Chalk line precision

[canopy]

I do layouts using chalk lines and bubble levels as timbers aren't accurately cut and have a lot of wane. I noticed during layout of long timbers something was a little off and it took quite some time to trouble shoot the problem. It turned out to be the chalk line. When chalk lining 20' timbers the line moved off center 1/16" even when keeping the line as tight as the strength of the string would permit and snapping dead vertical. The error can be seen below.



Then I found an old timer with the simple answer. When chalk lining long runs secure both ends of the string, then press the midpoint of the chalk line to the timber with your finger. Then snap the left and right side independently while holding it down in the middle. Using this approach the accuracy in my case became dead on. Another old timer tip: lightly snap the chalk line in the air first. This will knock excess chalk off and result in a thinner line. Using these techniques the line is so thin and accurate I cannot see the chalk line under the string.

[jueston]

when I was stick framing, and we needed to snap a long line we always held it in the middle and did it in 2 sections too. I always found the line to be more accurate and of a more consistent thickness then 1 long snap.

[Jim_Rogers]

We also replace the standard chalk line with a braided Dacron fishing line to get a finer line then the fuzzy wide fat line that standard chalk lines come with.

Jim Rogers

[onegunsmith]

Black chalk also produces a much finer line but is permanent.

[LeeB]

If you need a permanent lay out line, a light coat of clear spray lacquer will keep it from disappearing on you.

[submarinesailor]

We also replace the standard chalk line with a braided Dacron fishing line to get a finer line then the fuzzy wide fat line that standard chalk lines come with.

Jim Rogers

I agree with Jim.  I have replaced all my caulk lines (blue, orange and black) with 50 lb test Spiderwire braided line.  I really like being able to put a good HARD pull on it before I snap it.

Bruce

[grweldon]

Wow.  Who would have known?  I've wondered in the past why I've come out with inconsistent cuts after using a chalk line.  Makes a bunch of sense... guess I don't have much!  ;)

[beenthere]

A chalk line will always have some weight and will always dip "some amount" along its length.
Seems that amount of dip will either be acceptable, or not, over the length of the string.
If not acceptable, correcting it by holding it midway is a good way to at least cut the dip in half or a bit more.

[giant splinter]

I second everything mentioned (with the exception of the last words in grweldon's reply .... "  Makes a bunch of sense... guess I don't have much! ", He figures a lot of things out on his own ..... thats what engineers do.
One thing that should be considered in addition to all other tricks mentioned ( you need to be very careful when you lift your string to keep it perpendicular to the work plane of the material your marking, use a lot of lift off pressure on a very tight line with minimum distance from the work @ 90°). experiment to see what happens it you are not lifting off at a right angle to your work piece.
The 20# or 30# test braided dacron is very strong and will cut into your fingers if you are trying to see if you can break it so be carefull.
In setting up your new chalk reel, try pinching the felt gasket at the opening the line rests in, fill the chalk box to the top and when you are paying out line you will want to hold the chalk box at an angle to prevent the chalk from spilling out around the felt seal, once the line is payed out give it i little flick before you get it close to the work piece to make sure there is not any more than you need on the braided line to make a perfect layout line. Braided line will not leave a fat and fuzzy mark and the layout line you will have is going to be a very narrow in width and have a very even and well defined sharp edge.  ;D. GS

Boatbuilders have a method of holding a chalkline so that it will create a rough type of radius on a hull or deck plank that leaves a little extra wood to allow a closer fit when fairing in a plank to fit up tight. Try it some time and be sure to hold the line a little off center.... about 5° off or more if needed to get the effect you want, another way to layout a curve or arch is by stationing and it will allow the you to draw a radial line on any radius even if you are in a small room.

[bmike]

We also replace the standard chalk line with a braided Dacron fishing line to get a finer line then the fuzzy wide fat line that standard chalk lines come with.

Jim Rogers

I had issues years ago moving my lines to fishing line (spiderwire I think, have to check the package out in my rolling chest). Seems the line would get tangled and lock up inside the reel.

Is this an issue?

I do like my modern ink line.

[Glen Sutton]

At power plants we use taut piano wire for machinery alignment. Its incredibly accurate considering the technology was invented by the pyramid builders. The math goes like this: h=wL^2/8P.   ( ie L-squared). h is the deflection from ideal straight. W=weight per foot of the line. L is length of the line.  P is the pull on the line.
For machinery installations, the P is exerted by a 30 weight, with the line led over a little sheave, and the weight hanging by gravity. Fancy opticals and expensive lasers have been around for years, but the roman/Egyptian technique persists. Somehow the millwrights prefer it. Go figure !
I did some math for fun, just to see what the error introduced by gravity could do to a chalk line.
For a 20 ft timber, using 40 mil cotton string, and a P of 20lb, the error is 0.015 inches at the mid point.
If you substitute Dacron 20# line, keep the same P, you'd get 0.005 inches (with a superior line definition)
If you half the length of timber to 10 feet, the Dacron sag becomes 1.5 mil, since the formula has length squared.
How to measure 20 lb in a Dacron line on a saw mill ? Pull until it breaks. Fix it. Don't pull quite so hard next time.

[Brian_Weekley]

At power plants we use taut piano wire for machinery alignment. Its incredibly accurate considering the technology was invented by the pyramid builders.

I can picture it now...the piano bars in the pyramids with Pharaohs drinking cocktails as they listen to bad lounge singers...   :D

[Dave Shepard]

If you only snap in a vertical orientation,  then it shouldn't make any difference what line or tension you are using.

[LeeB]

Unless the winds blowing hard.

[Dave Shepard]

Then you are pretty much done for the day.  :D