Narrow Hub

Making a Narrowed Front Hub

7/2010 - A project by Tom Porter

This article is how to make your own front hub. Itís been about 15 years since Iíve done this so I had to relearn almost everything I did last time. Here we go.

I used 1.75Ē (44mm) 7075 aluminum round stock. Got a foot of it from Mcmaster Carr. First thing is to get the O.D. perfectly round on the lathe because all metals have tolerance specs. and are always a few thousands of an inch off to accommodate this. Then the ends are squared off and in this job are bored to 5/8Ē and deep enough for the hub flange length of 19mm.
I than used layout dye on the ends and tried to scribe crosslines with a tool bit. Didnít quite work here but I wasnít going to take the time to make it perfect as I just need a rough approximation for the bore hole for the bearing.
 I ground my own tool bit to make the bore hole. First I bored for 5mm depth leaving about 2mm for finishing the OD of the bearing. This gets easier after doing this a few times.
 Hereís the finished bore hole with the bearing checked for fit and installed. The bearing is a 12mm x 21mm x 5mm ceramic hybrid. I got them at VXB for about 15 USD each. It seems best to make the bore hole first because if you get it wrong you can make another easier before proceeding to turn the outside of the hub flange, which takes longer than the bore hole.

 Here Iíve put layout dye on the outside and measured and marked my cut lines for the roughing out of the hub flange. This is a carbide tipped threading tool which takes making deeper roughing cuts easier.
 The first step is to use the depth end of a digital caliper for locating the shoulder for the radius. The hub flange width is 3.5 mm and the shoulder is 3mm x 3mm. The tool is cutting the rough out for the tube that will be pressed onto the hub flange. This cut is to 28mm. Notice the tool bit leaves angled sides, after the correct depth is reached the ends of the cut will be squared off with a left and right hand cutting tool bit. You could do this with a necking tool but this seems easier.
This is a necking tool used to square everything thing off to finish the cuts. This tool usually causes chattering if used for turning and the only cure is to take lighter cuts which takes forever.
 Here is a left hand carbide tipped turning tool to square off the shoulder cut. This shows why I used the pointed threading tool because this tool doesnít have the room for a narrow internal cut that the hub flange uses.
Pointed threading tool fits the narrow confines easier than any other tool bit I have.
This is the cutoff or parting tool. This how you remove your turned piece when itís done. The trick is to watch carefully for chip build up as you plunge deeper into the stock to prevent binding and jamming and causing all sorts of hell. I back the tool off and remove chips that would cause problems quite often as I go deeper.
There are couple tools you can use to round off the spoke hole flange, this is a U shaped bit the cuts both sides at one go. The other option is to use left and right handed external radius bits. This seems to work OK though.
This bit is shaped to cut an internal radius behind the spoke hole flange. I usually cut both ways to get a smooth radius.
Hereís a set of hub flanges completed and ready for the next step of drilling the spoke holes.
Not having a chunk of ĹĒ aluminum sheet of the necessary dimension for easy layout I made this degree wheel to mark out the spoke hole spacing. This ended up being more difficult than having a large enough piece to layout with the small protractor I have.
 I taped the degree wheel to the piece of stock I had on hand.
 I then used a center punch to locate my drilling holes. You only really need to drill three holes to do the whole thing. This is one of the things I had forgotten and rediscovered as I started drilling spoke holes. The holes you need are the center hole for a ľĒ bolt and two adjoining holes at the proper spoke hole diameter 20 degrees apart for 18 holes, this is easier to layout that 32 or 28 holes as the degrees are fractional.
 This is the hub flange bolted to jig plate. The center piece is turned to match the internal dimensions of the flange and cut to clamp flange to plate when cap screw is tightened down. The first thing is to drill a 2.5mm hole at the correct spoke hole diameter.
After having problems with spacing I put the degree wheel under the flange. Here I forgot that I only need 18 holes and have marked all 36. Things like this lead to problems if you donít catch yourself in time (like I did).
After drilling your first hole, insert a piece of 2.5mm drill rod or a 2.5mm drill bit. You do this to locate your next spoke hole. Notice how Iím about to drill a hole 10 degrees apart instead of the correct 20 degrees. Yeah, I screwed up the flange and had to make another.
Here I get all sorts of things wrong, well live and learn from
your mistakes.

Here Iíve gone back, relocated the center hole and marked the correct 20 degree spacing.
Next problem was the drill bit walking so I decided to use a 1/8Ē ball mill to make a start hole for the drill bit.
After using the 2.5mm drill rod to space the holes I drilled the 2.5mm spoke hole.
After changing the drill bit to a countersink. You have countersink to seat the spoke head in each hole on both sides.
After some drama both hub flanges are done. My calculations show that a 13mm x 1.125Ē x .065 piece of 6061 aluminum tube is used to join the flanges using a press fit. This means the area where in ID of the tube is about .002Ē big for a tight fit. Press fit was done with a bench vise.
This is the front axle being turned to 12mm using 7075 aluminum round bar stock.
To prepare the axle for the 5mm bore, a drill/countersink is chucked into drill.
The 5mm bore is drilled. My tailstock has only a 1.5Ē travel so I have to move the tailstock to complete the borehole.
Here is the completed front axle. Checked the axle for fit into bearings.
Next a spacer sleeve is made and length adjusted to contact bearing race. This prevents crushing the bearing races and binding when screw collars are added to axle.
These are the individual pieces.
Everything is assembled and checked to see if anything binds up, all OK. Phew.
Now two 6mm wide collars are made, these will clamp to axle and hold bearings in place.
The axle ends are machined down to 9.4mm by 5mm to fit the fork dropouts.
The last thing it to drill and tap for 1 set screw into each collar. This allows the axle to be held in its proper place. Yeah, itís a lot of work but I need a 55mm over locknut front hub for the lowracer project. Nest is the building the fork.

Truing a wheel that has a narrow 55mm hub in a normal truing stand

This shows the 32H Velocity Razor rim I had from the last lowracer I built about 10 years ago.

The narrow front hub is the second generation one I made because the original hub bearings in the hub I built above werenít large enough and didnít last very long. The spokes are 15 ga laced in a cross two pattern, something Iíve never used before. Also shown is the quick release I modified to work with the 55mm overlocknut dimension. Itís a 20year old American Classic steel skewer with aluminum ends.

 I couldnít of course true the wheel in my normal dimension truing stand because it doesnít have ability to clamp such a narrow spacing.

I came up with the idea of making an adaptor so that it would. I machined two identical aluminum extensions that could be used with a 100mm overlocknut skewer and the place in the truing stand. The inner end is machined to fit over the 9.5mm end that goes into the dropout and the outer end replicates the 9.5mm end.

Here the adaptor has been mounted and the wheel placed and clamped into the truing stand. It all worked just fine. Careful tensioning of the spokes when adjusting spoke nipple spokes makes truing for roundness easy and less time consuming. Iíve always found this the difficult part of truing a new wheel.


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