Cutting Centering Rings

How can one cut Centering Rings out of plywood accuratly without fancy tools?

What sizes? I found a 29mm holesaw.

Define 'fancy tools'..

What do you have in the way of tools? Do you have a drill press? If so, a fly-bar cutter is probably your best bet.. A little investment for years of centering rings!

Sorry I knee jerked reacted and posted when I should have searched. Lots of info found. Thanks anyway for your help. I've got making plywood fins down but the CR's are not worth it unless you already have the right tools. Cheaper for me to bite the bullet and buy them on line.
Thanks

If you would, please post what you decide on, thematetial, process and results. I'm interested in this topic.

Thanks.

Not already owning the required tools and not willing to purchase them just for a few jobs, I will just purchase the parts I need on line. I enjoy making my own fins but I have a small table saw.

I searched centering rings and got lots of good info

I have made pretty good centering rings with just hole saws and a drill press. If you cant get the exact size just use the next size up and sand it down. You can mount the CR in the drill press (use a hole saw as a mandrel) and make quick work of sanding it to size.

I can tell you things can get VERY interesting using a fly cutter in the drill press... Make sure you have the piece held down to something solid that won't move, and cut the smallest hole first. If your drill press has the ability, the slowest speed is advisable.

Wouldn't you want to do the largest first, the outer ring? And then use the same center hole to make the inner cut? Or am I thinking of a different process?

Or just get a double cutter.

dhbarr said:

Or just get a double cutter.

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Ooh, that's a good idea. I didn't know they made one. I just used something my dad had...

scadaman29325 said:

Wouldn't you want to do the largest first, the outer ring? And then use the same center hole to make the inner cut? Or am I thinking of a different process?

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Well, in my case I was cutting them out of a larger square which I screwed down to an other piece underneath. I tried the larger hole first and things were more difficult to hold.

scadaman29325 said:

Wouldn't you want to do the largest first, the outer ring? And then use the same center hole to make the inner cut? Or am I thinking of a different process?

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Much easier to cut the inner hole first. (Using a drill press). You would hold the material to the press bed, cut the inner hole, and while the material is still held in the same place, alter the cutter and do the outer hole. Guaranteed concentricity.

dhbarr said:

Or just get a double cutter.

Click to expand...

Ha! Never thought of it that way. Set the double cutter to cut both inner and outer size at the same time. Would have to be careful when going through that the finished ring didn't fling off.
Cheers

Okay, I am not a high power guy, but I like to think outside the box.

What’s the deal with requiring rings to center the motor mount? How about three or four flat linear plywood strips, thickness exactly the space between outer edge of motor mount and inner edge of body tube, cut to the length of the body tube, maybe a bit shorter to leave room for a foam board bulkhead. Glue And fillet them to the motor mount tube, slide the mount into the body tube. They could double as attachment points for through the wall fins.

For motor ejection deployment, it WILL need a forward bulkhead to keep the ejection force from blowing back between the centering strips. These can easily be cut from foam board, may need some reinforcement with something like JB Weld.

BABAR said:

What’s the deal with requiring rings to center the motor mount? How about three or four flat linear plywood strips, thickness exactly the space between outer edge of motor mount and inner edge of body tube, cut to the length of the body tube, maybe a bit shorter to leave room for a foam board bulkhead. Glue And fillet them to the motor mount tube, slide the mount into the body tube. They could double as attachment points for through the wall fins.

Click to expand...

Should be possible to do it with just six popsicle sticks, skewers, coffee stirrers, etc.

BABAR said:

How about three or four flat linear plywood strips, thickness exactly the space between outer edge of motor mount and inner edge of body tube, cut to the length of the body tube, maybe a bit shorter to leave room for a foam board bulkhead.

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Not too unlike some plastic fin cans I've seen.

Router table and a pattern following bit. Use another centering ring as a template.

Thorfire said:

Router table and a pattern following bit. Use another centering ring as a template.

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This is exactly what I do and I make templates out of MDF and label them for future use.

I use a cheap Ryobi router, 1/4"bit and a Jasper cutting jig. Double-side tape plywood down to a base sheet of plywood. Perfect cuts, everytime.

John Taylor said:

How can one cut Centering Rings out of plywood accuratly without fancy tools?

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Tabbed rings for an upscaled Gyroc. Jeweler's saw and printed patterns adhered to plywood with glue stick. Sandpaper adhered to the concave side of a scrap of body tube to clean up the outer circumference of the rings, and wrapped around a dowel to clean up the inner circumference. I used a stepped drill bit in a hand drill (with a jig to keep it perpendicular to the stock) to remove most of the material from the holes for the 2X24mm rings, then a half-round file to get them to size.

You can make a drill press fixture by putting tape on a flat board as well as the wood you're cutting and superglue that together. Plenty flat, holds well and just peels off when done.

I'd go with an adjustable boring head with some sharp inserts for light ply, a fly cutter isn't ideal for boring holes. That said, be careful side loading a drill press. Using the boring head shouldn't give you too many issues, but the tapers on a drill press don't have any form of retention outside of the taper itself. Using a drill chuck to hold a boring head or fly cutter isn't a great idea, either.

I haven't tried these but I'd like to:
https://olfa.com/professional/product/heavy-duty-circle-cutter-cmp-2/

https://olfa.com/craft/product/rotary-circle-cutter-cmp-3/

I plan to make a fixture similar to that paper circle cutter but have my jigsaw on the end, slow and steady should work, then final sand.

I found a few links: jigsaw fixture and a adjustable hole saw.

Hole saw or a lathe works well also.

~John

GalantVR41062 said:

... that paper circle cutter ...

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Paper yes, but according to link, also: "[...] carpet patching, installation of recessed lighting, cardboard, mat board, thin plywood, drywall, paper, acetates, rubber gaskets and more." So the unknowns are the kinds and thicknesses of wood it can handle (with a reasonable number of passes).

It may still be a "fancy" tool, but other than a compass, a cardboard template, and an X-Acto, it's the cheapest one I know of!

I do arc-scribing as in this article, with homemade tools costing about 25 cents or less:

https://georgesrockets.com/GRP/Articles/CentRings/Rings.htm



Beyond 1/16" it is not much fun. If I need thicker, I make multiple and sandwich them. There are some models with 1/8" ply rings that would be fine with 1/32, but the vendors don't make thinner rings. Overkill a lot of the time.

Funkworks said:

Paper yes, but according to link, also: "[...] carpet patching, installation of recessed lighting, cardboard, mat board, thin plywood, drywall, paper, acetates, rubber gaskets and more." So the unknowns are the kinds and thicknesses of wood it can handle (with a reasonable number of passes).

It may still be a "fancy" tool, but other than a compass, a cardboard template, and an X-Acto, it's the cheapest one I know of!

Click to expand...

I have the smaller Olfa circle cutter -- or one a lot like it. Used it, most recently, on this

It raises the question of why the OP wants to make the rings out of plywood and whether fiberboard or chipboard would work for their application? Plenty of mid power rocket designs use paper CRs, and for a rocket through wall fins, that's really all that you'd need.

If the OP has a Dremel, there is also this.

https://www.dremel.com/en_US/products/-/show-product/tools/678-01-circle-cutter-straight-edge-guide

I think I have something like it -- an unbranded circle-jig that was in the box with my yard-sale Clark rotary tool. I used it once, to cut a circular patch from a scrap of gypsum board. I haven't seen it in a while, and I kind of think I might have given it away. It would certainly have worked for cutting mid-power/high power rings (maybe down to 24mm MMT), but I'd still reach first for a coping saw and sandpaper.

jlabrasca said:

It raises the question of why the OP wants to make the rings out of plywood and whether fiberboard or chipboard would work for their application? Plenty of mid power rocket designs use paper CRs, and for a rocket through wall fins, that's really all that you'd need.

Click to expand...

I used basswood plywood to make a custom 5-motor cluster mount for the 1969 Saturn V, mostly because it was conveniently available at the local Michaels store I like to browse. Used compass, template and X-Acto for exterior and a hole saw on a drill press for interior. I just don't do enough motor mounts to justify buying even an Olfa circle cutter.

Never thought paper centering rings would be reliable on a mid-power. Since everyone uses epoxy instead of wood glue, I would've thought motor mounts also needed to be as rigid as possible without excess weight.

I'd like to have a Dremel, but I always end up buying a new rocket instead.

Funkworks said:

Never thought paper centering rings would be reliable on a mid-power. Since everyone uses epoxy instead of wood glue, I would've thought motor mounts also needed to be as rigid as possible without excess weight.

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https://www.apogeerockets.com/education/newsletter63.asp
https://www.apogeerockets.com/education/downloads/Newsletter126.pdf <-- May be of interest the OP too.

Funkworks said:

I used basswood plywood to make a custom 5-motor cluster mount for the 1969 Saturn V, mostly because it was conveniently available at the local Michaels store I like to browse. Used compass, template and X-Acto for exterior and a hole saw on a drill press for interior. I just don't do enough motor mounts to justify buying even an Olfa circle cutter.

Click to expand...

Went down to the shop to look. That is the circle cutter I have. I got it, and a pair of rotary cutters from a friend who thought she'd be way more into scrap-booking before she realized how rarely it involves car chases or shooting zombies.



I have to say, the rotary cutters are/have been really handy. Especially when my kid was too young to be trusted with an Xacto. They are just the thing for long cuts in all kinds of sheet stock and textiles.

The circle cutter gets less use. The coolest thing I've so far done with it; discs of sandpaper adhered to a circular saw blade with spray adhesive. Makes glass-smooth cuts for gluing up panels (goes through sandpaper and Super 77 pretty fast, though).

Funkworks said:

I'd like to have a Dremel, but I always end up buying a new rocket instead.

Click to expand...

In my experience, rotary tools are always almost the right tool for the job. I've ruined more things than I've made or repaired. A file or a saw will do a better job for most of the stuff where a Dremel might look like a solution.

I use my Dremel with the 678-01 Circle Cutter and Straight Edge Guide...