Scroll Edges Fraying when Painted

[16BitIRL]

I've been scroll sawing for a few years, I mostly do wood-cut version of old video game sprites. I've been gradually having an issue with pieces from my scroll saw that I don't have with my jigsaw. After I paint the sides, no matter how much I sand, and how smooth they feel before painting, they start getting frayed. In the first pic from a Halloween decoration, the black-painted piece, this is off my jigsaw. I barely had to sand it. In the second pic, from my scroll saw, I sanded this edge down and it felt smooth, then I painted it and it frayed, sanded again, re-painted. After every painting, it frays.

When you step back and look at the whole piece you don't notice and it's fine, but this feels like it's getting worse. I mostly use 1/2 inch sande plywood from Home Depot, but I will also sometimes use a baltic birch from a lumber yard. Sometimes I mix in 1/4 inch pieces for 3D effect. The issue is not as bad from the baltic but it still happens. I use the Behr interior paints from Home Depot for the colors. Just looking to try and improve my skills.

[Wichman]

Welcome to the village.

What blades are you using? That edge is pretty chopped up. 

My first suggestion would be to get a sample pack of blades from the "big three"; Flying Dutchman, Pegasus, and Olsen. Try all the blades and see if there's one that just cuts well for you.

[Randyw81]

Most interior paints are latex (water-based). The water is probably swelling the wood fibers in the end grain layers of the plywood. You could try sealing the edges with a shellac or sanding sealer before painting. I'm not sure if it will help,  but it's worth a try. 

[JTTHECLOCKMAN]

That is end grain on plywood. It is swelling the grain because of the water based paint. Sealing it as suggested is probably a way out. Or use hard woods. Sande plywood is not the best plywood on the market. The top surface is fine but end grain will expand when wet. 

[jollyred]

I will seal the edges of plywood with Elmet's Glue All.  Other white or yellow pva glues will also work, but the Elmer's is cheaper.  Just apply a thin coat to all exposed edges using a brush, or your finger on straight edges.  I usually don't even sand the sealer after it dries.  Try it on a scrap piece of plywood to see if you like the results.

Tom

[Tomanydogs]

I don’t know what sande plywood is, but I use Baltic birch plywood  paint all sides except the bottom. I use acrylic paints. I don’t seal the edges and haven’t had the problem you are experiencing.  

[JTTHECLOCKMAN]

21 minutes ago, Tomanydogs said:

I don’t know what sande plywood is, but I use Baltic birch plywood  paint all sides except the bottom. I use acrylic paints. I don’t seal the edges and haven’t had the problem you are experiencing.  

https://www.h2ouse.org/sande-plywood/

I built my entire shop from Sande wood. Stable wood and back when I did my shop some 30 years ago or so.  I got  it at Home Depot very reasonable. One thing very different with BB(more layers and thinner layers) and Sande plywood is amount of layers. When they make plywood they alternate grain direction on layers to give stability and less warping and one reason you do not see as much grain raising as his problem. 

Edited October 13 by JTTHECLOCKMAN

[Tomanydogs]

19 minutes ago, JTTHECLOCKMAN said:

https://www.h2ouse.org/sande-plywood/

I built my entire shop from Sande wood. Stable wood and back when I did my shop some 30 years ago or so.  I got  it at Home Depot very reasonable. One thing very different with BB(more layers and thinner layers) and Sande plywood is amount of layers. When they make plywood they alternate grain direction on layers to give stability and less warping and one reason you do not see as much grain raising as his problem. 

Thank you for this information, I read the article too. I happen to have a project I want to do and I want to use Marine plywood however it’s expensive. I just googled my Home Depot and they don’t have Sande plywood unless they carry it under a different name. Maybe we can’t get it in Canada. 

[16BitIRL]

Thank you for all the help. I was assuming the paint was the issue, but then the pic with the black paint is from the same piece of wood with the same Behr interior and it’s fine with almost no sanding. I have been looking at possible better blades. My jigsaw was rough as well before I got better blades and I was shocked how much it changed things.

[16BitIRL]

My main effort is to build out a shop just the same. I try to make sure I can make this stuff so kids and families can decorate with them and not get too expensive so sande has been great. I have had people point out bits of edge texture in a good way and say it them feel more “real”, so this hasn’t been a killer issue, but since I have design and workflow down pat I want to tighten the craft side up.