Ask the Experts: Issue 6Comments (0)
This article is from Issue 6 of Woodcraft Magazine.
Avoiding Raised Grain
Q: I make finger labyrinths. This is basically a maze of concentric grooves routed into a solid piece of wood that you trace with your finger. I want the grooves to be smooth, but the grain keeps raising every time I varnish the workpiece. I’ve sanded and applied a second coat, but the grain raises again to make rough spots. I’m using Minwax Polycrylic. Any suggestions?
A.J. Hamler responds:
Minwax Polycrylic is a water-based finish. Water-based coatings have gained popularity due to their low odor, easy cleanup and fast-drying properties, but all water-based finishes raise wood grain to some degree. There are four things you can do to remedy this:
• If you apply a coat and then sand very lightly when it’s dry – just enough to remove the raising and no more – a second coat shouldn’t raise the grain as much, if at all. Eventually, you’ll get a good coat with no grain raising.
• You can “pre-raise” the grain before applying the coating. Sponge a bit of water over the bare wood to raise the grain. When it’s thoroughly dry, sand the raised grain off, remove all dust, and then apply your coating. You’ll still get some grain raising caused by the water-based finish, but it shouldn’t be nearly as bad. Lightly sand off the raised grain and recoat.
• You can apply a sealer coat of any non-water-based finish before applying the Polycrylic.
• Finally – and this may be the most obvious solution – don’t use a water-based finish.
A.J. Hamler is editor-in-chief of Woodcraft Magazine.
Touching Up a UV-Damaged Finish
Q: I have an oak front-entry door with sidelights that I installed three years ago. I used an oil-based stain and Helmsman varnish to seal it. I waited a couple of days for the stain to dry, and the same for the varnish. The door doesn’t face directly into the sun, but it does get morning sun and is covered by a porch overhang. The stain and Varathane are beginning to peel, although 95 percent of the finish is still in very good shape. How can I touch up the spots that are peeling?
Bob Flexner responds:
Ultra-violet rays in sunlight can break down any clear finish and cause it to peel. It doesn’t help much that the sunlight strikes the door obliquely or for only part of the day; the UV light will still destroy the finish far faster than if the door were totally shaded.
Pigment in the finish – that is, paint – is most effective at blocking UV light. Next are UV absorbers in the finish. The best are marine varnishes, which you can buy at a marina if you live in a coastal area. If you can’t find them locally, you can also order them through catalogs or over the Internet. Marine varnishes are far more effective UV blockers than home-center varnishes such as Helmsman.
Concerning your current problem, there are two considerations: missing color and missing finish.
It isn’t easy to fix the color damage so it blends perfectly, but you might be able to come pretty close. First, remove all loose finish with a light sanding, being sure to sand enough to smooth any roughness in the wood caused by exposure to the weather.
Then try wiping with the same stain you used originally and wipe off all the excess. (Try this on a small section first to see what happens.) Determine how close this comes to matching, and adjust the color from there. Apply a second coat to get the wood darker, and wipe with the thinner recommended for the stain to lighten the wood.
If you’re satisfied you’ve gotten the color close enough, let the stain dry and apply finish to the damaged area. When this finish has dried, give it and the entire door a light sanding, remove the sanding dust, and then coat the entire door.
It’s best to apply four or more coats. Then every year or two – or when the finish begins to dull, which is the first sign of deterioration – sand off the dullness and apply another coat or two to keep the finish up.
If you can’t get the color close enough for your satisfaction, you will have to strip the door, sand it and start over.
Bob Flexner is author of “Understanding Wood Finishing,” now in its second, fully revised edition.
Eliminating Blade Burn from Scroll Sawn Work
Q: Some woods, like cherry, burn easily when cutting on a scroll saw. Is there any way to eliminate this?
Robert Letvinchuck responds:
There are a few things that should be considered when it comes to your scroll saw, and the wood you’re cutting. First of all, you should check to make sure the thickness of wood being cut is compatible with the blade you are using – you don’t want to use a #02 fine blade to cut a piece of ½" cherry. You also wouldn’t use a #07 thick blade for cutting 1/8" material.
Blade speed should also be considered. When I am cutting finely detailed pieces with tight curves, I usually turn my blade down to half speed. Just because the blade speed is faster, doesn’t necessarily mean the cutting speed will be faster. The faster the blade is moving, the more burning you’ll get.
There are times, however, when I will use a thinner blade on thicker stock, but to eliminate the burning I will use a clear packaging tape, and simply adhere a strip of the tape over the cutlines on top of the workpiece. The tape acts as a lubricant and keeps the blade cooler during cutting, thus eliminating the burn marks. Using the tape also helps to extend blade life by as much as three times longer than normal. In the illustration shown, you can see where the tape was applied. I cut a piece of ¼" cherry using a #02 skip-tooth blade. It doesn’t take long for the cherry to start burning, but when the blade reaches the tape, the burning stops immediately, starting to burn once more after it has passed the tape.
Robert Letvinchuck has published numerous scroll sawn intarsia projects and articles. His latest project appears on page 38 of this issue.
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