# Large Rings & Bulkplates

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#### dixontj93060

##### Well-Known Member
Since Pat Waite quit producting centering rings I have been making my own with the device below (see attached). This has worked just fine, but he limit is 5.5" in diameter. I am now putting all the parts together for my L3 rocket and I'm short two bulkplates and a CR. The rocket is using 7.5" LOC tubing and since the arc on a 7+" ring is pretty shallow I was just going to put 6 or 8 drill holes around the outside diameter and use a jigsaw to complete the ring cut out. But before I began to desecrate this nice piece of aircraft plywood in my workshop, I just thought I'd check, how do those of you that build large rockets do your rings and bulkplates?

#### dave carver

##### ....what hump?
I found a Roto-zip type attachement that will cut a 16" circle. It doesn't cut very deep but I tend to use thinner and more CR's on my projects so it works fine for me. On smaller rings I use a fly cutter like yours to extend the life of the other unit, I can't seem to find cutting bits for the larger cutter. It's a 3 fluted cutter with a flange then the shaft sticking out. I use my 1/4 die grinder for power, cuts a ring in seconds

#### rocketsmith

##### Well-Known Member
I usually keep a stock of centering rings, one of each size I use. I trace the centering ring onto a sheet of birch plywood and use hole saws or forstner bits to get the motormount hole the correct size, using a drum sander on a drill press to get to the final fit. Then I cut the outer diameter close to the line with a scroll saw. Then I slide the ring I am making, slightly oversize, onto the motor tube with the pre-made ring and using a pencil I trace the outer size onto the oversize ring. I use my bench belt sander to take the outer diameter down to the edge of the line. Test fit often to get the size just right. Always keep the original ring from which to make new ones. I have saved hundreds doing it this way. By the way, I always use 3-4 centering rings (sometimes as many as 6), 1 at the top for recovery attachment, 1 at each end of the fin thru tabs and one at the bottom (it necessary). I always fillet the fin thru tabs before installing the bottom ring.

#### hardinlw

##### Well-Known Member
There is a circle cutting attachment for a Dremel tool. I've not used this one, but I've used the same principle and a full-sized router to cut a 13' radius arc in oak. There is a centering pin that slides in the slot shown in the link below. You drill a center hole of the appropriate diameter and set the guide to cut the OD. Once that is done, you cut the ID. The trick is to make a number of shallow passes and not get impatient. It cost me two router bits to learn that last part.

http://www.smarter.com/other-power-...ter-straight-edge/pd--ch-47--pi-15569003.html

#### n5wd

##### Well-Known Member
There is a circle cutting attachment for a Dremel tool. I've not used this one...
Well, I have tried the Dremel circle cutter route and while it's not the easiest tool in the world to work with, it will work if you're very, very patient and aren't using anything very thick. The screw-down tends to work loose while you're cutting the circle - all of a sudden you find yourself cutting a new path in the wood, and keeping the cord out of the way requires you grow a third hand. But, if it's all you've got...

I managed to make a couple of useable bulkheads - never could get a useable CR made, though.

#### dixontj93060

##### Well-Known Member
Yes, I don't really see my Dremel or my father-in-law's Rotozip working in this application, i.e., 1/2" 9-ply.

Well, I have tried the Dremel circle cutter route and while it's not the easiest tool in the world to work with, it will work if you're very, very patient and aren't using anything very thick. The screw-down tends to work loose while you're cutting the circle - all of a sudden you find yourself cutting a new path in the wood, and keeping the cord out of the way requires you grow a third hand. But, if it's all you've got...

I managed to make a couple of useable bulkheads - never could get a useable CR made, though.

Best,

Bob

#### Bravo52

##### Well-Known Member

It's basically just a piece of all-thread that I can screw into a block I attached to the router. On the other end is a similar block with a 1/4" dowel sticking out. I drill a 1/4" hole in the plywood, then use the jig to guide the router in a circle.

-- Roger
It doesn't get much better than this! Well thought out and functional at a small price.