Cut Cylinderical Lens without Frosting , Is water jet suitable ?

Mustafa Umut Sarac · Aug 11, 2013

I found that pouring and setting big cube of acrylic and cutting cylinderical lenses in it is good idea for diy lens. I got a pm from Steve Smith advising me laser cutter. But as long as I see laser cutter frost the plastic. AFAIK water jet cutters used in glass lens production.

I want to learn do water jet frost or scratch the acrylic ?

Umut

Steve Smith · Aug 11, 2013

Laser can give a surprisingly good finish to clear acrylic but however you cut it, I think it would need some polishing.

Steve.

Mustafa Umut Sarac · Aug 11, 2013

Yes Steve , I looked to youtube and laser frost the acrylic heavily. I am thinking to not use spacers , aluminum parts when making lenses and I am thinking to cut everything in one package. I mean acrylic would be the lens and the case. So I cant polish the lens element because they are tightly packaged.

I skip the laser cutting and turned in to water jet. I need to know how it does work ?

Umut

lxdude · Aug 11, 2013

Water jets typically use an abrasive in the water. Even using pure water and no abrasive the finish will be frosted.

www.youtube.com/watch?v=foWsg4rDrKk

Mustafa Umut Sarac · Aug 11, 2013

Thank you very much lxdude. I think there is only one option remained , laser and water wont work.

Does CNC mill cut clean ? I went to GM Fanuc CNC programming course but I did not experience live about plastics. I learned there there is a option for polishing with cnc mill but I dont know.

Do CNC mill cut clean ?
By the way I will look at youtube also.

Umut

Mustafa Umut Sarac · Aug 11, 2013

http://www.youtube.com/watch?v=qyIVZD7rPzM

cnc mill also frost the lens , project is dead.

Umut

bsdunek · Aug 11, 2013

You might look into amateur telescope making. My late uncle used to hand grind up to 14 inch mirrors for telescopes. Here are a couple of sites that might give you some ideas.
http://mysite.verizon.net/res6jv9o/astronomy-trains/id20.html
or
Dead Link Removed

Mustafa Umut Sarac · Aug 11, 2013

Hello Bruce,

I am looking for a way to manufacture your own lens product in mass quantities with the help of most widely available machine park.
To do it , I selected cylinderical lenses because you can route it from the top with laser , jet or mill. I bumped to a technological problem is frosting of cut plastic. I think there might be a honing cnc machine to remove the frost from the plastic. If I cant overcome this , molding the acrylic in to shape is the only answer to problem.

Hand grinding spherical lenses are ULTRA dangerous and they cut your hand until the bone.

Umut

AgX · Aug 11, 2013

Mustafa Umut Sarac said:
Does CNC mill cut clean ? I went to GM Fanuc CNC programming course but I did not experience live about plastics. I learned there there is a option for polishing with cnc mill but I dont know.

CNC milling machines use the same tools as manual controlled machines.

Using a rinsing fluid might have positive effect by removing those cut off bits of plastic. The same time the cooling might be counterproductive on the surface smoothness.

Mustafa Umut Sarac · Aug 11, 2013

Hello AgX,

May be rinsing oil is helpful but how do they interact with plastic , I dont know. I am going to ask all questions to cnc machining forum and report here.

Umut

Chris Lange · Aug 11, 2013

Expecting to create a lens from blanks with no polishing stage whatsoever, and only a grinding stage is a ludicrous idea. Trust me, I've done it by hand using blanks I rolled myself from molten glass.

With glass or plastic you will need multiple stages of polishing, with glass you work down to a mixture of crushed-up sea creatures called Cerium, and do that two or three times to give the glass as perfectly smooth a finish as possible...yet even then without serious lensworking equipment the glass will not be as smooth as a cheap projector lens.

AgX · Aug 11, 2013

Umut, for milling metal an emulsion of special oils in water is applied for cooling and rinsing. For plastics I just would use water with surface active Agent. If at all.

Steve Smith · Aug 11, 2013

I can get a better finish laser cutting acrylic than I can CNC cutting.

Steve.

Mustafa Umut Sarac · Aug 11, 2013

Thank you Chris and AgX.

I opened an thread at cnczone and waiting answers.

Umut

Mustafa Umut Sarac · Aug 11, 2013

Thank you for the tip Steve. How deep can a laser cut a cylinder in the acrylic mass and how depth effect the precision. How do you polish the Surfaces.

Umut

lxdude · Aug 11, 2013

Steve Smith said:
I can get a better finish laser cutting acrylic than I can CNC cutting.

Steve.

Yes.

lxdude · Aug 11, 2013

A CNC could be set up to polish, on the idea that if a cutter can come into contact with a part, a polishing device could also be brought into contact with the part. Numerous polishing stages would still have to be done. I don't think it would be worth the cost to do it that way, but it is technically possible.

richard ide · Aug 11, 2013

AFAIK lens polishing using a pitch lap is capable of holding or adjusting curvature to approx 1/4 wavelength of light. I do not believe that a CNC generated profile would come close to that although possibly the highest quality machine (read highest cost) might come close. Having ground and tested a telescope mirror; I still marvel at the close tolerances obtained by a hand process. There is a very good reason that lenses are made the way they are.

VPooler · Aug 11, 2013

Acrylic is "defrosted" by applying heat AFAIK, from a butane torch. It melts the surface and makes it transparent again. But you would get some distortions I believe.

lxdude · Aug 11, 2013

richard ide said:
AFAIK lens polishing using a pitch lap is capable of holding or adjusting curvature to approx 1/4 wavelength of light. I do not believe that a CNC generated profile would come close to that although possibly the highest quality machine (read highest cost) might come close. Having ground and tested a telescope mirror; I still marvel at the close tolerances obtained by a hand process. There is a very good reason that lenses are made the way they are.

It would be a matter of having the equivalent of a pitch lap mounted to the CNC bed, to achieve the final curvature.

And you are right about the precision possible with hand work. I worked in a shop that was making a small double side 7075 aluminum turbine impeller with extremely tight tolerance on perpendicularity to axis, and width and parallelism between sides. The brand new Hitachi CNC machine could not hold the tolerances. So they bought a new Sunnen (top name) machine to lap the two sides into parallel while maintaining perpendicularity. It couldn't do it without taking way too long- a serious production bottleneck. We ended up doing the finish work by hand using a surface plate with sandpaper taped to it. After a little experience, it was easy to judge the amount of pressure to use and where to apply it. Measure, sand on 400 grit, repeat as necessary. Switch to 800 grit to refine the finish and bring to final size, then put the part in the Sunnen to establish the final finish, or switch to 1500 grit paper and do it by hand.

The final finish was not necessary to bring the part into surface finish spec., but established the look expected of precision machine finishing.
It was a political thing. They bought brand new machines that "of course" could do anything the salesman said, and if the machines couldn't, it had to be our fault-they would not accept that hand finishing could be more precise than one machine and faster than the other.

Mustafa Umut Sarac · Aug 12, 2013

CNC machines can get ultra precise results. It depends on the speed of your spindle. 18000 revolution is enough to shape any desired strange curves on to lens. They use these lenses at military to laser fusion experiments and there is no way to carve a lens to these shapes with hand.
I am researching reports from databases for least 12 years and I found a vast use of cnc machines to carving lenses.

And I researched impeller making in this time range and all your success and final finish depends on your software , not machine. There are lots of new cnc machines everywhere but few softwares to direct the spindle with correct curves. And these softwares are expensive like a new machine . You must buy the impeller specific software. I am still receiving reports , etc.

Same thing for submarine propellers , 25 years ago Toshiba sold cnc cam software to ABB and they sold it to Soviets , with that software , Soviets accomplished to make propellers 5 times more silence than the past. us banned the toshiba for 10 years.

Other thing for lens cnc is the metallurgy of cutting tools and Leica kept it as secret.

Steve Smith · Aug 12, 2013

Mustafa Umut Sarac said:
CNC machines can get ultra precise results. It depends on the speed of your spindle. 18000 revolution is enough to shape any desired strange curves on to lens.

Mine runs up to 40,000 rpm but if you run too fast you will melt the material you are trying to cut.

Steve.

Steve Smith · Aug 12, 2013

lxdude said:
And you are right about the precision possible with hand work.

Absolutely. At work I am often asked to make jigs to aid assembling parts together. My suggestions that our staff are capable of assembling by eye with greater precision than I can make a jig often fall on deaf ears (mainly for small parts).

I usually end up making the jig anyway and proving its inferiority!

Steve.

Mustafa Umut Sarac · Aug 12, 2013

I could tape a slide on to drum with 1/125 mm precision on to its axis in one seconds with bare hands and eyes or register a 70x110 film in 3 seconds. But at 99.

Cut Cylinderical Lens without Frosting , Is water jet suitable ?

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