Could you show the optical prism as there are a couple of types which need different mountings to adjust. Circular movement and centering. Also an adjustment for vertical position. This means a grub screw to set it in the vertical plane. All fixings have been soft setting epoxy glue as araldite will crack the prism(Glass) on setting hard. and causing stress in the glass.

maybe mount on a circular mount with a sloping side so that long grubscrews can be used to move it set at 120 deg.

Close focusis essential and I assume you will mount it on a taper or parallel stub to hold it.

Mark

I made a centring microscope that followed D A G Brown and R O Stephens' design which appeared in the Model Engineer in September 1999. I made a couple of changes: Used different focal length lenses (that were available) and a prism instead of a mirror. In both cases the mirror or prism was fixed and adjustment was made by moving the graticule. The graticule carrier was laterally held in place by four grub screws.

The microscope is a useful tool but suffers from two failings: The object viewed needs to be well illuminated and one needs to be a bit of a contortionist to use it in a vertical milling machine. If I was making one now I would try to put a camera on it and view using a computer.

JA

I made the Hemingway centring microscope which I highly recommend and wouldn't be without. The prism is glued in place and the graticule centred using four screws.

I have experience with optical instruments. I see you have assembled the components except for the spindle mount. the current image location could give you an idea of the adjustments needed. I would lock the eyepiece in place in the tube to eliminate movement. I would also Lac the reticle in. Some eyepieces have a wire ring to hold it in, some have push in type holders some have screw in type holders. I have seen some where the reticle would rattle in place if moved. Clean the reticle well on the eyepiece side prior to setting in place. Depending on the quality of the reticle there can be small black dots on the photoetched side that are not removable. The photoetched side goes toward the eyepiece. If using a small compressed air can hold it upright pointing up to avoid the liquid propellent being sprayed on the surface making a worse mess than you started with.

It looks as if your prism mount slides in a round hole and the fit will effect the adjustment. I would put adjustment screws in for left-right movement and up-down movement. If your image is satisfactory that may be all that is needed. A second set would give an angular adjustment pointing to the left or right and angling up or down.

What I wold call collimating the center finder means that you need to rotate the center finnder 180 deg. to see what errors you have in the 2nd. face. This means you need to adjust half on the graticule and half on the mechanical body.

You carry out this procedure until you eliminate the errors, the graticule should stay central in all positions around the degree scale. Remember to clamp the tailstock if doing it in a lathe.

And I thought I was the only one who had made this mistake – mine, after many hours are 'usable' but nothing like 'right'.

@Michael, thank you (once again) for your ability to find relevant information on the web – I don't think I am any slouch on this subject but you are orders of magnitude ahead of me!

Next rainy day task – dig out binoculars and fix – finally!

One point – a Morse taper shank could prove very annoying in practice as you wind the mill head up to fit the microscope, then wind it down to centre the point on the workpiece, then find you don't have enough headroom to take the 'scope out of the spindle without moving the table. May be shorten the taper radically or fit a plain shank for a collet? (Then you find there isn't even enough headroom to remove the collet on the next job!)

Not so much of a problem on the lathe of course.

Great topic, thank you for sharing
I've just started my own centering scope build (just ordered all the parts, nothing to show yet)

I was wondering though, what size tap did you use for the objective?
I couldn't quite figure it out.

Thanks you,

T

I used a standard Whitworth form microscope thread, probably RMS, since the design I copied used it. The thread is very strange, 51/64" x 36tpi. I did not even try to find taps and dies but screw cut all the threads, external and internal, with a single point tool. This was not difficult since only brass and good quality aluminium was used. However before cutting the threads it is wise to make a couple of thread gauges, particularly for the internal threads, from steel.

JA

Edited By JA on 06/12/2021 14:49:15

Thanks

RMS 0.8 x 36tpi was also what I figured out. My lathe can do TPI, but I also found out that adapters from RMS to M42x0.75 are cheap.

Stuff's underway, looking forward to doing this project, I'll share some pics when I have them.

Thanks again, have a nice day.

Edited By The Scientizt on 07/12/2021 11:09:08