement and was a much better fit. More importantly the scale could be read. I think a previous owner was a heavy smoker as there was a thin brown film over everything inside.
359944
As you can see, it's a whole lot better. All I need to do is sort out a badge
359935 359936
I did hope to convert it to metric but parts are not available for it at the moment if they ever will be - and some parts for the newer versions don't fit the old versions like this, so it will have to stay Imperial (I spoke to Long Island Indicator, seeking some advice about it - their response was that hearing the issues involved they would not attempt to repair it, both because of the complexity and the damage it looked to have sustained. I guess I got lucky)
Michael
359938
Recently on ebay I put in a silly bid for one that had been seriously abused. A few days later for US$60 I was the owner of a rather beat up version - but if nothing else I could see how it worked. Strangely, the seller's photos and description did not mention anything about green paint everywhere...
359934 359937
As you can see, someone had given it an Dulux overhaul. The arms were also a bit loose and the crystal had been cleaned with abrasive. To repaint I had to strip it right down. Lots of tiny parts - the width of the unit is 60mm, and most of the screws were in the 1 to 2mm diameter range. Green paint had gotten in everywhere -
359940
I carefully masked up and resprayed. It has a hammer tone finish and to get something close to the original colour, I actually bought 3 different cans and tried them out to get the best match.
After painting came reassembly. The photo shows how it works - the arms have quadrants on them and are wound in and out using the worm on the main shaft. That is spring loaded so that if the arms encounter resistance (a bore) the worm travels down the shaft. The dial movement (fitted in the second photo) has a pin that rides on the collar above the worm in the first photo. If the worm moves, the collar does. If the collar moves, the needle does. Simple really.
359939 359943
Also in that first photo you can see the pivots for the arms. The pivot is a pin with conical ends and seated in conical seats. As part of the reassembly process I managed to adjust the slack out - I suspect that it may have sprung the frame when dropped
A couple of interesting things I found while taking it apart - the movement is dated July 1961. That makes it over 50 years old. The 'good' one that I have is a whippersnapper by comparison, as it's build date is only 1982.
359941
The black half round knob next to the display can skew the scale across a thou either way. How? the top of the scale is mounted with springs in slots so that it can move. Those cunning Swiss!
359942
The crystal needed to be replaced, so I cut another out from poly carb sheet. The first I used the old crystal for a template but I think it was also a replacement as it turned out not to fit. The second go was made from measurement and was a much better fit. More importantly the scale could be read. I think a previous owner was a heavy smoker as there was a thin brown film over everything inside.
359944
As you can see, it's a whole lot better. All I need to do is sort out a badge
359935 359936
I did hope to convert it to metric but parts are not available for it at the moment if they ever will be - and some parts for the newer versions don't fit the old versions like this, so it will have to stay Imperial (I spoke to Long Island Indicator, seeking some advice about it - their response was that hearing the issues involved they would not attempt to repair it, both because of the complexity and the damage it looked to have sustained. I guess I got lucky)
Michael