Lens Grinder on rail + no cnc + for diy men

Mustafa Umut Sarac · Jul 17, 2007

I am researching for diy lens grinding . This paragraph is somehow technical and forcing the limits of my english.
As I told at my previous mails and as agx points , lathing is a way for lens grinding.
I am meaning with lathing , a motor is turning with the glass piece and a norrow grinding head is drawing the shape of the lens in 2 dimension on the glass piece and removing the material.
I am a person who wants to manufacture many same lenses for diy camera for example lomo anamorphic lens copy.
I will be needed to carve may be 6 surfaces with high precision.
I have a solution IF you have similar needs , and if cnc electronics , controllers and motors seem to you very expensive.
I think grinding turning head could be built to move on interchangable rails to move for grinding the glass.
These rails could be built relative cheaply at cnc shops one time but can be used hundreds times.
CNC machines work 1/1000 mm precision but even a leica apochromatic lens element have a 1/125 mm precision. That is a important point or barrier , you can cross it on rails.

Best ,

Mustafa Umut Sarac
c copyright

Mustafa Umut Sarac · Jul 17, 2007

may be laser cut titanium spacers can be used as tooling guide

AgX · Jul 18, 2007

So instead of having the lens grinded on a CNC-lathe in a specialised workshop, you intend to use a manual lathe of your own, attach some custom made sort of rails and replace the standard perpendicular movement of the tool by a movement of the tool on these rails instead?
(I guess the proper term for these rails would be `cammed guides´ or something like that.)

Concerning the precision of a lathe, as far as I know a common statement is the perpendicular deviation of the turning axle. I this involves an angular movement the error will be greater at the perimeter to be turned at its perimeter in axial direction.

freygr · Jul 19, 2007

Have you checked to astronomy sites?

Mustafa Umut Sarac · Jul 21, 2007

I am checking everything but it does not mean i m remembering or understanding everything. There are commercial grinders outside , like using magnetic or chemical liquids , or using diamond coated turning circle as the grinder or cnc lathes or negative spherical iron lens molds which shapes the turning glass with liquid barrier.
I think my method is easier if you use laser cut spacers as guide , for example.
If you lost one part or if you have customers who want from your lens design , you can produce it with your interchangable spacers , i think.

best ,

mustafa umut sarac

Mustafa Umut Sarac · Jul 21, 2007

AgX , do cnc shops grind lens ?

freygr · Jul 25, 2007

Mustafa Umut Sarac said:
AgX , do cnc shops grind lens ?

I would not think so, as the abrasives used (link: http://www.covington-engineering.com/grits.htm) would damage CNC machines requiring a very costly rebuilding.

Dan Fromm · Jul 25, 2007

freygr, what Mustafa suggests seems very impractical. But and however, patents have been issued for turning lens elements on a lathe using a diamond bit. No grit is involved.

richard ide · Jul 25, 2007

I have seen a video of machining contact lens blanks made from hydrophilic plastic. I forget whether or not they were finish polished using abrasives. Glass and other mineral crystalline materials used for lenses would be very difficult or impossible to produce this way. I think Mustafa should acquaint himself with traditional lens grinding techniques. If there was a better way they would be doing it.

AgX · Jul 25, 2007

Dan,

Whether one uses a diamond (scraping?) or a carbide grinding tool, the whole procedure will make a mess. Something which could be taken care of with a custom lathe, but sure means asking for trouble at a standard cnc-workshop.

Dan Fromm · Jul 25, 2007

AgX, I think we agree that Mustafa's idea isn't great.

Cheers,

Dan

freygr · Jul 27, 2007

Dan Fromm said:
freygr, what Mustafa suggests seems very impractical. But and however, patents have been issued for turning lens elements on a lathe using a diamond bit. No grit is involved.

Unluckily the chips (material taken off by the cuter) is GRIT and it is abrasive, Silicon Oxide one of the many choices of sand paper. The final polishing of the lens used very fine abrasive. The lathe used in the lens cutting is not a standard Machinist machine tool.

AgX · Jul 28, 2007

Dan Fromm said:
AgX, I think we agree that Mustafa's idea isn't great.

Dan,

To be fair on Mustafa, I have to admit that it was me who raised that idea of selfgrinding a lens element three months ago, and Mustafa liked it. It was just an idea out of the blue as I have no experience in glass grinding (except household DIY...), and soon raised (amongst others) the issue of tolerances.
I also raised the question of spoiling the lathe, but the same time stated that on a sort of customized lathe one could encapsule part of it. Still I think this would be the least problem. As long as one does not go to a cnc-shop around the corner.
Mustafa's idea of using a custom made cam would in principle enable one to use a manual lathe at home, where all those special precautions involved in grinding/turning glass could be cared for.

Whether the basic idea of turning/grinding a glass lens on a lathe is a sound one is still open...

Dan Fromm · Jul 28, 2007

Well, at least one lens manufacturer does turn some aspheric elements on a lathe. But I don't think the tolerances needed can be achieved with the typically wobbly (not very) really good lathe.

If the bit follows a cam, where's the need for CNC?

AgX · Jul 28, 2007

Mustafa's idea, as far as I understand, was to calculate the lens and, most important here, the lens profile. And with that data have a sort of cam machined corresponding to that profile on some cnc machine .

jmcclure · Jul 28, 2007

Many years ago (about 40) I worked for a company that among other things made various products that used both custon lenses and mirrors. The machines that they were made on were refered to as lathes. They did not look at all like the lathes seen in a machine or woodworking shop. They all had a turntable upon which the blanks to be ground were placed. Above this was placed another turntable with the grinding tools. The lower one (containing the lens or mirror blank rotated on a fixed center. The upper one(containing the tools) also rotated about its center, it also swept from side to side becoming off center as required and was allowed to roll as necessary. The tool and finished product blanks coud be flats or molded blanks as required. Lots of water flew around the room where the machines were located. A keen eye was needed to insure that the grits and water were placed to keep the grinding proper. For a simple description of the process and how to make simple lenses and mirrors look at the instructions give in telescope making books. The easily made shapes are made by "walking around a barrel". The machines duplicate this process.

Many of the lenses start with molded blanks which only need to be finish ground and polished.

While these older machines were rather crude I am sure that the newer ones are very much more technical in design.

The turn tables for flat products were flat and those for rounded products had a radius shape. Depending on the lens being ground the blanks could be on either a raised or concave table with the tool on the oppsite.

AgX · Jul 28, 2007

To my understanding these machines you describe are the typical or common lens grinding devices in the optical industry.
However they employ another principle than we here understand as a lathe.

Mustafa Umut Sarac · Jul 29, 2007

If you search google as lens grinding subject , you find there are many machines to cut the lens with spy satellite precision with lathes and diamond tip. AgX s idea is great. And other story , archeologists found at europe some aspherical lenses which turned 1000 years ago by vikings. Rodenstock says they are good as 1950s aspherical lenses.
They didnt have electric motors , cnc created lathe parts but they succeed it. May be we can learn something from the past.
One of my friends is a cnc repairman and i asked the price of 15000 rpm electric motor , it costs 15000 dollars. He said i can do the same with 6000 rpm machine with using gear train and it costs a 6000 dollars.
I got 15000 rpm specification from a diamond turning lathe seller for lens grinding. This is a thing worldwide used , accepted technology , i removed the precision moving sensors , control electronics and piezo motors and changed them with basic spacer - or cam -.If you really dive in to this business and search for yourself , you find that if you havent got 20000 dollars , you come to my port.
The best question is this :
What is the lowest rpm for to diamond tip turning lathe a glass lens ?
As we know , human power can shape a 0.7 meter diameter glass telescope mirror in few hours. I am talking about coarse spherical shape.
We are lazy , we have no waiting customers and we dont want too much motor noise in home.
What can be the slowest turning lathe speed without loosing precision or increase low frequency vibration.
Think you are viking and your head is in danger , you have to make the lens with a turning lathe - it is believed viking used one - .What do you do ? Escape ?

Best ,

Mustafa Umut Sarac

jmcclure · Jul 29, 2007

Mustafa

By using a high speed die grinder with a suitable burr held in the lathe holder one could grind any necessary shape on a cnc lathe. Glass worked in a lathe can be held in place with a suitable adhesive. Different burrs would be required for rough and finish grinding and also for polishing. Large amounts of coolant would help flush away the grindings to prevent machine damage.

This way only the burr would have to operate at very high speeds. Some die grinders easily work at 15,000 RPM.

By the way high speed grinders a sometimes used this way in machine shops even on manual control lathes.

The clasical method of lens making is to use two pieces of material. One for the finished piece and the other for the tool. If you place them together with a suitable grit and water you only have to use the proper motions to produce a lens. ie walk around a barrel and move the tool piece in the proper way while in contact with the lens blank. This technique has been used for hundreds of years to grind various shapes. It has been suggested the it was possible that at least simple lenses were used in ancient Rome and Greece.

Mustafa Umut Sarac · Jul 30, 2007

jmcclure said:
Mustafa

By using a high speed die grinder with a suitable burr held in the lathe holder one could grind any necessary shape on a cnc lathe. Glass worked in a lathe can be held in place with a suitable adhesive. Different burrs would be required for rough and finish grinding and also for polishing. Large amounts of coolant would help flush away the grindings to prevent machine damage.

This way only the burr would have to operate at very high speeds. Some die grinders easily work at 15,000 RPM.

same question : what is the lowest rpm possible for to turn the glass with burr ? and why slow speeds are not the subject ? what happens if the speed lowers very much for example 200 rpm where the motors come less than 100 dollars ?

jmcclure said:
Mustafa
By the way high speed grinders a sometimes used this way in machine shops even on manual control lathes.

The clasical method of lens making is to use two pieces of material. One for the finished piece and the other for the tool. If you place them together with a suitable grit and water you only have to use the proper motions to produce a lens. ie walk around a barrel and move the tool piece in the proper way while in contact with the lens blank. This technique has been used for hundreds of years to grind various shapes. It has been suggested the it was possible that at least simple lenses were used in ancient Rome and Greece.

I have doubts about the use of female mold at ancient times , if they used it , which technology produce it ?

lets come to recent times , what can be the material used at female turning mold ? tool steel ? i heard cast iron but i dont know why they use it ? can you explain ?

and i saw at biggest military and esa telescope mirror producer for chile , at moscow based company , they were very coarse steel burr turning the satellite optics before liquid based abbrasive work .do we need to do the same at our lenses with female mold +liquid technology ?

And what about the chaotic vibrations of abbrasive liquid between glass and female mold ? Are they less than diamond turning ?

it is even difficult to know when to stop liquid abbrasive work ?

Where will we find liquid abbrasive ? is it expensive ? is it possible to use the abbrasive liquid after contaminated with glass particles ?

I think higher the rpm , higher the frequency of vibration and smaller the wavelenght of wobble ? May be we need to lower the force in to the glass by diamond turning for to get more peaceful vibration with hyper low rpms ?

Best ,

Mustafa Umut Sarac

Mustafa Umut Sarac · Jul 30, 2007

I HAVE a new idea , if we made a hole in the flat panel and inject high pressure abbrasive liquid through the hole and if we contact the high pressure norrow liquid zone with moving glass , we can shape the glass !!!!!!!!!!!!

AgX · Jul 30, 2007

Mustafa,

With your last idea (moving glass), if I got it right, you are imitating industry techniques.
But I thought you were trying to come up with a technique people at Apug could reasonably employ in their home workshop.

I assume that grinding lathe with that cam would be the most reaonable way so far. Though I'm still not sure where on the lathe to position such a cam best.

freygr · Jul 30, 2007

But I'm worried about a person trying the cut the lens without water. The glass powder will slowly kill you if you breath it long enough, just like Black Lung!

Mustafa Umut Sarac · Jul 30, 2007

Yes AgX , my main concern is homebrewable technologies. My last post is very interesting and it can be made with magnetic liquids.
Magnetorheological finishing commercial technique employ a wet long horizontal zone as a freezed magnetic liquid zone but my method is doable at home. pump glass
xxxx mag xxxx plate glass
xxxxxxx netic xxxxxxxxxx magnetic liquid glass
xxxxxxx wind xxxxxxxxxx with particles inside glass
xxxx ing xxxx plate glass
pump glass rotating and moving on
a cam

Mustafa Umut Sarac · Jul 30, 2007

pump
magneticxxxxxxxxxxx wallll glass
winding xxxxxxxxxxxxxxxxxx glass
xxxxxxxxxxxxxxxxxx glass
xxxxxxxxxxx walllll glass rotates and moves on cam
magnetic liquid
with particles inside
pump

Lens Grinder on rail + no cnc + for diy men

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