Using Laser Level to Flatten Workbench
Was wondering if anyone out there has has tried using one of those rotary laser levels to flatten a workbench. I have used winding sticks, but have a difficult time seeing minor wind between the sticks. I then tried putting 2 levels on each end of the workbench in place of winding sticks. This somewhat helped as I could see the difference in the level settings. Then I got to thinking about the following: Set a rotary laser level in the middle of the bench. On either side of the bench, set MDF boards about 6″ wide on edge. On one end of one of the boards, make a mark about 2′ up form the bottom. Set the laser level to that hight. Then mark where the laser hits on the other side of that board and the two ends of the other board. It seems to me that this should show any wind in the bench. Any thoughts would be appreciated.
rc
Replies
flat work surfaces
It took me a minute or two to be sure you weren't yanking our chain here...
In my experience, all you need to do is lean over to table height and eyeball the top without any contraptions or gizmos. If it looks OK then it's OK for all woodworking intents and purposes.
From time to time we all need a surface that is perfectly flat, but it's not the workbench. A cast iron sawtable or other such machined top will always be a better reference surface for perfect flatness than any wooden bench you or I can make.
If you need an assembly station that is perfectly flat then make one up in addition to your workbench, with a torsion-box top using MDF.
David.. No hate here.. BUT.. If you need an assembly station that is perfectly flat then make one up in addition to your workbench, with a torsion-box top using MDF.
Not that I want to disagree with you... However a torsion-box top is only as accurate as the top and bottom and the sticks placed inbetween the layers! And how well all was clamped. I for one do not think a table top for woodworking needs to be as flat as a LASER table!
Close but maybe not perfec for woodworkingt? Just a thought I had at the moment.
Out Of Date
My information is probably out of date, but Back In The Day, when I was in construction, the bead on lasers was about a quarter inch tall, and so accuracy was never better than about 1/8th of an inch, because "marking the top of the bead" wasn't that easy to do. Even using the same guy's eye, if you went back and checked things with a whisky stick, you'd find out there was error.
Add that to the tolerance, (mine are something like 3/8 over 100 feet), and I never trusted them for finish work; what I used them for was things the eye would never pick up. Drop ceilings, floor tile, or their most common use, form work.
So, if 1/8 or a 1/4 was close enough, (formwork) and there was room, I used a laser. If not, I used other, more accurate methods.
Good luck!
P.S. We never set a laser on the work. They're as sensitive as a Builder's Level, or a transit, so we always set them on something as secure and as far from the work as space would allow, and one of the ways to improve "accuracy" (or minimize the degradation of it, at least,) was to restrict the angle that you were checking level through. Checking all 360 degrees would be certain to add to error.
laser accuracy
I agree with the others that the accuracy of the construction-grade lasers isn't as good as one might hope - the beam is just too fat. A lab-grade laser might be a different matter, though.
Then, there's the possibility of using a high-powered lab laser to burn off the offending irregularities. ;-)
Ultimately, I agree that the workbench shouldn't be considered a precision surface. Kinda-flat is good enouth.
rc:
Perhaps you could examine your winding sticks to find tweak(s) so they work for you. Sometimes it's hard to see mine against the background, so I brace a piece of whiteboard or plywood behind. I've also had better luck after adding a narrow strip of maple to the top edges of my mahogany sticks. Most often, I'll reach for my 36" winding sticks instead of the shorter ones, as they better magnify any wind.
Winding sticks are handy to use for more than just annual leveling of the workbench, so finding a tweak to make them more functional would be my suggestion.
Thanks guy
I didn't realize those laser levels were that far off. I have a torsion box table for assembly, but nonetheless I was trying to get my work table as accurate as possible,
A Crazy Idea...
Reading this post got me to thinking, (a dangerous thing for an engineer).
Are those granite countertops dead flat? I know some guys use granite flats for sharpening.
Suppose you sandwich a granite countertop between two pieces of MDF, say 1/4" on the bottom and 3/4" on the top.
Would that make a flat workbench top? OK, I'm ready; shoot me out of the saddle...
Sighting winding sticks through a pinhole
A tip I got from Christopher Schwarz is to drill a small hole in a thin piece of wood (or a business card for that matter) and sight the winding sticks through the hole. It sharpens the image and makes it easier to see the alignment of the sticks. This is the same technology used in peep sights on rifles ( put one on my CVA Frontier Carbine and now shoot much straighter). For those of us over 50 this tip is a God send.
gdblake
Thanks to all of you for your suggestions
I do understand that my workbench doesn't need to be dead-flat, but as I will be using it for glue-ups (resting cauls on bottom), planing, etc., I would like to avoid any real wind in it. The ideas re tweaking the winding sticks are terrific and I will definitely give them a try. I am also going to try another experiment. I bought a couple of strong laser pens with very fine lasers (the dots look to be a bit under 1/16"). I am going to make two winding sticks, drill a hole in each end of one of the sticks, glue the pens into the holes as level as possible, set the two sticks on a flat level surface about 6" apart, turn on the lasers and mark where the dots land on the other winding stick. I think this should give me a pretty good way of checking how much wind is present in my work benck (and other projects). I will let you know how it goes.
rc
Take top to cabinet maker with CNC machine
For those that love hand planing, cover your eyes.
CNC macines have what is called a "spoilboard" on top of the vacuum table that is part of the CNC machine base. The "spoilboard" is typically MDF, which is less expensive that the vacuum table, so when a tool cuts a bit too deep the "spoilboard" gets "spoiled" and not the vacuum table.
Before the "spoilboad" can be used it is machined parallel to the vacuum table. There is a special bit to do this. It does not take long and the amount take off is measured in thousands.
If a workbench top needs flattening, compared to using a plane, seems like having a CNC machine do this task would be a big saving in time, the amount taken off would be less, and it would be much flatter. Probably the most time consuming and tedious part would be the set up. Probably cost under $100.
Then you can use all the time you saved to make something with your hand tools that will be much more fun that grunting through flattening the workbench top.
what about a water level?
for all the fuss with lasers, etc, wouldn't it be easier to use about 20' of hose to make two water levels? Possibly faster and more accurate..
Eric
Water level
Old school works very well, water levels were used to set grades for the egyptian pyramids, and they're still standing. ;-)
The trick is reading the miniscus of a water level properly ;-)
But that's only good if you want the table top parallel to the floor.
The floor is level??? Whats with that?
parallel to the floor?
Who said anything about the floor being flat......
Water levels ignore your floor, preferring the approximate centre of the earth as the reference point for the gravitational forces being utilized....
The trubble with the new-fangled technology is that it has multitudes of caveats and often times is providing a 500$ solution to a 25 cent problem, oftentimes requiring only 15 minutes of practice to transform a neophyte into a competent practicioner...
sighting sticks, water level, or even a good quality bubble-stick would solve this problem very quickly.
Work SMART!...if it don't make sense, give yer head a shake, and rethink your solution
Eric
Hi,I,m an old guy with experience in both machine shop practice as well as cabinetmaking.Anyway flatness is a relative concept looked at in many different ways.First,a granite surface plate is 1 example of flattness.These are available in many different sizes.and vary in grade depending on your level of flatness for a given length and width.Remember in this case flatness is expressed in .0001 of an inch per foot ,much like a precision stright edge.How stright is stright I ask?Bridge City Tools makes a nice line of precision stright edges,ideal for measuring just how far our your bench top is out of tolerance.Just like the stright edge,the surface plate is machined to a fine tolerance. Some aerospace specs. require such tight tolerances that ambient temperature must be observed since as we all know when things are warm or hot usually any given substance will be Larger than a similar sample of the same material.What this means for the practical woodworker is this;I have a cute little pink granite surface plate which is primarly used for various tooling measurement and inspection.I like to tape a fine abrasive to the surface and surface my plane soles.and flatten my chisels ect. this works with very consistent results. You can emulate a large wooden surface plate ie,your work bench pretty easily.My work top is butcher block which is both quite stable dimensionally and physically.All you need to do is make 4 wooden stright edges,and frame the perimeter of your top.Next make a sledd from 2 more stright edges and a piece of 3/4 ply wood.Mount your 2-3 hp router to this sledd and by moving back and forth across your top you in effect have made a gantry sort of mill capable of milling a very accurate top.Use a large diameter cutter,and take care in all your assembly steps and you should be able to arrive at a very suitable work top.Put a good durable finnish on it and you have it.Remember,if you can anchor your table legs and use a good level,you will achieve not only flat but level as well,if this is of importance.Good luck to all Fred the ole guy
You can use strings. Monfilament fishing line that is about 20# test.
The fishing line is light so it sags less and with the 20# you can stretch it real tight. The tighter the better.
You can check for wind by attching the lines to the corners with an X in the middle.
Attach the lines to the table and then mill four blocks the same height.
The blocks go under the line and stand it off the same distance on all four corners.
Where the lines cross in the middle, they should just touch.
For bumps and valleys you can take a fifth block and check under the line.
Stretched lines don't lie. They might sag a bit, but they don't lie, ever.
Oh, and they're cheap.
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