72 replies to this topic

[Pappy]

Thanks Gene.

 

I'm pretty sure I'm just not heating the plastic long enough. When I stick my hand on the platen I feel suction and I am getting little dimples in the plastic at the uncovered holes.

 

I made my frame so narrow because I didn't have enough aluminum angle to make it larger, when I get the bugs worked out I'll get more angle and make it and my platen larger. The body I'm trying to make is very small so the frame is large enough at this time.

 

Stay tuned

[Pappy]

Gene,

 

I tried to pull a body and some of it went real good but I got a lot of wrinkles or folds in the plastic. Most of them where it wouldn't hurt the body but I got one big wrinkle right across the middle of the body. I'm thinking maybe I shouldn't have covered up all the extra holes, that maybe the air couldn't get out properly.

 

What do you think?

 

Butch

[Gene/ZR1]

Gene,
 
I tried to pull a body and some of it went real good but I got a lot of wrinkles or folds in the plastic. Most of them where it wouldn't hurt the body but I got one big wrinkle right across the middle of the body. I'm thinking maybe I shouldn't have covered up all the extra holes, that maybe the air couldn't get out properly.
 
What do you think?
 
Butch

Pappy
Sometimes this will happen if your plastic is too hot.
I photo would sure help.

Regards, gene

[Pappy]

Hi Gene,

 

I just used my last piece of PETG and almost got a perfect body. I'm pretty sure I just need to re-make my guide that keeps my plastic/frame centered over my platen. The plastic is hitting the mold before it's centered and screwing it up as I center it.

 

When I get more plastic I'll try again. I'm going to keep trying with the .030" plastic because I like the strength for this particular body. It's a Formula Ford body that we run here locally. Some of the chassis are made out of popsicle sticks but you can use wood or plastic for the chassis. The whole body is only 1 7/8" wide and 4 1/4" long.

 

The body is actually usable but wouldn't win concours. 

 

Butch

[Thom]

I just completed my first and second pulls with my new platen and pump as recommended by Gene.
 
Success. My goal is good pulls every time and no waste. I can tell you that if you listen to Gene and follow his examples to a "T" you will have success.
 
I am using.020 PETG and heating it at 375 degrees till it sags about 1/2 " to 3/4".
 
Pics of my platen and pulls.

[olescratch]

Did you form your platen using the directions/example given by Gene?  If so, how did you make it look like 1pc?  BTW, good job!  Now what ya gonna make?

[Pappy]

Gene,

 

I'm using a Toaster Oven to heat my plastic. I slide the frame in, turn the oven on and keep the door open. Should I preheat the oven and then slide the frame in instead? I have the oven on bake so there is heat top and bottom. What temperature should I set the oven at, I've been using 300 degrees, I see where Thom is using 375 and getting great results.

 

I'm going to go ahead and redo my platen and frame before I waste anymore plastic. 

[Thom]

[quote name="olescratch" post="719266" timestamp="1525143855"]Did you form your platen using the directions/example given by Gene
If you look at Gene's posts # 11 and # 14 above and compare them with mine they are almost dead ringers. The only thing I did different was instead of particleboard for the base an an aluminum sheet for the cover, I used MDF covered with a piece of laminate.
d

[Pappy]

Hi Thom,

 

I'm thinking about doing it like Gene recommends except using 1/8" baltic birch plywood for the top instead of the sheet metal. I'm pretty sure I have a piece of the wire mesh like Gene uses laying around here somewhere. Even though my platen is not all that big I still want to cut down the volume of air that has to be extracted by the vacuum pump.

[Jay Guard]

Hey Butch:

I noticed in your post #24 that you said the platen was a box that is 2" deep.  If there is an inch or two between the top platen and bottom platen that would be a lot of volume for your vacuum pump to remove quickly and might be allowing your plastic to cool before being pulled down tight.  If I'm understanding it correctly Gene only has the thickness of the expanded metal mesh (i.e. volume) to remove.  Hey, I hope I'm not being "Captain Obvious" here, just trying to help a friend.

[Pappy]

Hi Jay,

 

That is one of my problems. I found my metal mesh that I knew I had but it's smooth on both sides so the air couldn't flow between the openings. I also found some chicken wire where the perpendicular wires are on top of each other so it would create an air space for the air to flow. So what I think I'm going to do is put a piece of chicken wire on top and one on the bottom of the metal mesh. That should allow the air to flow freely but still cut way down on the volume of air that has to be removed.

 

Getting the plastic lined up before it cools is also a problem. I'm still thinking about that. I'm thinking of making a hinged, spring loaded wooden frame that I can quickly put the aluminum frame with the plastic into and then just press down and it would already be centered on the mold. 

 

I'll keep trying, I know I will eventually make it work. 

[Jay Guard]

Sounds like you are on the road to success.  The quicker you can get the hot plastic over the mold the better.

[Gene/ZR1]

Hi Jay,
 
That is one of my problems. I found my metal mesh that I knew I had but it's smooth on both sides so the air couldn't flow between the openings. I also found some chicken wire where the perpendicular wires are on top of each other so it would create an air space for the air to flow. So what I think I'm going to do is put a piece of chicken wire on top and one on the bottom of the metal mesh. That should allow the air to flow freely but still cut way down on the volume of air that has to be removed.
 
Getting the plastic lined up before it cools is also a problem. I'm still thinking about that. I'm thinking of making a hinged, spring loaded wooden frame that I can quickly put the aluminum frame with the plastic into and then just press down and it would already be centered on the mold. 
 
I'll keep trying, I know I will eventually make it work.

Pappy
As far as the mesh grill, go to any Walmart, Meijers ,Ace and go to the outdoor cooking area and you will find the diamond grill as I have shown in my post, very inexpensive, should cost about $4.00, the metal plate is a piece of hvac duct work, Home Depot or similar place, small piece about $2.50 .

 

https://www.meijer.c...70882089479.uts

 

 

Grand Gourmet 16" x 12" Disposable Grill Topper, 3 Pack

$3.99   /ea

 

Regards gene

[Pappy]

Thanks Gene, I'll be going right past a Meijers this morning. I have some sheet metal, but I use to be a cabinet maker and I just like working with wood more than metal. I also thought if I need to drill more holes later it would be easier to do in wood than metal. Maybe I'll make one of each and see which works best.

[Pappy]

Gene,

 

Here's where I'm at. I made a new platen, the inside dimensions are  8"x9 1/4" by 3/16" thick. My .030 PETG arrived yesterday.  All I need to do now is make some sort of guide so the plastic gets centered oven the platen quickly. 

 

I want to make one good body and then fill it with plaster to make two more molds so I can pull three bodies at a time.

 

Here's some of my questions before I waste any material.

 

1. What temperature should I set my oven at?

 

2. Should I pre-heat my oven with the door closed for more uniform heat?

 

3. How far apart should I space multiple molds? They are about 1 1/4" high.

 

Thanks

 

Butch

[Jay Guard]

Hey Butch:

 

One thing to keep in mind is that the closer you put the molds together the thinner the material will be on the adjacent sides of the parts you are pulling.

 

Captain Obvious out!

[Gene/ZR1]

Gene,

 

Here's where I'm at. I made a new platen, the inside dimensions are  8"x9 1/4" by 3/16" thick. My .030 PETG arrived yesterday.  All I need to do now is make some sort of guide so the plastic gets centered oven the platen quickly. 

 

I want to make one good body and then fill it with plaster to make two more molds so I can pull three bodies at a time.

 

Here's some of my questions before I waste any material.

 

1. What temperature should I set my oven at?

 

2. Should I pre-heat my oven with the door closed for more uniform heat?

 

3. How far apart should I space multiple molds? They are about 1 1/4" high.

 

Thanks

 

Butch

 

 

Butch

Try letting your plastic sag 1-1\4"~ 1-1/2"

Try pulling 2 bodies at a time, stagger the 2 molds, place the rear of the molds to the center of your platen and over lap if needed. Try and get 2" between molds. 

I would at least for now pull single bodies. multi pulls have their issues resulting from failures, varying body thickness.

 

regards g;

[Pappy]

OK Gene, will do.

 

Thanks

[Pappy]

Hi Gene,

 

Getting good results but I'm having a problem getting my mold out so I need to clean it up a little. I did manage to get one pulled that I can use for a mold to make more molds.

 

Would mold release help?

 

My wife says she can take a picture with her smart phone and email it to someone, so I'm going to email pictures to Cheater and see if he'll post them for me. It won't be until tonight.

[Gene/ZR1]

Pappy,

Sounds like you're heading in the right direction. 

Look at your mold from the side, especially the front and back to see if you you have any undercuts or area's that allow your plastic to tuck under your mold. If you have undercuts you may have to do mold feathering or fill and blend in these areas.
 
An old trick is to blow, say 100psi burst of air along the side of the mold to pop off the body. You may also try some 0.020 petg. 
 
Cheap mold release - a light dust of baby powder.
 
regards,

gene

[Pappy]

Gene,

 

My mold is one of the bodies that we use on these cars that's made out of casted resin. It's heavy and needs a lot of dremel work underneath to clean the excess resin off to use it on one of these cars, that's why I'm making them out of PETG. I built up the bottom of the mold with two layers of 1/8" baltic birch plywood so you wouldn't have the rounded corner at the bottom of the body. The edge of my baltic birch plywood is kinda rough and I think that's what's keeping it from coming out of the body. I'm working on cleaning that up. I might take it off and redo the whole thing.

 

I'll try the air trick.

 

Thanks

[Gene/ZR1]

Pappy.

You can use auto Bondo to smooth your wood mold platform edges and sand smooth.
 
g;

[MattD]

Paint the edge of the wood, maybe just sand it  with fine grit paper. 

I'm trying to learn from you guys.

[Pappy]

Gene,
 
I thought about using Bondo because I use it on wood all the time. But I just took some regular wood filler and did the edges. Matt's idea to paint it will probably help a lot. Thanks, Matt.
 
If it doesn't work real good I might try replacing the plywood with some real slick plastic that I have. I don't think the hot PETG will affect it.
 
Stay tuned.

[Pappy]

I want to give you a little history on these cars. This class was started by a guy named Dan Dyke here in Cincinnati. He was the first to cast the bodies in resin and make up the rules for this class. Starting out the chassis had to be made of wood. Most of the guys used popsicle sticks for the main rail of the chassis. 

 

One of the guys in the series made a mold and casted chassis out of plastic. The guys liked it so plastic and wood chassis were legal. Since plastic was now legal I had some 1/2” thick plastic in yellow and black that I cut into nose pieces and motor brackets. I then bought a piece of 1/16” phenolic (which is plastic) and cut out the pieces to hold the motor bracket and the nose piece. I use little 1.6 x 4mm flat head screws to hold them together.

 

Dan is no longer making bodies and we basically out of them so another guy in our group made a 3D printed body and chassis combo. You just snap the motor and guide flag in, install your axles and gears and you’re up and running. Since his body is a lot lighter than the casted resin bodies I decided to make them out of PETG.

 

So that’s where we’re at right now. It’s a fun little car to race, the motors cost about $1.50 if you order a hundred of them so that’s what Dan and I did, we split a hundred of them. I’ve never had to replace a motor yet and we run them on 13.6 volts. I’ll be selling these bodies for $3 each and I sell the motors for $3 each. I’ll be rich before you know it. LOL

 

The first two pictures are my vacuum-forming machine. The 2x4 post's are my guides to keep the frame centered over the platen. In the background of the second picture is my toaster oven I use to heat the PETG. 

 

Third picture is my vacuum pump (it's old but it works) and the fourth picture is the frame that holds the PETG.

 

The fifth and sixth pictures are the mold that supports the body so I can back-pour it to make more molds. The seventh picture is the body I used to make the mold and I'm going to use to back-pour.

 

 

 

 

Eighth, ninth and tenth pictures is my mold. It's one of resin-casted bodies that we race that I modified to work as a mold. As you can see I put some wood filler on it but it still needs some sanding and cleaning up.

 

 

The rest of these pictures are just to show you how we make these cars. All the bodies are plastic resin and the chassis can be made of wood or plastic, no brass or piano wire.