What's the most abundant component in a high power rocket? Is it fins? Airframe tubes? Couplers? Rocket motors? Nope, none of the above. You need rings and you need lots of 'em. Centering rings, bulkhead plates, thrust plates — you can't build a rocket without rings!

I've used several methods to cut out wooden rings, including fly-cutters on a drill press, jig saws, and router tables but by far, the easiest and most accurate method I've found for cutting wooden rings uses a circle-cutting jig and an ordinary plunge router.

Jasper's Model 200 circle cutting jig.

Cutting wooden rings has never been easier.

The result is a nice, clean ring.

I use a circle-cutting jig from Jasper Tools. Used with a plunge router, it can cut circles from 2.25 to 18 inches in 16th of an inch increments. Available from several Internet retailers including Woodcraft and Parts Express, the Jasper circle jig was designed to cut openings in speaker cabinets for woofers and tweeters. Turns out, it's the perfect rocket building accessory too.

Jasper Tools sells four different models of their circle cutting jig:

• Model 200 makes circles from 2-1/4" to 18-3/16" in diameter in 1/16" increments
• Model 270 makes circles from 7" to 18-3/16" in diameter in 1/16" increments
• Model 300 makes circles from 7" to 52-3/4" in diameter in 1/4" increments, and
• Model 400 makes circles from 1" to 7-1/2" in diameter in 1/4" increments.

The heavy duty plastic jig attaches to the base of 19 different plunge router models. The one I use is the Model 200.

To use the circle jig, lay out your rings on the selected stock with a compass. Clamp the stock to your bench with a sacrificial base material — I use 1/4" luaun sheets (cheap and smooth) to prevent "tear-out."

Drill a 1/8" hole in the ring's center and place the stainless steel centering pin in the drilled hole, protruding about 1/4". Place the jig over the stainless steel centering pin, with the pin placed in the appropriately sized hole. If you need an inside cut, such as the motor mount hole in a centering ring, the measurement is the actual size (i.e. for a 3" hole, place the pin at the 3" mark on the jig). If you need an outside cut, such as a centering ring or bulkhead plate, pick the appropriately sized hole plus 1/2" (assuming you use a 1/4" router bit).

Tips for success:

1. Use a 1/4" carbide spiral upcut bit - it pulls the chips out of the cut.
2. When cutting centering rings, cut the outside first, remove the jig and re-center for the inner cut.
3. Use double sided tape when cutting centering rings, or when the stock is too small to clamp.
4. Don't bog the router - make multiple successively deeper passes when cutting thicker material.
5. Hook up your ShopVac and use hearing & eye protection.

You can also cut dados or "ledges" on the outer diameter of thicker stock to make 1 piece bulkplates which fit inside a coupler or airframe tube and rest on the outer edge.

Once you get in the groove, you can knock out large numbers of identical rings in no time at all.

Websites:

Woodcraft: http://www.woodcraft.com/
Parts Express: http://www.partsexpress.com/
Jasper Tools: http://www.jaspertools.com/

For Jerry's contribution of this article, he will receive a free Rocketry Planet T-shirt. This sponsorship is made possible by our friends at Graphix & Stuff, producers of high quality hobby apparel and vinyl signage. Want your own free gifts? Read the program details page for complete information.

07-30-2007 06:15 PM  #1
StuBarrett Certified Level Eleven   Joined: Aug 2006 Posts: 84	Excellent!! I've been thinking about some kind of jig to work with my router to do just this. Now I don't have to search. Stu

07-31-2007 02:15 PM  #2
Sandy H. New Member   Joined: Jul 2007 Posts: 4	I have used the model 200 and 400 in speaker building applications and have found it best to make sure you drill the 1/8" pilot hole very carefully. If you are doing this with a hand drill, make sure it is as close to perpendicular to the sheet as possible. Ideally, a drill press makes this even easier. If you need a hole that isn't in the 16th's, you can use a different diameter router bit than the 1/4" bit that the jig is calibrated to. You'll have to do a little math, but I believe the manual outlines the process. Lastly, I the model 400 jig cuts in 1/16" increments, not 1/4" as listed. This error appears to actually be on the Jasper website as well, which is probably where the misinformation came from. I have used the model 400 jig for many different applications where 1/4" increments just wouldn't cut it. If nothing else, look at the number of holes in the picture. If it were only in 1/4" increments, there would only be 27 holes and there are many more than that! I agree that the Jasper jig is indeed a good tool for making good quality round cuts. Sandy.

07-31-2007 05:26 PM  #3
MWeaver New Member   Joined: Nov 2006 Posts: 5	Router Great Article! What is the Porter Cable router model number?

07-31-2007 08:04 PM  #4
vahpr New Member   Joined: Feb 2007 Posts: 5	It's a Porter Cable 7529 - not sure if that particular model is still available, but I'm sure a similar spec model is available. Regarding Sandy's comments, I've found that the 1/16" resolution of the Jasper jig is not an impediment for making tight rings for rocketry. Truth is, some tubing sold for airframes is not truly round, the jig itself after time opens up, and your 1/8" hole might not be perfectly true, but none of that really matters. A little bit of play allows for easy adjustment and good glue adhesion. Jerry O Quote: Great Article! What is the Porter Cable router model number?

09-18-2007 11:53 AM  #5
Cas2047 Certified Level Two   Joined: Jul 2007 Posts: 68	Great article! Thanks for posting.