Uses for a long compass?

[John Coloccia]

I use it to make radius dishes for sanding/gluing flattop guitars.

I'm curious what other uses does the long compass have in the shop?

[Steve Rozmiarek]

John, I use a large beam compass, just a stick with a couple Starrett or Stanley trammel points attached for layout sometimes. Big arches can be "tuned" in full scale this way. Used it on a gazebo to set the brace arches, and several projects to find my choice of curves for corbels.

[Frank Drew]

Laying out big curves or circles? Like table tops, architectural features, etc.

[harry strasil]

Using the 3-4-5 method to scribe short arcs to check corner squareness of plywood sheets.

Laying out a door to fit an unsquare opening.

Cork stopper on the sharp end and then using as a back scratcher, a framing square works well too.

[John Coloccia]

It just occured to me that many probably aren't familiar with the long compass. I wasn't until I needed to be. Here's a good explanation of this handy device:

http://gicl.cs.drexel.edu/people/sev...g_compass.html

So I personally use this technique to make an accurate 24' radius dish (that's a 24' radius on a 22" diameter dish...not a 24' diameter dish!), something that would be pretty difficult to accurately cut otherwise.

[Lewis Cobb]

Originally Posted by John Coloccia

It just occured to me that many probably aren't familiar with the long compass. I wasn't until I needed to be. Here's a good explanation of this handy device:

http://gicl.cs.drexel.edu/people/sev...g_compass.html

So I personally use this technique to make an accurate 24' radius dish (that's a 24' radius on a 22" diameter dish...not a 24' diameter dish!), something that would be pretty difficult to accurately cut otherwise.

I for one was wondering "what's this lad going on about" - thanks for the link !!

[harry strasil]

Been using that method of striking an Arc since the 60's while in the navy, I used it lots in civilian life to cut sheet steel to match the OD of grain bins and oil field tanks among other things. Just never heard it called a long compass before.

To determine how far above the outer points to place the center one, I always took the chord height measurement.

[Mike Henderson]

To me, the long compass is best for really a big radius when all you want is an arc and not a complete circle.

For my work I generally use a couple of trammel points on a beam. I haven't had the need for really big circles but a friend of mine used a long compass for making a curved top driveway gate. He only wanted an arc and not a half circle so the radius was huge. I think he used a couple of 2x4's and had some helpers when he laid out the cut.

I never heard the term "long compass" before, either, but I don't remember what people called it.

Mike

[Chaz Alexopoulos]

That is a great tip, John. I could of used that for the sides of the shade canopy I built for a porch swing. I ended up wasting half-an-hour sketching it freehand. Great link.

[Steve Rozmiarek]

Hmmmm.... I can't think of any benefits for that approach over trammels, or a string or whatever. Seems that the structural integrity of the rig would limit it's size, and it would become pretty clumsy with any size at all. For smaller stuff, seems more trouble then it's worth. Clever though. What am I missing?

[John Coloccia]

Originally Posted by Steve Rozmiarek

Hmmmm.... I can't think of any benefits for that approach over trammels, or a string or whatever. Seems that the structural integrity of the rig would limit it's size, and it would become pretty clumsy with any size at all. For smaller stuff, seems more trouble then it's worth. Clever though. What am I missing?

What makes it cool is that you can make rigid fixtures out of them. For example, I put a router in mine and slide the whole assembly back and forth to make a large radius.

[Steve Rozmiarek]

Originally Posted by John Coloccia

What makes it cool is that you can make rigid fixtures out of them. For example, I put a router in mine and slide the whole assembly back and forth to make a large radius.

See, I knew I was missing something!