Is there an alternative to ball bearings?

[Jaibe]

Hi,

A few years ago I designed this turbojet engine:

Paper turbojet - YouTube

As you can see, the main shaft doesn't rotate so well. It is made of two toothpicks linked together by a small section I cut off from a lollipop stick. You can better see the inner arrangement here (before assembly):

Papercraft turbojet compressor - YouTube

During assembly, I made the shaft pierce through the frontal section of the truncated cone (which forms the compressor) and through a small disk at the front, forming a set of inlet guide vanes (IGVs) as displayed below:

Guide vanes 1 - YouTube

In the previous video, to test the smoothness of the rotation, I gently blew on the compressor through the IGVs. The other end of the shaft is resting on the cutting board. I only placed the shaft through the holes of a pair of tweezers - like these: - to prevent it from moving from side to side.

Rotation seemed smooth indeed, but I couldn't replicate the same result in the final assembly. I do not intend to buy mini ball bearings so do you have any idea how I could improve the existing concept?

If necessary I can provide you with a rough schematic of the current design.


Edit:
Here is the schematic

Parts in green are the lollipop stick sections

The stripe pattern denotes that two adjacent pieces are glued together. For example, turbine 1 (T1) is glued to the shaft via a lollipop stick/toothpick fixation. Tf2 (the guide vanes located between T1 and T2) is stuck to the nacelle (N) and allows the shaft to freely rotate inside the green lollipop part. The shaft itself may move back and forth by epsilon = epsilon1 + epsilon2.

There are three areas of friction:

1- The Tf2 rotation axis
2- The annular contact between the main shaft and Tf1 (which may increase/decrease as the shaft moves back and forth)
3- contact between the lollipop parts of T1 & Tf2 or between Tf2 & T2.

To me, 2 and 3 are non-negligible. One of the videos above show that 1 may be neglected as the contact is rather small, but if I can improve upon/modify the design I will also minimize 2 & 3. I was thinking of having only single contact points at both ends but I don't know how to make them in a reliable and consistant manner.

[aansorge]

Makes me remember using beads as bearings for windup airplane propellers. Those had wire shafts.

[John Wagenseil]

Originally Posted by aansorge

Makes me remember using beads as bearings for windup airplane propellers. Those had wire shafts.

A hardened steel needle, or piece of piano wire rotating on a glass bead is probably the way to go. It is same principle as the jewel bearing found in high end antique watches.
Or if you have a machinist friend see if he can make a tiny bronze bushing for you. Or you could do it yourself if you have a hack saw or jewelers saw , a file , and a #60 drill bit.
A lot of US hardware stores stock Oilite bronze bearings. I assume that they are also available at a DIY (do-it-yourself) store near you.
Buy a largish Oilite bronze bearing, then cut out and drill a small piece of it, mount the piece on an arbor or glue chuck, and turn it or file it down to make a tiny bearing for your turbine's needle shaft.
Or buy a junk pocket watch and salvage the jewels and pivots for your turbine bearing, or see if a local watchmaker is willing to sell you a couple of watch jewels and pivots from his scrap box.
Hope this helps.
Or if you want to keep things crude and simple, try using a piano wire or sewing needle shaft that rotates in a hole drilled through a piece of thick paper that has been hardened by applying Cyanoacryllic glue.
You can keep the wooden shaft rather than replacing its entire length with a long upholstery needle or piece of piano wire, by drilling small hole at either end, and inserting a needle or piece of piano wire into the hole. Your bearing sleeve will have to be tapered, or capped by a piece of smooth metal or glass to keep the shaft from slipping too far along the direction of its axis.


PS. Your turbines are impressive pieces of paper engineering.

[murphyaa]

I know when Papermate does his rotating propellers, he uses a small piece of brass tubing as a bearing. He's got a tutorial on here somewhere that shows how he does it.

[Zakopious]

Could you put a trace of wax on the bearing surfaces ?

[T haf]

I have used a small bead from a necklace and a sewing pin needle. Those two together work super well and have the smallest amount of friction.

[Jim Nunn]

Mini ball bearings will not work, your best bet is to use a brass eyelet and make the shaft out of a hard wood. Bamboo skewers come to mind as a good choice. The shaft will need to be a little smaller than the bore of the the Brass eyelet and very smooth. Apply wax to the shaft that will run inside the eyelet. this will be a nearly frictionless bearing.

Jim Nunn