The Molly Project: Planning Stages

A friend contacted me a few weeks ago asking about the possibility of having me build something for her. Her name is Molly. We soon met to talk over the project and some of its details. It sounded interesting enough that I knew I had to find time to fit it in if I could develop a workable design based on her concept and requirements. I worked out the design, and recently met with her to discuss details and cost. We have a preliminary agreement to build as a result.

I am still working on that large shelving unit project for myself, but its project timeline can slip some though. This project is core to my workshop mission, and the first entries I write here will discuss the build process before I discuss the specific need that this project addresses. It is definitely one of the more interesting projects that I have been asked to be a part of.

Shelving Units: Expecting Too Much Sometimes

The machine pictured here is a combination planer-jointer. It can easily convert between one machine or the other. It is configured as a jointer in the photo here. I love this machine. I also hate this machine sometimes. I purchased it because I was doing smaller work in this not-too-large workshop of mine. It was perfect for that work.

I replaced the combination planer-jointer last summer by dedicated machinery with more accuracy and capacity to handle projects like the large shelving unit side frames pictured below. Yet the planer-jointer stays where it sits because it can surface a board flat that is 10" wide. I use it now almost exclusively in that capacity to surface one side of a board completely flat before running it through the dedicated planer or drum sander. Doing so helped create almost perfectly aligned mortise and tenon joints used in the construction of the shelving unit side frames pictured here. I love it for that reason.

This particular planer-jointer was designed with some limitations that make it more attractive to a woodworker like me with a smaller shop and budget. It has tables made from aluminum rather than cast iron for instance, and only the outfeed table is adjustable using simple set screws which periodically go out of alignment like they did today, and then are rather difficult to adjust. I hate it for that reason.

I like perfection in my machinery and in my work too, but with respect to the planer-jointer, I decided I had to accept the fact that it was not designed to offer perfection, but rather capacity and functionality within the reasonable price I paid for the machine. I therefore pay closer attention to its alignment now, and make adjustments when required. I accept this imperfection because of what the machine can do for me within the limitations of my workshop space and budget. It has a very welcome place here as a result.

Shelving Units: The Engineering Case for Quantifying Quality

Tolerance stack-up is an engineering concept defined as an accumulation of dimensional variations in a part or assembly made up of multiple parts. No part can be made perfect, and many mechanical drawings include dimensions with specified tolerances such as 15.000" +/- 0.005" to convey an acceptable range within which the dimension meets specifications.

The usually accepted tolerance range for most professional woodworkers is +/- 1/64" or  +/- 0.016". This degree of accuracy is not hard to obtain given experience and good equipment. The problem lies in a design that combines multiple parts in such a way that the dimensional variations add or subtract. The accumulation of dimensional variation can become significant if many parts are used to make up a single assembly as in the shelf unit side frames pictured here. Viewed in another way, if four sequentially assembled parts are off by only 1/64", the final accumulated dimension represented by their assembly will be off by 1/16". And that is significant. The same holds true for angular dimensions and perpendicularity.

I am not able to measure the shelf unit side frame diagonals during the glue-up process because the many clamps required interfere with the measurements. I rely on taking measurements with an accurate square in each of the internal frame openings and adjust clamping pressure where required to get good readings. The side frame diagonals are within 1/16" of each other or better when the clamps are removed.

Diagonal measurements within 1/16" or better are generally good enough to consider larger assemblies acceptably square. My designs often rely on ultra-accuracy to insure the overall object assembly comes together well. The Alice Table comes to mind as a good example.

Tolerance stack-ups are analyzed in terms of either a worst case scenario where an assumption is made that all dimensions will end up at one of the outer extremes of the specified tolerance, or statistically where a probable average of variation is assumed. I will often consider my woodworking technique and shop equipment good enough where I assume a probability of small average variation.

I should maybe consider playing it safer the next time I evaluate a particularly complex design by using a rough worst case analysis. It might save an unpleasant surprise. The computer screen might tell me I can build something, but reality might dictate otherwise. So far though, the shelf unit side frames are gluing up well.

Shelving Units: Starting Out

The last two projects I wrote about were items I built for myself. The next few posts will be about a set of four shelving units I started to build this weekend also for myself. I decided that a set of shelves will best and most economically hold my growing collection of integrated technology that includes the computing, audio, and display systems I use in my work and life at home. One of the shelving units will also act as a bookcase.

I had two goals in mind as I set out to design the four shelving units. Each should reflect the quality my workshop is capable of producing so that they properly communicate my design and skill level during their lifespan, and yet the construction of each should attempt to minimize schedule and cost burden as much as possible.

I achieved the first goal by using mortise and tenon joined frame constructions for both side and shelf frames to give the shelving unit assemblies a simple and unified yet professional look. I am going to achieve the second goal by using as many commonly dimensioned parts as possible to minimize machine time and setup. Each shelving unit is therefore part of a product family based on a nearly common product platform.

You know how difficult this winter has been especially if you live and work in the upper Midwest as I do. I made a wood run for the project this morning sorting through a pile of lumber in an enclosed but unheated shed with the air temperature still in single digits looking for boards that were as straight as possible. I quickly stickered them on two even saw horses when I arrived back at the shop to minimize their chance of warping.

Finding New Ways to do Things Differently

This business of design as practiced through woodworking is often and basically one of trial and error even given a broad depth of experience. I will never stop learning and being frustrated and amazed by the path to outcomes no matter now long I stay with it. The table just completed here is so basic and simple. A simple tapered leg table. Yet it exists because I need to always learn more which is basically something my dad taught me.

I decided to build this table as part of the glue strength test project I began last fall. The project had two components really. One was an actual test of the glue strength itself, and the other was to be an application of the glue to a typical project. The project did not happen as I planned because the glue did not test well with respect to strength. I was going to use the new glue to join the table apron pieces to the tapered legs and therefore prove a substantial time savings but instead, completed the project by using a traditional wood glue.

I did a number of things on this project that were either new or something that I do not always get the chance to do though. I built tapered legs on the table saw. And I employed a different finishing process. I also got the chance to employ one of the unique period profile router bits I have to the table top. The table base is simple and fundamental, yet the profile around the top is complex and elegant. Both statements work well together. I think I already knew that they would though since that seems to be inherent in a lot of my work.

I both expanded and reinforced knowledge by doing this simple project which seems far from the main goals I set for my workshop last summer in building a new pipe organ. I think there will continue to be projects like this again and again on this blog space because after all, I can never stop learning.

The Drop Leaf Table Addition: The Incremental Cost of Design Complexity

This entry builds on a previous one where I described a part design paradigm based on complexity where every new feature added to a single part required more caution than the last, because once a part began to acquire more features along with the time and effort required to produce those features, the part itself began to incrementally increase in value. A mistake with each additional new feature machined would therefore prove increasingly more costly than the operation itself to complete that feature, as the number of features were added to a part to complete it.

I found myself trapped in that same concept as I routed the final half-inch quarter-round profile on the two opposite edges of this table top. Each part that makes up the top assembly is fairly simple in and of itself not counting the walnut panel quadrants with their computer numerically control routed circles, but the assembly of those parts was done in stages that included a complex cope and stick edging process between the center panel and its two opposing front and back edges. Routing the small dado that ran along both side edges underneath the top was difficult enough until I had to begin the last process.

The last process in completing the top was to route the large quarter-round profile on the two side edges without the router bit blowing out the ends. I really had no choice therefore but to use a hand-held router instead of the router table, and because of the larger router bit, I had to use a plunge router instead of one of the smaller, more easily controlled hand-held fixed-base routers I own.

No single one-pass, large removal of stock occurred as I routed the quarter-round profile. It was light passes all the way, taking off only a little at a time to insure a clean, smooth, issue-free profile using a tool not exactly well know for its finesse. A mistake here could have cost the whole top. I obviously pulled it off, but if I had not, that incremental cost concept would have come around to hit me hard. Very hard.

Like the saying goes, just because you can doesn't always mean that you should. Although in the end, risk paid off in the final result.

The Glue Strength Test: How It Informs Design

I began a simple project in the workshop that will wrap up soon to test the new cyanoacrylate glue that recently came on the market especially formulated for woodworking applications. This project is a simple tapered leg table with tenoned apron sections glued into mortises that are routed into the legs. The fast set time of the cyanoacrylate glue would greatly facilitate the assembly of the legset.

Recall that I conducted a strength test of the glue with the help of the engineering department here at the University of Minnesota before I began building the tapered leg table as described in a set of earlier posts that are listed below. The glue strength test indicated that the new cyanoacrylate glue did not bond as well as traditional woodworking glues, and for that reason I decided to assemble the legset using a traditional glue even though I think that the strength of the joinery used here would not have been an issue. I like to be sure about these things though when it comes to my work.

http://stevepanizza.blogspot.com/2013/11/the-glue-strength-test-results.html

http://stevepanizza.blogspot.com/2013/11/the-glue-strength-test-engineering-test.html

http://stevepanizza.blogspot.com/2013/11/the-glue-strength-test-introduction.html

The process of gluing and clamping the legset was done in two stages, and each stage took a full day of clamping. Using the cyanoacrylate glue would have meant that the glue-up phase of the legset could have been completed in only one day as quick dry time is its primary advantage. The benefit of strength won out over completion rate though.

Another way to look at the glue strength test results though as they relate to this project design is that I could have increased the size of the apron part tenons to increase the glue surface area if completion time had absolutely been an issue here as more glue surface area increases joint strength. It may help to know in the future that I have this option during the design stage of any project.

I think that uses for the new cyanoacrylate glue will eventually develop where its short drying time can be used to advantage in situations where strength is less important. So for now it stays in the shop as another tool to use when appropriate.