Adding a Crosshair

to the

Student Grade Premiere Microscope

I purchased this student grade 20x microscope to assist in indexing cutting tools on my EMCO Compact 5 PC Lathe. The microscope is inexpensive and once a crosshair is added will serve this purpose quite well. Premiere Microscopes does not supply a crosshair for this scope so one must be fabricated.

A crosshair must be made from an extremely thin filament which is also very strong. In the past the web from a black widow spider has been used for this task. Since I live in Tucson, Arizona, finding an accommodating black widow would be easy. Before I went looking for the spider and her web, I remembered that I had a spool of Kevlar thread on hand and figured that I could unravel it to get a single fine filament. Shown at the right is a short length of this thread after unravelling. You can see the individual fibers.

The easily removable eyepiece has the standard recess built into it. It is into the bottom of this recess that the crosshair must be placed. On a better grade of microscope the eyepiece tube will be threaded to adjust the lens spacing and to add the crosshair fitting. If the crosshair is not in the correct focal plane, it will be out of focus.

Before machining the crosshair fitting, I decided to do a quick and dirty test of the Kevlar filament and of the assumed focal plane.

In the image at the right you can see a single filament stretched across the bottom of the recess. It is temporarily held in position with tape. When I looked through the eyepiece, I could see that everything was in focus and would, indeed, work as desired.

The next step was to machine a mounting ring for the crosshair.

I chose to machine the plastic fitting on my watchmaker's lathe. The setup is shown here.

A 3/8" long section of heavy walled PVC plastic tubing was the basis for the fitting. Here you can see it mounted in the lathe chuck ready to have the cut end squared off.

After squaring the end, the slide rest was rotated to zero so that a square shoulder could be cut on the plastic.

The worst part of this whole project is the fine strands of plastic which are removed. They static cling to everything!

The shoulder should be square like this.

It is a good idea to make certain that the turned shoulder fits the eyepiece tube.

I next reversed the fitting in the chuck to machine the other end so that it would align properly with the end of the eyepiece tube.

Shown here are the finished fitting and an extra piece of PVC tubing.

The next step was to add the Kevlar filaments to this fitting. Things get pretty difficult to see during this process and the microscope can be used to make the job easier. I covered the black plexiglass microscope base plate with thin plastic wrap to protect it while attaching the filaments. Super glue was used as the glue for attaching the Kevlar strands to the plastic ring. You do not want to get this on the black plexiglass!

These images illusttrate the attaching of the crosshair filaments.

The fibers were held stretched until the glue set.

Instead of Kevlar fibers, single strands from nylon panty hose could be used.

Below are images showing the modified microscope in use.

The crosshairs.

Indexing a tool.

I mounted the whole microscope assembly onto a magnetic indicator base to temporarily attach it to the lathe bed while indexing tools on my EMCO lathe.

The magnetic base came from Harbor Freight and the post was slightly smaller that the original microscope post. A brass bushing was made to take up the "slack".

This bushing was made from three different diameters of thin walled brass tubing as found in hobby and hardware stores.

The tubing lengths were soldered together. Notice that the largest diameter tubing forms a collar on the bushing.

The wall of the bushing was slotted in four places to allow it to collapse as the microscope clamping knob is tightened.

To do this job correctly, I should have machined the bushing from solid brass bar and slotted it on my milling machine rather than free hand.

I was lazy today! It works.

The bushing was then slid onto the magnetic base post - collar down.

The scope was slid down onto the post around this bushing and the knob tightened.

Here is the complete setup - ready to mount on the lathe bed.

I hope this web page will help others who are trying to machine metal and plastics on a limited budget. Enjoy.