Precision Preschmision.

When it comes to manufacturing process, there is a direct relationship between precision and cost: the more precise the product, the more expensive it is.

The reason for this is simple: making precise products requires the use of even more precise tools, and it requires additional steps to measure and verify that the accuracy is within tolerance.

This applies to the home shop as well.

If you want to work precisely, and repeatably, you need to set up your tools perfectly, you need to measure and verify your results, and you need to plan your moves ahead of time, to make sure your plans for assembly and finishing allow you to maintain the accuracy of the components in the finished product.

All accuracy takes time, but there are two different classifications of precision in my mind, and one matters far more than the other.

• Absolute Precision: making components exactly 3-inches long, or exactly 45-degrees
• Relative Precision: making components that fit together exactly, with little concern for absolute dimensions

For example: I can make a table with a top that is exactly 6-feet long and 2.5-feet wide, made from 5 planks that are exactly 0.5-feet wide and 6-feet long: this table looks nice, is well made, and is absolutely precise.

OR: I can make a table that is about 6 feet long and about 2.5-feet wide, made with planks that are all the same length and width: The end result looks the same, and has the same quality, but all of my “measurements” are really just making sure the parts fit together. This is relative precision.

Sometimes absolute precision matters: In mass production you need to be able to provide predictable dimensions so that the packaging and usage can be consistent; replacement parts must meet exacting specifications.

But at home it’s often less important that the part be a certain number of inches, and more important that is fits, works, or looks good, whatever the length ends up being.

This is a liberating principle for me. I don’t need to spend hundreds of dollars on Starrett measuring tools to make six cuts of the same length; I can just make the first cut however I like and then keep the setup in place for the next five.

Now, this does require some forethought. If you are planning to repeat the same cut, you need a setup that will allow it. Your bandsaw and tablesaw should have a sturdy fence (but Biesemeyer and Kreg are probably overkill), and you should use stop-blocks and simple jigs where needed.

You may be thinking: “if you’re making something exactly 6-inches wide, isn’t that just as difficultas making something exactly as wide as something close to 6-inches wide?”, and the answer is: …sort of.

You see, I like to start building based on a concept in my brain, and progress through the project adaptively, with the results of each step determining the details of the next.

I don’t want to sit at my computer planning the minutia of the project in Excel when I could be spending valuable time at the bandsaw. And since nothing turns out perfect anyways, my measurements would invariably need adjustment as the project progressed, which then begs the question: Why measure in the first place?

As noted previously, the tape-measure has it’s place, and the blade of any saw should be square to its work surface, but there is nothing magical about hitting the inch within a fraction of a millimeter: These are arbitrary lengths that were made up in antiquity.

The real test of valuable precision is simple: Does it fit? Does it work? Does it look good? If so, it doesn’t matter what the ruler says.

Inca Bandsaw Fence – Part 3 – The Fence

And so we come to the conclusion of the Inca Bandsaw Fence series.

At this stage I had a rail for the fence to slide on, a carriage that follows and locks onto the rail, and a mounting bracket extending vertically from the carriage for the fence itself.

The best material I found to make a fence was extruded aluminum rectangular tubing (about 1.5 inches wide and 3 inches tall). Aluminum extrusions tend to be very straight and since my saw’s table is also aluminum, using a harder metal could possibly damage the table over time.

I picked up a 36-inch piece of the aforementioned tubing as a remnant from the local metal supply store ($2.70 per pound) and cut 16 inches off to make my fence.

The fence needed to be connected to the vertical bracket attached to the carriage. My first thought was to attach it with bolts on the backside of the fence, but then the width of the fence would be limiting the cutting capacity of the saw by a full 1.5-inches. So I decided to attach the bracket to the inside of the tubing.

In order to do this I cut a slot in the bottom of the fence, right along the front edge where I wanted to attach it to the carriage.

Then I drilled and countersank two mounting holes. I transferred the location of these holes to the bracket and then drilled holes in the bracket accordingly.


Note: If you are a particularly observant reader, you will notice that I showed a picture of the bracket in “part 2” of this series, but here I am claiming that they were drilled as a step in “part 3”.  Well done.

The arrangement of the holes is not merely aesthetic. If the holes were aligned with each other horizontally, they would provide only limited vertical support. Likewise vertical holes would provide limited horizontal support. My theory is that diagonally arranged holes will be the best of both worlds.

I inserted brass (because it’s pretty) machine screws through the holes and secured them with washers and locknuts (to prevent loosening during operation).

And that’s it.

There is a bit of flex on the far end of the fence if to apply a lot of lateral pressure, but since my workpieces will be small and kickback is not a concern on the bandsaw, I won’t be pressing hard against the fence, so I think it is rigid enough.

That said, I’ll probably tinker with it at some point to make the far end lock in place as well.

Inca Bandsaw Fence – Part 2 – The Carriage

For lack of specific knowledge and due to a general laziness when it comes to looking things up on Google, I’m calling this part of the bandsaw fence a “carriage”:

(actually, I’m not certain my affliction can be considered “laziness” since I just went through the trouble of drawing a picture instead of just looking up the correct name… maybe I just feel like it is a carriage, whether or or not that’s what it’s officially called).

In any case, after completing the rail, I turned my attention to the part connecting the fence to the rail.

Essentially this works like a C-clamp, with the rail being pinched between a screw and a pressure plate. The construction may vary, but the most important aspect is that the carriage must be designed so that it is rigidly square with the rail when it is tightened in place.

I used a small piece of angle iron to act as the pressure plate. I shortened one side of the “L” (the “pressure plate” side) so that it wouldn’t hit the bolts on the underside of the rail.

Then I attached a vertical piece of steel that I milled flat and square. I kept it parallel to the angle iron by clamping a piece of metal in between it and the short end of the angle while welding it.

I drilled and tapped 1/4-20 threads into the vertical piece of steel and ran a Rockler star knob through it.

This tested okay, but I didn’t want the screw to mess up the rail over time, so I added a thinner piece of steel that was flexible enough to allow the fence to move while the knob was loose and still bear down hard on the rail when the knob was tightened.

So now I had an assembly that could be locked into any location with a mounting surface that was consistently parallel to the rail. The next step was to make a bracket that the fence itself could attach to.

I made the bracket out of a piece of trailer hitch tube I had leftover from another project.

I started by milling two sides flat and square with each other.

After that I cut off the other two sides and shortened one side so that the other would stick up above the bandsaw table perpendicular to the shorter side which would be mounted to the rest of the carriage assembly.

Like so:

I mounted this with a single 5/16″ bolt through the carriage assembly, which allowed it to be pivoted as necessary to keep the upright portion vertical (parallel to the blade).

And now I could turn my attention to the final component: Part 3 – the Fence!

Coming soon.

Inca Bandsaw Fence – Part 1 – The Rail

My little Inca bandsaw, which I love, came without a fence. For many uses this is okay, but the functionality and precision really are limited without a fence, so I set out to build one.

I picked up a piece of 2″x4″ rectangular extruded aluminum tubing from the local metal supply store to act as the fence itself, and for the rest I used other scraps of angle iron and trailer hitch tube I had saved from previous projects.

There are basically three parts to the fence assembly (and three corresponding blog posts):

1. the rail
2. the carriage
3. the fence

The carriage and the fence are connected to each other and slide along the rail to set the distance between the blade and the fence. The carriage must be able to lock itself in place at any point along the rail.

My typical approach to any project is to just start building and figure things out as I go (for typical results, see my cyclone separator). I tend to rely on relative measurements (“about this big…”, or “the same size as that…”) rather than actually measuring with a ruler or tape measure. Since this project required a greater level of precision than my typical project, I did nothing different (I’m not entirely certain where my ruler and tape measure are anyways).

I determined the length for the rail by marking a piece of scrap hardboard while holding it against the bottom of the saw’s table.

After cutting the rail (a piece of 1″ angle iron) to length I used the same process to determine the proper location for the mounting holes. I drilled the holes a little large, so that there was some slack for adjustments.

Short segments of angle iron are pretty straight but they have some scaling and bubbling from the forging process which I filed off and sanded a bit to ensure that the surface was flat (enough).

I happened to have a couple of metric bolts and lock washers that fit the threaded holes in the table, and installed the rail.

Next step: the carriage…

New Table Saw Fence

My table saw is an old Rockwell 10″ contractor saw, which is an excellent saw, but one of the first things people tend to do with these saws is upgrade the fence.

The factory fence tends to be difficult to keep parallel to the blade, easy to push out of alignment, and has a limited capacity (the maximum distance between the fence and the blade is about 24″, so longer cuts require using the miter gauge or making the cut freehand).

One of the previous owners of my saw knew this, and so upgraded the fence… to a factory fence from a different saw. I’m guessing his buddy had a saw with a slightly better stock fence, and gave him the stock fence when he upgraded to a better one. The “upgraded” fence on my saw had a better cut capacity, but was still difficult to square and easy to push out of alignment, and the rails were too tall, causing them to interfere with my miter gauge (the top of the guide rails were higher than the bottom of the miter slot). So upgrading the fence was still on my to-do list.

I had been researching tables saws ans fences and I knew that the gold-standard for accurate fences was the Biesemeyer T-Square fence, but these are expensive, and although I use my table saw often, I am not a professional cabinet maker, so I couldn’t justify buying one of these fences.

After reading reviews and comments on all the t-square style fence systems I could find, I settled on the Delta 36-T30 30″ T2 Fence System, and found the lowest price on Tools-Plus.com.

I used the new Amazon.com Universal Wish List plugin for Chrome to add the fence to my wishlist, and my lovely wife bought it for me for my birthday.

Some of the negative reviews for the new fence had complained about having to drill new holes in the fence rails to install it on their table saw because the pre-drilled holes did not line up, so I was expecting to put some effort and ingenuity into this installation, but first things first, I had to remove the old fence.

The old fence was fairly simply installed. Its rails consisted of parallel tubes on the front and the back of the saw, separated from the table with spacers (the spacers came in to play later in an unexpected way) and bolted directly into threaded holes in the edge of the cast iron table top. I think just removing the old fence was a significant improvement.

Upon removal I noticed that the holes in the table top were significantly larger than the remaining original holes. The previous owner had drilled out the original holes and re-threaded them to fit the “upgraded” fence, so I now had holes that were too large for the mounting screws that came with the new fence. But I figured I could find a way around this.

The new fence came with a large number of screws, washers, nuts, and bolts, and when I read through the directions, I couldn’t find a need for all of them, so I decided to just use them as I saw necessary and see if I could make the fence work without drilling any new holes.

Luckily, although the holes in my table top were too large for the mounting screws, they did line up with the holes in the fence, and I was able to put a nut of the back side of the hole in the table top in place of the threads in the cast iron itself.

I then adjusted the rail until it was parallel to the table top and started working on the back rail.

 

On the back, for whatever reason, the bolts for mounting the rail were the correct size to thread directly into the larger holes left by the old fence. I was happy about this but ran into a new problem: I didn’t have the required 8mm Allen wrench to tighten these bolts.

I dug through my tools and scraps and eventually found a small nut that perfectly fit in the head of the bolt. I mounted the nut onto a small bolt and tightened it down with a slightly larger nut.

This assembly acted as an adapter: the 8mm nut fit into the 8mm Allen bolt, and the 9mm nut fit into a 9mm socket, so I could ratchet the bolt into place.

After finally installing the back rail, I checked it for parallel before moving on to the next step.

 

I had intended to re-install the extension wings, but at this point I realized that the spacers (mentioned earlier) that held on the old guide rails, were not used with this new fence system, and so the distance between the front and back rails was too small to fit extension wings.

This was disappointing, but I have been considering making my own extension wings, so I figured I’ll just make that my next project and set the old ones aside for now (I may add some washers to the rails as spacers to allow the wings to fit, but I haven’t decided yet, since I don’t really like the open aluminum wings much anyways.

The next step was to install the guide (square tube) for the fence itself. This was fairly simple, but the trick is to make sure it is parallel to the rail it is bolted to (and thus parallel to the edge of the table top). By tightening down one end, and taking a measurement, and then adjusting the other end to match, getting the guide parallel to the rail.

 

The remaining steps were fairly quick, and involved setting the fence in place, adjusting the various set screws in the fence until the fence was parallel to the miter slot and blade and square to the table top, and calibrating the measurement indicator. On this last step, I realized that my fence system was 2″ too far to the right for the attached measuring tape on the guide, so that when the fence was against the blade, the indicator was 2″ to the left of zero. The only way to fix this is to move or replace the measuring tape, and since I’ve seen adhesive measuring tapes before for pretty cheap, I’m not to worried about this for now… but it is a little sad.

 

Despite the various complications, I was able to complete this installation in about an hour, and the result is a sturdy, accurate fence that is easy to adjust and a big improvement over the fence the saw had when I bought it.