| Hezz |
Guys,
I finally started building my hand made lens to replace the fresnel between the objective and the LCD. This is kind of an experiment and I want to document what I'm doing here in case anyone else wants to do the same thing.
I started out laminating several short pieces of 2x6 together. I didn't have any long clamps but I did have some pony clamps left over from a speaker building project. They work quite well for things like this and they are relatively cheap.
I used polyurathane wood glue because I had some and because these were old pieces of wood that were kind of warped. The polyurathane glue foams up and expands somewhat to fill in oarger gaps.
I didn't take a picture of the glue up phase but here is a shot of the block mounted on a stand that I make from an old disgarded semi wheel. I don't have a workshop so I am somewhat limited but I do have a welder and so I build this pedestal stand out of scrap metal for nothing since I had the scraps laying around. |
|
|
| Hezz |
Next I printed out a 1:1 profile of the lens curve which I hade calculated in the freeware version of OSLO, which is a lens design program. My printer can print on 11x17 paper so I drew the profile of the lens in TurboCAD and then printed it at it's 1:1 scale. I had a picture of the printout but it wasn't very easy to see the lines so I'm not including it here.
I then transferred the profile of the lens onto the sides of the wood block after trimming the block down the 12.5 x 9.5 size. Then I went to work with only hand tools. I first used an old circular saw to remove as much as I could close to the lines. Then I made cuts of varying depths close together making sure not to go too deep past the lens profile.
I then took a 1 1/4 inch wood chiesel and cleans it up the best I could on the long profile which was with the grain of the wood. It is not possible to get this really perfect and that is not the idea. Just as good as I could get it without diggint into the lens area if possible.
Here is a picture of the block with one contour cut with a chiesel. After the chiesel I cleand it up some more with a medium sized wood plane.
Don't you just love this. I feel like Roy Underhill. Making high tech things with low tech tools is really cool. |
|
|
| Hezz |
Next, I made a scraper and guide out of a piece of 6 x 18 inch sheet metal. This is thich enough metal so that it doesn't bend too easily or it will through off the measurements.
I then took the saw out and made some cuts that cut off large pieces of material on the ends. I kept doing this until I goe as close as I dared to where I thought the lens sphere would be.
The only reference points I had were the edges and the center of the lens which is the highest point. After taking as much as possible off with both the cirular saw ans a combination of hand saws I then went to a large wood rasp. Most of the rest of the shaping was done with this wood rasp and a little bit with a plane.
After a while I started using the sheet metal curve guide to tell where the high and low spots were. When I got it about as close as I could with the tools I was using I took a orbital radial sander and cleand it up a little.
It is important when doing the rasping and the sanding to take even arcing downstrokes from the center of the lens sloping down to the edges. The short side edges were already very close and so most of the work was on the long side edges.
I walked around the piece taking even strokes making sure not to flattern or take material off from the crown of the lens because it was already at about the right height.
So far everything I have described is about 5 - 6 hours work in two days. When I got the lens curvature about as good as I knoe I could get it then I made a quick sanding and applied some bondo to the gouges that I had made do to a combination of sloppy chieseling and impatience.
Here is a photo of somewhere along the process. |
|
|
| Hezz |
And another photo of how the mold blank looks right now with bondo curing on it.
The mold blank is actually more spherical in shape then this photo makes it look. Because it was 40 degrees outside the bondo wasn't curing very fast so I had to hang it up for the day.
I now have to make a special tool to get the lens mold blank perfectly spherical. That will be done in a few days as I have to get a bottle of dry garnet power or course abrasive powder to make the next tool. Stay tuned for the next part hopefully not too long. |
|
|
| ace3000_1 |
| nice work hezz, it will be interesting to see how it turns out, by the way u better empty that bin in the background lol |
|
|
| Hezz |
Ya thanks Ace,
It's the recycled plastic bin so it doesn't get emptied with the other trash. It has a tendency to stay because we have to take it ourselves to recycle it.
Hezz |
|
|
| ace3000_1 |
no probs buddy was just having a joke, what material are u going to make the lens out of? i hear that acrylic or plexi is near to optical grade, i know polycarbonate is too. actually how thick is the lens going to be?
Trev |
|
|
| Hezz |
It's Ok I knew you were joking but I had to explain that thing because it does look kind of stupid in the picture.
Anyway, for a long time I was going to melt down optical grade acrylic pellets but I don't really have the equipment for that. I found a company that is near me that sells a deep clear polyester casting resin that is really clear and I think it will work reasonably well.
The finished lens will be about 3 1/4 inches thick at the center and I worry somewhat about reduced light output but if it creates a superior image I will be willing to sacrifice some light output.
The polyester resin is really easy becasue it is a room temperature pourable thermoset plastic I just hope I can mix it without introducing many air bubbles.
Hezz |
|
|
| ace3000_1 |
u can melt plexi down useing that bbq in the back ground, its like melting chocolate u need 2 pots one with water and the other inside with the plexi, a heat gun over the top will help speed up the process, i think the better thing to use would be olive oil as it doesnt boil and gets hotter.
Trev |
|
|
| Doon1 |
Cool Idea! I'd like a copy of that TurboCAD file if it's ver. 5.0 or earlier.
To remove the air bubbles from your "mix" put your electric sander upside-down in a vise or between your knee's if you can stand it and place your mix container on it while your mixing. All the bubbles will rise to the top very quickly. Don't forget to take the paper off the sander first.
John |
|
|
| Hezz |
Ace_3000,
What is the water for. To increase humidity inside the oven. I'm going to try the polyester casting resin first and if it doesn't work I'll try clear plexiglass. I know that you can buy optical grade acrylic in pellets because thats how they make a lot of small lenses. They would be easier to melt but then again I can get remnents from a local plastic sign shop for 1 dollar a pound. It would take a lot of little remnents. Thanks for the ideas, I have to calculate the exact volume that I need for the lens.
Doon1,
I didn't save the Turbocad file becasue all it was was an arc with a 12 inch radius and then I drew a line 3 1/4 inches from the upper point down and then drew perdendicular lines to the circle and then cut the larger portion of the circle out. It was in version 8 anyway. Do you have an older version of turbocad?
This lens has about an 18 inch focal length. My DIYLABs triplet fuocuses at about 17 inchs from the LCD. Anyway I wanted a longer focal length to reduce the thinkness of an already thick lens and because I want to get a larger, longer focal length lens in the future.
Hezz
P.S. Doon1, If you need I can e-mail you another file in DXF format. Your older TurboCAD should be able to read that. |
|
|
| Hezz |
Ace_3000,
After thinking about it I realized you were talking about a double boiler. Will that get hot enough? Acrylic needs to be heated to nearly 400 degrees to melt I believe. That would require some more direct heat wouldn't it.
Hezz |
|
|
| ace3000_1 |
| quote: | | After thinking about it I realized you were talking about a double boiler. Will that get hot enough? Acrylic needs to be heated to nearly 400 degrees to melt I believe. That would require some more direct heat wouldn't it. |
heya hezz, ya plexi needs about 300deg c to melt it into a liquid, thats why i said use olive oil, u can get olive oil upto that on a stove no worries, (trust me ive had it smoking before lol) the double pot method is so u dont burn the plexi with direct heat, thats why u use the same method with chocolate , it will burn on the bottom if u dont use this method, in a industrial machine its not much different, they use air presure to push the pellets through a large pipe with like an electric type boiler surounding it, i think they use oil too not sure but its very hot and its a fast process, in our diy setup we dont have a termostat so we would have to keep an eye on it and by using oil u wont burn the plexi to the pot, but dont let it boil, the best pot to use would be a stainless steal pot as it wont have paint on it and will beable to conduct heat better on the sides, a pot that is also abit thicker on the base then the sides would be ideal as the base will retain the heat for longer while pooring it, in an injection moulding system they use presure to stop the plastics from boiling and also to get them in a very liquid state, not sure if a presure cooker would work, somthing we would have to experiment in.
Trev |
|
|
| Hezz |
Update,
The big lens project is on hold for a couple of weeks through the holidays until I get some more supplies and cash. Christmas soaks me dry. I went to several places locally to try and find some coarse grit aluminum oxide powder. All I could get were 50 pound bags of the stuff and I only need a pound or two. I may have to order some over the internet as I don't want to spring for a large bag that I won't use.
Hezz |
|
|
| Psionic |
hmm...
How are you going to melt plexi over that?
If you just stick the plexi on the mold, then heat it, and wait for it to conform to your mold, i dont think it is going to be even.
I think you should have made a female for the lens instead of a male.
If you have a female, you could melt a piece of lexan glass over the hole. (Imagine a block with a hole in it that is the exact shape of the lens. This way when you melt the glass, it will conform perfectly to the hole.
I dont think wood is what you want either, I would have make a box that is the length, width and height of the lens plus 1 inch in each dimension. Then I would fill that box with concrete or plaster, and create scoops to scoop out the excess concrete. The scoops would have to be like 1/2 circle shapes that are the exact curvature of the lens.
Let me know if you dont understand what im saying |
|
|
| jcbklyny |
Psionic has a point.
I love the idea of big lenses and making your own would be even better... but I dont think wood is the way to go. |
|
|
| buckster |
| I could be way off guys, but I get the idea Hezz is making a form that can be used to make the molded shape in a casting medium, then the melted plexi can be poured into the mold. |
|
|
| Hezz |
OK Guys here's the scoop,
I found a nearby source for silicon dioxide powder so I have now cast the tool to do some better grinding of the mold blank. And yes, I know that wood will not make a good lens but it does make an easy to form mold blank!!!!
Here is the process for those of you who don't quite see what I'm doing.
Step 1: Hand forming of a mold blank out of scrap wood. This is because wood is easy to form.
Step 2: Once the mold blank is contoured to sufficient size and quality it will be used to make a mold in a high grade sand or plaster for making the rough lens blank out of optical grade thermosetting plastic. This is done to make the lens cheap to produce. It would take a year of heavy work to hand grind a lens this size out of glass and the glass lens blank would be expensive.
Step 3: Hand grind and polish the rough lens to optical standards using hand work and custom made tools.
Step 4: See if it works better than a fresnel.
Hezz
Some pictures are in the works but I don't have a digital camera so I have to wait until I take more standard pictures. |
|
|
| Hezz |
Sorry,
it was silicon carbide powder. What was I thinking.
Pisonic, you must first have an accurate representation of the original lens before you can make an accurate female mold. We are talking about a process here which will make something that is extremely accurate not hacked out. Although it may seem that way. I have thought about this a long time and also have three years education in manufacturing engineering. While I'm not an expert this process is designed to reduce hand work to acceptable levels. If you just wanted to make one mold you might be able to hack one out with a beach ball impression in sand but it would not be very accurate. I wanted something that I could easily make several lens blanks with in case this turns out well and others want to buy a lens blank.
Also once the plastic lens is cast it will be much more work to get it right if the cast part is not very close to final dimensions. Our goal is to get the lens within a couple millions of an inch to spherical condition. If not that to within at least +\- .0001 inch.
A little more work up front but it offers much greater repeatability.
Hezz |
|
|
| ace3000_1 |
maybe a pre heated mould would work too as another hint so the plexi dont cool down too fast, i dont think hezz is using plexi psonic he is using some other resin gear.
Trev |
|
|
| ace3000_1 |
yeah thats what i was thinking in but with plaster, if u add some bondcrete into plaster the stuff sets rock hard, u could make a 2peice mould with it to separte the lens from the mould after pooring, u would probally have to oil the mould too before pooring.
Trev |
|
|
| Hezz |
The two piece mold out of hard plaster is a good idea although it would leave a parting line. This would be less of a problem though than an indentation in the first mold because that would leave a divit in the final lens that would have to be sanded out.
It will take some time to get the first mold blank into good enough condition but once it is the rest shouldn't be to hard.
A four part hard plaster mold would be ideal because it would be easier to remove. The beauty of sand is that it is simple but it is not as accurate. It would require more hand finishing.
Any good ideas you guys have are welcome.
Hezz |
|
|
| ace3000_1 |
Hezz have u done any foudary work before and made these sand moulds? i have, and what they do is craft the thing they are going to mould out of wood (ive seen plaster before too), then mount that on a peice of marine ply and the actual mould is just a casing like a small rectangle frame with a locating pin on each end and what they do is put the wood in the middle that has also the locating holes and then put the mould together and then ram the sand into it, then the mould is separated and the wooden male mould is taken out then the mould is placed back together ready to be poored, its an old method but its still used very widely today, and most things get machined for the clean up process these days, but its a thought worth to keep in mind cos it is very acurate, it depends what size sand grit u use to get a better finish, silica sand would be the best, u just mix that with oil and a small amount of clay, once its rammed its hard as a brick, after the poor all u do is knock it on somthing solid for the dirt to break loose and u have your articale in the middle.
anyway hope it helped sorry for the crappy post its late here lol
Trev |
|
|
| Dnt32 |
I worked for a foundry too, several actually this proccess thaT YOU are attempting has my attention. I would like to also say that one of the foundries I worked at, had a diffeent process than the othes I worked for. They would use wax( not parafin) lol
Then they would dip the wax parts in sand and solutions which would make a kind of firebrick around the part then they would melt the wax from the mold then pour the metal into it for the finished product with minimal clean up work after.
What I was thinking if you could get a hold of some of that wax you cuold cut/carved grind it then make a mold around it etc.. just ideas |
|
|
| Psionic |
DISCLAIMER: I'm no expert in anything said here, its all based on personal experience and opinion.
Now that we have that out of the way...
I have also thought about this process for a long time, it is very close to the cylindrical anamorphic lens project I was going to do.
I dont have any formal education in this area, but I do have alot of experience making custom body panels for my honda.
To make body panels you:
1) carve a male out of blue styrofoam using a rasp and sand paper
2) spray laytex primer on it
3) apply your separating agent (which is some type of wax),
4) lay the fiberglass and apply the resin
5) gel coat the hardened fiberglass to make it smooth
Although that is the process for making custom autobody panels, some of those principals may be applied to this project.
Are you going to use a separating agent between your mold and the glass? I dont know if the lens material will adhere to your mold when heated.
I can't see why a beach ball type impression in something isn't going to be 100% accurate, and wont make a reusable mold. Although I dont think I would use sand. I would use something similar to bondo that doesn't react to heat. Probably joint compound, or plaster. Then you could gel coat (if you have a spray gun) the inside to make a smooth finish. You could also just use sand paper.
As I said before (but didn't explain too well), I would make the hole with a scoop. The scoop would look like a perfect cross-section of the lens. Each end of it would be mounted on a pivot point so that I could rotate it around the x axis, and scoop out the excess mold material.
I don't think casting is the way to go. I would melt a single thick piece of lexan glass over the hole. That way the entire top of the mold would be covered with a thin layer of lexan glass. You would have to watch the lexan melt, so that you dont melt the whole thing right down to a puddle in the middle of your mold.
Then you remove the glass, fill the hole with mineral water, and fasten another piece of lexan glass overtop of the mineral water
top piece of glass
|
_________________________ < top piece of glass
__...............................____ < bottom piece, fastened to the top
....\....water in here....../
.....\________________/
...............^
bottom piece of glass
(ignore the periods, pretend the bottom piece is the shape of the lens)
The final result wouldn't be a solid piece of glass, but it would be 2 materials that have the same index of refraction (same as DIY anamorphic project)
I dont think I fully understand what you are doing here. You didn't seem to explain very well what you are doing - well maybe im just dumb. You are casting silicon power into sand?
A female mold can only ever be as good as its male counterpart. Are you going to fix the female up later? If so, you might as well just start with the female.
Oh and blue foam is easier to work with than wood. It is also very strong and smooth. Its the easiest thing to carve thats why you use it for custom body panel construction.
Let me know if any of this made sense or if im just an idiot. |
|
|
| Hezz |
Pisonic,
There is nothing wrong with your method and thinking and for a while I was going to do something just like you described but there are a couple of factors that you are not considering.
It would be very hard to get sand or bondo to scoop out with a cross sectional scoop in a very precise manner. Although I'm sure it could be done it would be more work to build the apperatus to make it line up perfectly.
Remember that we will be hand surfacing the final lens and any excess of material will add hours to the finishing process.
I need a mold blank that is stiff and firm enough so that I can either pack sand around it without deforming or pour a more liquid molding material around it.
The beach ball method would deform to some degree in sand but might work with a pourable mold material. The only inflatable balls that are about the right size are those exercise balls but thats an extra $30. Even if the ball deformed an 1/8 of an inch that would add a tremendous amount of work to the final project because you would have to remove all the exra material down to the lowest point of the surface to get perfect sphericity.
The wood mold is the most precise method other than milling metal on a CNC mill. And it's cheap.
I spent about an hour today hand grinding the mold blank and it is coming up nicely. I'm going to have to do some more bondo work to fill small holes and bring up some areas near the edges that I took down to far with a rasp.
Hezz |
|
|
| Hezz |
Dnt32,
The wax method you describe is called investment casting or the lost was process. It is very precise and good for small intricate parts. It could be done to make the lens but then you would have to built a new wax mold blank everytime you need another lens. This is OK in a large factory where they have CNC mills automated to cut the parts out of wax. They can cut thousands of parts in a few days. The wax parts are then dipped in a liquid ceramic slurry that hardens. After that they fire the ceramic and the wax melts out then they cast liquid metal into the mold and let it cool.
A variation on this is to pour the liquid metal into the mold without removing the wax. This is called the lost wax method. The hot metal vaporizes the wax. This is how they build engine blocks in Detroit now except they use styrofoam instead of wax. They machine styrofoam into a perfect engine block and then do the slurry treatment.
I could have a wood or wax block CNC machined. $700 UDS,
Hezz |
|
|
| Hezz |
Ace3000,
What you describe is what I intend to do if I use sand. If I use plaster I will still probably do something similar. The multipart mold cavity is great but it is hard to get the parting lines correct unless you can machine the mold from clamped together blocks.
The nice thing about sand even though it will not make a good surface finish is that it is never hard to remove the part from the mold.
The nice thing about the plaster is that I can get the plaster to set up partially around the mold blank and get a better surface finish which might reduce hand work. Assuming no other flaws on the lens need extensive work.
I haven't really decided on the casting method yet.
Hezz |
|
|
| Hezz |
And one last thought,
In the real world plastic lenses are injection molded or compression molded. This is the most economical process if you are making thousands of lenses. Because the first mold is a high precision metal mold that will cost 5000 - 300,000 USD to manufacture it is not practical for one offs or even for a few. When making tousands of lenses the cost can be amortized over the cost of the lenses. Check out this link:
http://www.uspl.com/pdf/Chapter1.pdf
Buy thye way I've found out that optical plastics are actually better than most glasses at passing light in the visible range.
Hezz |
|
|
| Dnt32 |
| Thanks I couldnt remember what you called it, its been 10+ years since I heard the term...Just glad I dont do foundry work anymore. |
|
|
| Dnt32 |
We also did large parts ouch my back .We did 350 pounders
Pump casings actually just FYI lol |
|
|
| freeupyermind |
| is it possible to make your own projection lens as big as the lcd iteself, that way we wouldnt have to lose so much room in the area between lcd and projection lens, or we could just buy one, but does someone manufacture and sell them at this size??? |
|
|
| Hezz |
It's possible to make a giant projection lens but it will not be necessary. The first lens can capture enough of the LCD's light and collapse the light cone down into a smaller cross sectional area so that lenses of moderate size can be effectively used.
The wider the angle of vision that needs to be projected in focus the more complex the lens system needs to be to get good focus but because we are putting the LCD so close to the big lens it should funtion in a relatively paraxial fasion making the big simple lens useable.
In order to get the most perfect imaging possible the lens system needs to be designed with the exact requirement in mind. In the future I attempt to do that but for now I'm using off the shelf parts except for this big lens I am making.
Hezz |
|
|
| freeupyermind |
| cool hezz, after your done with the conventionals and all the normal parts, and you decide to give the more radical of ideas a try be sure to keep me posted!!! |
|
|
| Hezz |
Here is some of the stuff I am using to finish the lens mold blank to a higher state. I found some silicon carbide powder at a nearby rock and lapidary shop. It is 60-90 grit and was 4.95 for each bag. I've also got two identical plactic bowls that I purchased at the local dollar store.
I then cut the bottom off of one of the bowls.
Hezz |
|
|
| Hezz |
The custom made tool that we will use to grind the wood blank more spherical will be made of silicon carbide powder and polyester body filler. It is important the the tool material be about the same hardness as the wood. This is why I choose the body filler. It is NAPA economy 4.99 USD filler.
Some kitchen plastic wrap is then stretched across the surface that we have rounded with eyeball methods with a wood rasp.
The I placed the cut bottom bowl upside down on the wood blank. It will become the form to make our tool.
Hezz |
|
|
| Hezz |
I put about 3/4 of one bag of the grit into the other bowl which was identical so that I could easily estimate how much material to mix. Then about 3/4 of the can of body filler goes in with the grit. It takes a while to mix it together well because it is very thick. This is how it should be or the grit will be too diluted in the mix. It should be a very thick dough like consistency.
After the grit and the polyester filler are thoroughly mixed it is time to add the hardener. It also must be mix in very well and should be poured in the mold as quickly as possible as the more soft it is the better it will fill in the mold.
Hezz |
|
|
| Hezz |
| I then put something heavy one it to hold it down and put it out of the way for a while in a warm but unused room. There are some fumes here so use precaution if you do this indoors. |
|
|
| Hezz |
Once the tool was fully hardened I glued a wooden square of MDF to the back with silicone glue after flattening the back of the tool with a file. The tool will take on the form of the curve and allthough it is not perfectly spherical it will wear down into a near perfect sphere with the right grinding technique.
Here is a picture of the tool after about an hours worth of grinding. You can see if you look closely that the tool is making contact all around the edges and at a large patch in the center of the tool. It is hard to see in the photo but if you look close you can tell. The grinding process needs to continue with this tool until it has seated all the way down and is touching on nearly all of it's surface.
Hezz |
|
|
| Hezz |
At first the tool will not grind very well by itself and I had to sprinkle about a half teaspoon of the loose grit onto the surface of the wood blank to get it going. Once it starts grinding it goes pretty fast with wood and body filler.
I used a cordal stroke going outward from the center of the lens to the sides and walked around the lens in a circular pattern. I would take about four stokes and count them and then move about an eighth of a turn around the lens and then turn the tool about the same amount beforre taking the next four stokes. This is very important because in order for the tool to wear spherical you must turn it everytime that you move on the lens. I doens not take much pressure and every attempt should be made to keep the tool from rocking as much as possible. This is easier said then done.
Because I had gone to happy with the wood rasp I had to add quite a bit of filler to the outside corners. These then have to be taken down with a file to near where the curve is supposed to be. The lens blank is coming together pretty well and I think it needs about two more hours of grinding before the tool completely seats.
Here are a couple of pictures that show the outline of the lens blank in two different directions. You can see that the curvature is becoming very round and spherical. |
|
|
| Hezz |
And from the other angle:
Hezz :cool: |
|
|
| Doon1 |
Hi Hezz,
I have version 5.1. I just got a mailer the other day for 9.0. I can get it for $169 if I order before 1-30-04.
Have you thought of setting your oven 10 deg over the melt point of your plexi and melting it like that? I've done that to soften Lexon sheets that I had to bend around a radius. It worked very well.
John
I just had a thought. Your casting looks like a stone wok. I remember seeing/reading something about a wok is part of a sphere. Some ancient religious reasoning about focused energy.
I'll go check it out. |
|
|
| ace3000_1 |
| quote: | | I remember seeing/reading something about a wok is part of a sphere. Some ancient religious reasoning about focused energy. |
u wouldnt happen to have a pocal point on that engergy would ya doon? lol
Hezz great work, i can see u are realy getting somewhere with this.
Trev |
|
|
| Doon1 |
The one on the left is a semi-spherical wok. The one on the right is a full spherical that is within .005" true. the outside diameter is 355mm.
If you lightly coat the inside with a high-temp spray grease and fill it with the pellets. then put it in an oven with the temp between the melt and boil point of the plastic you would end up with your lens. Right?
John |
|
|
| Doon1 |
Scratch the grease idea. If you place it in the freezer after it's cooled to room temp the pan will contract and probably pop the lens out.
John |
|
|
| Hezz |
Doon1,
In the early days of this project I thought about the WOK but it is hard to find one that isn't flat for a small area on the bottom. Even so, finding a wok with the correct radius curvature is even harder. A good wok with a totally round bottom would work but the wok would not be safe to use after for food.
I am not locked into any one lens configuration. If I need a lens with a different focal length I can make another blank for about $20.
Ace3000,
Thanks for the Kudos. I hope I can pull this off. I think that I am going to buy a dial indicator and make a sphereometer so that I can have an idea on how round the lens is before I commit to the final finish. I think I will gel coat the mold to make it smoother and easier to get out of the mold. If it has a glass like finish it will be very easy to remove from the mold with a little PAM sprayed on.
I'm leaning towards sand casting for the first try because it is easy. I'm going to make a small wood frame like you suggested and then get some fine mortar sand and vegetable oil to prepare the sand. They have some special oils that they use to mix with the sand for casting but some of them make it less easy to dispose of. With vegetable oil I can just dump the used sand out in the garden when I am done. I will post a model of what the casting form will look like.
Hezz |
|
|
| Hezz |
Doon1,
Were you talking about TurboCad earlier. If you don't need the radiosity scene rendering you can save a lot of money by getting the standard version. I think it's only about 70 - 80 USD.
I would be interested in seeing your results with a wok but I found that I couldn't find a wok with a close enough size radius. If you could make a rough lens within .005 - .010 you would have a good start on the final lens.
I am still sticking to my method as I am as much trying to create a repeatable method for making the lenses as I am trying to make the lens. Also I found that woks are about 90 - 130 USD. I felt that was too steep for a form that wouldn't give me the exact curvature I desired.
Hezz |
|
|
| ace3000_1 |
| quote: | | I'm leaning towards sand casting for the first try because it is easy. I'm going to make a small wood frame like you suggested and then get some fine mortar sand and vegetable oil to prepare the sand. They have some special oils that they use to mix with the sand for casting but some of them make it less easy to dispose of. With vegetable oil I can just dump the used sand out in the garden when I am done. I will post a model of what the casting form will look like. |
no problem bud, when u want a hand with lining up the male mould give me a shout cos i can help u out in that, its easier then u think. Im actually thinking in doing the same thing your doing but with the sand casting at a later date, its fun casting things lol
Trev |
|
|
| Hezz |
This is my idea for a form for sand or plaster casting to make the female mold. The bottom will be secured with zipper screws so that it can be turned upside down and filled and packed with sand from the bottom while the mold blank is in place.
Hezz |
|
|
| ace3000_1 |
yeah thats the right idea hezz, tell me, the lens u are making is it a plano convex? also in your pic u will need a top plate, the reason i say this is that if u make a top plate once poored if u are fast enough place a top on it to compress it slightly to have a nice flat bottom of the lens meaning less clean up and a truer lens.
Trev |
|
|
| Hezz |
Trev,
Yes the lens is a plano convex. What you mentioned is a good idea. Actually gravity is pretty good at levelling things off but it will probably leave a menicus around the edges that will have to be removed. This is no big problem as I will be hand lapping the flat side also and polishing it up to high standards. Probably with a large piece of plate glass.
I want to be able to mount the LCD directly to the flat side of the lens because the closer it is the more paraxial the light path will be through the lens. Also the lens will act as a big heat sink with air rising up and out the enclosure and moving all around the big lens.
Hezz |
|
|
| ace3000_1 |
ya thats right and also for a tip u can use cut back polish to cut back the surface of the lens to clean it up, ive been fooling with polishing this stuff up but becarful not to get one with any harsh chemicals as it will deteriate the acrylic.
here is a link to some proper acrylic polish, there are 3 grades, there is a harst cutback being the number 3 to the just polishing being the number 1
http://www.americanacrylics.com/polish.htm
Drop me an email for a better price
Trev |
|
|
| Hezz |
Thanks for the info Trev,
By the way your projector is coming along nicely.
The wether has been pretty wet and snowy around here lately. There was 24 inches out on the side lawn a couple of days ago. As such I havn't done much in the last week or so. Maybe in a few days the wether will clear so that I can go outside and work on the lens. I will keep posting when progress occurs. Also I need to get a dial indicator because the plunger type that I now have isn't the best for what I need to do.
Hezz |
|
|
| CRISPdollaz |
A long time ago I wanted to use that setup. I decided to try out a high bay reflector because its working in the same way as you want, but it just didnt work as I would have liked. I would have had to place the LCD way too close to my 400 watt metal halide.
Dont get me wrong, this type of reflector is probably the best for bulbs like these, but currently we have no way of getting them, unless we start a venture to have a manufacturer make some for us, like for the 15" fresnels....
What we need is a reflector with the right focus and small enough that the opening can fit a reasonable size condenser lens, which we can in turn apply to the fresnel and get the best result. I doubt anybody can hand craft a reflector to those specifications, unless you are a professional and have design tools for the job.
Good luck tho!
:smash: |
|
|
| Hezz |
Crispdollaz,
Your post seems to be rather off topic. Did you post here by mistake? If not your message does not make much sense to me.
Hezz |
|
|
|
