laying out an arch

[Brad Wood]

Hi,

I'm working on the design details for a dining table the LOML has asked for. I've attached a 2d sketch up drawing I've been working on. This isn't drawn out to any particular scale or adherence to dimension (in other words, I am severely new and challenged with sketch up)

Anyway, I'd like to draw your attention to the arch in the table skirts and end stretchers....
I'm thinking I want to create a template so I can get both symmetry in the arch itself and between the various matched pieces.

I am struggling with how to lay the arch out on a template to I can take the wood to the bandsaw and make the cuts. I'm thinking its a pretty darn big compass that would be needed.... there must me another method and hopefully you all have the secret.

oh, and, I wouldn't mind comments on the overall design in general while you are at it.

Thanks

- Brad

[Scott Loven]

I would make a bow with a strip of wood and a loop of string with a stick in the string to tighten the string until I got the arch I was looking for. Use it to make a template if you like.

Scott

[Jim Kountz]

I would make a bow with a strip of wood and a loop of string with a stick in the string to tighten the string until I got the arch I was looking for. Use it to make a template if you like.

Scott

Ditto, Scott beat me to it but thats exactly what I would do, especially the template part. Templates are your friends, treat them well but use them often!!

[Brad Wood]

great suggestion, thank you. When I read it, a light went off in my head .... ding!! Duh, once I read it, it seemed so obvious.

Thanks guys

[Chris Padilla]

http://www.sawmillcreek.org/showthread.php?t=104059

The above thread has a forumula to calculate the radius of an any arc if you know the length and height of the arc, which you do in your case.

However, I'll admit that this formula, while useful, isn't very good for cutting very mild arcs that have a very large radius...like yours is likely to have.

[Lee Schierer]

I've used teh string and strip method as well as the large compass method. Since I draw up my plans in CAD, I usually know the exact radius so making a long compass out of strip of wood isn't a big deal. I can anchor the center on one work bench and lay the piece to receive the curve on my saw table extension. I've drawn 8'+ radius arches with a 1/4" thick x 3/4" wide strip of pine, a nail and a pencil in a hole in the end of the strip.

To get both pieces exactly alike, fasten them together with double sided tape. Draw the arc, cut them out, sand the curve and then separate the two pieces.

[Chris Padilla]

There is another way to cut an arc without having to resort to overly long radiuses but unfortunately, it is on Woodnet and I can't post it here. It is a very clever and cool idea...all geometry. PM me and I'll send you the link for whomever is interested.

Alternatively, you could do a search on the subject: How to make a gentle arc. It is posted in the Woodworking forum there, BarryO is the thread starter.

[Don C Peterson]

There is another way to cut an arc without having to resort to overly long radiuses but unfortunately, it is on Woodnet and I can't post it here. It is a very clever and cool idea...all geometry. PM me and I'll send you the link for whomever is interested.

Alternatively, you could do a search on the subject: How to make a gentle arc. It is posted in the Woodworking forum there, BarryO is the thread starter.

Now that method takes the cake for simplicity and accuracy. I have used the bent slat method but have been less than happy with the results. If the slat isn't exactly the same strength across it's entire length, the arch won't be even. It might be close enough, but then again, maybe not... BarryO's method just requires two straight sticks that are joined securely at their apex. No math, no calculations, no errors. Thanks for sharing that.

[glenn bradley]

I would make a bow with a strip of wood and a loop of string with a stick in the string to tighten the string until I got the arch I was looking for. Use it to make a template if you like.

Scott

Ditto, Scott beat me to it but thats exactly what I would do, especially the template part. Templates are your friends, treat them well but use them often!!

+1 on that. 1/8" tempered hardboard will make one that lasts, almost any thin material will make one for "right now".

[Prashun Patel]

I had to do the same thing on a coffee table I just made (legs and rails and stretchers):
http://www.sawmillcreek.org/showthread.php?t=108061

There's a very easy way to 'fair' a curve that doesn't require you to make a fairing stick with a string:

Draw a reference line on a piece of hardboard the length of yr apron.
THen tap nails into the hboard at the endpoints.
Then take a thin 1/4" thick piece of wood or hardboard and push it against the nails. Then draw yr curve on the top side and use that to make a template on your bandsaw. Cut the template and sand it smooth and use it as a template with a patternbit and router on for your aprons.

By altering the position of the nails relative to the reference line, you can get a variety of curves.

'Fairing' a curve this way or with a stick and string produces more organic and flowing curves than strictly following an arc on a circle. They're of course a little harder to cut, as you can't use a router with a trammel.

[Chris Padilla]

Now that method takes the cake for simplicity and accuracy. I have used the bent slat method but have been less than happy with the results. If the slat isn't exactly the same strength across it's entire length, the arch won't be even. It might be close enough, but then again, maybe not... BarryO's method just requires two straight sticks that are joined securely at their apex. No math, no calculations, no errors. Thanks for sharing that.

Don,

If you've actually done this, could you start a new thread and post how to go about it? In this way, we can have the content more or less transcribed over to SMC!

Thanks!

[Don C Peterson]

I haven't used it before. I was just struck by the idea as being one of those that's just too good NOT to use. I was thinking of making a set of sticks and demonstrating their use anyway, so your suggestion provides the additional nudge that I need to do it.

I'll do it over the weekend.

[Don C Peterson]

I came home tonight and after the kids were put to bed, ran downstairs and threw this together:

http://www.sawmillcreek.org/showthre...=1#post1105264

[Patrick Laflamme]

I had a similar problem with a dining room table I built for my parents house. An eight foot long table with a shallow curve in the skirt makes for an enormous compass just to draw the curve out. This may seem a bit round a bout but it worked very easily, very well, and very quickly. (as I wasn't trying to get my router or jigsaw to cooperate with a compass that spanned my entire basement)

I made the curve I wanted in AutoCAD (same could be done in Sketchup) making certain the curve was to scale and saved it as a jpg. I took the file to the Staples that's about two minutes from my house and had them print it on thier plotter to actual size. ( I chose Staples because at $.50 a square foot for plotter they were by far the cheapest and most of the other places in my area couldn't print an eight foot long continuous sheet.) I took the rolled up sheet home and taped it to a sheet of hardboard and traced the curve with a dull awl I keep around for the purpose. Then it's just a matter of cutting most of the curve away with a jigsaw and the finer work up to the line with a coping saw, file, and sandpaper. I then ripped the hardboard down to a strip that was wide enough to account for the curve plus a few inches for stabilities sake.

I clamped the skirt pieces together square with the hardboard template on top. Use whatever guide bushing you want and a spiral cut bit and run your router along the template. Leave both pieces clamped together until you've sanded the curve.

[Jim Tobias]

Using the strip of thin hardboard is the method I use also. One exception is that instead of using string or nail, I just lay down a brick (wrapped in duct tape to prevent scratching)on either end in a position that allows you to press the center of your hardboard to the desired arc. You are using the bricks as anchor points for either end of the stick. As long as you have the 2 end points on your template piece, it will be accurate. I think I picked this method up on David Mark's show or read it somewhere. Any of the other methods work, I just find this simple and fast.

Jim