Template brain-buster. Cutting small circles accurately.

[Glen Butler]

I need to make a template for cutting curved handrail pieces. The best way I can think of is to take a CAD to someone with a CNC machine and have them cut it. But I am pressed for time I need it in the next couple days. You can see in the image below the top view of a handrail (red) that has to swoop inside a wall (green). The purple line is what the template needs to look like. Simply cutting close and sanding to the line is not good enough cause it needs to be very even. I have cut circles with the router in the past, but these are too tight for my jig. Any ideas. Again this is just for the template not for the handrail itself. Don't be shy because of all the measurements. That is irrelevant to you also. I just need to know how to cut small diameters accurately.

[Glen Butler]

No takers? Isn't there some sort of circle cutter that has an "infinite" number of positions along a bar. Is there some sort of dremel attachment I could hook a base plate to?

[Van Huskey]

http://www.generaltools.com/Products/Heavy-Duty-Circle-Cutter__55.aspx


Thats one, I have seen a bunch.

[Doug Shepard]

No takers? Isn't there some sort of circle cutter that has an "infinite" number of positions along a bar. ...

Yup.
http://microfence.com/circle-complete-p-54.html
I cant tell the radii sizes on your pic but they also sell longer guide shafts if you need them and an accesory that lets you cut smaller circles than the normal circle jig will allow. call Rich up at MF.
Pricey but a first rate tool.

[Larry Edgerton]

I would make that piece with a pattern cut exactly like you have drawn, and follow with a top bearing panel bit that is as large as your inside radius will allow. The larger diameter pattern bit will have less tearout than a small one, a consideration when you are going cross grain as you will have to do in that situation. I use 1 1/2" Whitesides for that kind of thing.

Check with, and I forget the name but it has "wolf" in it, a fellow here that specializes in staircases. His work is awesome, and I bow to his expertise.

[Walter Plummer]

Good Morning. I would use a 2 5/8" hole saw for the inside radius and the router trammel for the outside. Use 1/2" MDF and make two pieces larger than a quarter circle. Cut them on the radial line and glue them back together in the "s" shape you need. Leave the other ends as long as you can to start and stop your cuts on when you make the rail. Hope this makes sense to you. Good luck.

[Richard Wolf]

Glen, it looks like you have a really exact part there. That's a high tech S turn. I'm not sure that a dremel with a trammel point will even cut a radii that small. I think you need to find someone with a milling machine with a boring head that will be able to cut very exact radii. But I am wondering why such tight tolerances? Best of luck with it.

Richard

[Keith Outten]

Glen,

Micro Fence has a small diamiter circle cutter that is a very high quality router attachment.

http://microfence.com

If you only have a couple of days you might have to find a local CNC operator. You can post a classified want ad here or go to the ShopBot Forum and request a quote from someone in your area.
.

[Glen Butler]

Glen, it looks like you have a really exact part there. That's a high tech S turn. I'm not sure that a dremel with a trammel point will even cut a radii that small. I think you need to find someone with a milling machine with a boring head that will be able to cut very exact radii. But I am wondering why such tight tolerances? Best of luck with it.

Richard

It needs to be really close because both sides of the handrail will be cut with the same template, by simply flipping the piece in the template. Any variance will compound the error and be noticable. Also the closer it is the better the handrail will go together. It doesn't however have to be so close that I must have it done on a cnc mill. I just can't seem to find another way.

The circle cutting bit may work. I will have to use it by hand, but I will cut my initial template in MDF so it may not be too bad.

[Myk Rian]

I would make that piece with a pattern cut exactly like you have drawn, and follow with a top bearing panel bit that is as large as your inside radius will allow.
+1. You can get a bit with upper and lower bearings.

[Mark Beall]

The smallest radius you have there is 1.3", the trammel I made (from Bill Hylton's "Woodworking with the Router" book) will go down to almost 3/4". I did a quick search but don't see the plans on the web anywhere. All it really is is a base with a slot in it. In the slot is a bar with the center pin in.

I guess that suggestion isn't very useful unless you have his book (or someone else can post a picture - my camera is dead) other than to say that you can do it with the right trammel.

mark

[Paul Atkins]

I make handrail corners as well as bar rail corners on my lathe. Here are some samples of inside, outside and upturns. I'm now working on a 5' diameter crown moulding. (Oops forgot picture) As far as the template circle, I can cut very small circles with my router by drilling a 1/8" hole in the sub base for a center pin. I have a plexi base that I use just for that that now has many holes in it.

[Paul Atkins]

Here is the picture

[Richard Dragin]

Paul,
Do those get quartered?

[Paul Atkins]

They get quartered for 90 degree corners, but any angle is used. Here is a funny rail for Sierra Nevada Brewery.

[Richard Wolf]

Nice work Paul.

Richard

[Glen Butler]

I did alot of driving around today and ended up with a jasper circle jig. I think it will do the trick. I need a plunge router now though.

http://www.amazon.com/gp/product/images/B00009K77A/ref=dp_image_0?ie=UTF8&n=228013&s=hi

[Larry Edgerton]

I make handrail corners as well as bar rail corners on my lathe. Here are some samples of inside, outside and upturns. I'm now working on a 5' diameter crown moulding. (Oops forgot picture) As far as the template circle, I can cut very small circles with my router by drilling a 1/8" hole in the sub base for a center pin. I have a plexi base that I use just for that that now has many holes in it.

Nice work Paul!