Hobby centric plastics forum?

[nickelflippr]

Looking for links or recommendations on a plastics forum with the hobbyist in mind. Is there an equivalent to Electo-Tech which has multi sub forums? Most of the hits I've been coming up with have been professional sites relating to subject matters like injection molding, or enthusiast related to a narrow field like car or motorcycle parts.

I hope to learn about abs, polycarbonate, or other materials for exterior UV challenged casements and prototyping.

 

[nickelflippr]

I think I've found one solution to the prototypes. Several mentions of using MEK and Lego (ABS) parts for slurry's and patches. So Lego blocks, posts, and other parts, will be cheap and easy to get to approximate supports, standoffs, etc.

 

[BrownOut]

Look into fiberglass forming. It's relative cheap, easy, abundant supplies and tool availability, etc. Start at a boat or automotive business ( even Home Depot has supplies ). Also, there is a plethora of book and other informative material available ( and I suggest you read as much as you can before starting. I can help somewhat, as I've done a few projects )

Oh, and when you’re looking, look at hand layup. Things like chopper spraying are more on a professional level.

 

[nickelflippr]

Thanks for the suggestion. Hopefully this would be more than a one off. Would like to skip having to include a paint process. Internal threads for a pipe thread or screws could be a requirement also. For those reasons, and the rather nasty resins you have to work with, I think fiberglass is out.

Have a friend who was into building racing hydros, he did some beautiful work with glass. They used honeycombed carbon fiber for structural support, very fancy.

 

[tvtech]

I fully support this idea. I have an electronics project which has been delayed for 7 Months due to issues with casing inconsistency involving the Base of the unit cast in a Polyester resin.

The outside of the casing is cut from 2mm Polycarbonate sheeting. Fine.

The bottom of the unit relies on a 10mm thick Polyester resin mold to hold everything together…..I cannot get production or ANY consistency with this. Whatever I try.

I phoned a Representative of a local company that specializes in stuff like this and he said I should mix talc or any similar powder which would thicken the resin and hence stop shrinkage. I did it to the Max. I ended up with shrunken molds still…that now smell of baby powder when dry.

I am at my wits end.

Surely, there is SOMETHING resin based that has minimal shrinkage @ a reasonable cost??

Cheers
TV Tech

 

[nickelflippr]

Haven't played with resins. I forgot about plastic shapes from the hobby store. Have used the square, rectangle and angle, but its usually in grey abs. Could you use polycarbonate shapes to gusset and glue the bottom to sides instead? Here is an example of some **broken link removed** in different sizes.

 

[KMoffett]

Check out TAP Plastics **broken link removed**. Lots of helpful info there.

Ken

 

[squishy36]

Ken's link to TAP plastics is something you should definitely check out. Note you can fabricate things with acrylic fairly easily, as it's pretty easy to "glue" with a solvent (e.g., methylene chloride). A similar situation exists with PVC, as you can use PVC pipe glue.

Also consider welding plastics -- some of them weld quite well. I have a small welding kit that I bought for plastic repair (it's sold to the auto bumper repair businesses) and I've made some repairs that have surprised me. The trick is identifying the plastic you're dealing with.

You can also buy bars and sheets and machine things to shape if you have suitable equipment. Things like acrylic, PVC, Delrin, and polycarbonate cut fine with woodworking tools like tablesaws and routers. I use my regular metalworking drills with this material, although if I had a lot of one hole size to drill I'd change the drill tip's included angle. I turn PVC a lot on my lathe (just did it today to make a special adapter for my sprinkler system).

 

[nickelflippr]

Hah, more good stuff, thanks. The silicone mold making was interesting, never thought about that. And yes, have got most woodworking tools, excepting a band saw and the wood/metal lathe. Making a jig for the router has come to mind for some aspects. Used a chop saw with a carbide blade to cut abs pipe before, it's gets a kinda hot though. Probably needs a finer pitch, and kerf, like a metal cutting blade.

 

[SABorn]

The bottom of the unit relies on a 10mm thick Polyester resin mold to hold everything together…..I cannot get production or ANY consistency with this. Whatever I try.

I phoned a Representative of a local company that specializes in stuff like this and he said I should mix talc or any similar powder which would thicken the resin and hence stop shrinkage. I did it to the Max. I ended up with shrunken molds still…that now smell of baby powder when dry.

I am at my wits end.

I have done a lot in glass and can offer a few tips, but its hard to know exactly what you are trying to do from information given.

For starters if you are casting a 10mm resin block yes you will get shrinkage due to the temperature generated by the curing process of the resin.
Resin has no strength without glass added, you would be best to do a lay up with resin and several layers of glass first, allow this to cure (24 hours) as its thin the temperature wont be to high and the shrinkage will be next to nothing.
Then build the mold up in further layers of glass and resin staying under 1/4 inch thickness in layers, again to keep the temperature down with curing, dont leave it more than a couple of days between layers or the bonding will not be as good.

Another method would be to cut a section of several layers of plywood and use that as a spacer within the resin casting, as the plywood will displace a lot of resin and this will decrease the overall volume of resin so it will lower the temperature generated by the curing process.

The other important thing to remember is the % of catalyst used, the greater the % of catalyst the higher the shrinkage will be, You should always weigh your resin out, and add 2ml of catalyst for every 100 grams of resin, (2% by weight) if the weather is hot then i reduce the catalyst to 1 ml per 100 grams, for thick resin casting i would only use 1% catalyst.

Another factor is old resin will set faster and generate more heat than fresh resin, so if the resin you buy has been on the shelf in store for some time it will be crappy to work with compared to fresh resin.

There is also "casting" resin avaliable which will not cure so fast and generate so much heat.

Using talc is common, but baby powder is normally not talc nowdays, so not the best to use.

If you post some photos of what you are doing and the failures you have had i might be able to help some more.

Pete.

 

[MrAl]

Hi,

One little caution about using resins though is that they can smell up the place pretty badly and the smell can last for days. Long time ago i lived in a two family house on the bottom floor and did a project that required several molds. The whole bottom floor smelled pretty badly as the stuff was curing and even the neighbors upstairs complained several times. You would probably be better off doing any resin work in the garage or even outside perhaps.

I used to do a lot of work with fibreglass and my father used to work with it and molds for it a lot. We used to get a powder that was used to thicken it when you wanted it to be like putty rather than runny but im not sure what it was called now. This was long time ago.

Also, the stuff can get very hot when curing if you use too much catalyst. It can melt plastic molds while curing and thus distort the shape quite a bit. It can also crack while curing if not mixed right.

I stopped using fibreglass because of the smell while curing, but would use it if something came up that really really needed it, but not otherwise.

 

[tvtech]

Hi SA Born

Thanks for your input Pete. Great stuff. I appreciate your help here.
I made progress today. Good, more consistent results here with the resin castings.

A little machining here and there and all fits into the wrap around Polycarbonate casing.

Did some tests today. Onto a hard tile floor, the unit withstood around 25 drops onto it’s body without breaking the inside Resin housing.

Looking better

Cheers
Tv Tech

 

[nickelflippr]

Pics? Would be interesting to see your case, and what type of molds used. Is the polyester, polycarbonate combination a common one?

 

[MrAl]

Hi,

I'd like to see some pics too. Always nice to see what other people are doing.

 

[tvtech]

Thanks guys for your interest.

I PM’d Electromaster many Months ago asking if he was prepared to let me Prior Art my project on this great forum. He said anytime with date/time stamped irrefutable evidence the design first appeared here on Electrotech. Originated by me. My protection against potential cheapskates who copy and don’t originate. And then try and Patent…….

Electronic design was solid from the start….the casing however has taken many Months to complete to my satisfaction.

Surprisingly, however, I believe I have solved the casing issue as well.

I need another Week to get all perfect and released here for the World to see.
Photo’s will be included too.

This project started as a simple LED Mains light last September….and has evolved to a battery backed up, fully sufficient stand alone light source that runs from 220VAC permanently if so required.

Almost the size of a normal light bulb with a BC Socket. In fact, it was designed to replace a normal Glass Bulb…

Thanks for your time folks.

As always
TV Tech

 

[SABorn]

He said anytime with date/time stamped irrefutable evidence the design first appeared here on Electrotech. Originated by me. My protection against potential cheapskates who copy and don’t originate. And then try and Patent…….

One thing i have learnt about posting project details on a forum is, if you give the full project details so anyone can build it for personal use, then you have full claim to the idea, as well as i have had more people contact me wanting the item supplied pre built as they like the product but are unable to build it.
Then i have had companys buy the rights to manufacture the product too, so there is a lot to be gained by posting an idea in full detail.

So many sit back and dont share their designs and it just falls in a black hole somewhere, where i have found to give it away for all to see, gives far greater returns over time.

If you search long and hard on the net often you will find it has all been done before, just you thought you were the first because you built it from an idea you had.
Been there several times.

Pete.

 

[tvtech]

One thing i have learnt about posting project details on a forum is, if you give the full project details so anyone can build it for personal use, then you have full claim to the idea, as well as i have had more people contact me wanting the item supplied pre built as they like the product but are unable to build it.
Then i have had companys buy the rights to manufacture the product too, so there is a lot to be gained by posting an idea in full detail.

So many sit back and dont share their designs and it just falls in a black hole somewhere, where i have found to give it away for all to see, gives far greater returns over time.

If you search long and hard on the net often you will find it has all been done before, just you thought you were the first because you built it from an idea you had.
Been there several times.

Pete.

I read you friend. This thing needs lot's of work to get all to production standards. Lot's and lot's of work.

I can easily share the circuitry that drives this beaut......but anyone who tries to copy/build it will need a Professional board house that can both make AND cut the boards accurately to within 0.2mm as my board house does. That is why anyone who tries to copy this WILL fail. The Polycarb casing wraps around the finished product. The outside of the boards are basically the shape/form of the inner casing of the units. No room for Chinese tolerance errors and hit and miss manufacturing.

Polycarb is 2mm thick. And as tough as nails.

I am seriously thinking of posting my little design on here for the world to see. Professonally made PC boards available from me with all the rest of the casing and parts and so on available as a kit.

In September this year, it will be a year since this project was initiated. Not one LED failure since the start. And I have not been using expensive LED's. I use these:

Have fun Guys

Cheers

Old TV Tech