Making a nose cone mold for an Explorer 2M glider
02-25-2011, 04:02 PM
Making a nose cone mold for an Explorer 2M glider
Hey all,
My Dirty Birdy Mold project was put on hold as I have never done this sort of thing before and did not want to screw up the orginal DB 60 fuse while learning how to do one.
So I decided to make a cowl of an Explorer 2M sailplane so as to find a workable method for myself and to share here on RCU for those who took their time and shared their experience with me on how to create a mold. I am so glad I did this too.
As the mold is complete, I’ll post over the next couple of days the process from beginning to the end of the mold making process I did and some ideas of what to do to speed up the process and some what not to do’s to avoid some time consuming mistakes I made along the way.
To my surprise, the process I used on the cowl worked exceptionally well after the bugs were worked out, and I plan to use it on the DB 60 mold thread now that I have a working method. I am not saying this is the best and only way to make a mold, but it was fast, and most important, I had no problem whatsoever when spliting apart the two mold halves, which came apart easily with a little help from an x-acto knife.
02-25-2011, 04:06 PM
RE: Making a nose cone mold for an Explorer 2M glider
The nose coneis from anold Explorer 2M gliderand had to be glued back together and prepared for molding as it wassmashed in a crash. I first used super glue to glue the pieces back together, then made a brace out of balsa for the inside to straighten out the sides and square them up and place a center piece of balsa for screws for mounting to the base parting board. I used epoxy and microballoons and bondo to file and shape the nose cone back to, as close as possible , its original shape. I dry sanded to 220 and wet sanded to 600 grit. I was told that by Frequent Flyer that 400 would suffice but I’ll put in the extra sanding til I get better at making molds.
I decided to use hardboard for the base and parting board as I had several pieces lying around. Although it did not casue any problems, I would recommend using a thicker board for the base as during the mold build the hardboard base ended up with a warp. Probably happened while the epoxy hardened. I will use at least 1/4" ply for my parting boards in the future, just to keep things straight and flat. I set the nose cone on a 6" x 6" board, drilled two holes for screws to hold down the nose tothebase later after the mylar is set on top. I set another board perpendicular at 90 degrees with a square and outlined the nose cone onto the latter board and cut it out. I would try to be as accurate as possible here as you’ll have to use modeling clay to fill the space between the parting board part to be molded. To big a gap and you’ll spend more time filling than finishing the mold.
02-25-2011, 04:13 PM
RE: Making a nose cone mold for an Explorer 2M glider
The CST sales website’s tutorial recommended using mylar, (mylar, *** is mylar) between the parting boards, part to be molded, and the epoxy tooling coat. After serveral weeks of searching internet for just what mylar is (just about any thin clear plastic sheet), I found out Aircraft Spruce had it by the roll 39” wide by as long as you wanted for about a $1.50 a linear foot. I bought 6 linear feet figuring that would give me at least four 1ft wide x 6ft long strips if needed. Finding mylar was a PITA!
I cut two pieces of mylar the same size as the two parting boards I was using cutting away the outline of the nose cone for main parting board and using the other full sheet on the bottom parting board.
I used 3M Drywall Cornerbead Spray Adhesive to attach the mylar to the parting board on The DB 60 mold, but misplaced it. The 3M 77 Spray adhesive I guess is the best but at better than $20 a can, at least at the one place I checked I decided to used whatever I could get my hands on, so I found an old can of Permatex Spray-a-Gasket Adhesive and it worked great. I fogged the one side of the parting board and one side of the mylar, waited a few minutes for it to dry and glued the mylar to the parting board.
If your just starting out like myself I would recommend the mylar sheet. I orginally was just going to wax the smooth side of the hardboard than spray PVA on it, but was talked out it by few members of RCU. Thanks
For those of you not in the know, as I was at first, epoxy does not stick to plastic(mylar) very well, if at all. Hence the extra protection as a parting surface.
First I attached the adhesive backed mylar to the adhesive sprayed base parting board. Next I drilled two holes through the base parting board for screws to attached the nose cone to the base parting board. Next I attched the mylar to the main parting board the same way as before and cutout the mylar from where the nose cone would be.
02-25-2011, 04:19 PM
RE: Making a nose cone mold for an Explorer 2M glider
To mount the base parting board to the main parting board I used 1/8” x 1” x 6” strips of balsa and super glued them together from the sides of the parting boards. This was an easy way to get everthing to stay together and would be easy to remove later when done.
3 pics
To fill the gaps I used regular modeling clay, the oil based stuf that does not dry. The nice thing about modeling clay is the more you work it with your hands the softer it gets due to it warming up. Soft is good, itgets it in the gaps and around the nose cone easier.
I found a set of dental tools perfect for mashing the clay into the gaps. I used astainless steal ruler to scrap off the excess clay and to square off the transistion from horizontal to verticle. As you work the caly into the gap it will squeeze out the back side of the parting board. To keep this from being a problem I place modeling clay on the back side of the parting board. I did this for two reasons. First to keep the clay from squishing throughand dropping offand to keep the tooling coat from leaking through.
Ready for wax and then PVA
02-25-2011, 04:27 PM
RE: Making a nose cone mold for an Explorer 2M glider
Next,iwaxed the parting surfaces with least 3 coats of a good Carnuba wax or parting wax. Since I’m trying to make this as inexpensive as possible I used a good Carnuba wax (pure wax no silicone.) Three coats spaced 15 minutes a part. The recommeded time between coats was a hour, but I didn’t want to wait that long, besides I figured I was using PVA anyway so hence the 15 minute interval.
The PVA on the other hand was a real PITA! I initially followed the directions, e.g. 80 to 90 psi and straight out of the container. At first I thought the PVA was bad due to sitting for about a year. No matter how I sprayed it it just went on to thick at that PSI. All I can say is that when it dryed it was a horrible surface. Totally orange peeled from one extreme to fish eyes and runs at the other.
I washed it off after it dryed then rewaxed and reapplied the PVA again at the recommended application settings with the same results. Totally frustrating. In the three pics below you can see me spraying it on. In the last pic you can see a white haze on the parting surfaces. This is way to thick you should not see a white haze at all.
02-25-2011, 05:47 PM
RE: Making a nose cone mold for an Explorer 2M glider
The fix
I’ve sprayed many different types of paint from store bought cans to expensive automotive base coat clear coat types. The auto paints usually require a reducer for different air temps. Slow for high temp, fast for low air temp, and medium for moderate temps (in between hi or low)
I figured since it is water and alcohol based a little water couldn’t hurt so I reduced the PVA with this ratio - 4 parts PVA to 1 part water. Next I got out my airbrush and set the pressure to 15 psi and viola! First coat misted per directions followed by two wet coats spaced about 20min apart. This time I did not get the white haze and when it dryed it left a very smooth finished almost like glass. No orange peel and no fish eyes. See pics.
Later on when I pulled the mold apart I took pictures of the PVA peeling off like pulling Saran wrap off a bowl of food you just took out the refrig. Nice
More to come later
02-25-2011, 06:54 PM
RE: Making a nose cone mold for an Explorer 2M glider
To fill the gaps I used regular modeling clay, the oil based stuf that does not dry. The nice thing about modeling clay is the more you work it with your hands the softer it gets due to it warming up. Soft is good, itgets it in the gaps and around the nose cone easier.
I found a set of dental tools perfect for mashing the clay into the gaps. I used astainless steal ruler to scrap off the excess clay and to square off the transistion from horizontal to verticle. As you work the caly into the gap it will squeeze out the back side of the parting board. To keep this from being a problem I place modeling clay on the back side of the parting board. I did this for two reasons. First to keep the clay from squishing throughand dropping offand to keep the tooling coat from leaking through.
A little clay tip: Vertical edges on the parting board are the most difficult to work with when working in the clay. As you found out, the clay is prone falling through requiring extra work. Putting a small 45* bevel on edge solves all these problems. I either make this with a chamfer bit in a router or just a dremel cutter held at 45*. The chamfer doesn't have to be very big.
Keep up the good work.
02-25-2011, 07:07 PM
RE: Making a nose cone mold for an Explorer 2M glider
Excellant idea. I built the mold about a 1/2" larger on the outside dimensions and was planning to square the edges off. Thanks for the tip.
02-27-2011, 09:30 PM
RE: Making a nose cone mold for an Explorer 2M glider
OK, meat and potatoes time.
For first coat of the mold I used an epoxy tooling gel. They are many different ones to chose from. The one I used was from Polymer Products. I told that you can make up your own by adding carbsol to any laminating resin, but I wanted to use a Tooling gel to get started.
The cool thing about tooling gelcoats is that they are very thick and stay put on vertical surfaces better than a regular laminating resin. I added Wests Graphite Power to my gelcoat at 10% by volumn of resin and hardener. This may not be necessary but grahpite powder is used as dry lubricant and is hard. I wanted the surface of my mold to wear and last as long as possible so I guess it wouldn’t hurt..
Note! due not lay any fiberglass cloth yet. Wait until the first coat sets than start laminating with regular resin. The tooling gel went on so well and thick I figured I would just start adding fiberglass cloth over it well still wet. Don’t do this! I ended up with two very big air bubbles due to the moving around of the cloth. I was trying to get the cloth to wet out and inadvertantly lifted the soaked glass cloth up as it stuck to the tool I was using. I didlay a 1.5" piece of .75oz fiberglass cloth half on half off as a release point later when pulling the parting board off.
This is a very cool tip for those that want to try it. I was able to go to Polymer Composites Manufacturing facility and take a tour. While there the chemist showed me how to get airbubbles out of the resin by using a heat gun. He applied the heated air just for a few seconds to a dummy mold. Pretty amazing as thebubbles fizzed right out the mixture. Another tiphe showed me was to usea microwave over to heat up the resin to speed up the hardingof the epoxy. Only 8 secondsinthe nuker for about 10 grams of resin. I used both these techniques thoughtout this mold build process.
Another quick note here. If you plan to use the graphite power in your mixture put the power in after you heat it up in the microwave. I tried this and the resin mixture harden within a few saeconds of pullling out the nuker.
02-27-2011, 10:11 PM
RE: Making a nose cone mold for an Explorer 2M glider
To finish this half of the mold in one afternoon I decided to use a different method to make the mold and this was so fast that I’ll probably stick with it for all my future molds. Instead of the normal laminating process e.g. mix resin, apply resin to surface, lay down glass cloth, wet out cloth, wait until epoxy gels, then repeat until thick enough, I used an Epoxy Clay product from the same source as the Tooling gel.
I have to say this stuff is sweet. It mixes in a 1 to 1 ratio and you just knead it until its one solid color. I next roll it out onto some mylar, about 3/16" thick, like you would if making cookies. I cut and pealed off pieces and placed them onto the tacked up tooling gelcoat I placed on earlier.
02-27-2011, 10:23 PM
RE: Making a nose cone mold for an Explorer 2M glider
Next I did one layer of regular laminating resin and 6oz fiberglass cloth to finish the outside of this mold half.
Another tip I got from my visit to Polymer Composites was that I could speed up the hardening process by placing the fresh epoxy and the mold under a 40watt light bulb. Since I had my heat gun handy I just warmed up the resin from about 12” away every 2 or 3 munites until the resin setup. I only got it warm only, not to hot to where you could not touch it.
02-27-2011, 10:38 PM
RE: Making a nose cone mold for an Explorer 2M glider
This part of the mold making process was really cool!
I waited about 2 hours after appling the resin and glass than took apart the mold. I used an exacto knife to get it started. I slide the blade all the way around with no problem whatsoever. Alittle twist of the knife andthe parting board fell right off.
I was worried aboutthe PVA after all the problems I had earlier but must of doneit right cause as you can see it pealed off like saran wrap. I can’t say enough out how stoked I was, at his point, andat how well the parting board came apart.
02-28-2011, 07:04 AM
RE: Making a nose cone mold for an Explorer 2M glider
The CST sales website’s tutorial recommended using mylar, (mylar, *** is mylar) between the parting boards, part to be molded, and the epoxy tooling coat. ...
This will save you some time ;
I use:
First choice is 3/4" MDF board
Second choice is a 3/4" High density particle board.
I coat both sides,((at the same time)) with epoxy, same time or it will warp.
Then i will use a finish sander for the tooling side only then a second coat.
I coat the entire 4 X 8 ft sheet and and cut-out only the part i need for
that project.
Use a thin card-board or a white poster-board from Wallmart to make a stencil
and when the size is correct,(usually 2-3 try's for me),transfer to the pre-made
board i just described, and cut it out.
Bille
03-06-2011, 04:59 AM
RE: Making a nose cone mold for an Explorer 2M glider
Thanks!
03-06-2011, 10:32 AM
RE: Making a nose cone mold for an Explorer 2M glider
bargie,
I'm sorry to say that I got my Explorer 2M already put together. It should be a simple to assemble the fuse. If you would like I can take pics of mine so you can have some type of guide.
There is only two things I would change form what ever the plan indicates.
1.Beef up where the t wing hold down dowel rods with 1/16 ply going at least 4" in front of the wing and 4"back behind the wing. Mine snapped into 2 pieces right behind the wing.
2. epoxy and fiberglass the wing together,
Bryan
03-06-2011, 10:58 PM
RE: Making a nose cone mold for an Explorer 2M glider
03-21-2011, 09:07 AM
RE: Making a nose cone mold for an Explorer 2M glider
bargie,
Sorry for the delay, here's some pics of my Explorer 2M. It's pretty beat up but still flys very well.
Hope these work, if not, tell me what section you would need a pic of .
03-21-2011, 01:07 PM
RE: Making a nose cone mold for an Explorer 2M glider
Ok I’m going to try and finish posting the mold making process.
I pealed off the old PVA and washed the parting surfaces to get a clean surface to start the process all over again.
This is the time to and indexing points so when the mold is finished the two halfs will always line up correctly. I used a 1/2” drill bit in 4 spots. You can use any method as you please for this part, just remember to keep bevels on them. You can see were I drilled through the Tooling coat to the epoxy clay.
No mylar this time as the new parting surface is the the other half of the mold that was just completed. The bottom sitll has the mylar, don't remove it.
Next, three coats of carnuba wax spaced 20 min apart, first 3 pics. Three layers of PVA sprayed the same way as before, thinned 20% with water and let dry, next pic. You want thePVAto shine like clear coat of paint.
Total time for 3 coats PVA and dry time 1 hour @ 75 degrees.
Last pics. I mixed up more of the tooling coat and brushed it on, remember to let this set up until tacky before you start the laminating process or in my case laying up the epoxy clay. I once again used my heat gun to speed up the process and again, not to hot, just get it warm and that should speed up the curing. One hour for total for the tooling coat to tack up.
03-21-2011, 01:16 PM
RE: Making a nose cone mold for an Explorer 2M glider
Next the epoxy clay layer. I tried to keep this layer about 3/16" thick. I also used my heat gun to speed up the curing on the epoxy clay. Tack time about 1 hour.
03-21-2011, 01:26 PM
RE: Making a nose cone mold for an Explorer 2M glider
03-21-2011, 01:40 PM
RE: Making a nose cone mold for an Explorer 2M glider
