Enclosures
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From: Tim Wescott on 23 Mar 2010 12:10 D Yuniskis wrote: > Hi Joe, > > Joe Chisolm wrote: >> D Yuniskis wrote: >>> I need a small quantity (~20) of small {plastic,aluminum} >>> enclosures. But, I'm looking for something other than a >>> simple rectangular prism shape. >>> >>> I'm wondering, instead, if I can't hack together something >>> with a sheet metal skeleton (or, maybe even a cardboard or >>> wooden form!) and fiberglass? This doesn't need to be >>> terribly strong, structurally. And, I could no doubt >>> come up with a way of mounting everything to a *base* >>> (i.e., to eliminate the need for fasteners *in* the skin). >>> >>> Has anyone done this sort of thing before? Pointers to >>> helpful tips as well as things to avoid... :> >> >> I've done fiberglass molds before. If you want 20 or so >> units I would do a female mold. Modeling clay, foam and Bondo >> work great for shaping the male plug and fixing any problems. > > So you are making the mold out of 'glass, too? You can make the molds out of anything that will stand up, but if you're going to be doing fiberglass work you may as well use that for the mold. Plaster is probably easier for onsie-twosie, but it doesn't last well. > >> I use tooling polyester resin. Any cheap resin will work. Any cheap resin will work for a while, but the quality of the mold determines the quality of the part that comes out of it. If you just want a few, get whatever is on sale. If you're going to pull hundreds of parts out of the mold then use the best resin you can get. (If you're going to pull tens of thousands of parts out of the mold then you should reconsider your process, and maybe plan on metal molds). >> Most >> local fiberglass suppliers will have some brand. Do not use >> styrofoam with polyester resin as it will turn into a lump of goo. > > Yes :> > >> Use a pvc foam - there are several makes. Use Bondo or some >> resin with a filler to coat all the foam and make sure and sand smooth. >> Coat with car wax or some other release agent. Then start to make your >> female mold from the male plug. Use lots of resin and a fine weave >> cloth for the first layer. For the other layers I usually use some >> fiberglass mat and any scrap cloth I have in the bin. Glass in >> some small wood blocks for stability in making the real parts. >> Let this all cure and then carefully pop the mold off the male plug. >> You might have to persuade it a little with a rubber mallet. Clean > > I had thought of trying something like plaster for the mold. > I.e., something that could either be *dissolved* or *fractured*. Only if you want a one-use mold. Even for your plug I'd suggest that you plan on something that'll stand up to making half a dozen molds -- this will give you the opportunity to re-do a screwed up mold, or modify the design without building a plug from scratch. And if you _do_ want a one-use mold, then the lowest-effort way to get that is to make a male plug that's undersized by the thickness of the glass, and lay up on the outside of it. Then pull the part. If the part has negative draft, or just if you want to, there's a "lost foam" method where you use a foam plug and destroy it to get it out. Use urethane foam and chip it out, or styrofoam (with epoxy resins, which are compatible) and dissolve it out with acetone or other solvent. This leaves you with some effort to finish the outside of the part, but it's likely less than the effort to make a really good mold. >> up any imperfections in the mold with Bondo and some sanding. Dremel >> with a cutoff wheel works great for cutting the edges of the mold. >> You can scribe drill marks and cut marks in the mold that will show up >> on the finished part. I have used a BB bonded to the female mold as >> a drill "center punch". > > Ah! > >> You can get gelcoat from local suppliers or on the net or you can make >> a poor man's version using some clear casting resin and some pigment. >> I have gotten pigment and supplies from TAP Plastic in the past. >> >> http://www.tapplastics.com >> >> For the final part make sure and wax the mold several times. I >> usually add some form of spray on mold release as the final step. >> Lay down a nice layer of gelcoat or resin and then use fine weave >> cloth for the first layer. If needed stiffen the part by using >> foam and glass on the inside in various locations. For standoffs >> and screw inserts you can use a small block of foam. I use screw >> inserts and just fill the threads with a blob of hot glue. Any >> resin just pops off and the hot glue plug will pull out of the > > Clever! What about just leaving a screw *in* the insert? > (and backing it out later) Curse those glued-in screws! At the risk of starting a flame war -- unless your part's exterior is textured, or you want it obvious that your part is fiberglass, _don't_ use woven cloth. The weave will "print through" the final finish any time your part is at a different temperature than it was when it acquired it's final finish. Clearly this isn't an issue if the part is textured (and try to keep a textured mold looking nice!), but if it's supposed to be smooth and shiny it does detract from the part's appearance. > >> threads. If there is going to be any real stress on the screws you >> can carve out a pocket in the foam and fill with a milled glass - >> resin mix. Let it cure for a minute or 2 to thicken and then push >> the screw insert into the pocket. Biggest problem I had was making >> sure they stay aligned. What I did for one part was made a wooden >> jig where I could screw 4 insert onto locater screws and then >> pressed them into the milled fiber mix. The jig held everything >> square. > > How did you later get the inserts "unscrewed" from the "locater > screws" (since the locaters were part of the wooden block)? Wax the screws, probably. > >> Take a look at http://www.fibreglast.com >> >> If you want to go the acrylic sheet method browse US Plastics >> http://www.usplastic.com > > Thanks! Lots to think about, here... -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: D Yuniskis on 23 Mar 2010 13:32 Hi Tim, Tim Wescott wrote: [much elided] >>> I've done fiberglass molds before. If you want 20 or so >>> units I would do a female mold. Modeling clay, foam and Bondo >>> work great for shaping the male plug and fixing any problems. >> >> So you are making the mold out of 'glass, too? > > You can make the molds out of anything that will stand up, but if you're > going to be doing fiberglass work you may as well use that for the mold. > > Plaster is probably easier for onsie-twosie, but it doesn't last well. I was thinking that plaster had the advantage of being easily destroyed (e.g., negative draft angles, etc.) >>> I use tooling polyester resin. Any cheap resin will work. > > Any cheap resin will work for a while, but the quality of the mold > determines the quality of the part that comes out of it. If you just > want a few, get whatever is on sale. If you're going to pull hundreds > of parts out of the mold then use the best resin you can get. > > (If you're going to pull tens of thousands of parts out of the mold then > you should reconsider your process, and maybe plan on metal molds). <grin> As I said, "small quantity (20)" :> I don't plan on going into the box making business! >>> Use a pvc foam - there are several makes. Use Bondo or some >>> resin with a filler to coat all the foam and make sure and sand smooth. >>> Coat with car wax or some other release agent. Then start to make your >>> female mold from the male plug. Use lots of resin and a fine weave >>> cloth for the first layer. For the other layers I usually use some >>> fiberglass mat and any scrap cloth I have in the bin. Glass in >>> some small wood blocks for stability in making the real parts. >>> Let this all cure and then carefully pop the mold off the male plug. >>> You might have to persuade it a little with a rubber mallet. Clean >> >> I had thought of trying something like plaster for the mold. >> I.e., something that could either be *dissolved* or *fractured*. > > Only if you want a one-use mold. Even for your plug I'd suggest that > you plan on something that'll stand up to making half a dozen molds -- > this will give you the opportunity to re-do a screwed up mold, or modify > the design without building a plug from scratch. > > And if you _do_ want a one-use mold, then the lowest-effort way to get > that is to make a male plug that's undersized by the thickness of the > glass, and lay up on the outside of it. Then pull the part. Doesn't this affect the surface finish of the part? (it also imposes constraints on the shape of the part since you have to slide one out/off of the other -- regardless of M/F) > If the part has negative draft, or just if you want to, there's a "lost > foam" method where you use a foam plug and destroy it to get it out. Use > urethane foam and chip it out, or styrofoam (with epoxy resins, which > are compatible) and dissolve it out with acetone or other solvent. This Ah! > leaves you with some effort to finish the outside of the part, but it's > likely less than the effort to make a really good mold. I had also thought of making ceramic molds and shattering them. >>> You can get gelcoat from local suppliers or on the net or you can make >>> a poor man's version using some clear casting resin and some pigment. >>> I have gotten pigment and supplies from TAP Plastic in the past. >>> >>> http://www.tapplastics.com >>> >>> For the final part make sure and wax the mold several times. I >>> usually add some form of spray on mold release as the final step. >>> Lay down a nice layer of gelcoat or resin and then use fine weave >>> cloth for the first layer. If needed stiffen the part by using >>> foam and glass on the inside in various locations. For standoffs >>> and screw inserts you can use a small block of foam. I use screw >>> inserts and just fill the threads with a blob of hot glue. Any >>> resin just pops off and the hot glue plug will pull out of the >> >> Clever! What about just leaving a screw *in* the insert? >> (and backing it out later) > > Curse those glued-in screws! > > At the risk of starting a flame war -- unless your part's exterior is > textured, or you want it obvious that your part is fiberglass, _don't_ > use woven cloth. The weave will "print through" the final finish any > time your part is at a different temperature than it was when it Interesting! This is because the weave expands differently than the resin? (tempco) > acquired it's final finish. Clearly this isn't an issue if the part is > textured (and try to keep a textured mold looking nice!), but if it's > supposed to be smooth and shiny it does detract from the part's appearance. Noted. >>> threads. If there is going to be any real stress on the screws you >>> can carve out a pocket in the foam and fill with a milled glass - >>> resin mix. Let it cure for a minute or 2 to thicken and then push >>> the screw insert into the pocket. Biggest problem I had was making >>> sure they stay aligned. What I did for one part was made a wooden >>> jig where I could screw 4 insert onto locater screws and then >>> pressed them into the milled fiber mix. The jig held everything >>> square. >> >> How did you later get the inserts "unscrewed" from the "locater >> screws" (since the locaters were part of the wooden block)? > > Wax the screws, probably. Set them *in* wax? (i.e., so they can be PULLED out instead of "unscrewed")
From: Tim Wescott on 23 Mar 2010 14:32 D Yuniskis wrote: > Hi Tim, > > Tim Wescott wrote: > > [much elided] > >>>> I've done fiberglass molds before. If you want 20 or so >>>> units I would do a female mold. Modeling clay, foam and Bondo >>>> work great for shaping the male plug and fixing any problems. >>> >>> So you are making the mold out of 'glass, too? >> >> You can make the molds out of anything that will stand up, but if >> you're going to be doing fiberglass work you may as well use that for >> the mold. >> >> Plaster is probably easier for onsie-twosie, but it doesn't last well. > > I was thinking that plaster had the advantage of being easily > destroyed (e.g., negative draft angles, etc.) But then you have to make a new mold each time. >>>> I use tooling polyester resin. Any cheap resin will work. >> >> Any cheap resin will work for a while, but the quality of the mold >> determines the quality of the part that comes out of it. If you just >> want a few, get whatever is on sale. If you're going to pull hundreds >> of parts out of the mold then use the best resin you can get. >> >> (If you're going to pull tens of thousands of parts out of the mold >> then you should reconsider your process, and maybe plan on metal molds). > > <grin> As I said, "small quantity (20)" :> I don't plan on > going into the box making business! > >>>> Use a pvc foam - there are several makes. Use Bondo or some >>>> resin with a filler to coat all the foam and make sure and sand smooth. >>>> Coat with car wax or some other release agent. Then start to make your >>>> female mold from the male plug. Use lots of resin and a fine weave >>>> cloth for the first layer. For the other layers I usually use some >>>> fiberglass mat and any scrap cloth I have in the bin. Glass in >>>> some small wood blocks for stability in making the real parts. >>>> Let this all cure and then carefully pop the mold off the male plug. >>>> You might have to persuade it a little with a rubber mallet. Clean >>> >>> I had thought of trying something like plaster for the mold. >>> I.e., something that could either be *dissolved* or *fractured*. >> >> Only if you want a one-use mold. Even for your plug I'd suggest that >> you plan on something that'll stand up to making half a dozen molds -- >> this will give you the opportunity to re-do a screwed up mold, or >> modify the design without building a plug from scratch. >> >> And if you _do_ want a one-use mold, then the lowest-effort way to get >> that is to make a male plug that's undersized by the thickness of the >> glass, and lay up on the outside of it. Then pull the part. > > Doesn't this affect the surface finish of the part? Most certainly -- that's one of the downsides, but it's equivalent to your idea of draping the fiberglass over a mandrel. > (it also imposes constraints on the shape of the part > since you have to slide one out/off of the other -- regardless > of M/F) That's the 'draft' that I keep babbling about. It's a casting term, meaning the degree to which all the sides slope 'the right way' to pull the part out of the mold. You can make a multiple-part mold for a part with negative draft that would otherwise get locked into the mold, but then you have parting lines on the part itself that have to be finished as a second operation. >> If the part has negative draft, or just if you want to, there's a >> "lost foam" method where you use a foam plug and destroy it to get it >> out. Use urethane foam and chip it out, or styrofoam (with epoxy >> resins, which are compatible) and dissolve it out with acetone or >> other solvent. This > > Ah! > >> leaves you with some effort to finish the outside of the part, but >> it's likely less than the effort to make a really good mold. > > I had also thought of making ceramic molds and shattering them. In what are you going to mold the molds? >>>> You can get gelcoat from local suppliers or on the net or you can make >>>> a poor man's version using some clear casting resin and some pigment. >>>> I have gotten pigment and supplies from TAP Plastic in the past. >>>> >>>> http://www.tapplastics.com >>>> >>>> For the final part make sure and wax the mold several times. I >>>> usually add some form of spray on mold release as the final step. >>>> Lay down a nice layer of gelcoat or resin and then use fine weave >>>> cloth for the first layer. If needed stiffen the part by using >>>> foam and glass on the inside in various locations. For standoffs >>>> and screw inserts you can use a small block of foam. I use screw >>>> inserts and just fill the threads with a blob of hot glue. Any >>>> resin just pops off and the hot glue plug will pull out of the >>> >>> Clever! What about just leaving a screw *in* the insert? >>> (and backing it out later) >> >> Curse those glued-in screws! >> >> At the risk of starting a flame war -- unless your part's exterior is >> textured, or you want it obvious that your part is fiberglass, _don't_ >> use woven cloth. The weave will "print through" the final finish any >> time your part is at a different temperature than it was when it > > Interesting! This is because the weave expands differently > than the resin? (tempco) As far as I know, yes. Even sharp changes in the thickness of the fiberglass will do it. Look at a Chevrolet Corvette with a trained eye and you can see where the factory put all their bonds -- and whether it's been through a collision repair, and how good of a job the shop did with it. >> acquired it's final finish. Clearly this isn't an issue if the part >> is textured (and try to keep a textured mold looking nice!), but if >> it's supposed to be smooth and shiny it does detract from the part's >> appearance. > > Noted. > >>>> threads. If there is going to be any real stress on the screws you >>>> can carve out a pocket in the foam and fill with a milled glass - >>>> resin mix. Let it cure for a minute or 2 to thicken and then push >>>> the screw insert into the pocket. Biggest problem I had was making >>>> sure they stay aligned. What I did for one part was made a wooden >>>> jig where I could screw 4 insert onto locater screws and then >>>> pressed them into the milled fiber mix. The jig held everything >>>> square. >>> >>> How did you later get the inserts "unscrewed" from the "locater >>> screws" (since the locaters were part of the wooden block)? >> >> Wax the screws, probably. > > Set them *in* wax? (i.e., so they can be PULLED out instead of > "unscrewed") No, wax them, then screw them into the inserts. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: D Yuniskis on 24 Mar 2010 00:29 Hi Tim, Tim Wescott wrote: >>> You can make the molds out of anything that will stand up, but if >>> you're going to be doing fiberglass work you may as well use that for >>> the mold. >>> >>> Plaster is probably easier for onsie-twosie, but it doesn't last well. >> >> I was thinking that plaster had the advantage of being easily >> destroyed (e.g., negative draft angles, etc.) > > But then you have to make a new mold each time. Yes. From a rubber mold -- pour in plaster, wait, lather/rinse/repeat. (I actually started thinking of this at a friend's ceramic business... but initially thought ceramic would be wasteful -- firing, etc.) >>>>> Use a pvc foam - there are several makes. Use Bondo or some >>>>> resin with a filler to coat all the foam and make sure and sand >>>>> smooth. >>>>> Coat with car wax or some other release agent. Then start to make >>>>> your >>>>> female mold from the male plug. Use lots of resin and a fine weave >>>>> cloth for the first layer. For the other layers I usually use some >>>>> fiberglass mat and any scrap cloth I have in the bin. Glass in >>>>> some small wood blocks for stability in making the real parts. >>>>> Let this all cure and then carefully pop the mold off the male plug. >>>>> You might have to persuade it a little with a rubber mallet. Clean >>>> >>>> I had thought of trying something like plaster for the mold. >>>> I.e., something that could either be *dissolved* or *fractured*. >>> >>> Only if you want a one-use mold. Even for your plug I'd suggest that >>> you plan on something that'll stand up to making half a dozen molds >>> -- this will give you the opportunity to re-do a screwed up mold, or >>> modify the design without building a plug from scratch. >>> >>> And if you _do_ want a one-use mold, then the lowest-effort way to >>> get that is to make a male plug that's undersized by the thickness of >>> the glass, and lay up on the outside of it. Then pull the part. >> >> Doesn't this affect the surface finish of the part? > > Most certainly -- that's one of the downsides, but it's equivalent to > your idea of draping the fiberglass over a mandrel. Ah, OK. >> (it also imposes constraints on the shape of the part >> since you have to slide one out/off of the other -- regardless >> of M/F) > > That's the 'draft' that I keep babbling about. It's a casting term, > meaning the degree to which all the sides slope 'the right way' to pull Yes, but I am refering to shapes that would otherwise require a two (or more) piece mold. E.g., imagine molding light bulb! (crappy example for this type of application but I was trying to illustrate how you couldn't do this in a one piece female mold) > the part out of the mold. You can make a multiple-part mold for a part > with negative draft that would otherwise get locked into the mold, but > then you have parting lines on the part itself that have to be finished > as a second operation. Unless you make a mold that can be destroyed cheaply. >>> If the part has negative draft, or just if you want to, there's a >>> "lost foam" method where you use a foam plug and destroy it to get it >>> out. Use urethane foam and chip it out, or styrofoam (with epoxy >>> resins, which are compatible) and dissolve it out with acetone or >>> other solvent. This >> >> Ah! >> >>> leaves you with some effort to finish the outside of the part, but >>> it's likely less than the effort to make a really good mold. >> >> I had also thought of making ceramic molds and shattering them. > > In what are you going to mold the molds? Make the positive out of something that can also be "shattered" (again, I keep thinking of the ceramic shop) or "flexible" (e.g., rubber). Use that to make lots of negatives (which you discard). Remember, I'm not looking for a "production" solution -- just something I can use to crank out some reasonably identical pieces (I even thought of doing the pieces in ceramic but they are just way too brittle) >>>> Clever! What about just leaving a screw *in* the insert? >>>> (and backing it out later) >>> >>> Curse those glued-in screws! >>> >>> At the risk of starting a flame war -- unless your part's exterior is >>> textured, or you want it obvious that your part is fiberglass, >>> _don't_ use woven cloth. The weave will "print through" the final >>> finish any time your part is at a different temperature than it was >>> when it >> >> Interesting! This is because the weave expands differently >> than the resin? (tempco) > > As far as I know, yes. Even sharp changes in the thickness of the > fiberglass will do it. Look at a Chevrolet Corvette with a trained eye > and you can see where the factory put all their bonds -- and whether > it's been through a collision repair, and how good of a job the shop did > with it. Hmmm... I'll have to keep that in the back of my mind. I think I need to go play with some of these ideas and see what the *real* "costs" are -- and the quality of the results, etc. Thanks!
From: Joe Chisolm on 25 Mar 2010 18:05
On Tue, 23 Mar 2010 01:46:52 -0700, D Yuniskis wrote: > Hi Joe, > Sorry for the late reply. I realized Thunderbird decided to not show any thread I had posted to. Back to Pan. > Joe Chisolm wrote: >> D Yuniskis wrote: >>> I need a small quantity (~20) of small {plastic,aluminum} enclosures. >>> But, I'm looking for something other than a simple rectangular prism >>> shape. >>> >>> I'm wondering, instead, if I can't hack together something with a >>> sheet metal skeleton (or, maybe even a cardboard or wooden form!) and >>> fiberglass? This doesn't need to be terribly strong, structurally. >>> And, I could no doubt come up with a way of mounting everything to a >>> *base* (i.e., to eliminate the need for fasteners *in* the skin). >>> >>> Has anyone done this sort of thing before? Pointers to helpful tips >>> as well as things to avoid... :> >> >> I've done fiberglass molds before. If you want 20 or so units I would >> do a female mold. Modeling clay, foam and Bondo work great for shaping >> the male plug and fixing any problems. > > So you are making the mold out of 'glass, too? > I make the molds out of glass also. One example I have is an airplane instrument panel. I cut out the basic shape from plywood. I did a couple of 3/4" pieces to give me a 1.5" flange around the perimeter. I then used foam and bondo to form other features. I sanded and filled any imperfections in the plywood with bondo or resin / microballon filler. Basically trying to get a very smooth surface. Then I coated this with several coats of resin, letting it cure and lightly sanding between each coat. The final product was a male plug, very smooth. Wax the hell out of the male plug and lay on a very thick layer of resin and let it set for just a couple of minutes. Then start laying down the cloth. This gives you a smooth surface on the female mold. This was not for some production setup, I did 1/2 dozen panels this way. Any small imperfections in the mold you can fix with Bondo and a little sanding. Unless you have a part with very long sides you dont have to worry much about draft. The final part is going to shrink some anyway. Wax and mold release are the key. The instrument panel was about 40+ inches by about 18" width and popped out of the female mode without any real problems. >> I use tooling polyester resin. Any cheap resin will work. Most local >> fiberglass suppliers will have some brand. Do not use styrofoam with >> polyester resin as it will turn into a lump of goo. > > Yes :> > >> Use a pvc foam - there are several makes. Use Bondo or some resin with >> a filler to coat all the foam and make sure and sand smooth. Coat with >> car wax or some other release agent. Then start to make your female >> mold from the male plug. Use lots of resin and a fine weave cloth for >> the first layer. For the other layers I usually use some fiberglass >> mat and any scrap cloth I have in the bin. Glass in some small wood >> blocks for stability in making the real parts. >> >> Let this all cure and then carefully pop the mold off the male plug. >> You might have to persuade it a little with a rubber mallet. Clean > > I had thought of trying something like plaster for the mold. I.e., > something that could either be *dissolved* or *fractured*. > I did this for the counter weights on the elevators. I wanted to increase the hinge to weight distance so I needed to rework the skin. It works for small one off pieces but generally a PIA. There is some polyurethane mold "rubber" you can get. It's a 2 part catalyzed process. You mix it up and pour it into a container and then you can put a part into it. It makes a copy of the part as a female mold. I dont remember the name or where I got it now. What I do remember is it makes one hell of a exothermic reaction! >> up any imperfections in the mold with Bondo and some sanding. Dremel >> with a cutoff wheel works great for cutting the edges of the mold. You >> can scribe drill marks and cut marks in the mold that will show up on >> the finished part. I have used a BB bonded to the female mold as a >> drill "center punch". > > Ah! > >> You can get gelcoat from local suppliers or on the net or you can make >> a poor man's version using some clear casting resin and some pigment. I >> have gotten pigment and supplies from TAP Plastic in the past. >> >> http://www.tapplastics.com >> >> For the final part make sure and wax the mold several times. I usually >> add some form of spray on mold release as the final step. Lay down a >> nice layer of gelcoat or resin and then use fine weave cloth for the >> first layer. If needed stiffen the part by using foam and glass on the >> inside in various locations. For standoffs and screw inserts you can >> use a small block of foam. I use screw inserts and just fill the >> threads with a blob of hot glue. Any resin just pops off and the hot >> glue plug will pull out of the > > Clever! What about just leaving a screw *in* the insert? (and backing > it out later) > That works also. I've done that for nut plates and such where some resin could get into the screws. Vaseline or some paraffin on the threads and you are good to go. >> threads. If there is going to be any real stress on the screws you can >> carve out a pocket in the foam and fill with a milled glass - resin >> mix. Let it cure for a minute or 2 to thicken and then push the screw >> insert into the pocket. Biggest problem I had was making sure they stay >> aligned. What I did for one part was made a wooden jig where I could >> screw 4 insert onto locater screws and then pressed them into the >> milled fiber mix. The jig held everything square. > > How did you later get the inserts "unscrewed" from the "locater screws" > (since the locaters were part of the wooden block)? > I drilled holes for the locater and had a insert. Basically the locater was screwed into a insert in the wood. Then I just unscrewed them from the wooden guide (and the insert now bonded to the part). >> Take a look at http://www.fibreglast.com >> >> If you want to go the acrylic sheet method browse US Plastics >> http://www.usplastic.com > > Thanks! Lots to think about, here... There are lots of ways to do tops and bottoms, inserts, etc. For small qty with minimal stress you can glue nuts on the back of a small flange to hold a panel in place. Fill the threads with hot glue and bond with some milled fiber. This is basically finely chopped fiberglass. You can get it from suppliers in bags. If you cannot find it locally try wicks aircraft or aircraft spruce. Look in their composite sections. You are better off with a small nut plate but finding the correct size can be difficult. Let's say you have a bottom plate of the box and you have made a small flange on the inside of the top. You want to screw the bottom on. You can use the nut plate on the back side of the flange. If the thickness is not enough, add a few small layers of glass, drill and be done with it. Again, small qty units, rivet the nut plate in with counter sunk rivets and a hand squeezer. Another method is using simple "brackets". Think of a box, sides and top and you want to mount a bottom plate 1) take a 2x4, maybe 8" long and warp tightly with a oven baking bag. The resin wont stick to this. 2) Cut 4 strips of cloth, 4 inches by 7in long fold them in half length wise to give you a "guide" 3) Put a coat of resin on the 2x4 and then lay down the cloth. Wet the cloth out layer by layer. Let it cure and pop it off the 2x4 form. If viewed from the end of the 2x4 the glass will be about 2" on the top of the 2x4 and 2" down one the side of the 2x4 What you have is a L shaped piece about 7 inches long. From this cut brackets maybe 1" wide, so you would get about 6 or 7 brackets. Trim as needed. You can use a pair of tin snips or a cutoff wheel for this. Now, mount the nut plate or bond a nut to the inside of the L. -------- | Nut plate | | Now measure carefully and drill holes in the bottom plate located such that this bracket will be as close to the side of the box as possible. What you are going to do is bond the vertical side of the bracket to the box. Mount the brackets and box bottom together. Mix up a thin slurry of resin and milled fiber. Coat the vertical side of the bracket with this mix. It will be thick enough to hold in place for what you want to do. Push the brackets and box bottom in place in the top, tape and let cure. Presto, unscrew the box bottom and you have aligned brackets bonded to the box sides. What you have is: bottom-------------------- outer|x============ outer|x| nutplate outer|x| outer|x|<-fiberglass bracket x=resin and milled glass This method also works for putting the nut plate on after bonding. Tape the bracket (or a dot of hot glue) to the bottom in the correct position. put the resin on the bracket side and place flush and tape. Let cure. You can then pull the bottom panel off, check everything and drill your screw holes and mount the nut plates. And one more thing. You can use plastic screws to temporary hold nuts, etc to keep resin out of the screws. Also, polyester resin will not stick to regular clear shipping / packing tape. -- Joe Chisolm Marble Falls, Tx. |