Saturday, June 30, 2012

Making Connections

I have a project for a west coast client to make Japanese joinery models, which I've been pecking away at here and there between other tasks. These models are at a large size, and it was tricky finding dry 16/4 materials appropriate to the task. I managed to obtain some Iroko and Bubiniga beams. The joints are made to have contrasting halves, and to be readily demountable. Apparently, the client, who is unknown to me, is fascinated by Japanese joinery mechanisms. We have that in common!

I thought I'd share a few pics of the two models I've made so far. The first is koshi-kake kama tsugi, the half-lapped gooseneck joint. This is a splicing joint often used on mudsills and purlins where they are adequately supported underneath. It is a tricky connection to fit properly as the head of the joint has sloped ramps which tighten the connection as it goes together.

The two joint halves, the Iroko on the left, and Bubinga on the right:


The joint assembles in one direction, which is a vertical drop in:


These are a couple of standard proportionings for this joint, and I went with the longer and skinnier necked version. There is also a tapered neck version, and some alternate shapes for the joint head as well, but the above is more or less standard.

As the joints slides down, it begins to tighten up:


A view from the other side:


I took these photos just prior to wrapping the joint for shipment, and did not push the joint all the way together. I had done so at the shop but omitted to take a picture. I resolved to be a little more organized in the picture taking for the next joint.

The second joint is a double wedged locking box joint, or shachi sen hako dome tsugi. This is a high class joint used for decorative alcove floor frame corners, and is seen on some temple mudsill corners. It is also used in framed furniture pieces on occasion, and it is a favorite of mine.

The two joint halves:



A view of the joint halves going together, the assembly rotated 90˚ up:

  

The two halves going together, conventional orientation of parts:

 

Completed joint, inside view:


The black locking keys, shachi sen, I made out of Gabon ebony. They have bulbous heads on them to make it a lot easier to pull the pins out. Normally, the wedging pins would not have such heads, and would be driven in with a hammer and likely trimmed flush. Once the shachi are driven in, this joint is tightened right up and the pins would be removed only by drilling them out. Finding the right position with fitting these pins so that the connection would tighten and yet not get too tight added a fair amount of time to the fitting process.

A view of the front, the intended position from which this connection is viewed:


Clicking on any of the images will render them in a larger format.

The joints are all hand planed clean, chamfered and then sent out. No finish otherwise. A very enjoyable project for me, and apparently providing much delight to the client so far. I hope the reader has enjoyed the look at these joints. I have about another dozen to make, give or take, depending. I'll probably post some follow up entries as these connection are completed. Thanks for your visit!

Update: after discussion with my client's representative, they would prefer no more blog entries of photographs on this topic. Sorry!

Friday, June 22, 2012

Chip off the Old Block (III)

In the previous post in this series I took a look at the various conditions which associate to the shaving types one obtains with a single blade slicing or scraping the wood at different angles. Those angles, in the case of Western bevel down metal bodied planes are typically 45˚, with a 'York' pattern plane having a 50˚ blade bedding angle. Perhaps if one were to average across the characteristics of wood species one might plane, an average point or compromise that would work to some extent in a wide variety of conditions would be around 45˚. A compromise however means that in some woods a 45˚ plane will not do a great job.

Japanese planes are much more varied in this respect, with certain bedding angles associating more specifically, and ideally, to certain wood species. For instance, when planing softwoods a blade bedded at less than 45˚ is going to give a cleaner surface than one bedded at 45˚ or 50˚. Here's a breakdown of some typical Japanese plane bedding angles and what materials they often associate to:

Class: soft woods (nanzai)

Woods: Paulownia, Cryptomeria, Cedar, Pine

Blade Bedding Angle: 31~38˚

Blade Bevel Angle: 20~24˚

--------------------------

Class: Medium hard woods 中堅材 (chūkenzai)

Woods: Oak, Elm, Cherry, Teak, Mahogany, Ash

Blade Bedding Angle: 39~42˚

Blade Bevel Angle: 25~29˚

---------------------------

Class: Hard woods 堅材 (kenzai)

Woods: Ebony, Bubinga, Rosewood, Wenge

Blade Bedding Angle: 45~90˚

Blade Bevel Angle: 30˚ and up

---------------------------

The connection between blade bedding angle and bevel angle relates to something called the clearance angle, which is the angle between the surface you are working and the underside surface of the blade bevel. Here's a generic example of a plane set up with a 45˚ bedding angle and having a 33˚ bevel, which leaves a clearance angle of 12˚:


Click on any of the illustrations for a larger size view. Western bench planes typically have a combination of 45˚ bedding, 30˚ blade bevel, leaving a clearance angle of 15˚.

The importance of the clearance angle is in what happens as the blade wears during use. At the start, we have a blade which is the mythic perfect sharpness, and the sharp tip of that blade, due to its small surface area, is able to realize thousands of pounds of force while cutting, and the cut will feel effortless:


After dragging the plane down several linear feet of material, the chip being pulled up the flat face of the plane blade has caused the blade's flat surface to start to take on a scalloped shape, and the bevel has worn near the tip creating a more obtuse effective cutting angle:


If we zoom into to look right at the tip, we can see that the wear pattern has left us with a blade having a considerably larger surface area than when it was sharp:


This new large surface area at the blade tip translates into a greatly reduced amount of pressure at the blade edge, perhaps hundreds of pounds per square inch instead of thousands, while cutting effort has increased considerably. It is at this point that the user may start to press the plane down more vigorously in order to get it cutting like it was just a few moments before, however this is largely a waste of time. The blade needs to be sharpened.

From what I have seen and experienced, a clearance angle of 10~15˚ is suitable. Japanese steels are pretty tough so you can get down to 10˚ clearance and have good performance as the tool slowly wears.

Connecting the bedding angle, bevel angle, and clearance angle together reveals a few points. Let's say we want to set up a plane for working a soft wood, and we cut the plane bed for 35˚. If we fit in the same plane blade that worked for a 45˚ bedding, a blade which had a 33˚ bevel, we end up with a very small clearance angle of only 2˚:


A clearance angle so small would give you very little planing joy before the tool felt dull and required a lot of effort and down-pressure to get anywhere.

Therefore, with a blade bedded at 35˚, a bevel angle of around 20˚ is much more suitable, as this restores a decent clearance angle of 15˚:


You could have pushed the bevel angle to 22~23˚ and things would have worked fine for clearance. In general, the better the cutting steel and skill of the blacksmith, the longer a blade with an acute angle is going to hold an edge while cutting.

Going the other way, what if we had some very hard wood to plane and we set up a dai with a 65˚ bedding angle, like this:


Here we can see that the clearance angle with a 33˚ bevel would be huge, however the blade is going to dull rapidly as it scrapes along and it has very poor support behind the edge. A more obtuse bevel angle, 50˚ in this case, would be better:


The problem with Japanese planes, as they are sold in countries outside Japan, is that you are buying a kit. The parts are made by different individuals - someone forges the blade, another may grind and sharpen it, another person make the block - and they are likely just to be making blocks, by the dozen, generically, and grabbing a blade off the pile and doing an initial fitting then on to the next one. If you didn't know any of that, you would likely assume that the blade and dai supplied are just a few fitting steps away from use, but this is unfortunately not often the case. These parts are thrown together as a kit and sent your way, so you may end up with a blade with an overly acute bevel for the bedding angle in the dai. and if the blade bevel is overly acute, or an inexperienced sharpener makes it too acute by overworking the softer iron, then the only recourse is tapping the blade out and regrinding a more obtuse bevel. And if you don't know how to do that, or are afraid of doing that, the plane may not work to it's fullest potential, let's put it that way. A 20˚ blade bevel bedded 40˚ and worked along some teak is a set up making for very frequent sharpening sessions. It is inefficient.

Further, if the plane sat on a shelf for a long time and wasn't forged particularly well, the main blade and chipbreaker are likely to have a pronounced cup along their lengths (does to stressing from the forge weld resolving themselves over time) which, for the inexperienced, translates into poor fitting and inconsistent sharpening. As you can see, start adding these factors up and you have a recipe for frustration, and tools sitting collecting dust. 

The only good way around 'the kit problem', as such, is to put that fact to your advantage, to order the plane with specific requests for blade bevel, chipbreaker type, bedding angle, and so forth, but until one has gained enough experience working with these planes, how would one know what specifics to request? And then there are issues with dealing with a knowledgeable vendor who is able to communicate with the blacksmiths and dai makers, etc. If you tell the vendor that you want a plane set up for Douglas Fir or Eastern Live oak, there is a chance that the people at the manufacturing end haven't made a plane set up for that wood (since they don't commonly use those woods in Japan), and are unfamiliar with the characteristics of those woods and what set up might be best. If you wanted a plane set up for Paulownia, then no problem of course, as the people making the plane in Japan would be very familiar with the requirements for that use.

For optimal results, there are certain combinations of bedding angle and bevel angle which are ideal, however it is also the case that a well-tuned chipbreaker can enable a plane with a less than ideal set up to perform adequately in situations where it would fail otherwise. A well-tuned chipbreaker can enable a plane to punch above its weight, to use a boxing analogy, and so those with only one plane at their disposal, assuming it is of average configuration, can often make that plane work decently in a wider variety of woods than would otherwise be possible. In the next post in this series I'll look more closely at the details for chipbreaker set up show how it can enable a plane to go beyond its pay grade, so to speak. I hope you'll drop by again. Thanks for visiting!  ...on to post IV

Wednesday, June 20, 2012

Dewalt De Fault: Postscript

One of the things that echoed in my head after the bad taste of the Dewalt purchase gradually abated was the way the product was described in the sales lit.:

"The DEWALT DWS780 12-inch double bevel sliding compound miter saw expertly walks the line between the rugged durability and fine precision that professionals need on the job site. From delicate woodworking to heavy-duty framing and deck building, the DWS780 provides the accuracy, capacity, and portability that cabinetmakers, trim carpenters, framers, installers, and contractors need."

I think the saw, like many other brands out there, would be fine for indifferent production cutting, tossing in the back of the pickup truck, etc. I was hoping for more, thinking that $600 should get me somewhat close to 'the basics done right', but it wasn't looking that way.

Waking up this morning I was still not quite sure which way to go. I was re-contemplating the Tannewitz saw again, and trying to convince myself that I could make one of the $600 sliders do a decent job with an MDF sub-table, judicious filing work on the fences, etc. Not leaving me with a warm and fuzzy feeling, I'll say that.

Driving to the shop, I decided to stop in a local building center, R.K. Miles. They are a 4-store outfit based in New England, and the staff in there have always been friendly - in a 'real' sort of way, not the fake sort of way as you get with the 'greeters' the big box stores put by their entrances to 'welcome' you in and with forced enthusiasm ask if they can 'help you find anything'.  I would commit hara-kiri if I had to do that job, so those people have my enduring admiration, when I'm not trying my best to avoid their approach at the entrance. I pulled in and grabbed by pile of reference tools to check out what they had on offer.

First off I looked at another Bosch 12" 'Glide' saw. This one had a really bad table, level at the back by the fence and tilted forwards to the handle end to the extent of 0.02". No, I'm not missing a '0' there folks -- it was on it's way to being 1/16" out of level (!). The glide mechanism looked cool, and I remember the hype about this saw several months back, but the glide was not as laterally stiff as one might have hoped. Pass.

Then I looked at their Hitachi 10" saws, and again found the tables not co-planar with the saw base. And after having owned a 10" newer type of Hitachi slider, and having used most of their other models, I wasn't interested. I don't like their split fence design as it is easily knocked out of alignment. Pass.

Check another 10" Makita DXT saw, and just like the one in the Orange Box store yesterday, was not level and neither were the fences square to the table. Pass.

Down to one last possibility: Festool Kapex. They had one in the store, folded up with its stand. I was eyeballing it and then a staff member came over and asked me if I needed any help. I told them I wanted to check out the Kapex. He wrestled it up and unfolded the stand (not the most impressive sort of stand), and then looked at me with a 'well?' on his face. I then moved in with the straightedge. The guy at the counter who was observing the scene said, "wow, we've never had anyone in here  looking at the tools with stuff like that!" I'm always happy to provide some entertainment to my fellow human beings. I tried explaining to them why finding a flat and square machine was important to me, and while they nodded and looked like I was making perfect sense, I suspect they thought I might be a tad OCD or something like that.


I placed the straightedge across the Kapex's table and base and it looked flat(!). Knowing that my eyes might be deceiving me, I pulled out the feeler gauge set and started with the usual 0.005" leaf under the straightedge. No way Jose. I eventually found that I couldn't even get a 0.001" feeler gauge under any portion of the table. That my friends, is suitably flat enough for me and any sort of woodworking I can envision. I then checked the fences to see how square they were and was surprised to find they were dead on 90˚ as well.  I know that some folks have criticized this saw for various reasons, having read the reviews like anybody else, but when it comes down to the basic functions of a cutting saw, this is the only one I have found on the market that actually has a flat table and square fence. I turned to the salesperson and said, "I'll take it".

Fitting it onto the Bosch gravity rise stand was a slight hassle, which was unexpected given that both companies are German and the fittings are metric. I eventually found that a 1/4"-20 Allen head cap screws and nuts were the ticket to fastening the saw to the stand without having to make modifications to either component.

The saw was a display unit and is missing the manual, so there are a few points of operation I haven't quite worked out yet. The saw can be had with an 80-tooth blade, the up front handle to adjust the blade tilt, the extra large protractor scale for tilt, and the excellent dust collection all seem like strong points on this saw. A three year warranty is nice too. And it weighed a good 10 lbs less that the Dewalt as well.  I'm sure the Kapex will have its faults in some way or another, but its basic accuracy promises more than any of the others at the consumer end of the miter saw market are capable of delivering.

Yes, I had to spend more than twice as much money to get a saw that had the basics done right. In the scale of things, when a Graule precision radial saw costs upwards of $10,000, the Kapex is still relatively inexpensive. I had hoped $600 would get me what I wanted, but it does not I'm afraid.

I now have a Forrest Chopmaster 12"x80T blade with a history of 10 test cuts on it for sale. Send me a message if you're interested in buying it, otherwise it goes up for sale elsewhere.

Thanks for coming by the Carpentry Way and comments always welcome.

Tuesday, June 19, 2012

Dewalt De Fault

As readers of this blog in past weeks may have noticed, I purchased a new sliding compound chop saw at the end of May. It has mostly sat in my shop since then, as I was waiting to obtain a support stand before setting the saw up for use. I bought this saw having had satisfactory results from a Dewalt 12" non-sliding chop saw I had used a few times, along with advice from a couple of other woodworkers who said their Dewalt 'worked great'.

I received the stand yesterday, a Bosch Gravity rise stand, which I obtained from Amazon for a pretty good price of $229.00, with free shipping. The best local price I could find on the stand was $329.00, so it wasn't even close. I would have preferred to support the local company, but $100 is a bit too much of a differential.

An hour of assembly later and I had the saw and table all set up ready to go:



The stand went together well and folds/unfolds without drama. Then I ran a couple of test cuts on the saw, and I discovered that out of the box, the Dewalt 780 doesn't cut 90˚ vertically or horizontally. And why should it? After all, isn't close enough going to be good enough? Why, from 10 feet away no one would notice that the horizontal alignment is 3˚ out. I hope my humor, a bit sarcastic as it is, translates. Perhaps you'll understand where my sarcasm comes from by the time you read through this entry.

I twiddled a few nuts and bolts and managed to get the saw to cut 90˚ both vertically and horizontally with minimal fuss. So, even though the saw didn't come from the factory set up square to cut, at least it could be made square to cut - or was I kidding myself? Turns out, I really was hallucinating, and not in a good sort of way.

While looking at a piece of wood sitting on the saw table, I noticed some gappage where there ought not to be any gappage: on the top surface of the table, and at the fence. This photo probably gives little hint as to how bad things were:


I'll start with that photo since I think it best to go easy on the tender eyes of my viewing audience, lest they develop the same nausea I suffered. Nearer the middle of the turn table the gap at the aluminum is bad enough, and I'll leave off mentioning the even greater gap above the through insert plate:


Hmm, well, my old eyes can be easily deceived even with the sun shining brightly, so I got out a straightedge and the feeler gauges, hoping that the cold hard numbers would be reassuring somehow:


 Well, on the left side of the table, with the saw set for a 90˚ cut, the total space is a canyon-like 0.009":


On the right side of the table, again with setting for 90˚, the gap is a more reasonable, but still unacceptable, at 0.004":


Now, not only was the table low, but it was canted to the left. I rotated the table to extremes left and right and not much changed.

The problem with a gap like that is twofold:
  • a stick which is long and spans the entire work surface will be partly suspended in the air when the cut is made, and will likely dive slightly down when the wood is cut through, potentially marring the cut line or binding the blade a little
  • since the table leans, to where exactly does one relate the 90˚ fence?
While the saw could be set up to cut well in a certain condition, change anything - like trying to cut a short piece for instance - and the geometry changes, unfavorably.

As for the fence, it wasn't square to the table or the base:


Again, that may look minor enough - let's zoom in a little shall we?:


I imagine the gap here was on the order of 0.009"~0.012" or so. I declined to find out a definite number. It was sufficiently non-square for me to cut the examination short. The fence on the other side of the table was okay, but of course I won't be doing all my cutting from that one side. I discovered later that the fences on both sides of the turntable were in fact co-planar to one another, however the tilted turntable made it impossible to get squareness all the way across.

With either fence though, there was no provision for making adjustments to get it square, other than by abrasive grinding. Ditto for the turntable - it cannot be adjusted or shimmed.

I called Dewalt to double check my conclusion, in case there might be some perfectly simple, rational way out of this problem where everything is fixed with the twist of a Torx screw. I ended up speaking to a woman at Customer Service, who, like any reasonable person who doesn't work with tools and never tries to do accurate work with tools (that's my presumption anyhow), I'm sure thought that I was some sort of nut bar for my talk of nine thousandths out! and such. She duly jotted down every word I said, then talked with her supervisor who then said just what I thought: there is no way to adjust the saw that way, so I needed to return it to the store where I purchased it.

And that store was the big Orange Box. Back I went to that box on this sunny Tuesday, this time with straightedge, feeler gauges, and try square in hand. I cannot recommend this strongly enough to someone in the market for a sliding chopsaw, especially if you want to have that appalled, shipwrecked sort of feeling, where despair takes over and the hope of a simple 90˚ cut result is but a faded dream....

I checked the Dewalt on the display and it also had a non-square fence and a table that was tilted and lower than the surrounding base platforms. It was not quite as bad as the one I had bought, but still pretty bad.

And let me say this: I'm not expecting the base and table to be within 0.0001" alignment here folks, I'd be okay if they were out by 0.001~0.002". At least then one could shim the table top with some tape, put in a sub-table, etc, and get on with things. I imagine those who do not seek precision in their cross cutting work would also be fine with a chopsaw with such poor tolerances of fit. Not me. Call me crazy, but if I cut two sticks off squarely on their ends, according to the machine's settings, I expect that I can butt those two pieces together endwise and they will be aligned in a straight line. I'm just not that into kinky things you see.

And let me say this, too: if a machine is supposed to cut a square-section stick at a particular angle accurately, then it needs to have a flat table and a fence which is 90˚ to the table. Period. That is the 'normal' operating parameter for a device like that.

Back to the adventure at the box store. I then checked the other brands of chopsaw on display. They all suffered from the same problems of tables low (though 1 had a table that was too high) and fences un-square to one extent or another regardless of brand, Makita, Ridgid, and Dewalt alike. I did find one Dewalt non-sliding chopsaw that was actually pretty flat across the tops, and this gave me some hope that I might find another Dewalt 780 which by stroke of luck, act of god, etc., had decent alignment of parts.

I dragged out one of the enormous Dewalt boxes and was midway into tearing the plastic wrap off when the tool department guy suddenly appeared. An older fella, older than me anyway. He asked me what I was up to in a friendly voice and I explained the issue I had with the 780 saw and that another sales 'associate' had given me the green light to open the other boxes to do any checks I pleased.

"Well, I can tell you right now there's no point in doing that as you'll find they're all like that," he said matter-of-factly. He was remarkably candid as he went on and told me that the new Dewalt products, since Stanley/Black and Decker (a.k.a. the Death Star) bought them out, were basically junk. I quote him verbatim: 'junk'.

Oh, I thought, and I had concluded only their portable planers were junk - I clearly needed to revise my low estimations of post-buyout Dewalt.

The tool 'associate' then suggested I find the newly obsolete Ridgid 12" sliding chop saw, as he had had good results with it (and had personally done some cabinetmaking, so he actually used tools, not just sold them or 'serviced' customers). Now, why he was working in Home Desperation instead of his own cabinet shop is a question I decided to take up at some later juncture....

I realized that although the Ridgid 12" saw was now discontinued, I knew of someone else who thought highly of it and also that another Home Depravation near my house (a half-size one) actually had one left on display, if my memory served me correctly.

Leaving the Home Deposit, I decided to visit their neighbor Lowes a mile down the strip to see what they had on offer. Again, I went in armed with straightedge, feeler gauges, and  try square. This time I checked the Bosch 12" Glide saw (result: table low and both fences unsquare to base) and the Hitachi ski boot-esque 12" sliding saw (also non-flat, non-square, and absolutely ugly). A short visit, and an unimpressive one.

At the end of the day I drove home and stopped, last ditch effort here folks, at that mini-me orange box store and yes, as I had remembered they had the 12" saw on display, one just like this:


I looked the saw over and checked a few things. First, since there is only a turntable and no flanking base decking, the only issue with the table would be whether it was flat. Checking with the straightedge, visually things looked good. Then I inspected the two fences for squareness - one was fine, the other not so much, but could probably be filed square. The saw had no blade and I noticed the box was not anywhere to be seen, a box containing the blade, manual, hold-down clamp, wrench, dust bag etc. None of that was critical but I thought it would be worth seeing if it could be turned up somewhere. I managed to find a sales 'associate' and he said he had no idea where the box was, so the saw would have to be sold without the blade, wrench, etc. Then I noticed the fence was loose, and one of the plastic pieces which is for storing the electrical cord was broken. It clearly had been on display a long time, and as this model had been discontinued, this saw was the last one they were ever going to have. I decided to ask if the price might be negotiable, considering the various issues. The clerk said that the best he could do personally was 10%, which brought the price down to $450.00. I thought they should be able to do better than this so I went off to locate the manager or assistant manager.

At the 'service' counter, the young lady behind the desk phoned the assistant manager for me. While they were speaking, she suddenly turned to me and asked, "what is this specifically about?". I explained the situation and she repeated my words more or less verbatim to the manager. Then she said, "Can you show me the machine in question?." I took her over to the tool section and explained the situation. She decided quickly that the discount was 10%. I gather that must be company policy, even if the machine had been dropped off a truck or urinated upon, you get 10% and no more. I gathered she came over to see it as the assistant manager couldn't be bothered with such matters. I said that 10% off was not attractive enough to persuade me to buy and made my way to the exit, keeping a couple of paces back of the young woman who had come over to look with me. As we approached the 'service' desk again, I suddenly notice an older employee with 'Gary' written on his apron - the very same name as the assistant manager. Hmm. Guess he was too busy to give me his time.

That my friends is how I make my very last trip into that particular Orange box. Sayonara. If the assistant manager can't give me two minutes of his free time on a slow shopping day, with a discontinued piece of merchandise, worn from years on display, well, they don't deserve any further business from me. It's the small things that make the difference in perceptions at times. It's actual customer service, not a friggin' smiley face badge on your apron.

So, I now have a shiny Bosch miter saw stand, and a new Forrest chopmaster 12" blade, and not quite sure which way to go saw-wise. The only two saws I have yet to look at are the Makita 12" (reviews on amazon are not promising), and then I would be looking at 10" saws, like the Festool Kapex, which also appears to  have some undesirable characteristics from what I have read - like a $1300 price point. This is a drag.

The conclusion I draw from this, and please slap me for being so late to figure this out, is that these large tool companies couldn't give a crap if their products actually worked well, only that they look flashy, look tough, look like something you could show off even, but as far as the basic operations they are supposed to carry out, well, who cares about stuff like that? It gets in the way of shareholder returns. Cut the costs, cut them down, way down to the bone, outsource it to the cheapest place and add some tits and ass to the adverts if you can and flog these junky pieces of equipment as fast as you can. And when the machine wears out and becomes so hopelessly inaccurate that even the most ham-handed begin to notice - ideally just a week or two after the warranty expires - come out with a 'new and improved' model with exciting new 'features'. You see, what sells are 'features', and 'perceived benefits', not quality of build, accuracy of work execution, or reliably solid construction. That my friends is hopelessly outmoded it would appear. Or, if you really want that, you need to spend thousands of dollars to acquire it and it usually comes from Germany. Silly me for even imagining otherwise.

I can take a least some satisfaction for having vented. Thank you for your attention.

Sunday, June 17, 2012

The Wooden Serpent

My wife and I were taking a drive up to Bennington Vermont the other day to check out the American Covered Bridge Museum. Bennington is a quaint town in the far Southwestern corner of Vermont. The museum was open but proved to be rather underwhelming. I did learn that at one point in time there were 600 covered bridges in Vermont, and around 100 remain.

On the way to the museum we drove up route 9, and approaching the dot on the map known as Searsburg I noticed something unusual by the side of the road, something snaking along and then ducking under the road only to emerge out the other side. This was something you certainly don't see every day: a wooden water pipe:


This pipe is part of a TransCanada Corporation's hydroelectric set up, and is in fact a penstock. It runs from TransCanada’s Searsburg Dam in Searsburg, VT to the Searsburg Station on the Deerfield River. The pipeline itself is about 3 miles long and is 8 feet in diameter on the inside. It’s made from wood staves (treated Douglas Fir - 3 million board feet were required!), similar in construction to a barrel; tongue and groove wood held together by metal bands. It flows water from the diversion (dam) to the powerhouse where the generator is housed.  The original pipeline was built in 1922 and last replaced in 1985.


It might need some attention again soon as it seems to leak fairly profusely from what I could see. These pictures don't show the leaking water on the underside of the pipe, but you can see some of the boards are wet on the outside:


This pipeline uses a wooden tension rod support cradle system. I've got to imagine that the leaking would cause problems in the wintertime with ice build up, and worse. I imagine that constant maintenance would be vital to realizing good long term service life. You have to keep the exterior clean and free from dirt to minimize opportunities for rot to begin. Repairs to wooden pipes are fairly straightforward though.

I thought this was a very neat thing to come across as I don't imagine there are many functional wooden penstocks left in North America:


Digging into it a little further, I learned that there are several functioning wooden penstocks in New England, including one just a bit further Northeast in Hillborough, NH. I'll have to check it out sometime.

I also found info on the company that had done the work to construct the penstock - Danbar, a Canadian outfit. A web page shows that there are still a few companies making wooden penstocks and that these wooden pipelines have certain advantages over other materials, in terms of handling corrosive materials, requiring minimal site preparation and they also handling abrasion very well. A fifty year durability is considered typical. Hooray for wood!

Here's a picture from Danbar's brochure showing some of the 1985 re-construction of the Searsburg penstock:



A couple more pages from that brochure:





I hope my fellow woodchucks found the above of interest. Thanks for dropping by the Carpentry Way.

Tuesday, June 12, 2012

Chip off the Old Block (II)

Time sure flies when you're doing too many things at the same time.

A few people have brought to my attention a video recently circulating around showing a Japanese experiment by professors at Yamagata University with chip breaker placement. This video is a follow up from a report issued by the same two professors several years backs and is quite interesting viewing. I suggest a visit to Wilbur Pan's site for those who haven't seen the video yet would be worthwhile.

Seeing the video did not alter any conclusions I had already drawn, though it did leave me wondering if I had much useful to add. I guess we'll see.

Bruce Hoadley's work Understanding Wood: A Craftsman's Guide to Wood Technology has an excellent chapter describing the process of chip formation with a hand plane. He describes shavings being of three types, however others have pushed this list out to four types. I've taken the liberty of reproducing the drawings of the chip formation types directly from Hoadley's book.

These shavings are all described in light of taking cuts along the grain, and measure cutting angle in reference to vertical, a 'large cutting angle' therefore being a blade with a low bedding angle, and a 'low cutting angle' would be something seen with a scraper plane having the blade bedded at an angle, say, 70˚ to 90˚ to horizontal. Here are the four types:
  • Type 0: cutting angle 'very large', producing a shaving which is relatively undamaged by the cutting process
  • Type I: cutting angle is 'relatively large', producing a chip which is characterized by a long jointed (ie., broken segmentally on its underside) curl. This type of shaving is characteristic of taking a thick cut along the grain:

The fact that the underside of the shaving breaks due to tensile failure leads to a shaving which curls pronouncedly forward. The tighter the curl, the more frequently the breaks are occurring in the shaving. A key point about the Type I chip is that the material is splitting ahead of the actual knife edge, as a result of the wedge action of the blade acting like a lever and pulling the material upward. This is not a shaving one would associate to fine surface finishing with a plane, but rather more to rough cutting in a cooperative material.
  • Type II: cutting angle is 'small', and the face of the knife produces more forward compression than upward lifting of the shaving:

This shaving also tends to curl forward and may have a somewhat accordion-like appearance, but is not segmented like the type I. Looking closely at the sketch, you can see a short angled plane directly above the tip of the cutter - the material deforms at this location as it is shaved.
  • Type III: cutting angle is 'very small', i.e., nearly perpendicular to the surface, and most of the cutting force is transmitted in direct compression to the wood grain, producing a scraping effect:

Scraped shavings tend to be short, and the majority of the material is removed via compression failure directly in front of the cutter.
I would imagine that most hand planing with standard bedding angles is going to produce Type II shavings. Type III shavings can be avoided, even with scraping planes, by taking a very light depth of cut, which causes in effect a Type II shaving to be produced.

The closer one can get to producing a shaving which can be lifted from the wood with a minimum of compression, the more likely it is that the surface will be cleanly cut without tear out. This fact however also associates to which species of wood is being worked and its unique characteristics. Some woods are plane friendly, and some, well, not so much.

In general, the softer the wood, the lower the cutting angle needs to be in order to take a clean slice. As Hoadley draws in an excellent analogy, imagine the wood is like a wet dish sponge and you are trying to take a slice off it with an ordinary kitchen knife. The sponge simply deflects out of the way and no cutting is accomplished. Try the same with a very sharp knife or razor blade and the sponge can be cut, however it will still deflect ahead of the knife. Some sponge will be sliced cleanly, while other portions may tear away in pieces at locations other than the blade edge. The irregular springback of material after the cutting edge passes gives a result of an irregularly shaved surface.

This springback effect occurs with all woods, regardless of how hard or dense they may be, and one can readily apprehend that a hard and dense wood would deflect and springback minimally and it would also strongly resist the entry of a knife into its surface. In certain cases a knife might simply deflect and pop back out, leaving at best chatter marks on the surface, and at worst, portions of the plane blade may simply break away at the cutting edge.

Those wishing to plane very soft woods, like Western Red Cedar, California Redwood,  and Paulownia would do well to employ planes with low cutting and bevel angles to obtain the best surface quality, however it isn't always so simple as that. If the wood's grain isn't uniformly in the same orientation, or is curly, or there are included knots, the low blade angle can be a recipe for short edge life and nasty tear out where the grain changes direction. Some soft woods are also surprisingly abrasive and thus a very acute blade bevel won't last very long before dulling. However, dealing with the issue by moving to a steeper plane blade bedding angle (and the more obtuse blade bevel angle which associates to it), while it will likely eliminate the tear out problem, will leave behind a less cleanly planed surface. Such a surface will look dull instead of glassy. A hand scraper will only leave the same quality of surface, and recourse to sanding softwoods is going to leave an even cloudier surface. Softwoods which are sanded are left so far short of their potential in terms of surface quality that the practice ought to be outlawed really. I guess I say that after seeing countless examples of woodworkers going over some generally plane-friendly wood like American Chestnut, or Yellow Cedar, say, mindlessly with their orbital sander, headphones on with classic rock, and yet they unknowingly (?) deny themselves the joy of taking a few swipes with the plane and leaving a glossy shimmering surface while leaving behind the noise and dust. It's a bit like a crime when you see it, and pointless to comment upon.

Planing soft woods without tear out is one place where a chipbreaker can however solve the apparent no-win position between avoiding tear out and obtaining a cleanly planed surface with a plane having a low bedding angle.

On denser woods, a quality surface is unlikely to be effective produced by a low blade angle, and higher blade angles, due to the toughness of the material and its tendency to be rather unyielding to the cutter, can produce excellent surface finish. I do not notice an appreciable difference the surface quality of Bubinga, for instance, when planed with a 45˚ plane or a 60˚ plane - though I tend to have fewer issues of tear out by far with the steeper cutting angle, at the expense of increased cutting resistance while pulling the tool and edge wear. That said, areas of the Bubinga with rowed grain (a type of grain resulting from the tree adding tissue in an alternating direction each year, where one ends up with a material in which the vertical grain portions, especially, are characterized by bands of material alternating in their grain direction) will show the shortcomings of the steeper blade, as the areas with the grain running backward will have a duller look than those areas which were planed along the run of the grain. Better that than tear-out of course.

Ideally one wants to use the lowest cutting angle one can get away with for easy movement of the plane and clean slicing, and yet avoid tear out. A certain amount of tear out can be avoided by being very careful to always plane in the direction of the grain, however with some woods, especially curly or rowed woods, this is simply not possible - you will have to be able to plane against the grain if you are to be successful. To plane against the grain means to find a way to minimize the tendency of the wood fibers to separate down below the surface planed as the blade levers the shaving upward. In the next post I'll take a more specific look at how a chipbreaker, or osae-gane as it is termed, can make possible the use of a lower bedding angle for a plane blade while minimizing the tendency to tear out that might otherwise associate to that blade angle. Thanks for visiting the Carpentry Way.

On to post III