Bill Tindall, E.Tn.
What follows is a description of how crown molding is made in the Mack Headley shop, Winchester, VA. This technique requires only 4/4 primary wood and it is easy to make a molding of any dimension.
A crown molding has 6 dimensions- depth of cove, width of cove and length and thickness of each side (PIC1). This tutorial will show how to make a cove with any desired size for each of these 6 dimensions. Some recollection of geometry will be helpful in understanding the process.
It is not necessary to construct a crown molding entirely from primary wood. The crown stock can be assembled from a piece of primary wood at least ¼” thicker than the depth of the cove and any backer secondary wood- pine or poplar for example, or primary wood with visual defects unsuitable for show surfaces(PIC 2). Setting up the saw will be less fiddly if the stock is a bit wider than the finished crown dimension.
Step 1 Lay out the profile on the end of the stock (PIC2). The two angles determine the length of the sides of the molding, which in turn determines how far out the molding sticks from the case side relative to the molding height. These angles are complimentary, that is they will add up to 90 degrees. If one angle is chosen to be 45 degrees the other is 90-45 = 45 degrees. In this case the crown molding will be symmetrical. It will stick out from the case the same amount as it is tall.
More commonly it is desired for the molding to stick out from the case less than it is tall. The smaller the angle is on the right side of PIC 2 the less the length of this side will be relative to the other side of the cove. For this molding I chose 35 and 55 degrees, PIC 2.
Often the thickness of the sides are not the same. The top of the crown may transition into a case top with a thin side, while the side against the case might be thicker to transition into some additional molding below the crown molding.
Step 2 Raise the height of the saw blade above the saw table equal to the desired depth of the cove. Measure the width of the portion of the blade that projects above the table . There are various conflicting recommendations for what blade to use, or to even use a molding cutter or specialty cutter for making coves. I find it easy to scrape away the saw marks so I use whatever blade is handy. Given how many minutes of one’s life will be spent shaping coves, optimizing the choice of blade is not something to fret over.
Step 3 Set the auxiliary fence. The width of the cove is determined by the angle of the fence relative to the front of the saw table.(PIC 3) At 90 degrees the blade cuts a slot. At zero degrees the cove width is equal to the width of blade that projects above the table.
Any desired width in between can be calculated by geometry (PIC 4). In words: divide the desired cove width by the width of the blade above the saw table to yield a fraction. The angle whose cosine equals this fraction is the angle to set the fence. I use a slide rule to calculate the cosine but others might prefer a modern telephone. If you don’t remember geometry the angle is determined empirically by adjusting the fence until the desired cove width is achieved, or by various means described by others. These processes are tedious compared to calculation and it will be worth the effort to find someone to do the calculation if geometry is forgotten.
Step 4 Cut the cove. (PIC 5) Starting with the blade about 1/16” above the table slide the stock across the blade. The crown stock will usually be a heavy piece of wood. Its mass will lessen the chance the blade will be inclined to throw it should you lose control. A push stick that provides some control of the stock is recommended.
Cutting the cove will be less risky if each cut is small to lessen the force of the blade on the stock. On my 10” saw I raise the blade 1/8 of a turn each pass, which is a bit less than 1/32”. There is little resistance with this sized cut. Wallowing out the cove will take 5 minutes so why rush it with heavy cuts and risk flinging the stock? For the last cut I raise the blade even less. It’s all over so fast it is difficult to fully experience the joy of this step.
Step 5 Scrape and Sand the cove. (PIC 6) It is much easier holding the stock at this point than after the angles are cut. I just clamp it in the bench vice. The cove is scraped and sanded to remove tooth marks. To sand I wrap a piece of 100 grit paper around something round like a can, or anything that is cylindrical with a radius somewhat smaller than the cove.
Step 6 Cut one angle, in this case the 35 degree angle. (PIC 7) The saw blade can be tilted up to 45 degrees. This limitation determines which crown angle is cut first.
Step 7. With the blade adjusted back to 90 degrees, cut the short leg of the cove to width. (PIC8)
Step 8 Now comes the risky part, cutting the long side of the molding. It can be done on the table saw (PIC 9). However, as can be seen in PIC 9 the blade is high above the table and there is limited way to secure and push the piece. The Headley shop has a special pushing device to push the crown through the saw safely. Or, the cut can be made on a band saw and the teeth marks cleaned up as needed with hand plane or jointer. (PIC 10)
Step 9 With the table saw blade adjusted to 90 degrees the length of the longer side of the molding is cut, yielding the finished molding (PIC1). Done in hardly more time than it took to study this description.
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- Crown Molding with a Table saw *PIC*