grrrrr CR cutting

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
Apr 24, 2004
Reaction score
i just got my new dremel tool today and im haveing a lot of trouble. it near impossible to cut a circular CR out of plywood. is there something other than a dremel i can use to make CR's our am i better off just buying them? straight cuts for fins are simple but CR's are lopsided and just really screwed up. help:mad:
Well, I know what you are feeling. I make all our rings myself. I use a Dremel too.:D Well, then I sand it down to a PERFECT ring. I just cut as close as I can to the circle I have drawn and then take it to the sander. Simple as that. To cut the inner hole out, just buy a bit from the hardware store. They sell 24mm bits.
Jojo - it takes some practice, so get some scrap ply or fiberboard and cut a dozen or so.

dremel or scroll saw works great for the outside edge, if you have a sander to touch it up. consider making a jig (a stick or board with a bolt in it) to hold the CR at just the right distance from the sander. then you can spin the CR around and the sander will even it up. but that doesn't help align or clean up the inside hole.

recently I bought a drill press just to use a "circle cutter" bit. this cuts the outside, and I use hole saws for MMT hole on the inside. the secret for the circle cutter is clamp the workpiece very well. then you can change the the circle cutter for the hole saw, and the inside hole will be concentric - exactly in the middle.

other fancier ways require making a jig and using a bandsaw or a router - might worthwhile if you are cutting more than 3 of the same CR!
I have the exact same setup as Cliff. Just have to clamp the piece securely.
is there anyway i can cut the innere hole without using a diffrent bit?
Hhmmmm. I think there is a device out there than allows a dremel to do circular cuts. It attaches to the dremel and you have a hole in the middle of the CR to act as the centre of the circle. I'm going to try to find one on google.
You can cut the inside hole with your circle cutter, too. You just have to turn the bit 90° and resize the cutter length.

I prefer to size the cutter using cheap plywood flooring before cutting the expensive A/C ply. "Cut cheap holes before the expensive ones." I also use double sided carpet tape on both the wood I'm cutting and the wood backer on the drill press table to hold the CR while cutting the inside hole.

Be careful with a circle cutter and run it at the slowest speed posible. They really hurt when they whack your thumb. Sharpen your bits often, too as they dull quickly and cut slowly unless sharp.

With practice you'll be able to get perfect rings quickly.
I borrowed Len B's drill press and made a set of CR's for my Level 2 rocket, a 3" Black Brant VI. I used a 1 3/4" Forstner bit to cut the inner circle, and a fly cutter to do the outside, IN THAT ORDER... that way I didn't have to move the clamp between cuts, to ensure that everything would stay near-perfectly centered. A Dremel's sanding drum widened the inner hole by ten-thousandths or so. The rings fit PERFECT on my MMT, and reasonably tight in the airframe. Life is good!
can't find the post right now, sorry ... but: a while ago someone on TRF posted that he put two circle cutters on the same mandrel, and that way cut both the inner and outer edges at the same time.

sounds like a great idea - could cut a bunch of same sized rings really quickly - but I do not see how to clamp the stock.
To cut both inside and outside of rings with a circle cutter with 2 bits on the same madrel.
First it is best to have bits on opposite sides of the tool.
Set the bit that is cutting the ID. a bit lower than the one cutting the OD. so that it cuts through first. Clamp your stock firmly around the outside.
Test cut scrap wood until you get the dimensions perfected.
I have used the dremel on alot of my smaller CR's(4" down to 38 mm) Once you get a ring that fits nice take it and save it as a template, that way all you need to do is turn the wing nut slide ite template up to the bit and off you go. Once yo uget the outside the way you want it then take the template for the inside hole and cut that. There is a lot of trial and error while trying to make templates it took me 2 12X24 sheets of 1/16 " ply and about 6 hrs to get them all correct, but now it takes no time to make them even out of ply up to 1/2 ". Hope this helped.
what bit do people use in the dremel?

I've tried the dremel in the past but had poor results
I don't recall what bit I used, but I had trouble getting a nice smooth cut,
or mabey I was pushing too hard, how many passes does it normally take?
I use a multi purpose bit #561 and the circle cutter #678. It only takes one pass to cut but you will need to sand a little ot get the burs off. Nothing major just a quick clean up with fine sand paper.