I am working on the apron for a dining room table that I am building. Instead of a straight across board, my wife would prefer a gentle arc. Does anyone know of a tool or technique that I can use to draw the arc?
Thanks
Cheers,
Velo
Discussion Forum
Get It All!
UNLIMITED Membership is like taking a master class in woodworking for less than $10 a month.
Start Your Free TrialCategories
Discussion Forum
Digital Plans Library
Member exclusive! – Plans for everyone – from beginners to experts – right at your fingertips.
Highlights
-
Shape Your Skills
when you sign up for our emails
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. -
Shop Talk Live Podcast -
Our favorite articles and videos -
E-Learning Courses from Fine Woodworking
-
-
Replies
I imagine you want an ellipse.Do a google search and you will find several different ways to accomplish this. I had a number of cased openings that required an ellipse at the head. I made a template from masonite and used it for both the drywall,framing and the trim. It is hard to explain without drawing it, but several websites explain it easily.
mike
Take a piece of wood about 1/2" x 1" a little bit longer than your apron, drill 2 holes one at each end and run a string to it.
Make a bow and use the stick to draw your line.
An other way is to put the same stick between two dogs on your bench, as you tighten the tail vise the arc becomes more pronounced.
C.
citrouille,
"An other way is to put the same stick between two dogs on your bench, as you tighten the tail vise the arc becomes more pronounced."
My dog will not sit still on the bench. She wants to chase the stick, even when I have her tail in the vise,as you suggest. But you are right, as I tighten the vise, her (b)arc is much more pronounced.
Ray
A tip I learned on this forum some time ago is to use a length of PVC pipe instead of wood for tracing an arc. Wood sometimes varies in flexibility, yielding an arc that is not smooth. PVC does not have this problem.Mike HennessyPittsburgh, PA
As a matter of fact I use a fiber glass sail batten.C.
" a matter of fact I use a fiber glass sail batten."
Hmm. That just means you are working instead of sailing. I see a problem.
Mike HennessyPittsburgh, PA
Hey velomark,
Mark out the three points that determine the beginning, end and apex of your arc. Then, take two thin pieces of stock and fasten them together (lapped is fine) so that they just touch the three points. Put a small nail at each endpoint, and put your pencil in the apex. Now, slide the works over the nails, from end to end, and you have drawn your arc.
Tom
Hello Tom. This is also the technique I use. To take a step farther, thing to do is to set the connected strips up with a wing nut. Permanent jig. You loosen the nut, set the angle joint to the highest desired point on the ellipse, tighten 'er up and away you go. Great tip, Tom.
Hey Blewcrowe," To take a step farther, thing to do is to set the connected strips up with a wing nut."Now why didn't I think of that? Sometimes the simplest solutions elude me.Tom
I have one I keep on hand. I made mine 3/4" wide. I kept the thickness of the wood at 1/4" to cut down on the weight resistance when sliding through the motion. The two strips I made each about 48" each. That enables me to make ellipses up to around 40" if they're not too tall, which is as big as any one I want to make.
There's nothing wrong with your method, and it actually has its advantage. With a one-shot fixed deal, you can drill a hole to hold your pencil in place (instead of trying to steady it in the crotch of the angle.
Velomark,
All I remember about that subject is from Sunday school. I believe that Arks are measured in cubits. :-)
Mel
Measure your output in smiles per board foot.
Excellent!! Thanks everyone!Cheers,
Velo
i want you to bill me an arc 40 cubits by 40 cubits by 20 cubits
right
whats a cubit
Mel,
So their volumetric capacity would be measured in cubic cubits?
"Noah, I want you to build an ark."
"Right..."
Ray
what a cubit bill cosby right
"I want you to go out into the world and collect all the animals, by two, male and female, and put them into the ark.""Right! You know, I went up to my best friend Larry. I said, "Lord, Larry- Larry, Lord". You walked off laughing, I had 'em all up there laughing, you know I'm the only guy in the neighborhood with an ark???"
"I cut this piece four times and it's still too short."
and then he got pissed of because he was the only guy in the neighborhood with an arc till the first sound of thunder then it was me and you lord right!!!!!!!!!!!!!
that man is the only man who can do 2 hr show not use 1 curse word and have you rolling in the aisles
great man cosby
Look for his album called 'To Russell, whom I slept with'. The has Monster Chicken Heart, Buck-Buck, Fat Albert, The Belt and a lot of other great bits.
"I cut this piece four times and it's still too short."
As luck would have it, today I had to draw an arc. I use the flexible batten technique. I draw the arc onto 1/4" mdf, cut and sand to the line, then use that as a router template. It's a positive method and gives me a template for repeat use if needed. Here are photos of today's set-up. I must point out that the arc I was doing today is unbalanced. The batten is a length of 1/8" x 1/2" cold rolled steel.
I've used that method but I'm not pleased with the outcome. The degree of arc lessens as one approaches the ends of the jig.
That is true and that is the whole point. I use this method when I wish to draw a spiral. For a circle (or part of) I would use a compass.
chicken heart is where he spread jello all over the floor and his father went ballistic
his brother russel was god dammit and he was jesus christ
That is some classic stuff.
"I cut this piece four times and it's still too short."
Two dogs go walking on a bench, one gets it's tail in a vice and that make him arc???
Coach,
You asked: "Two dogs go walking on a bench, one gets it's tail in a vice and that make him arc???"Who said the dog is a "him"?
The dog's name is Joan.
Joan of Arc.Life's a beach.
MelMeasure your output in smiles per board foot.
Nicely done...I should have done better, my shepard is a female and she has done sometime on the bench.
Coach
will work for tools
Edited 4/28/2007 9:51 am ET by CoachB
Bearing in mind we in the UK have had the wettest june on record, and many homes are flooded, are you sure folk are spelling Ark correctly? Or does someone have inside information.
Edited 7/6/2007 1:16 pm ET by mufti
Mufti,
Of course I know how to spell "ark". I was married to Joan of Ark in a previous life.
MelMeasure your output in smiles per board foot.
If you have room, you can mark a circular arc of large radius. I once cut a pair of aprons for a coffee table by attaching my router to a homemade trammel with a 17' radius. One cut, ready to finish.
Pete
I don't belive the measurements given will be big enough for two of EVERYTHING.
huh,maybe we're thinking of the same kind of arcs. I'll have to get back with all of you , right after I go call my buddy Noah and get his take on the situation.
Sincerely, Jim at Clark Customs
If you have room, you can mark a circular arc of large radius. I once cut a pair of aprons for a coffee table by attaching my router to a homemade trammel with a 17' radius. One cut, ready to finish.
There's an easier way to do large-radius arcs. I recently had to do one where the radius was over 38 ft.; the simple trammel method wasn't gonna cut it!
I ran across something in an old FWW article that explained another way. I looked into it, and it cleverly takes advantage of some geometric properties of a circle. As an illustration, see the following figure: View Image
Points A & B are points on a circle that has a center C. The arc we wish to draw runs between A & B and through point q1. The central angle of the arc is theta-1, and is fixed once A, B and the radius of the circle is chosen. q1 is an arbitrary point on the arc between A and B (it doesn't matter which point we pick), and q2 is an arbitrary point on the arc going the other direction between A & B. It can be proven that theta-2 = (theta-1)/2. It can also be proven that theta-3 = 180 degrees - theta-2. Therefore, theta-3 = 180-(theta-1)/2. This is true no matter where on the arc q1 is located. Since theta-1 is a fixed value, theta-3 is also fixed, no matter where q1 happens to be located. This property can be used to build a jig for drawing the arc (which can be alot smaller than 38 feet!):
View Image Just put some pins at A & B, and put the pencil at the inside peak of the fixture. Slide the fixture along the pins, and it draws the arc. What's more, one could mount a router on the fixture, and cut the template directly. If you turn the fixture over halfway through, only one of the legs needs to be long enough to reach from A to B. The other leg need only be a little longer than half that distance.
To construct a jig, you don't need any of the math; just attach two pieces of wood so that, when they are touching points A & B, their intersection is at the desired height above the center of the line connecting A & B.
For the full math: If the distance from A & B is c, and the height of the apex of the arc above this line is h, then theta-1 = 2 arcsin( 4 c x h / (c^2 + 4h^2))
Edited 4/24/2007 12:51 pm by BarryO
That is as concise and complete an explanation as I've ever seen. Thank you.Frosty
Barry, I have used that method a few times, and while it might be easier than setting up a 40' trammel, it still has its shortcomings. Lets say you need a long arc along the edge of a 10' long table. Using the normal set-up means that you need two legs about 10.5' long, or a fixture 21' long, and a clear space about 32' long to work in while you shift it along. I hope you have a helper to support the overhanging end that will be sagging as you near the ends of your work.And if you want to mount a router in it, then it needs to have wide wings to resist flexing on that plane.I am not arguing whether it works. I just have not found it to be all that great a trick when things start getting large, which is when I have needed it.I have gotten out on my parking lot and hammer drilled a hole for a lag bolt to swing a 35' arc with wood strips screwed together to make up the length, with a router in the end. Even that had problems as the middle would drag, and hang up, or flex a little, which changes a lot. I think next time I need an arc with a long radius to a specific length, I may try using a fine wire attached to the router and pin. Until then, I sure like the results that I got from compressing my aluminum extrusion in the pipe clamp as I described in my first post in this thread. There is no reason that something like a strip of mdf, or straight grain wood would not work.
It's true you need a space twice as wide as the arc in which to work. To me this method makes most sense for a gentle arc, where the radius is much larger than the arc length.
I think in alot of cases, it makes sense to keep the fixture fixed, and the workpiece movable, since the fixture is twice the size. For example, with a router, you can use a router table, and have the "wings" extend off to the sides, supported so that they are level. The wings have slots and you mount two pins in the workpiece. I'll be trying this method in the near future, and will post results when I do.
I haven't had much luck with the "draw a line with a bendy stick" method, and try to avoid it.
Edited 4/25/2007 4:22 pm by BarryO
I'm resurrecting this thread because I just actually used the method I described above, and it worked out pretty well. Perfect smooth template curve with no tedious filing and sanding!Rather than drawing the arc with a pencil, I wanted to cut the curve directly with the router. I needed a gentle arc on a piece of MDF between two points 43" apart. It appears this would involve attaching two >43" long boards to the router, and moving the whole contraption against two pins mounted 43" apart on the workpiece. As I mentioned above, rather than moving the router and the outriggers on a stationary workpice, why not keep the router and the two long outriggers stationary, and make the workpiece movable? That would be alot easier to manage. That's what I did: I took two >43" pieces of MDF and cut 1/8" grooves in them. I mounted them at an angle to each other on a router table. On the workpiece (which is actually a piece of 1/2" MDF intended to be a template), I put two short 1/8" diameter dowels in holes 43" apart. The dowels rode in the grooves as I moved the workpiece, and the router cut the arc. I also did another template, with the pins 13" apart and the two boards at a steeper angle, for another part of the project. Pictures follow. Here are the two "outrigger" boards mounted on the router table, shown with the MDF workpiece:
View Image The angle is easier to see in the setup for doing the smaller template: View Image Here's a close-up of the router table: View Image This shows the dowel pin on the workpiece: View Image Here the larger workpiece is being routed: View Image I made two passes at different bit heights, so you can see the first pass of the arc here: View Image The smaller workpiece: View Image Here is the smaller template workpiece, with the two passes done, and the groove for the arc most of the way through: View Image Now you'll notice I goofed a little: I put the router bit on the wrong side of the grooves on the outrigger boards. The consequence was, if I set the router bit high enough to cut completely through, I would cut off the guide pins (i.e., the guide pins are on the falloff piece). No big deal: I just stopped here, rough cut off the fall-off on the bandsaw, and then used a flush-trim bit to make the thin bandsaw-cut portion nice and flush with the smooth routed portion.
Edited 7/5/2007 9:30 pm by BarryO
Without drawing it, how do you know what the arc will look like?
Without drawing it, how do you know what the arc will look like?
There's no reason you can't draw it first. You could then just measure the angle needed between the two outriggers off the drawing. Or, if you already know the distance between the endpoints (c), and the offset of the apex from a straight line (h), the angle is: 180-arcsin (4ch/(c^2+4h^2)).
I am working on a project at the present that needed various arcs of differing lengths but with the same chord height. I didn't want to bother with finding the long R and setting up a trammel, so what I found that worked was to put a piece of aluminum extrusion that I had end to end in a long pipe-clamp. You could also use a good smooth grained piece of wood.
As I tighten the clamp screw, I can get a nice smooth arc with a shorter radius the more I tightened it. It is easily portable also.
Taunton Press has a handy little book in the Best tips from 25 Years of Fine Woodworking series called Workshop Methods of work. It has a good chapter on measuring, marking and layout. You'll find more than enough info there.
Work Safe, Count to 10 when your done for the day !!
Bruce S.
Hi Velo ,
You have been given many ways and answers to draw an arc , some are over the top on tech imo .
Drawing an arc can be easy and simple . For your table apron find half the width or length of the arc and the ht, of the arc . You can use a thin metal straight edge or a piece of 1/4" ply or other stock that will bend to the shape smoothly .
Trace the 1/2 of the arc from one end to the middle on to a 1/4" material for a template when it looks right cut it out sand to the line , make any adjustments needed then trace the half onto your apron and flip it over and draw the other half .
You can make a complete template if you have many to draw , but for only a few the half template works fine . One thing for sure the arc will be the the same on both sides .
hope this helps dusty
Why would you care if it is perfect or not?
I usually clamp both ends of a thin piece of stock to a piece straight scrap and then insert a spacer (1" might be appropriate for your table) in the center to bow the thin stock out.
Set this on the skirt. Draw along the curve. Cut with a band saw. Smooth. Natural variations make the piece made by hand not machine.
Set this on the skirt. Draw along the curve. Cut with a band saw. Smooth. Natural variations make the piece made by hand not machine
To each his own, I guess. Taken your position to the extreme, one could argue that you shouldn't use the stick, and instead draw the curve freehand.
Personally, I love skipping the "smooth" step, and there's still plenty of "imperfections" on my stuff.
This forum post is now archived. Commenting has been disabled