Bimota Forum

[steff_dk]

The machine shop finally finished the work and I picked up my wheel today.

I suppose my briefing and Fusion 360 drawing was not enough to make sense of because despite my best efforts to say that the hub should be 72mm wide and symmetrical (in both words and images) they managed to somehow fail in both regards

Not only did the width come out to 72,45 mm but somehow they also managed to take a good chunk more off one side than the other - even visible to the naked eye.



Here is a view of both sides next to each other ....



And an inside view where the asymmetry is even more clear.



Okay, it is not the end of the world but I am quite suprised because this is a place that run CNC machines etc. but I had never used them before -and obviously will not be back.

I will take this as the universe telling me to be absolutely accurate in my future work orders (should there be any) and also an implicit permission to go ahead and start building that milling fixture that would allow me to mill hubs myself

And there are even more good news!

I got a new toothbrush today as the old one was enlisted to clean calipers
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[steff_dk]

In my post-mortem of today's events I am coming to the conclusion that the machine shop must have measured from the surfaces where the brake discs were originally mounted and simply planed off a certain distance from there.

The original wheel hub was asymmetric due to what I assume is the ABS sensor plate.

But not to despair. I have one good side from where I can start taking measurements.

I printed a little template to see how it would fit.



I looks like 2mm more will have to come off one side of the wheel hub if I bring it down to where it will be symmetric and the steering pivot will be on centerline with the rim and tire.

My plan is to make two inserts that are clamped together from each side with six bolts. I whipped up a first draft to get an idea.



In order to ensure the surfaces are mated together properly inside the wheel I plan to use JB Weld between the two inserts and the wheel itself.

I recon that the forces operating on the hub are not pushing directly outwards on the bolts and there should be ample surface between the JB Weld and the wheel to hold everything in place.
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[steff_dk]

In my previous post I was trying to get my rather compact inner hub placed inside the wheel. The inner hub was originally intended to go inside something like the Aprilia Shiver wheel.



In the end I found the Yamaha F6Z wheel that had about 50mm more space inside and I was unhappy having to fill out all that space and at the same time being somewhat constricted in the steering pivot to about ±20 degrees.
So instead of continuing down a path I was not 100 percent happy with I have put that initial hub aside and made a new one that is designed to fit the Yamaha wheel perfectly.

I took a different approach since I started out with just looking at where the bearings would sit and then basically designed a shell around it.



I can reuse the 22mm x 20mm axle I already have as well as the inner bearings and at the same time give much more steering freedom and leverage to the caliper mounts.







Side by side ...



I have also been hoarding parts for my milling fixture for the wheel itself (yes - still not done) but let's save that for another post.
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[hindsight]

Thanks for keeping us updated. Keep going!

[hindsight]

Thanks for keeping us updated. Keep going!

[steff_dk]

After receiving the front wheel back from the machine shop in January I was quite surprised at how they had managed to botch the job.

Part of me wanted to get the tools myself and another part said to just pay another shop an get on with it ...

I already had a hobby lathe but I needed a milling machine to modify the wheel myself.

I had this idea in my head that came from owning a fishing reel 20 years ago where the spool was riding on three ball bearings with a conical plastic roller mounted in three points.

I wanted to do kinda the same thing but keep the wheel pinched on the outside lip and rotate it by hand under a milling machine.



So I set out to create the rollers on my hobby lathe. I had some POM (think pallet lift wheels) which is very hard and stable but at the same time very easy to cut.





Next I bought a 40 x 40 cm aluminium plate with M8 threaded holes every 2 cm. I was able to mill some slots in some steel plates and my wheel fixture was ready.







The next step was getting hold of a milling machine. It took a while, but in the end, a used small milling machine with digital read-out was found and acquired.

I was able to get it to my shed, but let me tell you ... even if you can deadlift 100kg on a barbell, it is an entirely different game lifting a 100kg milling machine - so a workshop lift had to be acquired as well.

Finally ready to go, the whole thing went down yesterday evening, and it turned out great!



I had to change to a 4mm end-mill to be able to shave off some of the inside because I was running out of distance from the edge of the wheel to the milling machine column.



It may look like a rubbish finish but it is just some fine chips you see on the last photo. It came out fine.
The wheel is now milled exactly symmetric on the sides and the inside has been milled a little as well to be able to center the inserts that will seat the bearings.

It is still a wonder to me how these cast wheels are pretty far from perfectly balanced as evidenced by the various amounts that needed shaving off on the inside.
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[steff_dk]

Just a quick update.
I have been wondering how to get the outer hub (the parts that seats the bearings and mounts the brake discs) made in such a way that has it has maximum strength to connect to the wheel and uses the least amount of material.
I decided to add a 3 mm "lip" to the edge of the wheel and a groove (blue colour) in the drawing so the wheel was gripped from inside and outside. Also I wanted something better to withstand the twisting forces when braking.





I was initially thinking of using JB Weld to seat it - but apparantly it is not the best solution with all the vibrations that occur but there are some other bonding solutions e.g. "3M Scotch-Weld Epoxy Adhesive DP125" and maybe also Loctite have some products that can do a good job.
I will study that some more before deciding. I also plan to machine grooves on the inside of the wheel and outside of the CNC parts to allow the bonding to get a solid grip.

I will clamp it together using five threaded rods where the brake disc bolts screw into the rods from each side and keep it all together.



The 3d step files have been sent to the CNC shop so parts should arrive in a week or two.


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[steff_dk]

Okay first the good news!

The outer hub parts arrived today and snapped into position with a satisfying *clack*

The lip from the wheel goes into the grooves on the CNC parts and it looks pretty decent if I do say so myself.











In my inner dialogue I am kinda falling in love with JB Weld for bonding the outer hub to the wheel again.

Here is a video about the miracle that is JB Weld -> https://www.youtube.com/watch?v=LGCJGNkEpy8

Also, I was very pleased to see that the width of the inner hub lines up very well so that the bearings will seat well between the inner and outer hub parts.





I have such an urge to press the bearing into place but I better wait for everything to be ready ...






Now the bad news ...



The is not enough space between the spokes and the brake discs ...



When the caliper is resting on a spoke you can see the problem.



The disc seems to be about 20 mm too close if I want 10 mm clearance between the spokes and the calipers.

To fix the issue I would need to have another ring made that raises the discs - which is what I will have to do...
F* me if I know how this happened.

Anyway, I suppose the clouds do have a silver lining as it will allow me to use bigger bolts to clamp the outer hub parts together in those threaded rods from the previous posts and that the brake disc bolts will only serve the one function that is to hold the brake discs.

There was also something slightly off with the brake disc bolt pattern that I get to correct now with the rings that raise the discs from the inner hub.

All in all I am quite happy with the progress and undeterred by my little setbacks
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[steff_dk]

It was new machine day (and home office) today!



I had finally gotten enough of my little crappy 3d printer and had decided to get a better one while taking advantage of the Black Friday deals.

So today this bad boy arrived.



It can even record and stream video of the process so thats pretty cool too. Best of all is the print speed.



I already had an idea of how to get the correct spacing between the discs, and with the new printer I can start prototyping again before sending the order to the machine shop.

Like I mentioned earlier it actually was quite the happy accident as it allows me to bolt the whole thing together with some beefy bolt sizes now that the brake disc bolts doesn't do anything else than hold the disc in place.

It gets me about 10mm of clearance between the spoke and the caliper so we should be "good to go".









Cleaned up the drawing and added some chamfers and tapers so this is what is going out to the CNC shop:


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[steff_dk]

Having an all new and capable 3d printer and just waiting for the CNC shop to finish the next couple parts I decided to print the parts and do a test fit.

Since the parts are just plastic I could sand down where the bearing press in which means the whole thing could be pressed together with my bare hands and should come apart again without much drama.
The width of the whole thing is about 5mm narrower than the original Yamaha wheel hub which is why the calipers will clear the spokes now ...

It will also allow me to start drafting the caliper mounts and get an idea of what I am working with.
The depth the caliper mounts have to clear is about 28 mm.

I don't really have an idea if that is okay or it will look weird but there is only one way to find out.
















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[atomibart]

I'm still amazed by your work Steff !

[steff_dk]

[steff_dk]

Received the disc spacers today.
They look great! Happy about the chamfers I managed to get added last minute before machine shop swung into action.
Bolt pattern for the discs was spot on. Had to cut threads in one of them tonight just to see how the bolts went in

I have a little (~ 0.10 mm) discrepancy in the with of the hub compared to the width of the wheel (see last two photos) but I haven't tightened everything down yet so I will see what that looks like after final assembly of the wheel. The most critical part now is to get the wheel assembled and everything lined up parallel in the wheel itself between the bearing seats, the discs and the edge of the wheel.

Not too worried about hub/wheel width right now as there should be a possibility to address that if needed - after the wheel is 100%

Now I need to get back to finishing the drawing of the caliper mounts.




































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