Scanner Mirror Modification

[planters]

In the thread discussing the Scanner Max scaners I described the modification I am working on to reduce the outboard weight of the mirrors by grinding the lateral, back edges down at an angle to produce a trapazoid cross section. The three optical fabricators that I have spoken with are either VERY expensive or unwilling to work with post pollished mirrors.

I have decided to atempt to modifiy these mirrors myself, but the approch will be different and maybe superior mechanically as well as easier to fabricate. I will use a high speed grinder motor (Dremel) mounted on a lab jack with a 1/8 inch shaft x 0.7mm diamond drill to drill a line of holes along the neutral (midplane) axis of the lateral edge of the mirrors. I already have the X/Y translation stage, the jack and a pair of nylon clamps to secure the mirror. I will mount the mirror face up with its reflective surface protected with a generous layer of First Contact and with an inspection microscope try to drill a semetrical line of holes. I will start with the big 14mm wide EM mirrors and if sucessful then I will see if Pangolin is willing to let me try on a pair or their 8mm's. My biggest concern is that the grinder bearings will allow too much play and that the speed will induce too much vibration. What I would really like is a reasonably priced higher quality alternative, but who knows, it might work just fine.

[absolom7691]

With your quality of work, I am sure you will figure something out. I am curious to see the results and if it decreases the rotational intertia by a decent factor. Good luck!

[mixedgas]

Remember to flood the mirror with generous amounts of thickened water, ie glycol or with a very light oil to flush the grit out and cool the cutting surface.

Steve

[planters]

Absolom7691,
Thanks. We'll see.

Steve,
This is the rub. At these speeds and scale, I will first atempt repeated shallow progress without cooling. I am concerned it will fill the hole and obscure the progress. If I can source a better motor and slower speeds, then cooling will be more likely.

Also , I didn't mention, I will texamine the reflected surface figure before and after the drilling to confirm that there is no change.

[mixedgas]

Eric, Trust me on this, wet the glass. The fluid (very thin oil, water, water with thickening additives, water with abrasives ) is part of the cutting process at the micro scale. Its usually flowed to remove the "dead" glass which otherwise clogs the process.

Usually we built a wax dam around the optic to be drilled. We fill that with some coolant, plain old water works fine for things that do not need a fine finish. The spinning of the tool circulates the water on small applications.

The only glass cutting tool that does not run wet is the belt sander in the glass shop, but it has a habit of cracking thin pieces from the heat.

You may find that clamping your mirror in the mill and using a thin 4" diamond blade with sprayed water (about 20$ at glass art places) is another way.

Pros "block" the optics up with pitch or wax "blocking" compounds. Although we found we could often skip that step at the university shop and hold the optic by clamps if careful.

Slow is the keyword here. A few RPM is all that is ever used with glass.

Steve

[planters]

Steve,

I agree with you and your methods are conventional. However, and I do have experience with large optic machining; rather a lot actually and I would normally attack this that way, but this is where things are a little unconventional. The tiny drill will have a very low surface speed at low RPMs and diamond likes to cut fast. Watch the Itallian glass carvers who use burrs to etch glass. They go fast, but yes they do use coolent. I just don't know how I am going to get it up the hole without submerging the whole thing. I am worried that the Dremel is just not good enough, but uninterupted cutting along the edge with a blade won't work. Bill is right (here at least) that a calculation of the inertia vs stifness needs to be made. The improvement with this design comes from removing mass at the neutral axis, but retaining enough material (about half) to resist aproximation of the tension/compression surfaces. The result is stiff and light ( look at an airplane wing) and if streightforward to fabricate would be an elegant improvment in these mirrors.

[mixedgas]

Sorry, I forgot you have the scope experience.

One thing,
I dont think a coating which passes the mil-spec tape adhesion test is going to be so hard to damage.

Meanwhile, for various reasons, I suddenly find myself without a double commute, so our project is going to heat up. :-)

Steve

[planters]

Actually, most of my big optics experience comes from machining optical blanks for astronomical telescopes; big slow tubes and blades submerged in a slurry of grit and coolent. I used to use pitch/parafan to protect fine surfaces durring those processes. I will add several layers of tape to the First Contact for this project and the notiched clamping blocks (plastic) will hold down the mirror over the two ends where the future lasers are not as likely to strike. I am afraid that any adhesive or coating under or around the edge of the mirror will prevent quick and square fixturing for each side-drilling operation.

Do you think Macona's Q switched 355nm laser can drill glass?

Meanwhile, for various reasons, I suddenly find myself without a double commute, so our project is going to heat up. :-)

OK then, let's see how this moves.

[daction]

Heya, I just finished re plumbing some old concrete buildings at a local university .
The concrete was very hard maybe 40 years old. We used are diamond tipped drill.
Perhaps we did 100 4 inch holes . We cooled the bit with water. Too much water deglazed the tip.
When I talked to someone that drilled holes all the time he said that the slurry was the cutting agent.
He also said that if it works for you that's good too.
Concrete slabs are a bit different to galvo mirrors thou.
Dan

[daction]

Sorry to much water would glaze the tip . If that happens you have to deglaze the tip. Running the bit in wet sand for half an hour should deglaze it.