Materials Testing: Fillets

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Zach
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Materials Testing: Fillets

Post by Zach »

I've been doing some testing of different products for doing fillet work prior to painting.

I'm finding that fillets get worse the more you goof with them, and am working towards the right combination of putty and tool to apply them so only a bit of hand sanding is required to give tooth for paint.

The white putty is Proset 185/285 http://www.prosetepoxy.com/fairing.html
It is hard to see from the picture, but it pulls a fillet that looks wet, and ready to paint with minor filling.

The purple/grey stuff is West System 105/205 mixed with 407 filler almost past peanut butter. This pulls smoothly, but hardens with a grainy texture. It leaves something to be desired on the cleanup to each side of the fillet.

The red putty is Awlgrip Awlfair http://www.awlgrip.com/products/search/ ... ir_LW.aspx
This doesn't pull well at all for fillets, and is the reason for my quest to find a suitable replacement. It works well, hardens reliably, and sands relatively easily on flat panels and for doing bulk fairing. Detail work, its not much fun to work with.

I have a can of West System 410 waiting for a test. 407 and 410 cost more per mixed batch than either Awlgrip or Proset, on account of the volume of powder required per batch to achieve consistency... and labor to mix them together.

The filleting tool is a 1 1/4 inch stainless steel ball that I welded onto a piece of a bolt. Commercially these it would be a "filleting tool" for installing wax fillets into fiberglass production molds, available from Bodi. McMaster Carr carries the stainless balls. A blob two inches or so wide is placed along the length of the surface to be filleted, every 4 or 5 inches. After the fillet is worked smooth, a west systems glue mixing stick comes along and cleans up the excess on each side. (hopefully without hitting the fillet, and causing the need for it to be re-worked.)

Trying to use a plastic squeedgee with the fillet cut in the edge works ok, so long as you hold absolutely steady perpendicular to the work surface... and pull it only from one side of the panel. When the panel changes angles or has a rolling bevel along its length, the fillet changes shape or leaves an undercut at the edge.

Ball or knife... it does matter that there are no lumps bumps or low spots that will effect the travel of the tool, otherwise they end up in the fillets. A good fillet covers a corner that has a wave and wiggle... but not big localized hump or low.

The shrinkage of the epoxy putties was unexpected... I forgot to take a picture, but you can see light around the entire ball, between where it touches the plywood on each side of the jig. What that means, is going around and pulling the fillets a second or third time makes a different radius (in cross section) than what was left from the first... It may not make a hill of beans, but when you have two or three fillets converging in a corner it is surprisingly noticeable when one side looks thinner than the rest. "All I wanted to do was fill the grooves and holes..."

Second thought on epoxy shrinkage: Sanding the fillets means that the sanding tool is smaller than the filleting stick you used to pull it... also subtracting the shrinkage, and the sandpaper thickness. 80 grit sandpaper is around 25 thousandths thick. 120-220 is 12-15 thousandths. That means .050 thousandths smaller diameter sanding block than the tool used, for 80 grit sandpaper alone... A 1/6th is .0625. Otherwise the tool contacts only the two surfaces each side the fillet, and grinds a groove on each side that shows in the paint work.

Epoxy continues to shrink until its full cure stage... a few weeks, which at that time it gets harder to sand and shape. It is a double edged sword as it is easier to work right after it has been applied and set, but it does move a bit after the initial sanding. New and old putty side by side, sand at different rates.

Have you guys any tips or tricks for fillets?

Cheers,

Zach
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1961 Pearson Triton
http://pylasteki.blogspot.com/
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Hirilondë
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Boat Name: Hirilondë
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Re: Materials Testing: Fillets

Post by Hirilondë »

I apply the filler with a plastic spreader that has been cut round to the size and shape of the fillet I want. I "trowel" it to the size and shape I want with this tool. I then let it start to kick. When it is still a little soft but firmed up a bit I wet out my gloved finger with mineral spirits and feather it out. It is kind of like finish trowelling concrete. You can no longer move the material, but you can finish the surface. Then I quit while I am ahead. Too much playing usually messes things up. If I am going for a really perfected finish I will be prepared to do some touch up work.

I like a mud made with West fillers. I use a little 406 for adhesion, and some 407 for body, and some 410 if much sanding will be done.
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
Gresham’s Law of information: Bad information drives out good. No matter how long ago a correction for a particular error may have appeared in print or online, it never seems to catch up with the ever-widening distribution of the error.
barrybrown
Master Varnisher
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Joined: Tue Aug 12, 2008 6:39 pm

Re: Materials Testing: Fillets

Post by barrybrown »

Zach,

I don't have your experience with fiberglassing and probably have lower standards for the finished product buy I have found that using peel ply lets me shape and work the fillet without damaging it. It also seems to reduce or prevent sagging and gives me a much better fillet usually not requiring sanding and to the best of my knowledge no blush.

Barry
Zach
Boat Obsession Medal Finalist
Posts: 684
Joined: Wed Jan 25, 2006 6:28 pm
Location: Beaufort, North Carolina
Contact:

Re: Materials Testing: Fillets

Post by Zach »

Thanks for the feedback guys, I'll give the west systems mud a try... and see what peel ply does for a fillet. I'll give the mineral spirits a try, I've used acetone and denatured alcohol trying to slick out the surface without much success... perhaps spirits are the trick.

Can't say I've ever thought about peel ply for that application!

Cheers,

Zach
1961 Pearson Triton
http://pylasteki.blogspot.com/
1942 Coast Guard Cutter - Rebuild
http://83footernoel.blogspot.com/
Hirilondë
Master of the Arcane
Posts: 1317
Joined: Thu Dec 28, 2006 8:50 am
Boat Name: Hirilondë
Boat Type: 1967 Pearson Renegade
Location: Charlestown, RI

Re: Materials Testing: Fillets

Post by Hirilondë »

Are you going to be glassing these fillets Zach? Or are these just a finishing touch for inside corners?
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
Gresham’s Law of information: Bad information drives out good. No matter how long ago a correction for a particular error may have appeared in print or online, it never seems to catch up with the ever-widening distribution of the error.
Zach
Boat Obsession Medal Finalist
Posts: 684
Joined: Wed Jan 25, 2006 6:28 pm
Location: Beaufort, North Carolina
Contact:

Re: Materials Testing: Fillets

Post by Zach »

These are just the finishing touch.

I generally glass with a west systems mixing stick size fillet, if the glass is not overly structural Then a larger fillet of putty on top to smooth things out and cover any inconsistency... and not have to grind/sand through the glass.

I've found larger diameter fillets under the glass make it more difficult to long board out new construction as the outer corners lift the board and end up making a dished panel or low spot a foot or so out. I try to keep putty to a minimum, a piece of 1/8th inch aluminum channel held with the point toward the work doesn't bow and pull a low spot in the center of a panel like a piece plywood with a straight ripped edge.

A large fillet makes it hard to work right up to an inside corner and make a dead flat panel without waves where the putty knife or what have you rides up the side.

I'm also not much for having to hose 10 coats of primer on to fill the inconsistency in inside corners, as it takes a lot of labor hours to get the required build and not have solvent popping problems.

Zach
1961 Pearson Triton
http://pylasteki.blogspot.com/
1942 Coast Guard Cutter - Rebuild
http://83footernoel.blogspot.com/
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