Thursday, August 21, 2014

Auto-Regulator chapter one: Breakdown.




 I suppose the first entry for this particular series should be about milling up the lumber. There are many, many instances where boards continue around corners, or where the grain continues from the movement case, past the waist of the case, and down the sides of the pedestal. There are so many individual parts to the case, that I didn't want to run the risk of having too many subtle differences in color, or texture, especially around the mitered corners. So, I cut every piece from a couple of huge beams of 12/4 walnut. Well, I tried to, anyway. In the end, I'd cut the front arch 3 separate times before I understood what was going on in the miter joint, so that's actually from a different piece of walnut.


 One of the many grain patterns that I ended up putting to use was to book match the wood around the edges of the front pillars. The pillars started out pretty thick... roughly 3" square in cross section... because they needed to be thick enough to allow for the wide sections at the end, where the miters are cut. At that point, the material is about 2 3/4" from edge to the widest point in the miter. But the blank is also square in cross section to allow for the sculpting that happened on the inside. (Click on the top photo, and take a better look at the contours on the inside of the case)

The diagonal grain near the top was a fluke. That's just what I happened to get when I opened up the beam... the grain went from being in-line with the board to 30-something degrees on angle from the face.

In the end, the pillars are a 3-part lamination: There's a 2 1/4" square core, which is destined to be sculpted down on the inside, faced on the outside with 3/4" thick pieces that are seamlessly mitered around that front edge. Those face pieces continue down into the pedestal, but the grain's pretty straight, so it's not so obvious at that point. And, the pedestal's not an open structure, so the solid core isn't there. (There's no need to sculpt anything, and we needed room for the clock's power supply, anyway.)

The pedestal parts aren't solid... they're all 3/4" thick pieces that are mitered into panels, and those panels are, in turn, mitered on the edges into a box. But, adjacent pieces along the edge from side to top were contiguous in the original stock, so that had to be taken into account.

Put simply, there was a lot to keep track of when I was breaking down the 12/4 stock... what pieces were book matched, or continuous, and with what. I went through (and broke) many crayons in the process, making notes on all pieces to indicate what went with what. Front pieces for the pedestal, orientation to keep grain continuity with the movement case pillars, or to keep continuity with the upper faces of the pedestal... Not exactly a Rubik's cube, but it felt a little like that sometimes.

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Note on the photos: All of the pictures of the finished piece were taken by David Schonbrun.







The Auto-Regulator


From January to July I worked ridiculously hard to develop this case prototype, and the associated process, to house the clock known as the Auto-Regulator. The creator of this particular clock has designed it to be the first atomic clock for home or office, so it's kind of a big deal.

This project was a monster on many fronts. There were many jigs to work out, many issues I hadn't foreseen, many, many late nights, and a lot going on at home, to boot. I haven't blogged since April because, quite plainly, I was fried, and had no time.

That's been getting better, so I'm back. In coming weeks/ months I'll go through the project from start to finish, and explain how it all came together, and how it's led me to where I am now.

Sunday, April 20, 2014

Circular Logic, Part II

Project X has been an utter monster in recent weeks. I hate calling it that. I'd rather come out with the name and details, but it's not my product, so I'm reluctant to say too much until it makes a debut somewhere. But this piece has required so much problem solving that it's eaten up a lot of time. Every time I solve one problem, another one pops up. It's resulted in a lot of sleepless nights, staring at the ceiling in the dark, trying to wrap my head around changing curves and angles, so I have a better understanding of what's going on. Then I have to figure out how I'm going to make all of that come together in the physical world. In theory, this piece will go into production, so I have to get it all figured out. It's forgivable to fudge a few details on a one-off piece, but once you get into multiples, the time spent correcting for errors gets magnified.

I can't wait to do a real write up on the project. I've been wrestling with some really interesting stuff, and came up with some cool solutions. But I hate reading... and writing... about abstract solutions without a meaningful context. I've had to re-invent the wheel on radius cutting, which has resulted in this series on dealing with cutting arcs and circles. I've made a lot of patterns to shape individual parts. There are some 3-way miters that are square, and some that transition into compound curves, that will be visible from all sides, so there's no room for error. I've had to re-examine accurate miter cutting several times over, as well as calibration of angle measurements. (Hence the review of the Shinwa bevel gauge.) And even once I could cut accurately, the first time I cut a test joint, it didn't come together at all. Normal 3-way miters are 45 degree angles, cut at 90 degrees to the surface. But once you move one of them away from 45 degrees, everything changes, and you get compound angles. And again, because it'll be visible from all sides, everything needs to be perfectly cut. Some of it starts to feel like a mathematical proof sometimes, because the ground work needs to be fully developed before it can be referenced in a larger work, and then there's still problem solving to be done on that higher level.

There's also going to be some work on veneered panels, possibly with marquetry in the future. There's going to be a bent lamination... and possibly a bent tapered lamination in future iterations. I'm still working out how I'm going to cleanly mount a piece of curved glass with radiused corners. And all of it has to be streamlined...

As always, the devil is in the details. So much effort goes into making everything look clean, so that the supporting elements can fade quietly into the background. But once you get gaps in the joinery, kinks in your straight lines, tearout, etc, the mistakes all stand out like a squeaky clarinet in an otherwise harmonious symphony. You'll notice nothing else.
 
Back to cutting curves...


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So, this is where we were last time:


Sliding center point base for the band saw, and for the router table. Dog-leg scissors jig with pins to mount to a blank, for cutting inside or outside radii, with a center pin that will transfer neatly from band saw to router table. For my next trick, I wanted to use it to make a pile of identical parts to use for making a bending form. I figured that would test the system, to see how robust it was.

I'll confess here to being a little too cerebral. Mark wandered over, asked what I was up to, and pointedly remarked that I was doing things in 'long-hand.' And he was right. There are many ways to skin this particular cat, and almost all of them are much more efficient. (Make one master curve, and pattern-rout the rest from that, would be the fastest.) But I wanted to see this experiment through, and see just what I could learn from it, and how much it would do that the regular screw-through-the-center jig wouldn't.


Using the jig for cutting radii in either direction (inside or outside) is pretty simple.  Because the jig has so many holes, it's easy to find a setup that will work. But I realized pretty quickly that mounting pin placement was an X-factor. The holes for the pins are drilled at identical distances from the center, but the distance between pins is also relevant. Once the arc is laid out to locate the mounting pins, you can drill anywhere along that arc. But the chord length- the distance between the two pins- will determine how far into the blank that curve gets cut. Two different chord lengths will result in two cuts with identical radii, but different placement of that cut in the blank. It was one of those details that's obvious in hindsight, but still made me scratch my head for a minute. Since the object is to create a bending form, all of the layers must be identical, so pin placement needs to be the same on all of them.



I laid out the first blank, and set up the pin holes to be exactly the same distance from each side, and from the front edge, and drilled them using a fence and a stop block. Drill, flip, drill, and I have two holes with identical spacing from the ends and edge.


To the band saw, and then to the router table...


Initially, I'd used a smooth pin to hold the center. I switched to a threaded bolt that ended in a smooth pin to hold the pivot point/center because there was slop with just the loose pin. It only made for a difference of maybe 1/64"- 1/32" from one blank to the next, but for a bending form, everything has to be exactly the same. This was the part when Mark made the comment about doing things longhand, and flush trimming being faster. Obviously, he's right. But I wouldn't have learned about just how sloppy the pin was if I hadn't gone this way. 

With the slop issue ironed out, the final stack was just about perfect. There were inconsistencies that I could feel, but they were small enough to fix with a plane. It felt a little bit like cheating, since I was trying so hard to make the the jig accurate enough to not need to smooth anything out, but any play in the pivot point makes inconsistency unavoidable. All things considered, it's still a very accurate system. The fact that I can re-adjust the center point and take a second pass, means I can creep up on a very accurate radius for a master pattern, or on a wooden part. And with the router table,  I can make a finished curved surface that's ready for sanding.


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Part 3 will go into a little more theory on dealing with radii. The form is a 2 part form, so it will have a mating piece. But cutting that means taking the convex off-cuts from the concave form, with identical but unknown radii, and finding a way to locate the mounting pins to change the radius.

Monday, April 7, 2014

Tool review: Shinwa Bevel Gauge, and a quick tip.

One of the phrases that I've come across in recent months with regard to layout tools is 'Accuracy has to start somewhere.' Typically, this phrase is used in conjunction with a review to justify a new try square or bevel gauge or some such, as a reliable reference standard. I'm in agreement with the phrase, and I'm using it in a tool review, but not the way I've seen it used.

I think accuracy has to start somewhere, but I think it has to start with an understanding of accuracy, and degrees of accuracy.

This is a picture of two lines, drawn with a sliding bevel gauge.


Please note that a) the lines diverge, and b) the divergence isn't really readily apparent for the first couple of inches. THIS is where accuracy begins: with the understanding that minor and minute errors aren't apparent until magnified or multiplied. And you may not detect them until they can affect a bigger picture. (If this was a picture frame, or something with big miters, and your angles are slightly off, your miters won't close. Period. Yes, you can use putty or wood filler, but the joint will lose strength.) It's easier to detect a minute discrepancy if it's projected out far enough. This is why you need to draw LONG lines to set your bevel gauge to. It's why it helps to have a bevel gauge with a long blade, AND a long beam: You want to make sure that the angle is true, even when projected out. 

I've seen some stores offer little 3" setup blocks milled out of aluminum from companies like Incra or Woodpeckers. I've also seen firsthand that even inside the 3", these little doo-dads weren't actually square. If you can't make a block square enough within 3", that's beyond egregious. If you're shopping at the store, ask to borrow a Starrett combination square to check any other squares or setup blocks, and see for yourself. 

These are my Shinwa bevel gauges, and my Starett gauge:


I bought the Starett years ago. I like it.

I like the Shinwa gauges better.

I like the 9" long beams, the 8" long blades, and the fact that there's room to write on them, to keep track of multiple angles. (Sharpie marker ink wipes clean with denatured alcohol) 

I also like that the handle has a hole, not a slot. The slot in the Starrett can lead to errors, like so:


I've exaggerated the issue for the sake of illustration, but a little bit of beam protrusion can interfere with the ability to set up the blade on a table saw accurately. 

Lastly, I like the screwdriver slot in the nut on the Shinwa. I don't torque down on it too hard, but the blade locks very rigidly in place. I usually set to finger-tight while I fine-tune the setting, and tighten afterwards, to lock it up.

Quick tip, for an even tighter lock-up, pulled from an old book on drafting: Old-school draftsmen would heat up their dividers and melt beeswax onto the pivot point. Unlike paraffin, beeswax is a little sticky. Melted into the milled steel surface, beeswax will add just a bit more 'sticktion,' which is the static friction that must be overcome before an object moves. In motion, beeswax glides beautifully. But it will also help hold a setting a little bit better. I haven't needed it on the bevel gauges that I have, but for those of you who have been fighting with the gauge that you have, it might help... And, it'll help prevent rust.



Friday, April 4, 2014

Circular logic, Part I

Things have been busy. It would have been great to get this series of posts out last month... preferably on Pi day (3/14/14) or just during last month, which was Pi month. (3rd month, of '14) Alas... c'est la guerre.

The top of my current project is curved. Most of the methods I've seen for cutting a radius involve driving a screw through the center, and using that as a pivot point. And that works well enough for many things. But in this case, it's a curved structural member, involving two different radii, one convex, one concave, and with two different centers. And that starts to get sticky. Added to that, I had this hair-brained idea of making a cut on the band saw, and a finish pass on the router table, to make for a smooth finished part. Lastly, I'm working with 12/4 stock, and the notion of just drilling a center through a beam that's wide enough to also contain the center, was just wasteful to the point of being dopey. So, I set out to untangle radiused cuts (inside and outside radii) on pieces that aren't wide enough to contain the pivot point.

The picture below is the starting point for the jig. As I said, most of the radius cutting that Ive seen involves driving a screw through the center of the curve, into a precisely placed hole that's the proper distance from the cutting action. But the screws are usually short, it's almost impossible sometimes to see where you're supposed to be driving it into... so I simplified things. The base mounts to the band saw table. And on top of that is a sliding dovetailed piece, to adjust for different radii, with two options for pivot centers: a removable pin that sticks up, to be used with a 1/4" hole, and a 1/4" brass shelf pin sleeve that serves as a bushing for a center that will be seen shortly. The pin started out as a 1/4-20 bolt that was only partially threaded. I cut it off, chucked it up in a hand drill, and domed the end with a bench grinder.


Making the cut on the band saw is as simple as I assumed it would be.


As I said, I also wanted to be able to make finishing passes on the router table. The jig below is a sliding mount for two more centers, as on the band saw. The idea is that I can set up whatever jig I'm going to use, and because the centers aren't drilled or driven into anything, I should be able to just move directly from the band saw to the router table.


Part of the problem with cutting an inside radius with the traditional screw-center method is that you only get one shot. After that, if the radius isn't quite big enough, you no longer have a center to work from, because you've removed the part being cut, from the center that was your reference point. I thought about using a simple jig that mounted to the center point, and to mount the blanks to that, but again, it seemed awkward. Eventually I came up with the idea of a scissoring pair of arms to mount to a blank, and the only problem I had then was that I'd cut right through the arms when I used it. So, I came up with this:


Again, 1/4" bolts cut off into pins. The pins slide through 1/4" holes in the hooked end, and into 1/4" holes in the blank. In this way, the pin can be removed to allow the blade to get in between the arms, and re-inserted before cutting. And the hooks are there to give clearance for the blade to exit the material without having to cut into the arms of the jig. And, the pin being used for the pivot point slides into the brass bushing in either the band saw, or the router table.


Coming up: laying out the mounting holes, using the jig to make a bending form, and a few other things...

To be continued.

Wednesday, March 26, 2014

BFFI to the rescue



Accuracy is still an issue. I have a long-term solution, but it hasn't been implemented yet. And, to borrow an unfortunate, albeit accurate quote, "You don't go to war with the army you want. You go with the army you have."

Bombs away...

Apropos, then, that I borrow from that great military tradition of Brute Force and Ignorance. If at first you don't succeed, get a bigger hammer. Above, I'm using a 3 lb hammer and a center punch to make the Kreg miter bar fit my miter slot in an ugly, if workable way.

Tuesday, March 25, 2014

Oldie but goodie shop tip: cheapo glue bottle



I put this up a few years back, and after a few years (!) of using my last one, I started refilling a small titebond bottle. But it's been a few months, the pull-open tip is very much the worse for wear after many clean-outs, and so it's come back to this. 

Glue bottles at the fancy store will run $2-3 at the minimum. You could go the restaurant supply route and pay the same for a refillable ketchup bottle. And in either case, they'll still clog up, need to be cleaned out with a drywall screw, and not last too long.

This one will only cost you a nickel, it comes with a drink of your choice, and for some chemical reason that's beyond my pay grade, the glue doesn't stick too well to the top. When it dries, it pops off pretty easily. 

No, it doesn't have a roller, and it won't get into crevices, but that's what glue brushes and scraps are for.

(S)Crap! Another use for scraps! I'll put that in the next roundup...