Ball bearing issues? How-to build a "sandwich" structure ball bearing bogie

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When starting to implement ball bearing into lego trains, I thought it would be a simple and straight-forward process. However, I soon came across various issues, so after some further work I now have an updated approach as can be studied in pictures and text below.


The content in this text is based on personal experiences and observations. Depending on the exact bill of materials, available tools and engineering skills, you may come to other conclusions. Still I hope some of my observations can be of help/guidance for you.

Ball bearings – Why?
-A fun technical challenge from an engineering point-of-view.
-Benefit of lower rolling resistance (good for ever wider and heavier rolling stock).
-Diversified bogie design and detailing,
-TLG metal axle based train wheel sets are no longer in production.

Technical challenges:
-To incorporate precision manufactured BB:s and axles, with less precise lego bricks (tolerance-wise).
-To find out an assembly method which can be repeated, with an even and satisfactory end result.

How to:
Let me run you through my prefered process, step-by-step, including some pictures (see above).
-Start by building a bogie frame. For tolerance and alignment reasons, I use two technic liftarm thick, which are sandwiched between elements 30414, 11211 and/or 87087 depending on bogie version. Also sandwich these bricks between 2-n plates to get a solid unit. No bricks on axle positions. Note that I only use bricks with hollow studs inserted into liftarms (for mechnical stress reasons).
-Firmly hold the drill with a pair of pliers (polygrip) and manually crank (rotate) the bogie around it, so you slowly let the drill go through both liftarms in the same operation. By doing this manually you remove a minimum of material, leaving a slim-fit for the BB. Drilling through both ensures a good alignment.
-Insert metal axle through both BB:s.My ”China-axles” are ever so slightly deformed in each end from the cutting process, so I use a hammer and gently tap the axle end to get it through.Note that other manufacturers (Bricktracks?) seem to have smoother axle ends allowing insertion into BB:s without any tools,
-Check that BB:s can slide sideways very easily on the steel axle. If needed, gently polish the axle surface with steel wool. It does not matter if the very end of steel axle is not perfect since that is inserted into the plastic train wheel.
-Remove 2-n support plates, and assemble correct plates on top of 30414/11211/87087.
-BB:s and axles shall be possible to be introduced into liftarms by hand. A small screwdriver may be of help to push each BB into the middle of each liftarm. Control again that axles slides freely sideways. (if not, try to polish further with metal wool).
-Put on plastic train wheels. Bricktracks wheels sit firmly on the steel axle without any need for glueing.
-Finish all detailing acc to your preferences.
-If successful, bogie should roll with a minimum of friction.

Notes to the above:
-I use technic liftarms, but I dare assume long technic bricks also would be fine. Just remember the later will give a ½ stud offset. It is better to use one long element, than individual bricks for each BB, because of tolerances and risk for misalignment.
-Be careful not to scratch or damage the axle surface. My conclusion is that a freely sliding axle is the best indicator of a good final result.
-Since my holes are enlarged to 5,0mm, I do not use M2-washers (which are 5,0mm O,D) since I've seen washers sliding into the brick causing friction.
-I have tried numerous ways of introducing BB:s into bricks without drilling. But regardless of assembly method, I have experienced problems with misalignment and occasionly stress cracks in bricks. It worked sometimes, but I never managed to get a safe and repeatable process. Hence my recommendation for drilling first....

Summary of key findings:
-Use few and long elements, sandwiched to a solid assembly.
-Drill a common through-hole.
-Ensure axle slides freely in BB:s.

Bill of Materials used:
-China produced BB:s type MR52ZZ.
-China produced cut steel axles, 2,0 x 40mm.
-Technic liftarms thick, #32524 or 40490.
-Bricktracks plastic train wheels.

Tools used:
-Hammer (depending on axle end …).
-Pair of pliers (polygrip).
-Drill 5,0mm, aimed for cutting metal.
-Steel wool. (polishing of axles, if needed)

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I’ve pressed maybe 25 BBs into a 1x2 bricks with a single technic hole and haven’t noticed any stressed cracks (but I will double check now).

I have 4 that don’t roll so well. I can see that some of the plastic material has ‘scrapped’ away from the wall of the technic hole which could be causing friction.   

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I gave this another try, and I agree with most of your findings.

I previously put some BBs in technic bricks (1x2 with 2 holes) and most of the times I found that it was really hard to line up the BBs, since the bricks could move quite a bit. Putting plates on the bottom side helps, but that results in problems on switches, so no option. I had reinforced them with liftarms actually, but never actually put the BBs in the beams itself.
I tried different methods to get the BBs in: drilling, heating the bricks then push in and simply pushing in without heating and using a hammer..

Now using your notes, things I observed:

- Drilling by hand is not fun :). I ended up using a machine anyway and simply drilling from both sides instead of all the way through. No noticable difference in terms of force required to insert the BBs (can be done by hand). A good quality drill is required (it needs to be 5,0mm)
- Simply putting the BBs in does not crack the liftarms. Except when I tried to remove the axle and wheels that were on the end of the liftarms. It required some force to get the wheel off, and that made both the liftarms crack :|. So even though it all fits nicely, I assume the liftarms are more prone to cracking, use a bit of care.
- The long (in this case) liftarms do make for a very easy way to make a near-solid structure, so once you line up the BBs correctly, it will stay that way.

I'm thinking of trying some longer technic bricks instead, to avoid any possibility for cracks (if there's a crack, the BBs can move more easily and mess up alignment with the BB on the other side)

Some other notes regarding BBs:

- I have the MR52ZZ, but I plan to order some BBs without shielding. The bearings I have don't seem very well lubricated, and the thinnest lubricant I could find, well, i'm totally not sure it actually got into the BBs. I'm not sure how much dust will affect them, but i'm not impressed with the quality of the current bearings I have at all.
- I used bricktracks axles and wheels. No hammer necessary. 
- Ball bearings are only significantly better running than lego wheel assemblies if you put weight on the wheels. Best reason to use them vs lego wheels is if you run long trains or heavy (8-wide?) trains. I do find it makes a big difference on my 7-wide rolling stock (see picture below). If you only want to make your wheels prettier, you should really consider if it's worth the hassle.
- Instead of the 1x4 bricks with studs on the side, I used some 1x2 technic bricks with 2 holes and technic pins, leaving the innermost open. this allows to put technic half pins in the liftarm on the outside to attach some detailing. I found that it did not compromise the strength of the complete structure:


- To aid in inserting the BBs, I put a nail in a piece of wood, and cut the top off. I put the BB on the pin, then insert the BB in the liftarm by pushing the liftarm down on top of the BB:



So, I simply copied your design more or less and tested the complete assembly on one of my rolling stock and it seems to work great:



Thanks for the write-up! It inspired me to try once more after my previous, more or less failed, attempts to convert my stock to BBs based wheels.



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Thanks for sharing your experiences. 

One immediate comment: I concider technic liftarms less prone to cracks, since they have a (thick) consistent wall thickness all way through the hole. If you compare with technic bricks where the middle section around the hole has quite thin wall, and here is where most cracks occur that I have seen. (look at the technic brick from underneath).

Concequently I was surprised that you had some cracks in your technic liftarms.

None the less, I am really happy if some of my findings helped you.


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Regarding the cracking: I don't have any liftarms with cracks after inserting the BBs and axles. The only 2 that cracked happened when I wanted to remove the axle again, and pulling the (excellent BrickTracks) wheels off requires quite a bit of force. That's when the cracks appeared.
Also, the cracks are in the exact same spot, at the very tip of the liftarm, right where the plastic is thinnest, I tried to take a photo of the liftarms with the cracks, but that proved to be difficult. Here's a quick picture that shows where the cracks are:


I'd say that during normal circumstances, cracks won't happen and are not an issue.

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Hi, I really like this and similar solutions and used it with great results, but I have a follow-up question: Has anyone found a smart way to fit the metal axle to a train wheel with axle hole? (Bricklink part number 55423c01)

Edited by HenrikLego

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I believe Andy from OKBrickworks posted a 1x2 brick to shapeways that will hold a larger bearing that fits technic axles, but I can't find it. They are pricey though. Assuming my recollection is correct that Andy made them, I bet if you contacted him directly that he could produce them himself for less than shapeways.


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On 9/20/2021 at 7:01 AM, HenrikLego said:

Hi, I really like this and similar solutions and used it with great results, but I have a follow-up question: Has anyone found a smart way to fit the metal axle to a train wheel with axle hole? (Bricklink part number 55423c01)

There are 8mm outer diameter bearings that will fit the technic plastic axle.  You'll have to enlarge the technic brick hole to 8mm to press in the bearing.  Alternatively, 3d print bricks with the larger sized holes.

If you want metal axles, you could cut and drill hole in technic axles to press in metal axles.  Then insert the cut axle into the train wheel.  Or 3d print an adapter to connect metal axle to wheel with technic axle hole.  :classic:


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