Composites Fabrication And Repair Carbon Fiber, Kevlar, Fiberglass and all the newest high tech composites

Avoiding are voids in corners

Reply

Old 10-09-2004, 12:39 PM
  #1  
tschmidt
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2002
Location: Fort Scott, KS,
Posts: 376
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Avoiding are voids in corners

I always have trouble with air voids in corners. What method do you guys use to avoid this problem? I usually make a mixture of cabosil and milled fibers to put in the corners before laying down the cloth. Do you let the corners get tacky before laying the cloth so it won't dilute while adding resin? I usually don't which is probably why I have problems. Let me know your secrets guys!


Todd Schmidt
tschmidt is offline  
Reply With Quote
Old 10-09-2004, 05:06 PM
  #2  
Ed Smith
Senior Member
 
Join Date: Dec 2001
Location: Brantford, ON, CANADA
Posts: 3,305
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

Todd,

This is what I do. On inside corners like for example the sharp corner of the wing fillet/saddle I lay in a bead of filler, cabosil/resin. To hold it all in place I lay in some strands of glass. On ordinary inside corners I again lay an a fillet and then a narrow strip of cloth, then the lay up.

On outside corners in the mold, again I use filler and then an appropriate size piece of cloth cut on the bias to wrap around the corner. Then the layup. The small pieces of cloth give something for the layup cloth to stick to other than just the sloppy filler.

I do not wait for the filler to go tacky.

Ed S
Ed Smith is offline  
Reply With Quote
Old 10-09-2004, 05:55 PM
  #3  
Mike James
Senior Member
 
Mike James's Avatar
 
Join Date: Jan 2002
Location: Anchorage, AK
Posts: 2,565
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

Todd,

Ed is right. Your trouble is probably mixing the glass fibers with your first batch of filler. I use #1099 surfacing resin, which won't run or drip, from http://www.fibreglast.com but resin and Cabosil works just as well. BUT... make your first layer without the fibers. Cabosil can easily be made thick enough where it won't run, (or use the surfacing resin) but save the fibers until later.

I know you know this, but it's key...
Whatever you use, take as much care as you can, when you mix it, to avoid introducing air bubbles. An impeller-type mixer, which goes to the bottom of the cup, is the best way to mix. Tap the container of mixed "goop" on the table to loosen bubbles, let it exotherm for a few minutes, and when you apply it, really press it into the corners tightly, to remove bubbles. (I typically use a gloved finger, or a popsicle stick to press the stuff into the corners.

One other thing...
I recommend applying the next layer, whether it's cloth or resin, before your corner fillet has cured, so that you get chemical bonding. (It would be difficult or impossible to scuff a cured fillet enough to bond mechanically, without scuffing the surrounding mold surface, PVA, wax, etc..)
Mike James is offline  
Reply With Quote
Old 10-15-2004, 04:03 PM
  #4  
tommyboy1229
Senior Member
 
Join Date: Jul 2003
Location: Richardson, TX
Posts: 186
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

Mike,
Do you use the 1099 white or do you use pigment? I have used pigment and it does not get as hard. In some cases I have had to remake a mold half.
tommyboy1229 is offline  
Reply With Quote
Old 10-15-2004, 06:52 PM
  #5  
Mike James
Senior Member
 
Mike James's Avatar
 
Join Date: Jan 2002
Location: Anchorage, AK
Posts: 2,565
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

I use #1099, with as small an amount as possible of black pigment. (also from fibreglast.com)

I too have had problems with the pigment seeming to mess up the curing of the resin, but over the last few years, have found that it was simply a matter of not mixing the tooling resin, hardener, and pigment thoroughly enough. On the past few years, I've continued to use the same chemicals, but have been more careful about the mixing, and have had no such problems.

As you probably know, it's very important to scrape the sides of the container while mixing. If you have uncured resin in the "leftovers" cup when you come back later, that's a sign of insufficient mixing. The tooling resin is so much thicker than laminating resin that it just takes a bit more work.
Mike James is offline  
Reply With Quote
Old 10-16-2004, 12:32 PM
  #6  
tommyboy1229
Senior Member
 
Join Date: Jul 2003
Location: Richardson, TX
Posts: 186
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

Thanks Mike,

I use the same pigment. I have noticed also that it is best to use as little pigment as possible. Since the 1099 is white it is very difficult to get it black, I have had better luck just accepting a kind of dark grey. I have been weighing the hardner and resin, then adding the pigment and mixing thoroughly, then adding the hardner and mixing thoroughly, and then I pour the contents into a new cup and mix again. I have never had a problem with it getting hard until I used the pigment. The less pigment I use the harder it gets. I have also tried adding just a little extra hardner to compensate for the extra weight of the pigment. This seems to help a little. Is this similar to the process you use?

Thanks,
Tom
tommyboy1229 is offline  
Reply With Quote
Old 10-16-2004, 01:59 PM
  #7  
davidfee
Senior Member
 
Join Date: Jun 2003
Location: San Diego, CA
Posts: 691
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

In my experience, dry (powder) pigments alter the physicals of an epoxy system far less than the gel (goo) pigments. For a black surface coat, try graphite powder (available from WEST Systems). It's pretty dark and adds abrasion resistance to your surface. Two birds with one stone, so to speak.

-David
davidfee is offline  
Reply With Quote
Old 10-16-2004, 05:34 PM
  #8  
Mike James
Senior Member
 
Mike James's Avatar
 
Join Date: Jan 2002
Location: Anchorage, AK
Posts: 2,565
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Avoiding are voids in corners

I mix as you describe, but I never alter the ratio of hardener to epoxy. (I use the West Systems pumps.)
Mike James is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy