Preventing Kickback II - Splitters vs Riving Knives

In my September 24 entry I discussed the importance of an accurate rip fence in preventing table saw kickback. Having an effective method of keeping the saw kerf open during rip cuts is equally critical if not more so. Stresses within the wood can cause the saw cut to either open up or pinch shut as it passes over the saw blade. If the kerf springs open so that it presses against the rip fence, the wood may be pushed against the trailing edge of the saw blade causing kickback. If the kerf pinches shut, it may grab the rear of the blade with the same result. The traditional solution has been to install a splitter behind the blade.

Traditional Splitter

The photo at right shows the type of splitter traditionally supplied with American table saws. These often come equipped with clear plastic guards. Both are generally removed and lost because they are so inconvenient to use.

The splitter does have some good features. The metal blade that makes up the body of the splitter is effective at keeping the saw kerf open. The toothed blade visible on the side of the unit, actually one of a pair that straddle the splitter, is a pawl that can grab the piece of wood if it starts to be thrown back at the operator, thus preventing kickback.

There are several drawbacks to this design. The gap between saw blade and splitter, clearly visible in the photo, is one of the most serious. This gap makes it possible for the wood to contact the rear of the blade before it even reaches the splitter, causing kickback. Many splitters of this type are also made of soft metal that is easily bent and difficult to realign.  The height of the splitter is also fixed, rather than raising or lowering along with the blade, so that it must be removed when making grooves or buried cuts, as in tenoning, etc. Once removed, the splitter is rarely replaced.

Riving Knife

The riving knife, long in use in Europe but only recently required here, addresses many of these issues. The riving knife is attached to the saw arbor so that it raises, lowers, and tilts along with the saw blade. As long as the correct size blade is installed, the gap between the riving knife and blade is constant and quite small. Finally, because the knife is slightly shorter than the saw blade, it can be left in place when making buried cuts. The riving knife must be removed when using a dado set or molding head but, at least in the case of the saw I own, this is easily done without tools.

Modern Splitter With Guard

The riving knife is especially useful for cuts where the operator needs to be able to see the blade clearly, as when cutting to a pencil mark. It lacks anti-kickback pawls and a plastic shield, both of which would make ripping long boards or cutting sheet goods much safer. On my saw, the riving knife is easily exchanged for a splitter of this type. Unlike the traditional design, this guard rides up and down with the blade, preserving many of the advantages of the riving knife. Presently, riving knives are only required on new saw designs, existing designs being grandfathered in under the new safety rules. I am convinced the new designs are worth the added cost.

The other anti-kickback device that has been receiving a lot of press is an electronically activated brake that instantly stops the blade if it contacts flesh. The action is so fast that no injury to the operator results. While this is an extremely important development, it is currently available only on one brand of saw. I suspect it will become more widely available in future, but for now most woodworkers will have to rely on accurate rip fences, splitters or riving knives, and their own vigilance to avoid kickback injuries.

New Project - Shaker Hanging Shelf

The Shakers produced several variations of this set of hanging shelves, some more elegant than others. My version takes its inspiration from the measured drawing in Ejner Handberg's Shop Drawings of Shaker Furniture and Woodenware. I decided to make my shelf unit roughly half the size of Ejner's original, appropriate for use as a spice rack or for the display of small objects. The original was designed to be screwed to a pegboard strip attached to the wall. I have incorporated a small length of pegboard into my design to allow the hanging of measuring spoons, keys, etc.

I produced a set of half-size drawings to allow me to tweak the details before committing them to wood. The front view shows the spacing of the shelves and the placement of the batten used for hanging the unit. I will have to check my stock of hardwood, but I anticipate making the first set of shelves from cherry, 1/2" thick. I think figured maple would also make be excellent choice here. I will wait until the design is finalized, however, before committing it to the more difficult to obtain maple. I will begin by preparing the templates and the hardwood stock for the project.

More to follow...

Setting up Shop on Etsy

Now that I've completed the sconces, I figure it's time I set up shop on Etsy. There is certainly an overabundance of advice for newcomers to the online craft world, and it would be easy to get stuck in an endless loop of reading the available information. Taking my usual approach, I just plunged in and registered on Etsy as OutOfWoods, which matches my email address and Twitter account and is close enough to the name of this blog. I also set up a matching PayPal business account to accept payments and have been perusing Etsy to get some ideas about how my page should look.

I am also looking into shipping options. I ordered a Flat Rate shipping kit from the Postal Service to see if that will work for me. The Postal Service provides free shipping boxes for this method and each box size has a fixed postage charge. The fixed charge would allow me to charge the same postage to all customers, but the free boxes only come in a few sizes that may not be appropriate for the items I will be shipping. My other option would be to get a postal scale, some packing materials, and charge according to weight and shipping zone.

None of this is as enjoyable as actually creating the items I want to sell, but I can't see any way to avoid the details. I think things will be easier to handle if I concentrate on one consideration at a time, so I will be settling on a shipping method first. Once that is done, I can tackle shop design, etc.

Obituary for a Fine Old Elm

I am saddened to announce the passing of one of the last remaining elm trees in my area. The tree, which has been a neighborhood landmark for nearly a century, finally succumbed to some combination of age, drought, disease, and the stresses of urban life. It is certainly one of the last remnants of the scores of elms that shaded the neighborhood before they were felled by the Dutch Elm blight in the sixties. We will miss its incredible crown of branches, its shade, and the character it leant to the block on which it grew.

We had an opportunity to speak with the homeowners this evening as we stood contemplating the remains of the tree, and it was evident that they were deeply affected by its loss. Because it grew between the sidewalk and the curb, the city will be planting a replacement tree. The crew that came to fell the dead tree allowed the owners to keep much of the wood and offered to cut them a slab from the base so they could count the rings and perhaps have a table made some day.

Elm has a reputation for being cantankerous, its grain tightly interlocked so as to resist easy splitting. It was, for this reason, the wood of choice for the hubs of wooden wagon wheels. I took away two small logs with the thought that I might make something from the wood in a few years. I can, at least, preserve its memory in that way. Ars longa, vita brevis...

Shaker Sconces Complete

I completed final assembly of the two Shaker sconces last night, too late to post at the time. After glue up, I did a final hand sanding with 220 grit paper to remove the remaining machine marks. The finish consists of two coats of Watco Danish Oil, allowed to dry for 24 hours then hand buffed with a soft cloth. The oil does a nice job of bringing out the grain, but is slow drying and smelly. I may experiment with other finishes if I decide to make these in quantity.

My next step is to set up my store on Etsy to see if this is a salable design. I personally find the proportions and gentle curves pleasing, but I have no way of gauging the general appeal of the design without putting it out in public. I expect to devote my next few posts to actually getting these items to market, etc. If they do sell, I will want to revisit the construction process to see if I can reduce the amount of time involved without sacrificing quality.

Shaker Sconce - Cutting Out the Pieces

Cutting the Curves

Using the templates I make last week, I traced the outlines of the back and sides of the sconce onto the 1/4" and 5/16" walnut stock I had prepared previously. With a 1/8" wide blade installed on the band saw, I used the machine to rough out the curves on these pieces, taking care to cut on the waste side of the line. I tried to stay about 1/8" outside the line to allow some material for trimming while minimizing the amount of wood wasted.

Trimming the Back

I used the templates again to trim the pieces to final size. Clamping them to the roughly shaped sides and back, I used my trim router fitted with a ball-bearing guided pattern bit for the final shaping. If I decide to make these sconces in quantity, I think it will be worth my while to make permanent jigs to shape these pieces. It would be more efficient if I could clamp the parts onto a more thicker and more durable pattern which I could shape by means of a router mounted in the router table. I would also make the pieces a little wider than necessary as I had some trouble with splintering at the edges, and could have used more material to allow me to trim off the defects.

Cutting a Rabbet on the Router Table

The original sconce appears to have used simple butt joints held together by brads and/or glue. I decided to rabbet the back and sides for added strength and to refine the appearance of the piece. I made the rabbets using the router table with a fence. Those on the sides of the back piece go only part way and I used a stop block, shown in the photo, to ensure that the length was consistent. It was also necessary to square up the top end of these stopped rabbets with a chisel to mate precisely with the sides.

The Finished Pieces

I sized the bottom piece by fitting it to the back and sides rather than trying to fit it by measuring. I softened the front edge of the bottom piece using a 1/8" round over bit in the router table in imitation of the original. In the end, I had parts for two complete sconces, ready for final sanding, glue up, and finishing.

Clearly, there are economies of scale to be realized if I make the sconces in larger batches. By doing multiples of each piece while I have my machines set up for a particular operation, I can save myself from having to do the time-consuming set ups as often. I can also save wood by laying the pieces out more efficiently for cutting. If this design proves popular, I will need to address all of these issues. For the present, I need to move on to the final assembly and finishing process. To be continued...

The Band Saw is Up and Running Again

Back Together and Fully Set Up

As of 7:30 tonight, the band saw is back up and running well. The repaired saw is shown fully reassembled at right. The new trunnions fit perfectly, though final adjustments turned out to be more finicky than I expected. As long as I had the table off, I decided to clean, lubricate, and adjust the upper and lower blade guide assemblies. These were heavily gunked up with pitch, sawdust, and the overall residue of the past seven years of use. Some of the guide adjustments were almost too stiff to move while others had enough play as to make accurate setting impossible. A minor overhaul seemed to be in order.

Blade Guides (Front) and Trunnions (Rear)

The next photo shows the new trunnions along with both blade guide assemblies. The guide assemblies incorporate both aluminum and steel components, so I decided it would be best to strip them down completely for cleaning. Formula 409 and a toothbrush were quite effective at de-gumming the aluminum parts while mineral spirits were used on the steel parts.

Each guide assembly contains a ball bearing, visible in the photo, which sits behind the blade to absorb its rearward thrust during cutting. Both of these were stiff due to lack of lubricant. I would like to have replaced them, but at a cost of $21.00 apiece from Delta, I decided to salvage them. I was able to pop the grease seals off with the tip of my utility knife, flush them out with solvent, and repack them with lithium grease. After all this work, I located a bearing distributer online who offers them for $0.99 apiece, plus shipping. Although I have not yet placed an order with these people, I think their site at http://www.vxb.com is worth checking out.

The two black shafts in the middle of the photo are the adjustment screws for the lower guide assembly. These steel screws turning in the aluminum guide assembly are prone to galling and similar issues, so I was meticulous in cleaning these up and lubricating them. One moves the thrust bearing forward and back behind the blade. Properly adjusted, the bearing sits a few thousandths of an inch behind the blade, only contacting it and actually spinning when the blade flexes under the pressure of a cut. The other adjusts the guide blocks which keep the blade from flexing side to side. These have to be adjusted so they sit just behind the saw teeth so the blocks do not get chewed up in the process. I have replaced the original steel guide blocks with graphite impregnated phenolic "cool blocks" which can be set more closely than steel blocks without risk of damaging the blade, thus providing a more accurate cut.

Checking the Position of the Broken Trunnion
 Prior to Removal

As I said previously, final adjustment of the new trunnions turned out to be problematic. Before removing the old trunnions, I made measurements with a steel square hoping that would make the final adjustment easier.

The photo at right shows me carefully measuring the position of the broken rear trunnion prior to removing it. In practice, these measurements only provided a starting point. I did the final adjustment by making an endless number of test crosscuts on the saw using the miter gauge and moving the table to compensate for deviations from square.

It took about thirty minutes to get the table accurately adjusted, which also turned out to be the limit of my patience. Since the new trunnions seem to be better made than the original parts, I have hopes of never having to go through this process again. Only time will tell. In any case, I am now able to resume woodworking rather than machine maintenance, so I should be able to get back to the Shaker Sconce project for my next post.