The standard scarf joint. Every carpenter is expected to make this field splice to join two lengths of molding. How often does the joint match perfectly? Any number of variables can affect the quality of the splice: Imperfections in the millwork, waves in the wall framing, taping compound buildup, inaccurate miter saw setup…The list is very long and well known to us all. I have intentionally assembled this scarf joint to resemble the kind of joint that occurs frequently on real job sites. The overlapping piece of molding has fallen a hair low and is out a bit at the top.
This is one of those joints that is really close, but not good enough to walk away from. If this were pre-finished material, it would signal a quick trip back to the miter saw. Luckily for us this is Poplar molding that will be painted. There is an easy way to fair this splice without damaging the profile. As you can see from the angle (right), the splice has full contact for glue surface, and other than the profile misalignment, it’s actually not a bad joint.
To solve this problem without a lot of tedious sanding I use contoured sanding grips. These are just little pieces of molded rubber similar to car tire material.
They come in a variety of shapes and sizes. You can purchase them in sets.
Wrapping the contour grip with regular sheet sandpaper creates a handheld sanding tool that will fit the various millwork profiles.
These are very similar to the sanding heads available for electric detail sanders. This one is from a $50-kit that I purchased for my Fein Multimaster. I was very disappointed with the kit for a number of reasons. For one thing, it was outrageously overpriced. More importantly though, the size and number of available profiles was so low it made the kit almost useless. To top it off, there is almost no tactile feedback when using a power detail sander. More often than not you will end up dulling the crisp edges of the profile while trying to smooth the joint because you just can’t see or feel what is happening.
So instead, I have been using my collection of sanding grips. They are available from several manufacturers. The ones shown here are part of the Tadpole series made by Perfect Panel Products. I buy them at the local Woodcraft store. They are fairly inexpensive with an average price of $6 per bag of 4-6 grips.
The most useful grips are the hollows and rounds. They do make other shapes, like these wedge profiles. These are nice for cleaning out v-joints and crisply cut fillets. They are cut at 30°, 45°, 60° and 90° angles. Series VII is the last set that I have seen locally. The Series I kit comes with a variety of shapes and also two different kinds of sanding pads.
Start off by finding the grips that will work best with your molding profile. This grip is excellent for fairing the flat portions of smaller moldings. For larger stuff, like baseboard, I use a sanding block.
Check the curves to see which radius fits. While the first one fit reasonably well, it’s usually better to select the smallest match. That way you will have better control and have less chance of inadvertently dulling the adjacent section while sanding.
This radius is too large for the job.
This little one fits like a glove.
Some of the radius grips are elongated so that they will work for both circular and elliptical profiles (they look like tadpoles too). Flexing the grip in sideways will sand this section in one shot.
The handles on the grips can also be used to clean out fillets and they can be flexed to pick up areas that do not fit the other shapes.
The smaller grips have narrower handles.
This handle is a little bit too big to clean out this fillet. You may have noticed that the last grip had a pointed handle. Most of the grips come with rounded handles. I have found that it is easy to modify the handles with a sharp block plane. You can cut chisel shapes, long tapers, or even just square the edge for crisp channels.
Like the traditional hand plane hollows and rounds, these are matched by radius. If you have trouble setting the paper in the cove shaped grip, you can always use the matching radius grip to tighten it up before you sand delicate materials.
So what about moldings that have some small details, and a few large ones like the cove on this crown molding? That’s a bit too big for the regular grips.
In circumstances like this I would normally use a large wooden dowel wrapped with PSA (Pressure Sensitive Adhesive) sandpaper. I have been known to use any cylindrical shape in a pinch, like this caulking tube. The key to using this is to sand diagonally while slowly rotating the tube. It’s kind of like using a rolling pin. Otherwise you could try the sanding pad, but I prefer not to use anything soft.
A full set of dowels comes in handy for tuning copes, and sanding odd shapes. I used a short length of 1 5/8-in. fir closet pole to remove the band saw marks from the radius cuts on these brackets. I didn’t have to pull diagonally in this case.
This is one of the sanding pads that comes with the Tadpole I kit. I used this last to smooth the edges of two double action doors that I rounded over with a 3/4-in. router bit. This pad helps fill out the shape of my hand while also preventing friction burns as I sand the entire stile in one pass.
Another useful thing to have is a set of sanding blocks made from small hardwood scraps. Wrapping these blocks with PSA roll sandpaper creates some very handy sanding tools. Crease the paper tightly when you wrap the block so that you will be able to get into 90° corners. Cut the blocks to the width of your PSA roll. 1×4 blocks work great for sanding plugs, and small 1-in. square sticks are handy to keep in your pouch. These are great for removing fuzz from miter saw cuts and any little touch-ups that you would normally use a small paper scrap for. Plus they are much easier to find in your pouch than sandpaper.
Sanding sponges like this have their place. I use these all the time for drywall touch-ups, but they are mostly useless for carpentry. There are other stiff sanding blocks like this that have grit all throughout. This is a soft sponge with sanding grit on the outside only.
You may be thinking, “Why not use the sanding grips to tune copes?”
The truth is that they are really too soft for this task. It would be too easy to distort the profile.
Besides, if you had an old Copemaster you wouldn’t need to tune your copes. Unfortunately, it seems that the Copemaster is no longer in production, and the manufacturer most likely went out of business. But maybe you can find a used Copemaster online!
Now that you know, let’s sand that splice starting with the flat section. If you have used yellow glue for the joint, it is imperative to make sure that both the glue and the wood are dry. The moisture in PVA glue will raise the grain of your molding. If you sand or plane the wood flat before the wood has dried, you will be left with a depression when the grain goes back down. Start in with short strokes so that you do not tear the paper or lift splinters from the overlap. Gradually increase the sanding stroke until you have smoothed the wood out at least several inches in each direction. Keep working the profile until you can no longer catch the splice with your fingernail. It should not take more than a minute or two to complete the job.
Work your way up the profile hitting every area that your current grip will fit. Use the handles to get into the fillets. The hardest spots can be reached with just the folded edge of the paper.
You may wish to go over the profile again with a finer grit. For this demonstration I have just used 100. Normally I would use 180 or 220 to fair my joints. By the way, the Norton 3X sandpaper is really great stuff. I was skeptical at first, but I have found that it really does last a lot longer and cut better than the old brown stuff.
All of the overlap has been removed in the final joint. You can still see the glue line because I did not apply pressure to the joint. I used 2P-10 for the test so that I could force the misalignment. Even though you can see the joint, you would not be able to feel it.
The joint is almost invisible when viewed from the end. You can also see that the molding is slightly hinged at the splice because of the misalignment. This was a continuous piece of straight molding before I cut it (note the grain).
Countour sanding grips can be purchased from a number of retailers; Lee Valley Tools sells a variety of sets online, starting at $5.20 for a set of 4 angled sanding grips.