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My furniture designs often slide, fold, or translate in some fashion. This often means that the location of holes and the length between them is carefully calculated. In fact, I find a good calculator to be one of my most used tools.
The problem with specific dimensions and most calculators, though, is that they don’t know carpenter scale (1″,1/2″, 1/4″, 1/8″, 1/16″,1/32″). My latest project, for example, uses a swinging link arm to control how far a drawer will pull out of a small table. It slides in a slot on one end, and pivots from the other. I needed very precise measuring for the slot in the back panel of the drawer, the location of two holes on the link, and the location to mount the link to the table underside.
It was very easy to know what all the dimensions needed to be. The link need to be 8.543″ between hole centers. Normally, I’d convert to 32nds by removing the “8”, and multiplying the “.543” by 32. In this case, 8 and 17.376/32nds isn’t an easy dimension to find on my tape measure. Being off by a 64th is something I wanted to avoid here.
Then I remembered my old engineering scale. You can find them at any college bookstore with a supplies department. I’ve had mine since taking an engineering structures course 20 years ago. Instead of using 8th and 16ths, this scale breaks an inch into 10 or 20 or 30 or 40 or 50 or 60 increments. The “20” scale, for example, would have a mark representing every .05 of an inch. The “50” scale marks an inch into 50 .02″ segments. It’s easy to take my fraction (.543) and divide it by .02 to know how many units on the 50 scale to count off.
Using my engineering scale I was able to very precisely (within .003″) lay out and create my control link. It’s now in place, and actually surprises me at how well it works.
My point? If you’ve ever need to break an inch into something other than 16ths, consider getting an engineering scale.
Dave
Replies
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....or just use a metric tape. I tend to think in inches and feet, but I find when I'm doing something that I want very exact it is way easier to measure in metric. (and there are no fractions to worry about.
*Ditto PD. Sometimes I hate those bleedin' before the wheel inch things. Haven't really used them for more than 20 years, and don't ever plan to go back to them, even though I do currently live in the US. ;-) Hey, David try it. It's a POP (piece of p*ss) compared to all that hard work you've been doing!! Sliante, RJ.
*David,Good idea. For calculations I use the "Construction Master IV" by Calculated Industries. Does everything from calculating hip and valley rafters to calculating board feet, pretty nifty little dude. As for actual measurements, these baby blues can't see much finer than a 64th.:) FWIW.Dano
*Ditto S D; I work to half a millimetre when I'm being pedantic which is as you are aware between the black bits and not hard to see on metric rules or scales (and that for our imperial friends is about 1/50 of an inch)As for subractions, divisions and all that other technical stuff it really is soooooo much easier you'd wonder why somebody.......... :-)Don
*50ths... 64ths.... it's time for a vacation. You can breathe on a piece of wood and it'll move more than a 64th. Do you think anything made of wood can really hold that kind of tolerance more than a fleeting moment? I doubt it.
*Charles,You might be right, however, let's say you are building a table with an octagonal base and the bevel is off by 1/64th, (I'll let some one else figure the degrees, I just got up). The cumulative error would be 1/4 of an inch, which IMHO, is unacceptable for framing a home much less a piece of furniture. Dano
*Metric scales are fine. Especially if the whole project, all your tools, all your bits and blades, etc., are metric.My shop, however, is not. The scale on the table saw is inches. The sequence of drill and router bits I have is in fractions of an inch. All my tape measures are in inches. My mind, unfortunately, seems to be permanantly programmed with inches.Knowing that, I offer the idea of using an engineering scale to those with similar deficiencies. The rest of you can just ignore me.As for precision, I can see the indivudual marks, every 1/60th of an inch on my engineering scale. (OK, I have to remove my glasses). That means I can see how much off I'd be if I miss one. Obviously wood expands and contracts as humidity changes. Plywoods, plastics, metals, and other materials are much more stable. I use all of these, and so do my students. I have seen plenty of projects where being off by a 64th made them less successful than if they'd been more precise. The most common mistake my students make in the furniture design workshops I teach is not being precise. As in the Octagon example above, there are unlimited ways a slightly wrong dimension can be magnified in a design. It's an almost daily occurance in my furniture class.I don't care if you personally don't need 1/50th of an inch precision. The Engineering scale can also be used to find 1/10th, and other more coarse dimensions that won't appear on your standard 1/16th tape measure. Use it when the fractional dimension you need is closer to a mark on it than on your tape measure.Dave
*The octagonal example is a good one Dano and I suppose I had not considered cumulative error (although I've never seen an octagonal anything that did not open some at the miters over time). I think one can pull off faceted construction very well with sheet materials, but are doomed to open joints if using solid wood.However, I stick to my original statement to David's original post about needing an extraordinarily high level of tolerance for some sort of sliding, pivoting, folding, or other kind of construction. It's hard to imagine that construction tolerances as close as 1/64th, if actually needed to make the piece "work" properly, could be held over time. I'd be scared crapless every time it rained.I treat everything in my shop beyond 1/16th as a 'cut to fit' situation so I suppose I'm working wood to high tolerances as well, just not with scales. But then again, my drawer bottoms rattle in the Winter.The best lesson I've ever taught in the furniture class that I used to teach (on a purely voluntary basis for the regular teacher who had a protracted, terminal illness - another story) was this... after a certain level of proficiency was shown by the student I made them design and build a piece completely on the fly and they were not allowed to use measuring devices of any kind whatsoever. They had to rely on their mind's eye for proportion and design, their sight and sense of touch for fit. The end results from the talented students was nothing short of extraordinary. This is certainly not an idea invented by me; I think several other schools use this technique as well.I have a different approach to the art which does not include relying on the 64th mark on some $10 plastic instrument that in and of itself is not capable of being manufactured to, or holding that kind of tolerance. But, there are many, many ways to skin a cat. Just thought I'd throw in a differing philosophy. If I was susceptible to that type of woodworking I'd probably look into the Incra line of measuring tools.Cheers.
*Charles,You do make some valid points, however, I do believe that regardless of whether a measuring device is used or not, precision is what we all strive for, especially in our joinery.FWIW, when I was doing a lot of kitchens, I wouldn't even use a tape measure or rule, except in "rough" measuring for estimating. I always used story sticks, which are, IMHO, more accurate than any tape or rule. The client was always amazed when I would show up with nothing more than a few battens, level, marking knife, and pencil. I would varnish one of them to be used for the final bill and receipt.I still think that Dave's idea is a good one. Bottom line really is that what ever one uses; tape, rule, or scale, that they be consistent. Whenever I need to replace a tape I always take my folding rule with me to "match". Drives the clerks crazy, but what the hey, they end up learning something.Dano
*Many year ago I was stuck in one system of measure too Dano. It was all Fahrenit(sp?) this, and feet and inches that. True, I use metric linear measure pretty much all the time now, but I know fine 30°C is too bleedin' hot for me and that's about 90°F. A litre? no problem. that's a lot of beer in one glass. A pint? which one? US style Queen Anne, or British 1824 Parliament legislated Imperial. What about a bushel? That's some English medieval thing that only Americans use. Our systems of measurements from around the world are all to hell, but somehow I manage to flit from one to the other as need be without too many problems. I can see David's methodology and reasoning, but to me it seems like a lot of hard work for no darned good reason when there's a system of measure already to hand. David, I count your lame excuse of inflexibility regarding reading or being able to convert your table saw tape, the tape measure you carry in your pocket, the wee 150 mm (6") rule that you carry in the top pocket of your pinny, and all those 'odd' numbered drills as being insurmountable difficulties that you can't handle as a bit of a weedy excuse. 1/4" is 6.4 mm, and 3/4" is 19.05mm. 25.4 mm is one inch, and frankly, I couldn't care less that any of them really convert to anything else, yet you show enormous abilities as a mental contortionist to get the best you can out of a poxy inch? An inch is an inch, and a millimetre is a millimetre. I talk to American clients that yabber on in feet and inches, and fractions, but the truth is I've only ever met one American that can really, really do the arithmetic easily in fractions. I certainly can't.Now, if someone were to take the foot linear measure, and divide that into ten times 1" units, which were then divided by units of 10 along the lines that David is espousing, I think we'd really be in business, because the foot is a beautifully handy scale. It's just those darned inches and fractions that get me!!! Sliante, RJ.
*Yep, having to deal only with math one can do with fingers is a temptation. My mind, obviously, could use less to do. I like meters, anyway. Maybe I should just scrap all the tapes and scales and other non-metric crud I have and "Go Metric"!Wouldn't matter.What matters, I've found, is that for any one project you pick one measuring system and stick with it. The nice thing about that engineering scale I found is that it's inch marks are that same distance apart as the inch marks on the tape measure I use. Since I started with inches, it was no compromise to continue with them. That engineering scale simply allows me to "metric-ize" my inches. In other words, it lets me divide them by ten. That just happens to be consistant with what my calculator likes to do with them.I like to think of it as the best of both worlds. Had I been playing in meters, there would sooner or later be a time when I needed 1/8th or 1/16th of some amount of them. Then I'd be scambling for a scale that took those meters and broke them into 16ths and 32nds and so on. You can't win.NEW SCALE!!!! I find I have inherited my grandfather's mason's tape. Yep, it's got inches on it. More importantly it is divided into BRICKS! From now on I design in brick units!Dave ;-)
*Lee Valley now sells a 10-foot measuring tape marked in decimal inches. Yep, you can measure dimensions like 87.53". $4, I think.
*Yeah, bet you can't wait till the US catches up with the rest of the world and goes metric. View Image
*David: If you were a patternmaker,your choice of scales would just be beginning. You would deal with shrink scales.Since metal shrinks in volume from the molten state to the solid,The patterns for castings are made oversize to allow for the shrinkage. If the cast metal is iron,you pick up a 1/8"shrink rule.This in a 24" length is by standard measure 24-1/4" long.different metals require different shrink values. If a master production pattern is to be made,in aluminum,for an item to be cast in steel,a second shrinkage is involved.A mahagony master pattern will include one shrinkage for the aluminum master plus the added shrinkage for the final cast metal. You can see why there are so many bald headed patternmakers. The advent of the hand held calculator ,for me at least, has changed all that.I add up all the shrink values involved for the job at hand.an example,3/16" for the master plus 1/8"for the final casting,giving a total allowance of 5/16"per foot required.I multiply every diminsion on the drawing by the shrink factor of 1.312 and note this in red on the drawing. Now forget all the different rules and use the same measuring tools that normal woodworkers use. I.E.steel flexible rules.dial calipers and micrometers.In the pattern shop, the only use for the steel tape IMHO is in cutting the rough lumber.¬¬¬¬¬¬¬¬PAT¬¬¬¬¬¬¬¬¬
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