Test Your Skills

[dusty]

and your Mark 5/V alignments.

With stringent tolerances in mind, not to be discarded along the way, make your own 7" and 12" 45 degree speed squares (right triangles). No lettering, just the bodies.

As I often do, I was tinkering with table alignments and toying with an alignment jig. Sort of a set of setup tools for the Shopsmith, Don't hold your breathe. I may never get them through the quality check.

I'm using my newer Mark V w/Model 520 upgrade and Table Tilt for the work and my older machine (a 510) as a test bed.

[algale]

and your Mark 5/V alignments.

With stringent tolerances in mind, not to be discarded along the way, make your own 7" and 12" 45 degree speed squares (right triangles). No lettering, just the bodies.

As I often do, I was tinkering with table alignments and toying with an alignment jig. Sort of a set of setup tools for the Shopsmith, Don't hold your breathe. I may never get them through the quality check.

I'm using my newer Mark V w/Model 520 upgrade and Table Tilt for the work and my older machine (a 510) as a test bed.

So the task you have undertaken is to use your Shopsmith to make two right isosceles triangles that are as precise in their outside dimensions as 7" and 12" speed squares?

I think that would be a surprisingly difficult task to accomplish with a Shopsmith -- or really any woodworking tools -- no matter how well aligned.

In my experience, it's not even a trivial task to cut perfect squares!

I guess if I were doing this I'd start with a piece of plywood with a good factory edge. Set the rip fence to about 7.5", make the first cut, rotate the stock 90 degrees, and make the second cut. That would give me, theoretically, a perfect 7.5" square. I say theoretically because stuff can still go wrong when making a rip cut that might leave you with unacceptable edges is you want to use these triangles as future set-up tools.

Assuming I had accomplished a perfect 7.5" square, the harder part would be to make the hypotenuse cut to leave me with two 7" legs. I'd use one of my an Incra miter gauges, probably the 5000, set at 45 degrees (or the Shopsmith Miter Pro if I had one) to make the hypotenuse cut. If you can line up the entry cut exactly with a 7" tick mark on one leg of the square, you should end up with two exactly equal 7" legs.

By the way, the reason I'd start with a 7.5" square is that if I start with a 7" square my hypotenuse cut would then need to start in (and perfectly bisect) a 90 degree corner angle. That's a miter cut I find very difficult to line up and execute. I prefer to start a miter cut a little away from the corner of a work piece where I can make a tick mark and bring the work up to the stopped blade to see if I will hit my mark. Sometimes I will lay a straight edge on the side of the blade to help get that entry cut exactly where I want it on the tick mark.

Even if perfectly lined up with a perfect 45 degree setting on the miter gauge, making that cut is still easier said than done without introducing some error. So you might need a lot of 7.5" blanks to get one that you felt was perfect.

Repeat the process for the 12" square using a 12.5" rip fence setting to get a 12.5" blank from which to then cut the hypotenuse.

Those are my thoughts. I don't have the time today or the plywood to waste on seeing if I can accomplish it. But I wish you luck and will be interested in finding out how you did it and what results you got!

[dusty]

I thought this would be relatively easy but it is quite the contrary. I may not be able to do this to the level of accuracy needed. I have not even attempted the 7" triangle yet.

The three sides on my most successful 12" triangle measure4 11.5", 11 15/32" and 16 9/32". I trimmed down the sides to get good sharp corners. That is why I have a shorter 12" triangle.

The three angles measure 89.95° , 45.40° and 45.25°.

I started by making a 12" square piece of hard board using some shelving from a salvaged storage cabinet. My first bad decision was trusting the 90° cut to be "right on". Three attempts later, I achieved the results stated above. I do believe that I better the 12" adjacent sides but my confidence wains from there. Fractional degree cuts are a real challenge.

I have done hundreds (maybe thou.ssands) of very accurate 45 degree and 22.5 degree molding cuts but I tested for visual fit and not really tight numerics.

[dusty]

Main Table Numerics

Main Table Numeric Coincidences.jpg (360.26 KiB) Viewed 1042 times

[DLB]

The three angles measure 89.95° , 45.40° and 45.25°.

Two thoughts. What are you measuring the angles with? (I don't think I have anything that would pretend to provide such resolution/accuracy.) 2)If I remember my trig (or geometry?) right these numbers don't form a triangle. They should add up to 180 degrees, even if they are not the angles you intended. (Implying a measurement inaccuracy?)

- David

[dusty]

The three angles measure 89.95° , 45.40° and 45.25°.

Two thoughts. What are you measuring the angles with? (I don't think I have anything that would pretend to provide such resolution/accuracy.) 2)If I remember my trig (or geometry?) right these numbers don't form a triangle. They should add up to 180 degrees, even if they are not the angles you intended. (Implying a measurement inaccuracy?)

- David

You are absolutely correct with all of your observations.

The length measurements were done using a steel rule divided in 1/64ths.

The angle measurements were done using my digital Husky Sliding T-Bevel and Angle Finder.

Typical low cost wood shop tools. This is not an engineering design project even though I intend to design and fabricate an alignment jig.

[edflorence]

Just a thought...what if instead of starting with the short legs of the triangle, you started with a long cut for the hypotenuse, making it a few inches longer than the desired finished length. Once that was cut, you could then mark off the desired finished length and from the end points of that baseline use geometry to lay out each of the non-90 degree angles, and then cut those legs. Without actually going into the shop to try, I think that is the way I would approach this interesting challenge

[dusty]

I have abandoned this challenge UNTIL I complete my new sliding cross cut table.

Trying to do this using the miter gauge is futile. The miter gauge works fine for cross cuts (short cuts) but not so well for longer cuts. At least with the cross cut sled the accuracy becomes more dependent on the accuracy of the sled.