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Old 03-26-2014, 04:09 PM   #31
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Oh, btw. Thanks to your hard work with finding the 3 roscolux filters, I'm going to add them to my sensor. This will make it more accurate. I just bought the roscolux swatch, hopefully, they'll have all 3 filters in there. It's cheaper than buying a big sheet plus shipping.
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Old 03-26-2014, 04:24 PM   #32
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Oh, btw. Thanks to your hard work with finding the 3 roscolux filters, I'm going to add them to my sensor. This will make it more accurate. I just bought the roscolux swatch, hopefully, they'll have all 3 filters in there. It's cheaper than buying a big sheet plus shipping.
Those little sample books are supposed to be free! I just picked up another one yesterday, and they had a whole carton of them to give away. My original book of samples is pretty well shredded from all of the pieces I have cut out to try over the past 2 years.

Jalopy mentioned casting housings for PAR meters, as a cheaper alternative to 3D printed ones. I've been looking at that too - TAP plastics has all of the resins, mold making materials, dyes, microballs, etc. needed, and they have a store near me. It is an interesting DIY method, but with a part having detail on both inside and outside it isn't the simplest thing to make a mold for. And, getting the right mix of resin, dyes and/or microballs to make a diffuser work right, plus being able to duplicate the mix easily will be a challenge.

EDIT: With a little more googling, it looks like making the mold would be pretty easy, so this could drop the price of the housings to a few cents each! (But, only after the trial and error process to get the proper mix for a translucent diffuser.)
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Old 04-03-2014, 12:39 AM   #33
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My latest attempt to make a housing for a PAR meter through Shapeways has arrived. It is the all white one shown above. The basic design looks promising, but finding the right combination of dimensions is going to be very difficult. As is, this one is too sensitive except in the 50,000 range, where it is a little too insensitive. So, it takes more than minor tweaks of the geometry to make it work as it is now. And, I'm not sure that having the whole housing somewhat translucent is going to work. It looks like much of the light getting to the diode is from areas that are thick, where I expected to get only trivial amounts of light.

I will be doing more experimenting to see what to try next.

EDIT: After using very fine sandpaper to "polish" the diffuser part of the housing, I made it read almost exactly 2X the correct readings, with the readout meter set at the 50,000 range. I can work with that! My next step is to drill the housing for the electric cable, do a little more "polishing", and try to cast one with clear epoxy http://www.tapplastics.com/product/m...ting_epoxy/386 colored with white pigment http://www.tapplastics.com/uploads/p...%20Pigment.pdf I should be able to change the sensitivity of the diffuser/diode combination by adjusting how much pigment I use.
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Old 04-05-2014, 04:47 AM   #34
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I just successfully made a mold for casting the PAR meter housing/diffuser in epoxy resin. It looks like it will work ok, but until I actually try it.....?

The mold is made of platinum cured silicone, following the directions in http://www.tapplastics.com/product_i...d_making_guide This looks like a very effective way to DIY something you have designed/made in big enough quantities to sell.
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Old 04-06-2014, 04:07 AM   #35
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Today I tried to cast one of the housings in epoxy resin. Unfortunately, it takes 2-3 days for it to fully cure, so I won't know how well I did until Tuesday. For sure, it was a difficult job. The housing uses about 2 ml of resin, but the smallest amount I could mix was 20 ml and even then I'm not sure I was accurate enough with using equal amounts of resin and hardener. I just used clear epoxy because, for now, I'm just trying to learn to cast one. If it works the next one will be with epoxy with white pigment in it. And, that means finding a way to measure 1/32nd of 20 ml! The pigment has the consistency of toothpaste, making that even harder to do. I suspect I will use a tooth pick and "scoop" what will fit on about 1/4" of the end of it. I need to be able to adjust the amount of pigment to get the translucence I need. Fun!
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Old 04-06-2014, 03:15 PM   #36
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The casting cured faster than I expected, and turned out pretty good!



The two problems I see are:
The mold isn't done quite right, so the casting is about 1/16 inch longer than the original, caused by the impossibility of shoving the original part into the half mold all the way in - trapped air in the recess stops it from going in all the way, resulting in a longer casting than the original.

And, there are a couple of air bubbles, not in critical places, but demonstrating that the mold isn't quite right for allowing the bubbles to float out as the resin is poured in.

There are a lot of things to learn about how to do this well. I need to decide whether to make another mold, or live with this imperfect one.

EDIT: I decided to continue with the current mold. All it does is thicken the diffuser area, which I was intending to do eventually anyway. So, I just finished casting a new body, this time with white pigment in the resin. That worked out very well procedurally.
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Old 04-08-2014, 04:20 PM   #37
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This is the first white housing I made with epoxy resin, clear resin with one smidgen of white pigment mixed in. This one test pretty close to what I want - it read 31 when it should have read 41. I need it to read either correctly or a little high (so I can add a diffuser filter to drop the reading down to the correct value. Today I will try this with 1/2 smidgen of pigment.
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Old 04-08-2014, 06:03 PM   #38
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You need a machine shop to machine a mold for you, I just so happen to work in one. have any 3D drawings of the parts and mold that are finalized and good? I have Solidoworks 3d software and work in a machine shop. Hoppy those molds look dang close to final part and the look pretty easy to machine, nothing crazy
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Old 04-08-2014, 06:05 PM   #39
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Reading a little more about the program you use Dassault is who makes solidworks so those parts you have drawn up i should be able to open up. are they .sldprt file?
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Old 04-09-2014, 03:03 AM   #40
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Originally Posted by Kaduhn1 View Post
You need a machine shop to machine a mold for you, I just so happen to work in one. have any 3D drawings of the parts and mold that are finalized and good? I have Solidoworks 3d software and work in a machine shop. Hoppy those molds look dang close to final part and the look pretty easy to machine, nothing crazy
I'm using the Shapeways 3D printed part as a model for casting a silicone mold. That mold is good for at least 100 castings, so I don't really need another mold. It would be easy to machine the model if I had a small machine lathe, but I don't, and Shapeways price is substantially less than the cost of a lathe, even when I add the $100 cost of the computer program for CAD.

Right now I'm quite happy with the shape of the model, so all I'm doing now is trying to find a pigment to resin ratio that will give me the translucence I need. Once I have two data points for two different ratios I can find out with considerable accuracy what ratio would work best.
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Old 04-09-2014, 12:35 PM   #41
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yeah, buying a few machines to make one part wouldn't be very cost effective and I didn't know how long that mold would last, 100 parts isn't bad though. Is this something you're eventually going to produce and sell? If you ever need an actual metal mold made let me know. I'd exchange it for a meter if they don't cost too much, I'd be making it on my free time after work so not a big deal to do, wouldn't be charging you a shop rate to make it- more so just helping you out. Go all out and make an injection mold make 2 of the holders and two lenses in one shot. How awesome would that be.
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Old 04-09-2014, 03:19 PM   #42
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Originally Posted by Kaduhn1 View Post
yeah, buying a few machines to make one part wouldn't be very cost effective and I didn't know how long that mold would last, 100 parts isn't bad though. Is this something you're eventually going to produce and sell? If you ever need an actual metal mold made let me know. I'd exchange it for a meter if they don't cost too much, I'd be making it on my free time after work so not a big deal to do, wouldn't be charging you a shop rate to make it- more so just helping you out. Go all out and make an injection mold make 2 of the holders and two lenses in one shot. How awesome would that be.
Thank you! I appreciate the offer. I do plan to make several more PAR meters, assuming this technique works out well enough. I doubt that I will make another 100 though. First step is finding out if this will work well enough. The big question is how sensitive the design is to variations in the mix of pigment and resin. If that has to be held constant within 10%, for example, it isn't really workable because the pigment is like sticky toothpaste and is very hard to measure accurately. But if it only needs to be held constant within 25%, I think I can make that work ok.
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Old 04-09-2014, 03:47 PM   #43
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are you weighing the pigments to mix them? we do ink for pad printing and its measured out by weight not volume.
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Old 04-09-2014, 05:53 PM   #44
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are you weighing the pigments to mix them? we do ink for pad printing and its measured out by weight not volume.
I have considered weighing it, but the amount of pigment is so tiny it would be very difficult to do it well. I do have the gram scale to do it. The resin and hardener are designed to be measured by volume, so I would need to carefully measure out the desired volume and weigh it, then try to hit that weight each time. If I decide to make a lot of these that is probably the best approach, just for consistency.
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Old 04-09-2014, 06:34 PM   #45
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Just throwing some ideas for you maybe a syringe if the pigment can be sucked up.
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