How do I cut an arch into a table apron?

[Wade Lippman]

I am making a table. The long aprons need to have arches cut into them. They are 36"x5".

The last time i did this I tied a pencil to a 10' rope and drew an arch. That was awkward and I am wondering if there is a better way.

[jack forsberg]

I am making a table. The long aprons need to have arches cut into them. They are 36"x5".

The last time i did this I tied a pencil to a 10' rope and drew an arch. That was awkward and I am wondering if there is a better way.


if its just a design arch most just use a thin stick bent to the curve they want.

286944

[Ken Fitzgerald]

Rip a thin strip of wood.......as show in Jack's post.

[Justin Ludwig]

I've never had luck using a stick and bending it. I figure the radius, make a stick (trammel) 2" longer and use a screw and pencil to draw my arch. It's very easy to do, but hard to explain.

[glenn bradley]

1/4" x 2" x 49" MDF.

286970 . 286964 . 286965 . 286966
286968 . 286967 . 286969 . 286971

I use the fairing stick to make the mark, rough cut it at the bandsaw and use a spoke shave to fair in the curve.

Example: . . . oh darn, only 8 pictures per post. Oh well.

[Mel Fulks]

I think you need a radius of 34.9 inches. A stick can be made to work but has a tendency to bend too much in the middle.

[johnny means]

Are you looking for an arc or an arch? Trammels and the like won't give you an arch. I'm not willing to try and explain it here, but there is a method for drawing arches involving two nails and a loop of string. I'm sure there are dozens of videos and how-tos on it.

[Justin Ludwig]

Trammels and the like won't give you an arch.

Incorrect.

Here's a trammel mounted to a router cutting an arch/arc.

http://3.bp.blogspot.com/-ovt4506lVF8/T4CFdqfK8DI/AAAAAAAAAfE/16t8yw58_Vg/s1600/blog%2Brouter%2Barc.jpg

[Yonak Hawkins]

Are you looking for an arc or an arch? Trammels and the like won't give you an arch.


Incorrect. Here's a trammel mounted to a router cutting an arch/arc.

Here we have a failure to communicate. johnny is distinguishing between an arc (a segment of a circle) and an arch (a segment of an ellipse).

Lud is assuming the arch is an arc (which it could be, but not necessarily).

If an ellipse is required, the two nails and a loop of string is one (less than accurate) way of doing it, but it takes a lot of conjuring or trial and error and depends on the distance between the nails and the length of the loop of string to get the height and length of the arch correct. Another way would be to find someone with CAD capabilities (if available) and ask them to plot it out (if available) and use it as a template. Another option is to use the geometry class method of drawing an ellipse on paper, using just a compass which I can't exactly recall right now but, surely it's on the internet somewhere and, if I am requested to do so, I would be happy to do some research.

[Mel Fulks]

An arch is not a segment of an ellipse. It is true that some substitutes for true ellipses are made by joining two small segments to a larger radius at tangent points. For the flatter "ellipses" the result is always ugly. What the op needs is segment (part of a circle) that can be drawn with a radius of about 35 inches which coincidentally is the length of the
desired segment or chord.

[Max Neu]

I use draw bows, either symmetrical, or Asymmetric, depending on what I am doing.

[Myk Rian]

While the rest argue arc/arch, just stay with the string protractor method.

[Justin Ludwig]

I think you need a radius of 34.9 inches. A stick can be made to work but has a tendency to bend too much in the middle.

Correct, if he's wanted to use the whole 5" of rise. 34-7/8" Imperial or 886.5mm.


Lud is assuming the arch is an arc (which it could be, but not necessarily).

Ambiguities... You draw a mathematical "arc" to build an "arch". One in the same.



@Wade - Are you wanting a simple arch cut into the wings? Does it have to be perfectly symmetrical? IMO, a bow stick is a crap shoot if you want a true arc, but the results can be just as visually pleasing.

[jack forsberg]

if the R is out side the shop space but you want a true segment.


http://www.blocklayer.com/arceng.aspx

[Brian W Smith]

I seem to remember a thread about how WW'ing may not "prepare" a student for anything later in life?

Yes,you need to discern your style first as the laying out is,or utilizes different approaches.My advice is to hit the books or images and really buckle down on what style and "scale" you want the piece.And even then,you may want to do a fullsize mockup out of some 1/4" ply........and stand back.Check it in varying degrees of lite(its a shadow thing).

[Mark Wooden]

The string method- http://www.mathopenref.com/constellipse1.html- will give you a pretty good ellipse, just be sure to use string that doesn't stretch too much, same goes for simple segments of a circle. I prefer to us a three point trammel for an ellipse (of which I could not find a good example of online, guess it's too old school;)) and a regular trammel for segments as they produce a very even line.
A method for drawing segments is here -http://www.mathopenref.com/arcradius.html- but most any of the methods given above work well too.

[ken masoumi]

Lee Valley sells the bending curve tools ,I have the blue flexible one and would not recommend it.does not stay in the shape long enough to draw. .
http://www.leevalley.com/en/images/item/woodworking/markmeasure/07k0101s2.jpg


http://www.leevalley.com/en/images/item/Woodworking/MarkMeasure/07k0110s2.jpg

[Wade Lippman]

if its just a design arch most just use a thin stick bent to the curve they want.

286944

That worked. If I needed it to be precisely something I suppose the trammel would have been the way to go, but all I needed was a smooth curve of approximately the right size.

I know that two nails and a string will draw an ellipse and nearly tried that, but thought it could take quite a while to get the right shape.

[Prashun Patel]

Actually, some people would say the trammel is precisely NOT the right way to go because it will scribe a circular arc. Some would say that a parabolic or caternary curve similar to the kind you get with the push-on-a-stick method looks more organic and natural.

[Mel Fulks]

Well, op called for "arch" which is sometimes used figuratively but derives from 'part of a circle'. The word "trammel " refers to something that restrains and controls movement as in the devices for drawing true ellipses,the fixed point center
of a circle is not a trammel. When you are painting your house some would say another color would be better....those
people are called "neighbors". I'm sensitive to these things because I have had to work with them for a long time. For
instance I have never made a mantel piece to go with an arched fire box without personally going to job site to verify the
radius or ellipse. Yes, the drawing is supposed to show that...but it's usually wrong. I'm sure there are others here who
will agree that the actual work is done corresponding to whatever form the mason had on hand.

[lowell holmes]

Show off

Show off

[jack forsberg]

could be the OP is talking about this ark? i read Noah had the same type of problems.:rolleyes:

First he had to get a building permit for the Ark construction and his plans didn't meet code:mad: So he had to hire an engineer to redraw the plans:eek: Then he got into a big fight over weather or not the Ark needed a fire sprinkler system:confused: His neighbors objected claiming he was violating zoning by building the Ark in his home shop so he had to get a variance from the city planing commission.:D

I not go in to the part were the carpenters formed a union but he did get sued:cool:


.

[Alan Schwabacher]

As I recall, Cosby explained all about Noah's problems with the ark, including the neighbor who wanted it out of his driveway.

Assuming you want an arch that is an arc (part of a circle) there is a way to draw or cut them directly even when a trammel would be too big to be convenient. Put two nails where you want the ends of your arc. Attach two straightedges together so they cross at another point on the arc, and one touches each nail. Make sure the straightedges are attached together so the angle between them can't change. Now slide the straightedges along the nails, and the point where they cross will trace out an arc. If you use a pencil, it will draw the arc, but you can also attach a router and cut the arc directly. This is most useful when a simple trammel would be ungainly or impossible to use, as you can easily draw an arc with a 40' radius while keeping all work on a normal sized bench.

[Yonak Hawkins]

That's a great space and time saving solution .. and accurate.