Welcome fellow Lumberjocks to the second installment of my blog.
I hope that you felt like the information presented in the opening episode of this blog was properly presented and that I was able to convey the information to you in an understandable manner.
Unfortunately, in the opener we had to cover a lot of necessary information and provide a lot of pictures so that all Lumberjocks could understand the concept and construction of the jig.
In this posting we will again be dealing with alot of preliminary information and as we deal with the creation of your wood blank, attaching our pivot point (or axle) to our blank, and we will assemble the jig parts and the wood blank into our working assembly or “sandwich”. I promise that after we get through this episode we will be well on our way to making your own dished serving trays.
Creation of your blank
For projects such as these a one piece blank is more appealing to the eye. But 22” wide slabs of hardwood, like those that are needed to make the large serving trays, are hard to come by (at lease they are out here on my neck of the treeless prairie), so we have to make them.
When creating large glue-up slabs, edge glueing techniques become a concern. I do not feel that it is necessary in this blog’s setting to discuss the specific techniques to create a large wood blank. Skills for edge glueing, joining, and planing multiple pieces of lumber into a single large blank are subjects that I will allow you to explore on your own.
I do however have several recommendations and points that I would like to make for your wood blank creation.
-If possible book match your boards, or in the least take careful consideration of the grain when slip matching.
-If you chose to use biscuit joinery, you will find it difficult to “dish out” the center of your work as the interior router cuts will expose and destroy your biscuits.
-My suggested technique is to use a locking router cut to join your pieces together, for as much strength as possible.
-I have had success with simple edge-butt glue joinery, but I have found that the router expresses a great deal of stress on the wood blank during the dishing process, and I have had several of these weaker joints fail during the routing process. (read that as: fresh firewood)
-If dishing the center of your work, I suggest using a minimum of 4/4 or 5/4 stock. A dished center on thinner stock will of course mean a shallower dish cut (that does not allow much edge material to shape the rim , or a center section that is thin and weak).
Sizing your blank
Obviously the overall size of your blank will be dependant upon the intended size of your project (duh?). One of the great aspects of this jig is that it will work for nearly any size of circular output desired. In theory, the working drawing submitted in installment #1 will work for creating circles up to approximately 22” in diameter down to 2 ½” (slightly larger than the center hub & axle) .
However, keep in mind that circles smaller than the overall width of our jig, are difficult to turn as there is no stock sticking out of the jig “sandwich” to grab ahold of and turn into the router bit. I do not recommend that you place your precious fingers at risk, by placing them inside the halves of the jig, with a hungry spinning router bit lurking between them. So words to the wise….for the smaller pieces, either use a smaller jig, or a different safer technique altogether.
Of course, if you need to create a circle larger than the jig constructed in blog episode #1, all you have to do is create a larger (longer) jig.
So now it is time to rough out the circular shape of your blank.
I feel that an important step in a obtaining a nicer finished product from this technique is to carefully consideration in placement of your center point. Try to mirror the areas of your piece by placing your center point on a central joint (if applicable). Otherwise your finished piece will appear lopsided.
After you have decided upon a center point, on the back or bottom side of your blank, using a trammel or compass, draw a line around the circumference of your blank at approximately your chosen finished project size.
Using a band saw, saber saw, table saw, an angry piranha on a stick, (or the saw of your choice) cut around the circumference line, staying to the outside of the line approximately ¼”. Save the scraps that you have cut off the corners, as they will be needed in the assembly step.
Attaching the Pivot point or Axle
In the initial entry in the series we talked about creating an “axle” that will snugly fit inside of the hub of the jig. This axle will temporarily attach to our blank, and act as the center pivot point upon which we will spin the blank around the stationary jig and router assembly.
The axle will attach to the back or bottom side of your blank at the center point.
I have used 2 different methods for attachment of the axle.
If you are in a hurry and/or the bottom side of your finished piece will not be in view, you can attach the axle to the blank with a wood screw. If you use this method, please make note that when routing out the dished portion of your blank, DO NOT allow your router bit to touch the hidden screw tip buried in the wood at the very center. There is also the very real possibility that after extraction of the screw, you will have a hole in the very center of your dished out tray.
To prevent the above problems, I have found that my preferred axle attachment procedure is to glue a “sacrificial” axle to the bottom side of my blank. This step requires additional drying time for the glue to set-up, and also means additional sanding of the glue residue after the axle is removed, but I find it a better alternative to the screw method.
When glueing the axle to the center, place a piece of heavy paper between the two glue surfaces (such as a scrap of brown paper bag). This makes the axle much easier to remove in the finish stages of the project.
Begin by placing the blank’s axle into the hub of the jigs sled base.
In order to for our blank to spin easily between the two halves of our jig sandwich, after it has been securely assembled, the ends of the jig halves (the area outside the edges of the blank) must be separated by a dimension that is slightly larger than the thickness of our blank.
When the router sled is placed into the sled base and over the blank, the 2 parts of the jig will be joined together at the ends via 4 long screws placed over the end blocks.
(see above picture of unassembled jig)
In order for the blank to spin in the hub, we must release the “sandwich pressure” from the blank. To accomplish this, place a thin shim board upon the scrap pieces placed at the ends of the jig. When the 2 halves are screwed together, the scraps and shims are drawn tight between the sled base and the router sled. The blank will be snug but free to turn between the top and bottom halves of the jig.
The trick here is use shims that are big enough to allow ease of spinning the blank, not too tight not too loose. Too tight and you will fight the work trying to get it to spin throughout the length of the project. Too loose and the blank will exhibit excessive wobble and you will get uneven depth results in your router cuts. As you gain experience in the technique, you will gain a better understanding of the shimming required.
Anchoring your working assembly
As mentioned above your router imparts a great deal of stress upon your work, and I might add that you are spinning (or trying to spin) your blank, so you do not want your working assembly moving around your work bench.
I found it necessary to place the assembly at the corner of my work bench, and use clamps to secure the unit the bench top. In the interest of safety I strongly recommend that you properly anchor your work at all times!
Whew! Ok…we have got most of the tedium behind us…bear with me gang. I promise that in the next installment, we will make mountains of sawdust. So get your jigs and blanks prepared, and we will make serious progress next episode.
-- Trevor Premer Head Termite and Servant to the Queen - Heirloom Woodworking