Plywood centering rings - How To???

I'm getting ready to create plywood centering rings to replace the rings that came with my Aerotech Mirage. I have a Dremel tool. I bought 1/4" craft plywood. But how do you insure that your rings center the motor? I can trace the already existing rings and then do my best to cut them. I guess what I am asking is are there any tips/tricks to cutting your own center rings?

The trick here is to make a jig. The jig can be a simple arm with a pin on one end that goes into a hole at the center of your centering ring. The other end of the arm attaches to your dremel (somehow?). Then you just turn the arm 360 degrees and let the dremel cut a perfect circle. You can then do the same thing for the inside diameter hole. If you've got a way to secure your dremel in an upright position, then you can make a router table. The dremel bit would stick up through a hole in your work surface. Then, you just need a pin fixed in your work surface that is the distance of one radius of your centering ring away from the dremel bit. Put the center hole of your centering ring on the pin, turn the plywood and let the dremel cut a perfect circle. Cutting the inside diameter is a little tricker this way. You'd need a starter hole.

Hope this helps,
Mark

I have no idea. But I will say that a lot of practice, an eye for perfection, and a steady hand would be a big help. Just remember that the size of the rocket will dictate the degree of accuracy required. Because if the deviation between the longitudinal axis of the motor mount and the longitudinal axis of the rocket's airframe is excessive, a rocket that is stable on paper, in stasis, or even a swing test will present some rather exciting possibilities as soon as it leaves the launch rod, rail or tower.
For example: 1/16 inches of angular deviation wouldn't be too bad in a 3 inch X 40 inch rocket with a 29mm motor, bit it could be a harbinger of disaster in a 1 inch X 18 inch rocket.
What happens is that the rocket is propelled off the pad because of the motor's thrust, but as soon as it leaves the stabilizing effect of the rod, rail or tower, the aerodynamic lift occurring at its center of pressure responds directly to the wayward thrust vector of a misaligned motor mount. The motor's thrust will definitely push the rocket and the rocket will definitely fly, but it's likely to become what is known as a "Sky Writer" or a "Land Shark".
If the rocket is not torn apart by the yaw it will experience during thrust and the motor burns out, the rocket will continue flying in the direction it was pointed at that time.

There are a few things I have done with my own plywood centering rings. If you plan to use more than 2 rings, you can use them in the middle positions and store bought rings on both ends. This ensures that the motor tube will be straight in the body tube. Another way is to use a store bought ring as a template as mentioned before, taking you time to sand after a rough cut, to test fit a ring using both your homemade and store bought for comparison on the motor tube and in the body tube.

I'm also working on a jig for a routing table using a router like mentioned above. It is 3/16 plywood with rail guides on the bottom and pre drilled holes for different size centerings. I will post plans and pictures on my web site when I’m finished. Good Luck.

I've got a $59.00, 8" drill press from Menards and a circle cutter ( I've alway's called them fly cutters. This works great, I've got a piece of wood on the table of the drill press and have it mounted down. Then my stock gets clamped down, I set the circle cutter for the inside dia. then cut the outside dia. Comes out perfect everytime. You can not use this cirlce cutter with a hand drill as it is an off set cutter, you must use a drill press.

Hmmm. I have a drill press. I could probably do that but how do you insure that you are drilling in the exact center of the ring? I did a bulkhead last night and found that I could sand the outside ring pretty good with a table sander. I'm just worrying about the center ring. I will look for a 29mm "fly" cutter tonight.

hehehehe... just found out what a circle cutter really is.... I didn't realize it is variable size wise. I understand how you do it now... I will go tonight and try to find one.... Thanks.

I got mine from Menards for $5.00.. here is a pic of it. and if you save the nock out's, you can use them for sizing later down the road. Once you get one that fit's good.

You have to be careful using these circle cutters. I have one too that I use once and a while. The problem is that when I bought mine, the blade was put in backwards (And I did not know it). As I tried to cut the first circle it started to catch and chatter on the wood. Then it caught and ripped up the wood so bad I had to throw the piece of plywood away. Also it takes time to get the right circle diameter without having to do some sanding, which could throw off the center of the ring.

Hi,

I'm a newbie here, but wanted to let you know how I make my CRs. For the larger ones I use two methods. One is a jigsaw for the outer edge and then I use a drill press with a circle cutter that you can purchase at my favorite store, Home Depot. Just put some very small nails in a wooden platform and place your drill bit (comes with the cutter) in your previously marked hole and press go. Sometime I use the cutter for both. Just depends upon the mood I'm in at the time. The cutter will leave a....beveled edge, for lack of better terms, but I like this because the epoxy has A LOT of edge to "bite" into.

Shane

"Press Go"? Please explain that part of the process.

if you aren't familure with the location of this button.. ask your wife.. she will show you right where it is.. They seem to think that we have a processor that you put honey do list into and press the "Go Button" and were off.... lol

Thanks for the clarification. It was a pleasant reminder of the main reason why I love being a bachelor.

Just following up on my thread... Well, here is what I did: I used 1 Circle Cutter, 3 1/4" plywood boards, 1 drill press, 1 jig, 1 dremel tool, 1 table sander and a partridge in a pear treeeeeee. Seriously, using all those things I am now the proud owner of 6 almost perfect plywood center rings and 2 deformed center rings. Thanks for everyones suggestions and help.

Here is what I did:
1) Make a jig (thanks Milo) with a right angle and clamp it to the drill press.
2) On the boards, mark the corner to go into the right angle.
3) Measure and circle cut (thanks Electrode) the center ring. By measure I mean stop frequently and put the motor tube in the hole to make sure everything is fine.
4) Once the first one is cut, cut as many as you have wood for. If you are like me, you will screw up a few so make more than you need.
5) After all the center cuts are done, measure and circle cut one of the outside cuts. This time use the body tube to measure.
6) Once you have cut all the rings, they will probably still have a lip on them, so you put all the rings on the motor tube. Pushing them all together you can then use a table sander to sand off the lip.

Voila. What you have left should be X number of equal center rings.

Cool... can't wait to see them.