Vol.1 No.15
4 September 2002

Julian Biggers Answers the Following Question, How do you Make Grooves in a Column that is Tapered

Q: How do you make the grooves in a pilaster that is tapered. I know they are shallow and narrow at the top and deeper and wider at the bottom. I'm sure I'm overlooking something obvious as the solution but I thought I was ahead of the game just figuring how to put the grooves evenly and of a precise depth in a parallel-sided pilaster (say that 3 times fast). This is the same problem as putting the reeding on a Duncan Phyfe leg. I can get the two outside reeds but the center one is a mystery. That can be a question for another day. JM

A: How do you make groves in a column that is tapered. I am assuming that this is the standard pilaster that projects from a wall to look like a support column, that it is tapered from bottom to top, and tapered on the sides. We want to groove/flute the front of the pilaster.

First, I would have to decide between using a "Bearing 90" or Bearing
45" bur to cut the grooves. (Bearing is the name for a shape of bur, and the number refers to the degrees angle of cut.) The "90" will give a regular right angle triangle cut, and the "45" will give an equilateral triangle cut. Size of bur (diameter) will depend on the size of pilaster we are working on.

Next a sled to hold the pilaster stock..just a piece of wood longer and slightly wider than the pilaster stock. This is to help slide the stock under the bur. Attach the stock to the slide, top and bottom, and equal to the sides.

Place sled and stock on drill press table. Bring the bur down to the smaller end of the pilaster stock, and set to depth needed for this top end. Cut pilaster stock from small to large end. If we are lucky, the taper in the stock will be right to give a deeper, wider bur cut at the bottom that is correct. If the bottom end is cut to deep/wide, then shim up the small top end a bit.(This is a bit of trial and error, but we should have a good idea how much to shim by the original cut.)File card stock is good for shimming. Make another cut with bur and adjust shimming accordingly. If the first cut we tried did not cut the bottom of the pilaster deep or wide enough, then shim up the bottom to take a deeper cut.

Once we have to groove cut satisfactory for the taper of the pilaster, then we can go to the easier(?) part of making the groove follow the sides properly. Mark off the top and bottom of the pilaster in the desired number of divisions i.e., starting and ending points on the pilaster. Hint: for odd number, say five, grooves mark the center and two outside points first, then mark the other two points half way between. Have an adjustable fence on the drill press table (long piece of wood held in place with "C" clamps). Place sled and stock on table with point of bur at mark for the center groove at small end. Slide fence up to sled, but do not tighten "C" clamps yet. Move sled to other end an check setting (point of bur should be over center mark of bottom). Adjust fence if necessary, then tighten clamps. Run the bur from top to bottom on all pieces of pilaster needed at this setting. Next, loosen "C" clamps and move sled over so point of bur lines up with top and bottom marks for outside groove, tighten clamps and cut grooves on all pieces again. Repeat this process of moving sled and aligning the fence to allow bur to cut the tapering groove top to bottom.

This seems long, but I am using a thousand words in lieu of a drawing. If it ain't clear, just ask. This assumes that you make an extra piece of pilaster stock for the trial and error portion of getting the depth of groove correct.

Grooving a Duncan Phyfe leg is a bit easier, I think, but saving that for later.

NOTE: Clear up/clean up discussion about "Bearing 90" and "Bearing 45" burs. The "90" cuts a groove as deep as it is wide, while the "45" cuts a groove twice as wide as deep i.e. shallower groove than "90". This is a lot simpler than what I said before. Selecting the appropriate size bur is important. Source: J.S.Ritter, 118 Preble St., Portland, ME 04101,
1-800-962-1468 has a wide variety of burs of different types and sizes.I suppose there are other jeweler's supply houses around the country, but this is one I've found cooperative.

That's all folks.

Julian

Tip, From Jim Morgan

Tip: We were talking in Linda Laroach's class at Castine and everyone was frustrated that they broke their jig-saw and jewelers-saw blades when they thought they were safely stored. Lo and behold--I got home and the new issue of Fine Woodworking had a helpful hint on the subject: buy, at the drug store, a packet of three plastic toothbrush holders ($ 1.00) that you use in packing for a trip. They are very sturdy--sort of rubbery--and don't break like the plastic tube your X-acto knife comes in. Come to think of it--that would be a good place to carry the X-acto knife since everyone seems to pack it with the blade left in.