Vacuum bagging a cavity mold
#1
Senior Member
Thread Starter
My Feedback: (2)
Join Date: Dec 2001
Location: Benbrook,
TX
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
I have done a lot of vacuum bagging of wings and parts over male plugs but I am a little confused on bagging cloth laid up in a cavity mold. I am concerned of two things,
1. Normally when I lay up cloth in a cavity mold I run cloth up and out the mold around ¼” and trim right after it starts setting. As it is a mess and next to impossible to trim wet how do you handle the extra cloth when bagging the mold?
2. How do you stop the bag from wrinkling inside the mold leaving nasty lines of epoxy?
Does anyone know of any web pages or do you have any pictures of bagging a mold? Thanks
1. Normally when I lay up cloth in a cavity mold I run cloth up and out the mold around ¼” and trim right after it starts setting. As it is a mess and next to impossible to trim wet how do you handle the extra cloth when bagging the mold?
2. How do you stop the bag from wrinkling inside the mold leaving nasty lines of epoxy?
Does anyone know of any web pages or do you have any pictures of bagging a mold? Thanks
#2
Junior Member
Join Date: Oct 2002
Location:
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Bagging female molds
The best way to haddle this problem is let the cloth hang over 1" instead of 1/4" and use some sort of release cloth, I aways use peel ply and let the peel ply hang over 1" more you can tape the peel ply, but when you apply vacuum slowly it will lay down perfect. Using peel ply that way you have a great surface to bond your formers too.
#3
Senior Member
Join Date: Mar 2002
Location: Plainfield,
IN
Posts: 151
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
Here is a neat bagging material for bagging concave molds. If George Sparr or CST doesn't carry it maybe someone can talk them into carrying it. Or one could buy a whole roll of it for 129.95 from Airtech.
#4
Senior Member
Join Date: Mar 2002
Location: Plainfield,
IN
Posts: 151
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
#5
Senior Member
Thread Starter
My Feedback: (2)
Join Date: Dec 2001
Location: Benbrook,
TX
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
Originally posted by winship
Here is a neat bagging material for bagging concave molds. If George Sparr or CST doesn't carry it maybe someone can talk them into carrying it. Or one could buy a whole roll of it for 129.95 from Airtech.
Here is a neat bagging material for bagging concave molds. If George Sparr or CST doesn't carry it maybe someone can talk them into carrying it. Or one could buy a whole roll of it for 129.95 from Airtech.
#6
Senior Member
Thread Starter
My Feedback: (2)
Join Date: Dec 2001
Location: Benbrook,
TX
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
Re: Bagging female molds
Originally posted by rcjetgirl
The bast way to haddle this problem is let the cloth hang over 1" instead of 1/4" and use some sort of release cloth, I aways use peel ply and let the peel ply hang over 1" more you can tape the peel ply, but when you apply vacuum slowly it will lay down perfect. Using peel ply that way you have a great surface to bond your formers too.
The bast way to haddle this problem is let the cloth hang over 1" instead of 1/4" and use some sort of release cloth, I aways use peel ply and let the peel ply hang over 1" more you can tape the peel ply, but when you apply vacuum slowly it will lay down perfect. Using peel ply that way you have a great surface to bond your formers too.
#7
Junior Member
Join Date: Oct 2002
Location:
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
trimming
all trimming should always be done when the part is Green, Green meaning not totally cured. So if you are using 1 hour slow resin wait about 1 hour 45 min and slide razor blade around part. if you wait till part completely cures your just waiting for the razor to slip and due some damage to the part and you.
#8
Junior Member
Join Date: Oct 2002
Location:
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Thinkness
The main reason to use composites is to build a light and strong part, as a norm I use three lairs one light two med and I insert my carbon after the first lair and follow with the second two, use peel ply, purple perf plastic, breath cloth and the bag using about 15 inch pounds Mercury. The fist cloth is about 5 mils the last two 10 mils. With carbon 5.7 oz. in different areas.
#9
My Feedback: (2)
Join Date: Jul 2002
Location: Calgary, AB, CANADA
Posts: 401
Likes: 0
Received 0 Likes
on
0 Posts
Re: Bagging female molds
Originally posted by rcjetgirl
The best way to haddle this problem is let the cloth hang over 1" instead of 1/4" and use some sort of release cloth, I aways use peel ply and let the peel ply hang over 1" more you can tape the peel ply, but when you apply vacuum slowly it will lay down perfect. Using peel ply that way you have a great surface to bond your formers too.
The best way to haddle this problem is let the cloth hang over 1" instead of 1/4" and use some sort of release cloth, I aways use peel ply and let the peel ply hang over 1" more you can tape the peel ply, but when you apply vacuum slowly it will lay down perfect. Using peel ply that way you have a great surface to bond your formers too.
#10
Senior Member
Thread Starter
My Feedback: (2)
Join Date: Dec 2001
Location: Benbrook,
TX
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
Re: Re: Bagging female molds
Originally posted by ptxman
Do you break the vacuum at a pre-determined semi-cure point & trim it green? Doesnt that then disturb the peel ply or do you just trim through bothcloth & peel ply on the joint & leave the rest in the fuse until cured?
Do you break the vacuum at a pre-determined semi-cure point & trim it green? Doesnt that then disturb the peel ply or do you just trim through bothcloth & peel ply on the joint & leave the rest in the fuse until cured?
#11
Junior Member
Join Date: Oct 2002
Location:
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
The Vacuum only serves to remove the air prior to the post cure, after the resin kicks you no longer need the vacuum. The peel ply cuts like warm butter, if you cut enough of it you will find, you will just barely need to slide your sissors to pre cut. So on the molded part itself no problem. As for the 1" when you apply vacuum you will find that the cloth will slide into areas were it needs to be so you want the extra, and the mold you constructed should have a wide flange all away around the part so you have room for bagging and trimming. The more you work with making molds, you will find things to make it easier for yourself and build them into the mold.
#12
My Feedback: (2)
Join Date: Jul 2002
Location: Calgary, AB, CANADA
Posts: 401
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
Originally posted by rcjetgirl
As for the 1" when you apply vacuum you will find that the cloth will slide into areas were it needs to be so you want the extra, and the mold you constructed should have a wide flange all away around the part so you have room for bagging and trimming. The more you work with making molds, you will find things to make it easier for yourself and build them into the mold.
As for the 1" when you apply vacuum you will find that the cloth will slide into areas were it needs to be so you want the extra, and the mold you constructed should have a wide flange all away around the part so you have room for bagging and trimming. The more you work with making molds, you will find things to make it easier for yourself and build them into the mold.
#13
Junior Member
Join Date: Oct 2002
Location:
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
prefect picture
This is a perfect example ! The more you work with bagging you will find all sorts of tricks. Try different types of bagging materials as well, if you are looking for a material to stretch try PVC bagging plastic. I have even used plastic trash bags and mylar tape. It also helps if you work with the stuff all day.
#14
My Feedback: (2)
Join Date: Jul 2002
Location: Calgary, AB, CANADA
Posts: 401
Likes: 0
Received 0 Likes
on
0 Posts
Re: prefect picture
Originally posted by rcjetgirl
This is a perfect example ! The more you work with bagging you will find all sorts of tricks.
This is a perfect example ! The more you work with bagging you will find all sorts of tricks.
#15
My Feedback: (2)
Join Date: Jul 2002
Location: Calgary, AB, CANADA
Posts: 401
Likes: 0
Received 0 Likes
on
0 Posts
Re: prefect picture
Originally posted by rcjetgirl
Try different types of bagging materials as well, if you are looking for a material to stretch try PVC bagging plastic. I have even used plastic trash bags and mylar tape. It also helps if you work with the stuff all day.
Try different types of bagging materials as well, if you are looking for a material to stretch try PVC bagging plastic. I have even used plastic trash bags and mylar tape. It also helps if you work with the stuff all day.
Do you apply the resin to the galss in the mold or externally squeegeed & then layed in?
What releasing agent or system are you using?
#16
My Feedback: (10)
Vacuum bagging a cavity mold
AV8TOR emailed me the other day and I didn't have time to respond till now. I figured that it would be better if I answered some of his q's here so that all can see.
As can be seen in my Tsunami project threads, I have been bagging wings and fuselages in the molds to give a strong composite structure with aeromat, balsa or similar core materials.
The threads are here (and are long!) they show construction of several wings, tails and fuselages.
http://www.rcuniverse.com/showthrea...268&forumid=113
http://www.rcuniverse.com/showthrea...684&forumid=113
http://www.rcuniverse.com/showthrea...441&forumid=113
For instance, on a fuselage, I usually cut the cloth oversize. I try to leave about a 1" lip over the edge of the mold. This is trimmed after the epoxy is dry and the molds removed. If you have more overhang, it is no big deal as it is trimmed off. Care has to be taken to not damage the mold when trimming, pull the part out, or cut too far and leave a gap in the fuselage. I usually get it close and then sand the rest off carefully.
My fuselages are typically one to two layers of cloth on the outer surface, some extra around the tail, firewall, and wing mount areas (layed at a 45 deg bias), then the core material. The core is sandwiched in with a complete layer on the top. I work this in with brushes until I am satisfied and then I cut peel ply to be placed into the mold. Usually, one has to cut strips, or chunks of the material to ensure that it conforms. After that, some breather is put down the mold and then the whole thing placed into the bag and then turned on.
While it is sucking down, I ensure that there is extra bag slack in the mold area so that it doesn't pull any of the edges of the glass inward and mess everything up. Once it gets close to having all the air escaped, one can make the bag fit and ensure that it can vacuum everything down. At that point, you let it sit till the epoxy has cured and then trim the edges the next day. The bag will get some wrinkles and some will transfer to the part. On compound parts, I don't really see any whay around this unless you have a bagging material that is really rubbery and can conform and stretch to everything.
I use anywhere from 10 to 15" Hg when bagging wings or fuselages in molds. It is really a lot of pressure per square inch even at 5"... But, if your mold is really robust, you can crank it up. After doing a few fuselages, you will see where you use a lot of epoxy and enough because the breather and peel ply will saturate if there is too much. Generally, any light areas mean that the area is somewhat dry.
The main advantage to this method is that by bagging, using peel ply, and breather cloth, you suck up any unecessary epoxy and have a surface that can be glued to once the peel ply is removed. It is strong and light weight.
Anyways, hope this helps. I've been playing with composites for several years and kinda taught myself by reading and looking at what others do. I found molding interesting and know how hard it can be to understand when you are first starting out. I like to share it because I like to see others build. There is what seems to be a decline of "real modelers" nowadays. And what I mean by a real modeler is one that builds and constructs airplanes. Too many people build arfs and it seems like the art of modeling is being lost.
Regards,
Michael
When do you trim the excess cloth that is up around the mold part line? Do you just cut it after the part is cured? In a cavity mold how do you prevent wrinkles from the bag? After the cloth is laid in the mold what do you add next, peel ply and blotter material then place it in the bag at 12hg?
The threads are here (and are long!) they show construction of several wings, tails and fuselages.
http://www.rcuniverse.com/showthrea...268&forumid=113
http://www.rcuniverse.com/showthrea...684&forumid=113
http://www.rcuniverse.com/showthrea...441&forumid=113
For instance, on a fuselage, I usually cut the cloth oversize. I try to leave about a 1" lip over the edge of the mold. This is trimmed after the epoxy is dry and the molds removed. If you have more overhang, it is no big deal as it is trimmed off. Care has to be taken to not damage the mold when trimming, pull the part out, or cut too far and leave a gap in the fuselage. I usually get it close and then sand the rest off carefully.
My fuselages are typically one to two layers of cloth on the outer surface, some extra around the tail, firewall, and wing mount areas (layed at a 45 deg bias), then the core material. The core is sandwiched in with a complete layer on the top. I work this in with brushes until I am satisfied and then I cut peel ply to be placed into the mold. Usually, one has to cut strips, or chunks of the material to ensure that it conforms. After that, some breather is put down the mold and then the whole thing placed into the bag and then turned on.
While it is sucking down, I ensure that there is extra bag slack in the mold area so that it doesn't pull any of the edges of the glass inward and mess everything up. Once it gets close to having all the air escaped, one can make the bag fit and ensure that it can vacuum everything down. At that point, you let it sit till the epoxy has cured and then trim the edges the next day. The bag will get some wrinkles and some will transfer to the part. On compound parts, I don't really see any whay around this unless you have a bagging material that is really rubbery and can conform and stretch to everything.
I use anywhere from 10 to 15" Hg when bagging wings or fuselages in molds. It is really a lot of pressure per square inch even at 5"... But, if your mold is really robust, you can crank it up. After doing a few fuselages, you will see where you use a lot of epoxy and enough because the breather and peel ply will saturate if there is too much. Generally, any light areas mean that the area is somewhat dry.
The main advantage to this method is that by bagging, using peel ply, and breather cloth, you suck up any unecessary epoxy and have a surface that can be glued to once the peel ply is removed. It is strong and light weight.
Anyways, hope this helps. I've been playing with composites for several years and kinda taught myself by reading and looking at what others do. I found molding interesting and know how hard it can be to understand when you are first starting out. I like to share it because I like to see others build. There is what seems to be a decline of "real modelers" nowadays. And what I mean by a real modeler is one that builds and constructs airplanes. Too many people build arfs and it seems like the art of modeling is being lost.
Regards,
Michael
#17
Member
Join Date: Jan 2003
Location: petaluma, CA,
Posts: 73
Likes: 0
Received 0 Likes
on
0 Posts
Vacuum bagging a cavity mold
Well said Michael, these people that try this for the first time have there hands full. Go back and read what Michael has to say, he said what I would teach my Students. This is a art that has to be learned my taking the Composites Course at your schools, or Self Taught in your Garage. You people here are making Models, if you get it wrong, it dies and not you. So start out using the cheapest way you can on your projects, and give it a try. What have you lost?? $20.00 big deal I say..
Mike
Mike
#18
Senior Member
Join Date: Jan 2002
Location: Anchorage,
AK
Posts: 2,565
Likes: 0
Received 0 Likes
on
0 Posts
Passing it on...
Oliver Wilson ("Ollie" here on RCU) recommended a great video to me last year, which shows the entire process, from plug making to mold making, through making actual parts. The video is called "Building Hollow Composite Aircraft Structures", and features the expert craftsmanship of Fred McClung. You can order it through "Soaring Stuff", at http://www.soaringstuff.com/
These are precise, lightweight, and VERY strong wings, capable of taking 40 to 50 Gs. Perfectly adaptable to scale, pattern, etc..
These are precise, lightweight, and VERY strong wings, capable of taking 40 to 50 Gs. Perfectly adaptable to scale, pattern, etc..