Router Compass

**joe greiner** · 3rd June 2007, 11:34 PM

I recently had occasion to rout some arcs in a thick plywood sandwich. To use a conventional router compass attached to the base plate, it would have been necessary to mount the bit with reduced purchase in the collet. I prefer to shun that, and longer bits are hard to find.

I made a beam compass to attach directly to the router base. The base has transverse holes normally used for attaching a fence accessory. A 3/8" piece of all-thread fit the holes perfectly. At the pivot end, I attached a coupling nut and a jam nut. I drilled a hole through the coupling nut to accept a brad with the point sharpened. For each of many candidate locations along the coupling nut, there were three opportunities to drill the hole correctly. I got it right on the second try; on the first try, the drill bit found an internal thread on the opposite side of the nut and drifted off perpendicular. I filled the erroneous hole with epoxy so I wouldn't use it by accident. Except for assembly, these two steps were the only manual labor required. I added a short bolt to pinch the brad against the end of the all-thread.

At the router, I used a bushing and a nut to position the all-thread at each end of the hole. This provides the radius adjustment. The bushing places the nut where I could tighten it. I measure the radius directly with the router inverted; a gage stick would be more effective than the tape measure, though.

It isn't necessary for the compass to lie along the line between the pivot and the bit. The 3/8" all-thread is stiff enough to prevent flexing. Except for the all-thread, which can be any length needed, all the components fit in a small pill bottle.

Joe

**Wood Borer** · 3rd June 2007, 11:47 PM

A nice and simple solution, thanks Joe.

**watson** · 3rd June 2007, 11:47 PM

Excellent Jig Joe

Will have a play with it tomorrowday.

**watson** · 7th June 2007, 08:35 PM

G'day Joe, made up one of your jigs, and it works a treat.
Just noticed in your third photo with the tape measure.........are you measuring in metric??

**joe greiner** · 7th June 2007, 10:49 PM

Glad you like it, Noel.

Originally Posted by watson

.........are you measuring in metric??

You bet. Easier to count 158mm than 6 7/32", especially with offset origin. I don't buy the notion of only one or the other. I mix 'em up as needed; some metric, some Imperial. Rat's ring, etc.

Joe

**scooter** · 7th June 2007, 11:47 PM

Is that your first longworth, Joe?

Be interested to hear your feedback.

Cheers...............Sean

**Gil Jones** · 8th June 2007, 01:22 AM

Joe, that is a great router compass idea!!!
Having been up-close and personal with your Longworth chuck, at the club meeting last Tuesday night, I will say that it is very well designed and built. The router compass tool worked nicely on milling the arcs.

**Munga** · 8th June 2007, 06:32 AM

What a great and simple idea thank Joe will make one this morning.

Cheers Arch

**joe greiner** · 8th June 2007, 01:47 PM

G'day mates. I was in Lowes (similar to Home Despot) this morning, and examined some of the routers. Looks like some of them might be harder to adapt the design; I guess I was lucky that my Ryobi has the holes oriented right. Some of the others have smaller holes, only penetrate one side of the base (need two rods for the fence accessory), or don't have a flat spot to engage the bushing. This last item might just need a bevel on the bushings.

Yep, Sean, that's my first Longworth. I've only used it on two bowls so far - one compression and one expansion (undercut rim). I haven't fully assessed my design modifications, although I've already started a couple revisions (without rebuilding). It was going to be just a test, but it works pretty well so far, and I might not build another. As soon as I collect my wits, I'll post a new thread about it.

One thing throws me about the Longworth: I'm thinking that routing the sandwich might just be for convenience, not a geometric necessity. Thus each disk could have been done separately with a standard plywood compass, and I wouldn't have needed this contraption. Still handy for other missions, of course, and I'm glad I made it.

Joe

**scooter** · 8th June 2007, 11:22 PM

Originally Posted by joe greiner

As soon as I collect my wits, I'll post a new thread about it.

Look forward to it

**joe greiner** · 13th June 2007, 11:08 PM

Originally Posted by scooter

Look forward to it

Here 'tis:
http://www.woodworkforums.ubeaut.com...ad.php?t=50923

Joe

**scooter** · 14th June 2007, 09:09 PM

Good job, Joe

**littlebuddha** · 16th June 2007, 11:08 AM

joe greiner, well you have me us UK guys always know that you yanks are always making it to me big and more, what a load of bull, but you know what mate, hats off this router jig is brill love it, nice and simple and does a great job, i love simple jigs that you don't have to spend hours on, this leaves you free to do the work you want.
From a happy UK guy, well at the moment anyway. thanks joe.

Still trying to finish this site, one day....
htp//www.shapewood.co.uk

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