# Centering Rings

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#### David Schwantz

##### Well-Known Member
TRF Supporter
Show me how you make them. What tools do you use? I have a laser engraver, but it is not powerful enough to cut.

#### FMarvinS

##### Well-Known Member
David-there are several approaches that work:

1. the use of concentric hole saws, as sold at big box stores, is probably the easiest if you have access to a drill press (for example see-https://www.buydrillbits.com/products/holesaws.php?gclid=Cj0KCQjw59n8BRD2ARIsAAmgPmJATTkAiE4vmVc4Z01Em5Pt58oUM0_nexO1VDupDrFj5W2MD3B6__IaAgBxEALw_wcB)

If the hole saw diameters available don't match your required diameters, then the use of a variable jig on your drill should (e.g. ttps://www.eastcoasthardware.com/122911-rotozip-circle-cutter-crct4.html?utm_campaign=google&utm_source=google&utm_medium=cpc&gclid=Cj0KCQjw59n8BRD2ARIsA)

2. If you have access to a CNC machine such as at a makelab as shown below:

3. Also the use of a laser cutter would always work see below:

Good luck,
Fred, L2

#### Banzai88

##### Lvl 1,Wallet....Destroyed
TRF Supporter
I select the centering ring material, then plot out my circle with a compass.
At the center, I drill a 1/4 " hole.
The blank is then rough cut on a band saw.
The blank then spins on my circle sanding jig.
After the OD is correct, I then use a hole saw that's approximately the diameter that I want for the ID.
Final inside diameter is massaged with a dremel and hand sanding.

Takes longer to talk about it than it does to do it.

Last edited:

Just 1 example

#### David Schwantz

##### Well-Known Member
TRF Supporter
Yea, I cut the OD on the bandsaw, sand OD on belt sander, mark the center, cut the ID on jigsaw, sand with drum sander. Was looking for a better , more accurate way. Does any one know what watt laser would cut through 1/8" ply and G-10? Or will all of them need several passes?

#### David Schwantz

##### Well-Known Member
TRF Supporter
I select the centering ring material, then plot out my circle with a compass.
At the center, I drill a 1/4 " hole.
The blank is then rough cut on a band saw.
The blank then spins on my circle sanding jig.
After the OD is correct, I then use a hole saw that's approximately the diameter that I want for the ID.
Final inside diameter is massaged with a dremel and hand sanding.

Takes longer to talk about it than it does to do it.

Just gonna have to make one of them.

##### Well-Known Member
TRF Supporter
Show me how you make them. What tools do you use? I have a laser engraver, but it is not powerful enough to cut.

#### dr wogz

##### Fly caster
flybar cutter. and a a drill press (firmly anchored!)

get two (or three, or ...) and cut away! Set them each for a specific diameter. Do the center hole first, then cut the other. paint eh end white or orange. it hurts a lot when you forget that bit hanging out as it spins!

#### Tyler P

##### Nom-nom-nom...
TRF Supporter
flybar cutter. and a a drill press (firmly anchored!)

get two (or three, or ...) and cut away! Set them each for a specific diameter. Do the center hole first, then cut the other. paint eh end white or orange. it hurts a lot when you forget that bit hanging out as it spins!

Do you reverse the point? The picture on amazon shows it cutting a slant inward.

#### gdiscenza

##### Well-Known Member
TRF Supporter
The cutter is reversible. It all depends on what you consider "waste."
Orient the cutter so that the bevel is on the waste side for the cleanest cut.

Also, paint the ends of the cutter arms with safety orange, makes a bright "circle of pain" when the drill press is running.

G

#### kalsow

##### Well-Known Member
Show me how you make them. What tools do you use? I have a laser engraver, but it is not powerful enough to cut.
I use the Jasper jigs (#200: 2"-18" and #400: 1"-7") with my router. They're graduated in 1/16" inch increments for the diameter. I usually tack down my material with a brad or two and cut both the ID and OD using the same 1/8" center hole. I love'em.

I can never seem to find a hole saw that's the right size. I've used fly-cutters. They are hard to set and evil in operation.

#### prfesser

If you're lacking tools, working mostly by hand (which I've done a number of times), OpenRocket or Rocksim will print templates for your rings.

Glue the templates to the plywood and use your favorite method to cut and shape. For the outside, a sanding block, and keep trying it on the airframe till it fits inside snugly.

For the inside hole I've drilled a bunch of holes in a ring for a rough opening. Knock out the center, then sand with a dremel or even sandpaper wrapped around a dowel or tube. As you get close to the line, use a larger dowel/tube. For example, the motor mount tube for a 38 mm is about 1.65" od. Start with coarse sandpaper on a 3/4" dowel, and finish with finer paper on a 1.5" tube.

A dremel makes it a lot easier, but it's also easy to over-sand and make the hole too big or the outside too small. Work slowly.

I've made bulkheads by cutting a rough circle in the plywood, drill the center and slide a bolt through, add nut and washer. Chuck the bolt end in the drill press or even a hand drill. Use a sanding block to shape. Gives a much better fit than hand work.

Best -- Terry

#### Banzai88

##### Lvl 1,Wallet....Destroyed
TRF Supporter
flybar cutter. and a a drill press (firmly anchored!)

get two (or three, or ...) and cut away! Set them each for a specific diameter. Do the center hole first, then cut the other. paint eh end white or orange. it hurts a lot when you forget that bit hanging out as it spins!

For the love of all that you or anyone you've EVER met holds holy.........crank way way down on that flying head.

I thought I had, almost to the point of breaking it, when mine came loose, flew across the garage at warp 9, and smacked me in the mansack. Oddly enough, I remember it in ultra 4K detail in super slow motion flying through the air at me........but my son remembers it as hearing a loud crack and me dropping like a string cut marionette in near instant fashion.

It was worse than kidney stone pain. Way worse. Took a while to heal and walk 'normal' again, too.

Thankfully I was across the garage retrieving another piece of material at the time, otherwise, close up, it might have caused some serious damage.

#### dr wogz

##### Fly caster
Do you reverse the point? The picture on amazon shows it cutting a slant inward.
Yeah, flip it to whatever side you want to be perpendicular. Again, why I say get to or three or.. (the one I linked to is w-a-a-a-y expensive. "Amazon: the new Ebay!") They can be a pain to get adjusted for the right dia. but once dialed in, crank it down, and leave it! I paid around $9 or$12 for mine at the local reno shop

Also you can adjust the height of the cutting tip, so that the centering bit has more "meat" to center itself on. I also tend to screw my board to a thicker piece of backing

#### Tyler P

##### Nom-nom-nom...
TRF Supporter
Yeah, flip it to whatever side you want to be perpendicular. Again, why I say get to or three or.. (the one I linked to is w-a-a-a-y expensive. "Amazon: the new Ebay!") They can be a pain to get adjusted for the right dia. but once dialed in, crank it down, and leave it! I paid around $9 or$12 for mine at the local reno shop

Also you can adjust the height of the cutting tip, so that the centering bit has more "meat" to center itself on. I also tend to screw my board to a thicker piece of backing
Awesome. Might have to try this. I've been doing mine the ole band-saw and router way.

#### Charles_McG

I print them.

##### Lonewolf.... No Club
I've tried a number of different methods.

What works best for me is making my own basswood plywood from to pieces 1/16" glued together. I then cut the shape out with a scroll saw.
From there you can hand sand the o.d. down for a slip fit into the body tube.

I've got a wood lathe... often times I'll chuck the motor mount up with the o.d. of the rings oversized... and then sand them down.

__________________________________________________________________________________________________________________________________________
The other method I use is to simply glue paper to both sides of some 1/8" balsa and then cut the rings with a real sharp Exacto knife. The paper keeps the balsa from splitting... but you still need to take your time and be patient.

#### Louis Wu

##### Well-Known Member
I'm terrible with tools, so I had two sets of rings, fins and baffle bulkheads laser cut online. I just got them delivered.

not unreasonably priced, and once I got the hang of the software, a piece of cake to make the file. I have ordered a set for another rocket. I used Ponoko.com

#### rharshberger

##### Well-Known Member
Heres an older thread with all kinds of jigs.

I use the fly cutters for internal holes and a jig to sand the outside round. See my jigs in that older thread.

#### markg

##### Well-Known Member
not unreasonably priced, and once I got the hang of the software, a piece of cake to make the file. I have ordered a set for another rocket. I used Ponoko.com

View attachment 436207
That looks like a good option - how much did this cost you? I wonder if it's cheaper to get a sheet full of misc CRs cut vs ordering them from BMS?

cheers - mark

#### Louis Wu

##### Well-Known Member
I didn't like the crs from erockets so I ordered these. This is great for ook items, or a large run. It's $14 for setup and the sheet was about$16

#### FMarvinS

##### Well-Known Member
David-as per your question about laser cutting CR's the one pictured in my post above I did on a makelab 90 watt lasercutter. It can cut 0.25 inch plywood with 2 passes. The CNC CR's pictured I did on an Inventible's X-carve (also at the make lab). Fiberglass cutting is easily done by CNC with the appropriate bit, but not by laser cutting. CF is also manageable by CNC but no on a laser. You can cut acrylamide (1/4 inch) by laser with a few passes and in certain layouts can simulate fiber glass (e.g. altimeter sleds).

Regards,
Fred

#### dr wogz

##### Fly caster
what else do you do with slightly warped fins?!? Warped enough for fins, not for CRs..)

#### David Schwantz

##### Well-Known Member
TRF Supporter
David-as per your question about laser cutting CR's the one pictured in my post above I did on a makelab 90 watt lasercutter. It can cut 0.25 inch plywood with 2 passes. The CNC CR's pictured I did on an Inventible's X-carve (also at the make lab). Fiberglass cutting is easily done by CNC with the appropriate bit, but not by laser cutting. CF is also manageable by CNC but no on a laser. You can cut acrylamide (1/4 inch) by laser with a few passes and in certain layouts can simulate fiber glass (e.g. altimeter sleds).

Regards,
Fred
So several passes is common on laser cutting? My set up also will take a bit.

##### Roger Smith
+1 on the Jasper jigs recommendation for larger rings. Before I bought one, I used a circle cutter (or "fly cutter"), but almost killed myself with it.

I have other tools in my aresenal now, but using the Jasper jig is too much fun to stop using.

#### Banzai88

##### Lvl 1,Wallet....Destroyed
TRF Supporter
.......... I used a circle cutter (or "fly cutter"), but almost killed myself with it.
Everyone who laughed at my post.......SEE, it's not just me!

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
After spending months a while back asking the same question, I ended up buying one of these:

It is rated to cut through 3/4" plywood, so I have not had any issues whatsoever with the much lighter weight plywoods I need for rocketry. I have not tried fiberglass yet, but it doesn't seem like it should be an issue. This is much safer than the single blade flycutters, mainly due to the integrated plastic shield. Works great in my drill press and cuts to any size I need.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Okay, they say ignorance is bliss, and I am L-0, but I have wondered for a while about this.

I use foam board for centering rings for low power and some mid power birds. I understand it may not be strong enough for high power. But it seems like it would be easier to cut longitudinal rectangular “spokes” out of wood that would easily center the motor mount. (Think attaching a ring fin to the outside of a body tube, except in this case the mount is the inside tube and the actual body tube is the “ring.”)

The downside is that these would not “seal” the forward end, so if you use motor eject or that’s where your ejection charge is, you need “something” to seal the compartment and prevent that ejection charge from blowing back between the spokes. Seems like foam board or a cut piece of plastic would work (remember, it has the spokes behind it, so it doesn’t need to be THAT strong. A thinner and easier to cut piece of plywood would also work.

As a bonus, if you do TTW fins and the spokes are in the right place , say just lateral to the slots, you can glue the fin tabs to the spokes for extra strength.

Like I said, ignorance is bliss. There is probably a reason it won’t work or somebody would have already done it.

On the good side, a long spoke gives you more options to drill your buttons into.