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Old 05-07-17, 09:38 AM
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Andrew R Stewart 
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If the wheel is off center within the blades AND the axle is fully in both drop outs then what John and I suspect is likely true, the fork is not well aligned. What follows is a post I made on a different Forum 4 years ago, restating another post a few years before that. This is more to inform about then teach how. Bending and filing away stuff can be a out of the pot and into the fire thing. hence my initial suggestion to find someone with hands on experience.


I posted about a low cost drop out aligning check tool a few days ago and mentioned that I used the same trick of looking through a small diameter tube in my, also, low cost method of checking fork alignment. Some have asked that I describe this fork checking process in greater detail. So here's what I do.





But before I continue a few comments about frames, bikes, people and their relationships. "Show me a perfect body and I'll build a perfect bike". This was said by Albert Eisentraut during a framebuilding class I attended 34 years ago. His point was that we are not perfectly symmetrical beings, favoring one side over the other with limbs of different lengths and curvatures where we might be straight. Additionally our bikes are not a perfect mirrored device. Wheels are usually off dish, stems/bars not perfectly square, horizontal, straight or symmetrically curved. Seats are off to one side WRT the rails that also might not be quite parallel. Then there's the "Q" factor and that many of our on topic cranks are not off set from the frame's center line equally side to side. So this pursuit of a well aligned frame/fork is tempered by the reality of the imperfection that we and our bikes are.





Fork alignment has three aspects/axis that we need to be concerned with.


- Steerer axis being parallel with the wheel's plane


- Axle being parallel with the fork crown


- Drop outs centered WRT the steerer's axis





I will establish one aspect then the next then the last during my process. As changing each aspect does effect the others I'll go around this process a few times, with each cycle getting each aspect closer to "good enough". At some point I find I am chasing very minor amounts of "offness" and will call the fork aligned. (More on this point later).





First I start by getting the drop outs parallel to the crown. Photo #0356 shows a pair of Campy "H" tools placed in the drop outs although any straight edge that fits fully into the drop outs would suffice. (The "H" tools double as drop out aligning devices saving a step). There is another straight edge placed on the blades front surface up near the crown. These two straight edges need to be parallel to each other. I will bend one blade forward or the other backward as needed to get the two straight edges parallel. Note that with the "H" tools being attached to separate pieces (drop outs) that as a blade is displaced the tool will no longer align with it's sister. So after each blade bending the "H" tools need to be realigned to each other to recreate a straight edge running through the drop outs. (A simple solid straight edge would not need this step for axle/crown aligning but the drop outs would need a realigning to each other after. The "H" tools just let you do this without changing the tools in the drop outs. The previously posted drop out aligning tool made from an axle cut in half would be the tool for getting the drop outs parallel to each other.)





Second step is to check the steerer and wheel's being centered WRT each other. This is where the sighting tool I have mentioned comes into play. You'll need a good wheel, dished on center and true with a Presta valve hole if possible. The sighting tube is any piece of tubing (I've used plumbing stuff and 4130 stuff before) with a length a bit more then the steerer's and an ID maybe about 3/16". Then tape (masking in this case) is wound around this tube in a couple (or more) places along it's length. This tape will build up the effective OD of the tube so that the tube can slip inside of the steerer and snug up with no play. One winding of the tape is slightly smaller in diameter so that it can butt up inside the steerer's butted section (like a cone would center on a tube end) and the other snugs into the full ID of the steerer. The windings are placed along the length so that a little bit of the sighting tube will stick out just past the bottom of the crown or steerer's bottom end and just above the rim. Photo #0350 shows a sighting tool made and ready to install into the steerer. The wheel is installed in the fork and lightly clamped in place so that the rim is centered between the blades up near the crown. The rim is rotated around so that the valve hole is lined up with the sighting tube's line of sight. I hole the rim in place with a rubber band to free up my hands. Photo #0351 has the sighting tube installed with the rim held so the valve hole is in line. Then by looking down through the sighting tube you can see across the wheel's diameter and to the rim on the other side. If the fork is centered the view will be centered on the rim. A mark on the rim helps this judgment. Photo #0354 is an attempt to show the spotting through the tube to the rim's far side. Now if the drop outs were too wide or narrow apart you would have to bend a blade in or out to get the axle to just slide into the fork's drop outs with out any blade movement when the axle securing is tightened. Also if the axle (and then the rim as seen through the sighting tube) was off center one or the other blade would need to be bent over to correct this. This drop out width and wheel centering correction is done simultaneously, back and forth with rechecking the axle's fit within the drop out width and rechecking the wheel/rim's centering as seen through the tube. When done the axle fits within the drop out width with very little slop and the wheel is centered WRT the steerer/sighting tube.





Last is the blade length. Note how with step 2 I was centering the rim near the crown by hand and then clamping it there, without regard to how deep into the drop out slots the axle seated. Now we check for whether the wheel sits within the drop out slots evenly. Loosen the axle securing and fully seat the axle up into the drop outs. I like to use both hands at each axle end to pinch it up fully before I resecure the QR or nuts. If you pull the rim up toward the crown it's easy to think you've seated the axle fully but I've been wrong doing this before. (Of course if the bike were upright gravity would seat the axle fully but that is not what the arrangement is for this process). Photo #0355 shows a wheel installed as though a blade was longer then the other (actual the fork used as the sample has already been fully aligned so I had to miss center it to show this). At this point there is a threshold to consider. Up to now all bending/aligning can be undone, no forks were injured in the making of this process. But this next step changes that. If one blade/drop out is longer from the crown then the other the wheel will sit crooked WRT the steerer's axis. So a blade has to be shortened. We do this by filing the slot of the long side's drop out deeper. This allows the axle to seat up further and the rim to, bit by bit, sit centered between the blades. Remember the levers at play. The axle is about 100mm wide, the rim is about 300+ in radius. So a 1mm deepening (by filing) of the drop out slot will equal a 3mm shift over of the rim between the blades near the crown. And the filing needs to be in line with the blade, NOT the angle of the slot. While I do this very often on new bike builds at work (it's surprising how off even cast suspension forks are) I feel that (unlike the TV commercials say) less is better. Only a few file strokes will produce a lot of rim centering movement. The file used should be sharp and of the same diameter as the slot's width (or the axle's diameter). I hold the blade at it's drop out and have the rat tail file run through both drop outs but only apply pressure on the drop out needing filing. This keeps the filing square and give one a bit of a guide. Again this is a point of no return. If you're uncomfortable with the possible consequences then STOP. Have a pro take it from here.





If you've done all these steps right and with care, then run through them a second and third time you'll see a fork that was off becomes more and more on center. The cost (besides the gumption to bend or file away at your classic fork) is very low. A good wheel (that we all should have anyways), a length of small diameter tubing, some masking tape, an axle to make a drop out aligning tool from with some extra nuts and the effort to have the fork bare of frame, caliper or fender.





Now back to something I mentioned but passed by. I said that alignment is not a perfect thing. I have had for a number of years a precision flat surface which is hand scraped to a VERY flat spec. I also have a fork steerer block clamp that bolts to this surface plate. With these I can use my dial indicators and "measure" the fork's center height off the surface, then the drop out's heights, place a dummy axle in the drop outs and indicate off it's vertical surface (or use a square) and check the axle's perpendicularity WRT the steerer and also the axle/crown parallelness. But just because I can see a single thousandth of an inch does not make it important or repeatable. I can refit the fork in the clamp and get different readings. I do check my forks with these "precision" devices but do my actual aligning and the running checks during the aligning with the low cost process described above.





I hope this has been informative to those who care about having a well aligned bike and like to understand processes. Andy.
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