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Accurate and repeatable measurements - your methods reqested

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Forum topic by RalphB posted 11-07-2009 07:00 PM 1988 views 0 times favorited 23 replies Add to Favorites Watch
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RalphB

25 posts in 2018 days


11-07-2009 07:00 PM

Topic tags/keywords: measurement question tip assembly tablesaw tape measure

OK, I admit it – I’m early in my woodworking skills development. But now that I have acquired a great tablesaw and superb blades for it, plus high quality routers and bits – I have noticed that my “parts” often come together with a variance from plan of 1/64” to 1/32”. This often leads to small gaps and misalignments. Don’t get me wrong, if I can cut the parts against the saw’s fence or use a jig or sled – they all come out the same size. But if I cut the two sides of a cabinet and then cut separately the top and bottom to fit into the rabbets – they can easily end up a small amount off in length. I realize that some of this can come down to doing things in the correct sequence – e.g. mill all the parts that share a dimension at the same time. That’s not always possible, though. But that’s not what I fear is my biggest problem: measurement. By that I mean when I go to measure a dimension I make my mark and work from it. But, how fine should the line/mark be? Does one always “take the line”, or do you “keep” the line? If, due to physical constraints you have to cut from the “part” side of the line or the “scrap” side of the line, how do you ensure accuracy/consistency? Do you always use the same measurement tool, rather than switching between multiple ones?

Perhaps I’m just being AR, but when you put together multiple parts these little measurement variances add up! Thanks in advance if you have some methods to share!


23 replies so far

View papadan's profile

papadan

1153 posts in 2021 days


#1 posted 11-07-2009 07:12 PM

Most important thing is to always use the same tape, ruler, or whatever to measure with on the same project. Lots of variances between tapes. Always cut the mark the same way, whether you cut centerline, left or right, always the same. Don’t forget the thickness of the cutting blade. For tablesaws, I keep my fence fine tuned for accurate cuts. I fully trust the gauge on my saw.

-- Carpenter assembles with hands, Designer builds with brains, Artist creates with heart!

View UnionLabel's profile

UnionLabel

660 posts in 1853 days


#2 posted 11-07-2009 07:21 PM

I agree with “papadan” A good layout ruler is a must. Agood tape measure is also a good idea. I prefer a flat back tape in the shop. Doing bookcases or tall cabinets I like a story pole and that way I have all my pertinent measurements at my finger tips. For critical measurements, calipers are great also, but always make a cut on scrap first. There have been times when I have almost made a project out of scrap as I cut pieces for certain cabinets.

-- Methods are many,Principles are few.Methods change often,Principles never do.

View Dez's profile

Dez

1113 posts in 2730 days


#3 posted 11-07-2009 07:47 PM

What you mark with can easily make a measurable difference as well. In the cabinet shop the boss always insists on a well sharpened regular pencil not a “carpenters club” as he calls it. I personally prefer a 5mm mechanical pencil for rough measurements and a marking knife for marking cut lines.

-- Folly ever comes cloaked in opportunity!

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knotscott

5454 posts in 2029 days


#4 posted 11-07-2009 07:55 PM

I try to measure once, then use a stop block for repeatability. If possible, it helps to get consistent length if you crosscut first then a rip multiple boards to width. Be sure your stock is flat and straight to start with, be sure your inserts aren’t flexing under pressure, and that your fence and miter gauge aren’t moving on you. You may find that the end dimensions don’t need to be within 1/32” as long as everything’s consistent.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Karson's profile

Karson

34876 posts in 3054 days


#5 posted 11-07-2009 08:06 PM

A fence that alows you to set and cut accuretly is a requirement.

I also cut my parts oversize and let them age for a while and I’m then able to trim to the correct size and yopefully use the same equipment setup.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware karson_morrison@bigfoot.com †

View GaryK's profile

GaryK

10262 posts in 2641 days


#6 posted 11-07-2009 08:08 PM

Another thing to remember is that wood doesn’t always stay the same size after you cut it. It will expand and contract according to the humidity. You can get two different measurements on two different days.

I always use a pair of 6” dial calipers for small parts.

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View TomHintz's profile

TomHintz

207 posts in 2051 days


#7 posted 11-07-2009 08:15 PM

I have a story on this very subject at the link below. This is a very common question at my site and sort of a right of passage for woodworkers. Practice is a big part of it but so is establishing good techniques ands ticking with them.

Cutlines Story

-- Tom Hintz, www.newwoodworker.com

View a1Jim's profile

a1Jim

112086 posts in 2230 days


#8 posted 11-07-2009 08:29 PM

If you can avoid measuring at all you ahead of the game. Many times you dry fit pieces together and your able to put pencils marks were your cut ,dados or whatever. If you can mark out were you need to do certain
operations without measuring at all you can avoid mismeasuring or transposing numbers or a very commend mistake were you measure off the 1” mark(also referred to as burning an inch) and forget that’s what you’ve done when you mark you work

-- http://artisticwoodstudio.com Custom furniture

View rtb's profile

rtb

1099 posts in 2366 days


#9 posted 11-07-2009 09:02 PM

if you are cutting multiable like pieces you only measure the first and then use it to mark up the second, third etc.
A lot will come with practice but, as we all have to learn the flaws are usually in the measuring and/ or set up. Most of us have had to learn by trial and discover. all of the things listed above are true. when you discover something work on it, practice. Don’t practice on good wood, the best kind is free, or scrap etc. Do invest in good measuring tools and marking tools. If you will start with a #2 pencil with a very sharp point, you begin on the right road. Throw away mechanical pencils are better.A small pen knife or a razor knife will do for a marking knife for the time being. Stop thinking about 1/8 inches and think about 16th or 32 nds. AN Incra rule will measure to the nearest 64th. If you have trouble with fraction’s and a lot of people do, go metric or use inch’s by the hundredths (metric measures are readily available and are often included on the same tools that we use for English measurements. Most of all watch this web site You can learn more here that if you subscribe to every woodworking magazine in the country AND you can always ask.

-- RTB. stray animals are just looking for love

View Thuan's profile

Thuan

203 posts in 2471 days


#10 posted 11-07-2009 09:32 PM

I don’t like to measure because all the little fractions confuses me. I just butt, mark, cut. Lots of time, I use the knife to mark since it cuts the fiber of the wood on a cross cut. Then I cut to the right, so I’m left with a cleaner cut.

-- Thuan

View stefang's profile

stefang

13024 posts in 1987 days


#11 posted 11-09-2009 01:01 AM

When I first moved to Norway I had to get used to the metric system. I can well understand the difficulties in converting to a new system and I’m not advocating anyone to do it, but in my experience the metric system is a lot better and easier to work with. So basically I just feel sorry for you guys that are stuck with the imperial system.

-- Mike, an American living in Norway.

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stefang

13024 posts in 1987 days


#12 posted 11-09-2009 12:10 PM

I guess everyone has their own way of insuring accuracy and consistency. I work a lot like Barry. I still make some mistakes, but for the most part everything turns out the way it should. You just need a way of measuring that you feel comfortable with. Our brains are all wired a little differently, that’s why there are so many methods and they all work when applied consistently.

-- Mike, an American living in Norway.

View acanthuscarver's profile

acanthuscarver

261 posts in 2365 days


#13 posted 11-09-2009 01:38 PM

Ralph,

One of the techniques I teach in my Fundamentals classes is to use layout sticks or story boards. Do all your measuring, and double checking, on the layout. Use the layout to transfer the marks directly to the pieces that need to be cut to size. If you’re cutting the top and bottom of a case, square one end then hold the layout stick in place and transfer the mark. Set a stop block and cut both pieces at the same time. If you can’t set a stop block, then use the layout stick to transfer the mark to both pieces thus giving you a baseline measurement (you’re not compounding a problem by cutting one piece and then trying to use it as a pattern…I’ve seen pencil lines make pieces magically grow). If none of this is clear, let me know and I’ll try to do a short video or blog post about it.

Good luck.

-- Chuck Bender, Senior Editor Popular Woodworking Magazine, period furniture maker, woodworking instructor

View KayBee's profile

KayBee

1007 posts in 1899 days


#14 posted 11-09-2009 05:28 PM

Lots of great advice given. Also, try to use the same edge to referance the whole time. I mean use the same edge to to referance or go against the rip fence, miter gauge or edge guide. Pieces don’t stay perfectly square and they don’t do it the same rate in the same board. It’s off by 1/64 here but 1/16 there type of thing. If you use the same edge for referance the whole time, it’s a least consistent. That way all those little 1/64 and 89.8 degrees don’t start multiplying.

-- Karen - a little bit of stupid goes a long way

View PurpLev's profile

PurpLev

8476 posts in 2302 days


#15 posted 11-09-2009 05:58 PM

I think one thing that escapes people’s mind when working with plans, is the purpose of the plan – and that is, to help the woodworker visualize the parts in question. NOW. once you actually start cutting – I think it’s rare that things actually follow the plan within 1/64” – some cuts gets shorter, some parts have to be recut, and the dimensions eventually will change from the original plan.

point is- once you cut your 1st part. everything else needs to follow and match that part, so use the plans for general dimensions, but do the actual cut based on the already parts you have to work with. measure against those to get your actual cut line.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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