Cutting arches

[Bhend18]

I'm looking for the best method to cut long arches. I make a template and use a router with a template bit to make the finish cut, but what is the best way to make the template perfect? I cut close to the line with my Carvex and then use a spindle sander to sand to the finish shape, but I still get some irregularities in the arch. Is there a better way?

 

[nclemmons]

I find it better to sand outside curves with a belt sander or something longer than just a spindle.  If you don't have a belt sander, you might try a piece of sandpaper stuck to a piece of wood and go over where you had used the spindle sander.  You can also use a hand plane.

The RO 150 might do the job since it is about 6" across so you could also try that.

neil

 

[stvrowe]

My experience has been that outside curves are best smoothed on a disc sander and inside curves on a spindle sander.

 

[Bhend18]

I was referring to inside curves.

 

[packratpop]

In end users router class a few years ago. Brian Sedgeley showed how we could use the MFS as a pivot point for a router. He only spoke of the technique and did not actually cut the arch but I was wondering if this is a solution for you. Problem is for a big arch the pivot point would be pretty far away. So the cut would be made with the router instead of multiple tools. Not sure what you are cutting or if it is a solution. Best regards. Hope you find your solution.

 

[packratpop]

Found a link that discusses the technique. Hope it helps
http://festoolownersgroup.com/festool-how-to/the-franken-arc-jig-(mfs)/

 

[tbellemare]

The MFS is an easy way.

The guide rail solution that Tom shows is another.

Scrap with two holes is a third way. One hole for a pivot and another for a guide bushing on the router.

A fourth is a trammel, either purchased or made, for a jigsaw. It could be the same as the scrap trammel above with a different mount.

Tom

 

[builderbob]

I have used my MFS to cut arches. Prior to that I used scrap plywood strips as a trammel. Both work excellent but as mentioned, you could be purchasing quite a bit of MFS profiles to make a long enough trammel.

 

[Memphis Larry]

Another method I've used with success is to put a threaded rod (5/16th I think?) into the built-in rod holder on the router and capture a screw eye hook between 2 nuts at the appropriate distance.  Makes a decent trammel and is also micro adjustable for length.

 

[Bhend18]

I like the trammel idea. Now I just need to wrap my head around the math to figure out my distance to the pivot point.  [unsure]

 

[Saskataper]

When I have to cut an arch in drywall I use a piece of my vinyl arch trim bent to the arch I want. If you find something that has the right flex it works really well to trace out a nice natural arch.

 

[tjbnwi]

I like the trammel idea. Now I just need to wrap my head around the math to figure out my distance to the pivot point.  [unsure]

rise squared + (span/2) squared divided by two times the rise.

Or just punch the rise and run into the BuildCalc app and hit Arc

Tom