Isoma Centering Scope A Dave Sobel Solution and Tribute

DeweyC

NAWCC Member
Feb 5, 2007
2,520
1,090
113
Baltimore
www.historictimekeepers.com
Country
I purchased this from Peter, Dave Sobel's son. Some here had the privilege of knowing Dave and the "sorrow" of buying from him. Although after he qualified you it was much less painful. He had no patience for smart alecs and the first buy or two was to test you out.

For those who did not have the chance to know him: Dave ended his career as a machinist selling high end machine tools; Sixis, Schaublin, Deckel, etc. He had a real love affair with them and he collected everything from early steam models to unique watchmaking tooling.

He had more knowledge of the evolution of machine technology in his little toe than anyone I have known or listened to.

He was the kind of guy who never bragged or self promoted. He just did the work and if he decided you were real, he would be very generous with his knowledge. But if you were a pretender, watch out. He would sell such people whatever they wanted but at double the price. Or more frequently, not at all. Old school.

I attended several auctions with him and he taught me the games played by machine tool auctioneers.

Anyway, I was intrigued by the modification of this scope with the bearing housing. I cleaned the optics and it is as close to accurate as I can measure (I like Isoma's current method of zeroing it in).

I could not figure out WHY Dave went to so much trouble. I opened the housing to find standard Fafnir bearings which I cleaned in situ and reoiled. Then I figured it out.

The stem on the Isoma is a factory mounted Schaublin 12 mm solid collet. Dave wanted to use it on a Tailstock. These have no provision for rotating so once installed, so you were stuck in the one position. Which means you really cannot verify centering (must verify in at least two positions).

So he fixed it!

Everything is a very close fit, especially the back cover with the mounting stem.

If you look closely at the mounting screws, you can the 12 and 6 o'clock screws are on center, 180 degrees apart. But you will notice the other two screws are actually above the center (think 10 and 2 o'clock).

This means the plate can only be installed in one orientation! Very thoughtful and something that certainly would not have occurred to me.

I am still trying to figure out how he machined the housing with plate. There is the seat for the bearings, the very fine threads for the bearing thrust backing, the seat for the back plate and then the back plate itself. The back plate is fitted so closely that after removing the screws, you have to tap a single edge razor into the joint to start lifting it. All the way around.

Dave did this kind of work for everything.

Here are the pics.

Vertical.JPG

horizontal.JPG

Plate.JPG

Boxed.JPG
 

Betzel

NAWCC Member
Dec 1, 2010
460
81
28
Country
Region
Likewise. If you want it done at all these days you probably have to make it yourself. Sounds like you lost a good friend, too. Sorry to hear.
 

wefalck

Registered User
Mar 29, 2011
725
92
28
Paris
Country
Making a centring microscope has been indeed a project idea for a long time and I collected various optical bits and pieces for it, but did not around yet to put this into action ...
 

karlmansson

Registered User
Apr 20, 2013
2,819
206
63
Linköping, Sweden
Country
Making a centring microscope has been indeed a project idea for a long time and I collected various optical bits and pieces for it, but did not around yet to put this into action ...
Please let me know when you get around to it Wefalck! I have dissected a pair of binoculars for the same purpose as well and would be interested to know how you go about it. I found a blog post somewhere a long while ago that I can't find now as to how one gentleman went about it. Stefan Gotteswinter also has a video on his version.
 

measuretwice

Registered User
Jul 28, 2019
132
40
28
Toronto
Country
Thanks for the write up Dewey.

Curious about the moving through two planes? If its dialed in correctly, why is that necessary? I've made spindles for indicator sweeping spindles for high precision applications. The motion itself is a source of error. i.e. when working to tenths, bearing runout can become an issue (I used P4 AC's, but still runout is not zero).

I've got one isoma, nice units, but I really pine for a W12 so have pondered the DIY route. Optics is not a strong suit (strikes one and two lol) but I think there has to somehow be an opportunity with these low cost digital microscopes. Mounting and adjustment aren't to difficult to figure out, what I can't figure out is how to get the graticule there. Doing so electronicially after the fact wouldn't seem to accomplish much, i.e. has to permanently located relative to the camera.
 
Last edited:

karlmansson

Registered User
Apr 20, 2013
2,819
206
63
Linköping, Sweden
Country
Dewey, I'm not entirely sure either why you would need to rotate the scope in the tailstock other than ergonomics. Having any visual reference in the field of view should allow you to see runout when rotating the work. Whether or not that visual reference is centered is probably of lesser importance. For stationary work it is of course very important but most of the time in a lathe the work is intended to rotate, no? I guess if you held it in a milling attachment it would be a different story but then the tailstock shank doesn't make sense.

Wefalck, this is the project I was refering to earlier: PJ OPTICAL - Centering Microscope (google.com)
 
  • Like
Reactions: measuretwice

measuretwice

Registered User
Jul 28, 2019
132
40
28
Toronto
Country
great article, thanks for posting it. I've wanted a W12 scope for awhile, now I'm on the prowl for a pair of binoculars to hack :)

My use would be with rotating and stationary set ups, but I still don't think you need to rotate it. Once its dialed it, it should be good to go for either. afaik the rotating between two planes bit is whats done to set it at centre initially or the occasional check - i.e. make the tiniest of spot drill marks the adjust the scope until its centred in two planes
 

karlmansson

Registered User
Apr 20, 2013
2,819
206
63
Linköping, Sweden
Country
great article, thanks for posting it. I've wanted a W12 scope for awhile, now I'm on the prowl for a pair of binoculars to hack :)

My use would be with rotating and stationary set ups, but I still don't think you need to rotate it. Once its dialed it, it should be good to go for either. afaik the rotating between two planes bit is whats done to set it at centre initially or the occasional check - i.e. make the tiniest of spot drill marks the adjust the scope until its centred in two planes
I guess that by rotating any parallax will become evident. The author of the article does adress this as well though. I want to make one for a W12 spindle as well. I would also like to be able to hold it in my drill chuck for my Habegger though. Should be possible to do both.
 

DeweyC

NAWCC Member
Feb 5, 2007
2,520
1,090
113
Baltimore
www.historictimekeepers.com
Country
Dewey, I'm not entirely sure either why you would need to rotate the scope in the tailstock other than ergonomics. Having any visual reference in the field of view should allow you to see runout when rotating the work. Whether or not that visual reference is centered is probably of lesser importance. For stationary work it is of course very important but most of the time in a lathe the work is intended to rotate, no? I guess if you held it in a milling attachment it would be a different story but then the tailstock shank doesn't make sense.

Wefalck, this is the project I was refering to earlier: PJ OPTICAL - Centering Microscope (google.com)
Karl,

You need to ensure the scope is collimated before doing anything. This is done by making a center in a piece held in the headstock. Then the scope is mounted in the tailstock and the graticule is adjsuted until it is centered on the workpiece center. Then you mount the real workpiece and position it in the scope center.

You need to check the collimation in at least two positions, ideally 180 degrees apart.
 

karlmansson

Registered User
Apr 20, 2013
2,819
206
63
Linköping, Sweden
Country
Karl,

You need to ensure the scope is collimated before doing anything. This is done by making a center in a piece held in the headstock. Then the scope is mounted in the tailstock and the graticule is adjsuted until it is centered on the workpiece center. Then you mount the real workpiece and position it in the scope center.

You need to check the collimation in at least two positions, ideally 180 degrees apart.
Yes, I get that for stationary work but for rotating work any visual reference should do. I've centered work in the lathe using a loupe with a reticle. Certainly not collimated. If it's running true in regards to a center or visual reference, a reference edge or point in a lathe workpiece should be running true. A reference circle in a reticle could be running true with a circle on the lathe work without them being concentric.

K
 
Last edited:

DeweyC

NAWCC Member
Feb 5, 2007
2,520
1,090
113
Baltimore
www.historictimekeepers.com
Country
Yes, I get that for stationary work but for rotating work any visual reference should do. I've centered work in the lathe using a loupe with a reticle. Certainly not collimated. If it's running true in regards to a center or visual reference, a reference edge or point in a lathe workpiece should be running true. A reference circle in a reticle could be running true with a circle on the lathe work without them being concentric.

K
Hi Karl.

I do not use the centering scope for verifying centering (runout) of the work for machining (jewel setting; watch plates, etc). I use wobble sticks or a DTI. I do use it for positioning the mill attachment (primarily) or to verify the positioning of the T/S; or as you observed, in the milling machine.
 
  • Like
Reactions: karlmansson

karlmansson

Registered User
Apr 20, 2013
2,819
206
63
Linköping, Sweden
Country
Hi Karl.

I do not use the centering scope for verifying centering (runout) of the work for machining (jewel setting; watch plates, etc). I use wobble sticks or a DTI. I do use it for positioning the mill attachment (primarily) or to verify the positioning of the T/S; or as you observed, in the milling machine.
Then it makes perfect sense to me! Thank you for explaining.

I still don’t understand the point of being able to rotate it in a lathe tailstock though. The only use there has to be centering.

Karl
 

Forum statistics

Threads
168,218
Messages
1,467,032
Members
48,171
Latest member
garyray
Encyclopedia Pages
1,060
Total wiki contributions
2,955
Last update
-