making rings

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Well-Known Member
Apr 7, 2004
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Hello. Here's a question I have been pondering for a while now. Say you have a 29mm motor tube and you would like a ring to fit inside, would a 29mm OD ring fit snugly or loosly?

Now say I want a 29mm motor tube inside a body tube 'X' diameter. Would the hole around the motor tube be 2*(wall thickness of motor tube)+29mm?

A 29mm motor tube may not (probably not) have *any* dimention that actually measures "29mm". When someone refers to a 29mm tube, they are refering to the size motor that it will take. It's a rocketeers shorthand, as I doubt if even the motor itself has any measurement that is *actually* 29mm. Kinda like saying "pi" is "3". It's sorta close, but I wouldn't start cutting lumber... :D

I couldn't say whether a 29mm OD ring would fit loose, snug or fit at all... Also, to make a ring to fit the outside of a 29mm motor tube it would have to be 2*(wall thickness of motor tube)+(inside diameter of motor tube)

What it boils down to is you need to know the dimensions of the motor tube. Knowing it is a "29mm motor tube" only tells you what motors you should be able to fit inside, but not really anything else. Different manufacturers will have different ID and OD on their tubes...

Sorry I couldn't be more help...


I think there are quite a few differents O.D. sizes for 29mm tubes!

The Apogee 29mm tube is 1.14" O.D.

The Totally Tubular 29mm motor tube is thicker and 1.21" O.D.

Quite a difference!

I have used a dial caliper to make measurements, and an engineering scale to set a compass with.
Kind of crude in the age of computers, but I can make what I need.
The Apogee tube is actually 1.176 OD. Because it is a thin wall
tube, old style F20s will fit without removing the label, unlike
some other motor tubes. I had some centering rings made up for
BT-60 and FT-70 contest rockets--the Apogee tubing was the
lightest I could find. ;)