Isoma Centering Scope

[Twizseven]

Just obtained an very nice Isoma Centering Scope.  It was an Ebay purchase and was an absolute steal.  It has built in illumination but the bulbs are all blown.  I believe they are 3.5v.  They are very tiny edison screw bulbs about 13mm long and 6mm dia.  Does anyone know the correct bulb model designation.

Colin

[Bluechip]

Lilliput Edison Screw ??  L.E.S.   aka E5

Comme ca

https://cpc.farnell.com/search?st=LES%20bulb

Dave

[nj111]

Useful bit of kit, I made one from the hemingway kit many years ago.

[Twizseven]

Dave,

Thanks for that link. Trouble is they do not show any 3.5v versions

The bulbs that are currently fitted only have the words ALBA stamped on them, no volts/watts info

Colin

[steamer]

Colin

What is the plug termination?    Mains?     220volt?

Something else?     It doesn't appear to have much room for any kind of electronics or power transformer....

Dave

[Bluechip]

Dave,

Thanks for that link. Trouble is they do not show any 3.5v versions

The bulbs that are currently fitted only have the words ALBA stamped on them, no volts/watts info

Colin

They are pretty much obsolete now. You ain't gonna like this but when I was at work we used a lot of the damn things prior to LEDs appearing.  I certainly had them in 1.5V, 3V, 4V and 6V.
I had DOZENS of each and slung them out some 6-8 years ago. Some had a lens moulded into the glass end. Also dumped were a great heap of the wire-ended lamps .. all sorts of voltages.

No-one wanted them. Neither did I so off they went. 

If you are at 3.5V or so you are in white LED voltages. Quite a lot have a V_f  around there so you may get away without a series resistor, MAY ?  

This one is a bit on the high output side ... but depends what the scope was like with the incandescent lamp >> 

https://cpc.farnell.com/multicomp/ovl-5521/led-5mm-mega-bright-white/dp/SC11563?st=white%20led

Dave.

[Jo]

Why do you think it is 3.5V? and how are you going to power it?

Deckel provide a 6v socket to plug their Isoma scope into.

Jo

[Bluechip]

Why do you think it is 3.5V? and how are you going to power it?

Deckel provide a 6v socket to plug their Isoma scope into.

Jo

Which you?  Colin or me ??

D.

[Jo]

Colin in his first post said 3.5V 

I can't see why you couldn't use a different voltage if you can find bulbs that fit if you don't have a PSU.

Jo

[Twizseven]

Dave,

I had a feeling that might be the case.  I guess I could go up to the 6v versions but i would like to know the light output.  I do not want to put bulbs in which get too hot.  Perhaps this is the best reason to go to LEDs. If can find ones which do not need resister that would be ideal.

I found a comment on a woodworking where someone had an identical scope and it was stated the voltage was 3.5v.  The ones in this scope have i think been blasted by a somewhat higher voltage as there is a odd 3 pin plug fitted (marked as 125v which has two vertical flat blades and a 'u' shaped earth pin.  Only has twin flex connected though.

I have in fact just found some 6-12v E5 LES led lamps on ClassicCarLED's which look to have a very low height bulb/led assembly.  Having used bulbs from them in my car I have taken a punt and brought 4 to try.  Can test them on bench PSU and then go through my selection of spare wallwart PSU's to see what I have suitable.

Colin

[Twizseven]

After some searching I located some E5 LES LED lamps.  These marketed by ClassicCARLEDs as replacement car instrument bulbs.. GLB280E5 LES Lilliput LED Bulbs 280  I ordered the White Negative ground versions.  Total price £3.98 inc postage.

They arrived this morning.  When screwed into the bulb support they are a fraction shorter than the standard bulbs by around 1mm.  I got roumd this by turning a 1mm thick brass washer to push the holder a further 1mm down the central pillar.  Connected it to benchtop PSU.  Threw 6V at it and it worked. 

Went to look for a wall wart PSU, couldn't find any then realised had junked most of them last year.  I suddenly spotted one at back of shelf and pulled it out.  Now there is a surprise it was a 6V PSU.  The cable had snapped its insulation as it exited the case, but amazingly the case was held together by pair self tappers rather than being glued/heat welded.  Open it up, desolder cable, reconnect the cable, figure of eight knot to stop it pulling out and couple of layers of heat shrink to clamp the cable in place, and all was good.

Found red and black powerpole connectors, crimped to the cable from the scope and PSU.  Plugged then together, crossed fingers and switched on.  The end result can be seen below.

Very happy with it.  Just need to fit on mill and test.

Colin

[steamer]

Saweeeeeeet!!!!

Dave

[Twizseven]

Thanks Dave.  Was good deal bought on Ebay (advertised at £20, offered £50, he countered at £60, I snapped his arm off) and paid £64 including postage.  £3.98 for 4 bulbs, Spare instock transformer and connectors.  A fantastic tool for not a lot of money.

Colin

[steamer]

I have a clone of that, though it doesn't have a built in light.    I've only used it in anger once!    but it seems a really nice tool!

Dave

[Mcgyver]

Colin, glad you got working, a very nice tool.  I've been looking for one as its often used in horological work.   For example, the hauser M1 jig borer was often purchase without a revolving spindle but with precision punch.  Hole locations could be laid out to tenths and then moved to a mill/lathe for machining with a scope used to pick up the punch mark

Can you comment on how its adjusted?  I was under the impression there were two plane adjustment screws for adjusting to centre but I don't see anything on it?

thanks

[Twizseven]

Mcgyver,
I was not sure about adjustment. I though the screws would be at the base near the lights. The only set of four screws I could see were I thought holding the eyepiece assembly in place. I managed to find an instruction sheet on the Isoma site and it showed these 4 to be the adjusters for the reticule. I have not tried it on the mill yet as am away helping daughters partner to build fitted wardrobes he has designed.
I am trying to decide what to use to produce a punch mark to calibrate against. Ideally I need a 20mm diameter parallel sharp pointed lathe centre. I can then use the same Bridgeport R8 collet to ensure concentricity. Initially I may just centre it on a random punch indent and then rotate it through 360 degrees and see how much it moves of the punch mark (if at all) as rotated.
Colin

[Mcgyver]

Maybe try making the smallest of dimples with centre drill or spot drill?  with a rigid cutter the mark should be right on the spindle's axis no matter what and it eliminates some sources of error with making/holding a punch