Author Topic: Anyone a Mountain Bike Expert?  (Read 12853 times)

Offline Arbalist

  • Hero Member
  • *****
  • Posts: 673
  • Country: gb
Re: Anyone a Mountain Bike Expert?
« Reply #25 on: November 12, 2015, 05:29:33 AM »
If only the axle is bent you could just replace it and get some new ball bearings. I would have thought though that the hub itself and the wheel (rim) is likely damaged as well as it takes a fair bit of force to bend an axle.

Offline sparky961

  • Hero Member
  • *****
  • Posts: 844
  • Country: ca
Re: Anyone a Mountain Bike Expert?
« Reply #26 on: November 12, 2015, 09:06:38 PM »
Can you not pull the axle out and straighten it in a press on Vee blocks? It's only short - even a bench vice might do it if no press to hand.

From my dim and distant recollection of bicycles I seem to remember that the axles are only a bar with bearing cones screwed on at each end with possibly flats. If straightening doesn't work, make a new one.

From the pictures I've been seeing in my own research, it would seem you're right.  There's not too much to the axle.  I'm not keen on the idea of straightening it though.  I'd be concerned about it riding correctly on the ball bearings when I was done, not to mention the stresses and bending fatigue that's present.  Perhaps I put too much faith in the original engineering and manufacture - especially since the original clearly didn't hold up.

If only the axle is bent you could just replace it and get some new ball bearings. I would have thought though that the hub itself and the wheel (rim) is likely damaged as well as it takes a fair bit of force to bend an axle.

As far as I can tell everything except the axle runs true and appears damage free.  I'm surprised too.

Now that I'm done completely disassembling the bottom bracket (post to follow) I'll work on the disassembly, cleaning and inspection of the wheel hubs.  I'll need to make two thin wrenches, 13mm and 15mm.  Bike tool salespeople would know these as "cone wrenches".  Shouldn't be too difficult.... might just use the drill and bandsaw.

Offline sparky961

  • Hero Member
  • *****
  • Posts: 844
  • Country: ca
Re: Anyone a Mountain Bike Expert?
« Reply #27 on: November 12, 2015, 10:44:52 PM »
I spent two evenings working on this next part.  The goal was to remove the bottom bracket nut from the chain side of the bike.  Since I was unsuccessful using conventional tools, I decided to make a wrench that would fit snugly onto the nut and allow turning with a 1/2" drive breaker bar.

When I'm making anything in my home shop, I like to have a drawing similar to this.  There are definitely WAY too many dimensions on there.  But its better to have more than I need rather than waste time making multiple trips back to my computer, which is at the opposite end of the house on another floor.  You can see I've also added dimensions showing the 1/4" end mill I plan to use and the exact movements I'll be making.  This removes any guesswork or figuring while at the machine and lets me just use the numbers.



It's nice to use up material you never thought you'd use but have been keeping in "just in case".  The four holes in this piece were existing and won't get in the way.  The first step was to give a light spray with flat black BBQ paint in lieu of layout dye.  A quick blowdry and we're good to start laying it out. 



The setup for machining is as follows:
- Rotary table mounted on 3x 1-2-3 blocks to raise it to where the quill of my machine can reach it (no knee or column adjustment)
- Sacrificial aluminum plate underneath part to be machined
- Clamps with t-nuts
- Spindle centered to rotary table and part's large hole

After aligning the centerline of the part with the machine, I noted the reading on the rotary table.  This can't be zero'ed so I did the math to figure out the angle at either end of the cut.  The angle written on the table is "zero".



I don't generally use layout lines to cut, rather as a double check to prevent me from doing something careless.  In this case I've moved the machine's table and the rotary table to where I think the end of the cut will be and just scratched the surface with the end mill.  It looks pretty darn close to me.



So I take the first cut using only the rotary table to feed.  I took it an about 3 passes with the last one using the sharper top end of the cutter to clean up the walls.



Well if that doesn't make you happy, I don't know what will :)

Would you believe I didn't plan this?  It's true.  Like the first slot, I plunged through for each end before cutting the slot.  The result made me smile.



It looks like there are a lot of burrs being raised along the edge of the cut but it's actually pretty nice for gummy P&O sheet steel.  The burrs can pretty much be brushed away by hand.  I continued cutting each arced slot then the line that joins them.  The last bit of the cut is always a bit iffy and you need to be careful with what happens to the slug that falls out!









With the large hole complete I rotated the part back to the initial "0" position and moved over to the small square hole.  I took several plunge cuts to get rid of the majority of the material before moving to a smaller end mill to get into the corners.



Unfortunately one of the table locks came loose during one of my plunge cuts and the table started move.  This caused a bit of cutting beyond the layout line but it won't affect the function of the tool.



Finally I went around the outside with a 1/8" carbide end mill running my machine flat out at a less than impressive 3000 RPM.  It did the trick and most importantly my 1/2" drive breaker bar is a perfect fit without too much slop.




My original plan was to saw cut and grind the outside shape.  There's really no point in wasting the time machining it.  With the inside done though, I was eager to try it out.  Again, a perfect fit.  The stock I hadn't removed yet got in the way a little but not so much that I couldn't remove the nut.





The tool has served it's purpose; probably once and for all since the new bottom bracket will use a different tool.  That didn't stop me from a quick trip over to the bandsaw to hack away some of the excess material.  I'll clean it up if I ever need to use if again.... that is, if I haven't thrown it out before then. ;)



Offline Arbalist

  • Hero Member
  • *****
  • Posts: 673
  • Country: gb
Re: Anyone a Mountain Bike Expert?
« Reply #28 on: November 13, 2015, 05:32:41 AM »
Nice work on the spanner Sparky!  :thumbup:

Offline sparky961

  • Hero Member
  • *****
  • Posts: 844
  • Country: ca
Re: Anyone a Mountain Bike Expert?
« Reply #29 on: November 13, 2015, 11:11:32 PM »
Well, I hacked a double-ended cone wrench out of of some sheet steel I had sitting around.  It was pretty brutal by my standards but what matters is that it worked.

I got both axles taken apart and all parts in the front actually look pretty good.  I'm going to try cleaning everything really well, re-packing with grease, and see how it feels on reassembly.

The back, as I had noted previously, is pretty seriously bent.  Though I could probably straighten it I do worry about a loss of strength from doing that, not to mention it may already be compromised.  These things are a surprisingly small diameter to begin with!  The cones and balls were in much worse shape than the front.  The cups, however, look like they want to be given another chance.  Re-using them may not result in silky-smooth running like I had hoped but if I were to get a 10x improvement I can live with that.  If that doesn't work then I'm into replacing the hubs or entire wheel assembly.  As much fun as the project sounds I'm not ready to go there quite yet.

I've ordered the bottom bracket and a complete set with the axle, cones, and caged balls for the back.  I'll probably have stuff to play with in a week or two.

When browsing around for parts I had a look at the splined bottom bracket tools and the freewheel lockring tools on eBay.  Coming from China these were running about $2 a piece.  I have to say, at that price it makes it very difficult to come up with any justification for making your own tools.  Of course with their "quality control" there's nothing to guarantee that the thing won't snap off when you apply a finger's worth of torque.  I have to this point remained vigilant in my resistance to temptation. 

I'd like to have a go at making the splined tools if for no other reason than to try out the new ER32 collet chuck I made for the rotary table. ;)

Offline sparky961

  • Hero Member
  • *****
  • Posts: 844
  • Country: ca
Re: Anyone a Mountain Bike Expert?
« Reply #30 on: November 19, 2015, 06:27:41 PM »
The new bottom bracket arrived in the mail today.  Like many others (as I found from Googling it), I was surprised to discover that one of the nuts/cups is plastic!  When I got to reading about it though it seems it installed to the proper torque it should perform just fine.  When you think about how it works, it isn't actually retaining the bottom bracket; that's what the attached metal thread is doing.  It acts as a shim of sorts to prevent any movement in the side opposite the drive - if that makes any sense.

I had considered making up a new metal nut/cup when I first saw it but after reading what others have to say about it I think that's a waste of effort.  Arguably so is my upcoming attempt at making a tool, but we've already discussed that one. :)



I also have to say that the bearing doesn't seem as smooth as I'd have expected.  Maybe this is what I get for purchasing an inexpensive product.  I'm hoping it will smooth out after some break in.

Offline Sid_Vicious

  • Full Member
  • ***
  • Posts: 103
  • Country: no
Re: Anyone a Mountain Bike Expert?
« Reply #31 on: November 19, 2015, 06:34:02 PM »
Most of these are possible to separate and change the bearings in them, but most of the time it's cheaper to just buy a new one.
Nothing is impossible, it just take more time to figure out.