As I could buy 152mm cranks already, I decided I'd make my jig for 100mm to 155mm in 5mm increments.   I took a piece of ½" x 4" flat steel that was about 2 feet long, drilled a hole in the middle of it and welded half of a BB axle into it.  I made sure that the BB axle was perpendicular in both axis, and that it was rotated to the proper point that a crank would be centered over the steel bar.

     From the center hole, I measured out on one side to 100mm, and then marked it out to 150mm in 10mm increments.  On the other side, I measured out to 105mm, and then out to 155mm in 10mm increments.  So, I had all the lengths I wanted, on the centerline of the jig with the BB axle, laid out in halfs on each side of the axle.  I center punched the marks, and drilled them out with a ¼" bit.  I planned to place the jig on the drill press table, put a ¼" bit into the chuck, then lower the bit down into whichever hole I decided to use.  Leaving the bit in the hole, I would clamp the jig firmly to the drill press table.  This accurately marks and holds whichever crank length I wanted to make, and all I would have to do is drill one crank, remove it from the jig, and put the other crank on it without ever having to reposition the jig or drill press table.

     The procedure I used to shorten these cranks to 130mm is as follows:

• I put the jig on the drill press table, and used a ¼" bit to line the jig up using the 130mm hole.
• I made sure the drill press table was tightly clamped to the column, and then clamped the jig to the drill press table.  Using a combination square, I already know that my spindle is 90 degrees to the table both left to right, and fore and aft.
• I placed the crank on the BB axle and tightened the axle nut to secure the crank on the jig
• I put a ½" bolt, with a washer and nut, under the pedal hole, to act as a support while I drilled the hole.  This would stop the crank arm from being deflected downwards by the drilling pressure and screwing up the alignment of the hole.
• I use a center drill to lightly mark the crank and then I check it one last time for center alignment on the crank arm.  It doesn't matter if it's not exactly at the crank length I wanted because both cranks will end up identical length anyway.  After the final check, I give it a good, deep centering hole for the drill bits to line up on/in.

• Then I drilled a ¼"hole, and stepped it up to a 3/8" hole.  I stepped it up because I wanted to be cautious, and remove as little material per pass as possible to lessen the stress and pressure on the crank arm, which might effect the hole's alignment.

• The final drilling step is to use a ½" bit.  While the proper pilot drill size for the 9/16" x 20TPI thread is 33/64", I didn't have a 33/64" drill bit, so decided to try it with a ½" hole instead.  It worked fine but I would be a little more cautious/leery of trying to remove so much meat in a steel crank though.  For steel, I'd likely just cut and re-weld the steel crank arms and make a jig that held the two crank pieces in proper alignment.  I know I keep switching cranks in the pictures, but for some reason I neglected to take a full series of pictures while doing one crank arm.

• I put a dulled center drill into the drill chuck, put the tap handle on the tap, put the end of the tap in the pedal hole, then lowered the chuck until the dull point of the center drill was pressed firmly into the center hole in the shank end of the tap.  This would ensure that the tap would cut the thread perfectly in line with the drilled hole.  You can see the dulled center drill pushing down on the butt of the tap, while the end of the tap is firmly pressed into the new hole in the crank arm.
• I used plain, old 3-In-One oil for cutting fluid, and kept steady downward pressure on the drill press handle, as I started cutting the threads.  I went slow because it was cutting extra meat due to the under-sized pilot hole.  As a side note, the Park Tool taps say on the package that they are not intended to be used to actually cut threads.  The taps are not as sharp as other taps I have used, but they went through the AL with no problem and cut beautiful, clean threads just the same.  I would definitely splurge on a 33/64" bit if I was going to do steel cranks.
• After doing the one crank, I took it off the jig and repeated the process for the other crank.
• After threading both arms, I left ~7/16" meat around the new crank hole, and cut it off on the band saw.  A hacksaw works fine too because the end will be smoothed and contoured on a sander anyway.

     To the right is the end result after the finishing details and cleaning all the mud off them.  They're compared to a standard 175mm 48/38/28 crankset.  The old end sections are beside the 130mm cranks to show how much was removed - almost 1¾".

     The real test was to put them on a bent and try them out.  The first and most important thing, is that there is either a very, very small mis-alignment, or it's my clips.  Right now I can't quite isolate if there's an alignment problem or not because it feels pretty weird going down to 130mm cranks.  Even if the alignment is off a little, it is extremely slight, and two other people that tested them didn't even notice it.  I'll need to put some kilometers on the cranks and see how the power, speed and endurance compare to the 152mm cranks that I'm used to, and if these actually is an alignment issue, and how much of a pain it is.

     I have another set of cranks and I'm going to drill them to 140mm just so I have another length to compare with.  So, with nothing more than a small drill press and basic shop tools (and the Park taps, of course :)) anyone can shorten their own cranks.

16 Apr 2006

     We took the cranks for a number of test rides including a longer 15km ride.  The "wobble" or alignment issues I was concerned about were either non-existent or so insignificant that they went un-noticed.  They feel well aligned. so I'm pretty happy about that.

     As for their feel for pedalling, I'm not so happy.  My legs are pretty much used to riding a bent after many thousands of km over the last three years, switching to 152mm cranks a few thousand km ago, and I also don't mind overspinning in the 90 to 130rpm range (or higher if I run out of gears).  I think that should have had me pretty well prepared to try out the 130mm cranks.  The cranks seemed "too short".  It was really difficult to get into any kind of rhythm with them and very hard to feel like you could put good power down with them.  When I switched from the 175/165mm cranks to 152mm cranks, it felt a little different, but in the first hour of using them, they felt better - like an improvement and at the time, I still wasn't much of a spinner.  Going from 152mm cranks to 130mm cranks felt very weird, and after almost 2 hours of riding on them, they don't feel like they're "better".  In short, I don't like them.  Possibly I'm not spinning at high enough RPM with them, but even with high RPM, it still doesn't feel like you have the power or torque to do what you want to do, and even while spinning, I could feel my knees loading up when I was trying to get the power to the road.  They felt really crappy for climbing.  I switched back to 152mm cranks on the same bent, and went for a 4 or 5 km ride with some hills.  It felt like a relief to get back to the old length.  Granted, I'm used to that length, but I could accelerate and ride at speed comfortably on the flats, and I could spin and accelerate up hills far better than with the 130s.  It's not a complette loss because I can always use them on a bent for one of my little ones, but I think I'll try some 140mm cranks, as I mentioned above.  Maybe the 130s were too big of a jump from the 152s.  If the 140mm cranks don't work out much better, then I'll have another set of short kids' cranks and make teh rest of the shortened cranks 150s.  The problem right now, is that you can't get 150mm cranks with removable rings - I can get around that now :) I also have a few Biopace sets that I'll try shortening and see how they work out.

3 June 2006

     I put the 130mm cranks back on the high racer and have been using them to commute and have close to 400km on them now.  There's a pretty steep hill on the way back and I definitely have to work a lot harder with the short cranks when I'm going up the hill.  The 150mm cranks were pretty good, but the 130's are definitely character builders.  I think part of the difficulty is that the largest cog on the cassette is only a 28, and with the 38 tooth chainring and 27" wheels, it's up near 37 gear inches for my lowest gear.  With a better gear range, or at least a 30 tooth cog, they'd likely be much better on hills.  In the mean time, aside from the grunt work on steep hills, they seem fine otherwise.  I might try some more 130's on a double chainring Biopace set I have and put those on my Catrike Speed.

23 June 2006

     With a little more than 1100km on the 130mm cranks, I am more than happy with them.  I managed to get a granny gear on the high racer so my low gear is now about 27 gear inches which is more than sufficient for hills now.  With that in mind, I decided to chop up my brand new 165mm Ultegras and turn them into the 130mm cranks they always dreamed of being. :)

     First thing to deal with, was the fact that the Ultegras used an Octalink BB, so I made a couple adapters to fit in the cranks and popped a ½" hole through the adapters.  I made them out of AL and faced off both ends of each piece so that the crank would be forced to sit perfectly aligned (or so I hoped) with the drill press table and spindle.  I also then needed to make a new jig for the Octalink cranks because I cleverly welded the BB piece into the other crank jig . . .  So, no problem, I used a short piece of ¼" x 2" flat steel, drilled a ½" hole in one end and drilled a bunch of small centering holes to allow me to set the proper crank length selection by using a center drill to line up the jig on the drill press table.  On this jig, I'd use the same basic procedure as for the normal square BB cranks, but I'd manually line up the center line on the cranks instead of the jig doing it automatically.  It was a little more nerve wracking to do it manually because I was concerned about how the cranks would "feel" if the holes were a little off center, and how much they would need to be off center for me to be able to feel it.  In the end, the cranks felt fine to use with both running shoes and my SPD's.

     The picture to the right is of the finished Ultegras at 130mm long.  The only thing I hadn't anticipated was that the Ultegras are "hollowtech" cranks so when I drilled the new holes, there was about an eighth of an inch of space between the two walls of the cranks.  I gave lots of meat between the new holes and the end of the cranks before I cut them off, and the aluminum was solid at that point.  When I installed the pedals, the pedal threads reached across that space and bit into the threads on the other side of the crank wall so I think I should be ok for the strength of the new holes.  Also, because A) I spin like crazy, and B) the short cranks have taken a bunch of my torque out of the equation, that should also take the load off the hollowtech holes.  At least, I hope :)  Time will tell and I'll check the cranks regularly.

     While on a roll, I took some old 170mm cranks and chopped them down to 145mm for use on a low racer project called the Nitro clone.  Again, the end result worked well enough to feel like they came that way.

     So the crank shortening is working really well with a very basic set-up and either the jig and my set-up is more accurate than I think it is (possible), or I have been extremely lucky 3 times in a row with the conversions (doubtful), or there are hole alignment issues but they are so small that I can't feel them, or the SPD's filter them out, or I am used to them already, or all 3 (highly likely).  Whatever the answer is, I am fairly confident in my ability to produce shortened cranks that are both comfortable and functional, and as of ~1200km of use, my poor, busted-up knees and ankles haven't complained yet about them.  Just about anyone, with a little patience, can shorten cranks for quite likely much cheaper than a "commercial" set.

21 Jan 2007

     In preparation for getting two more trikes up and ready for ice racing, I shortened two more sets of 170s down to 140mm.  The top set is a standard 130mm BCD spider, while the bottom set is, errr . . . was a 110mm BCD rivetted triple crankset.  I drilled out the rivets, cut off the outer ring just outside the rivets and then oversized the rivet holes to accept the crank bolts.  The whole thing tool me about 15 minutes, max.  Much cheaper than buying a complete set of new cranks with removable rings.  The reason I took the rings off was because they were a 42/34/24 triple, which was too low geared for my projects, and the middle chainring was pretty badly worn anyway.  I'm going to mount a 62/40 ovalized double chainring on the bottom one but I have to use another 110BCD to 130BCD adpater on the top set if I want to use the oval rings I made.

     During a race, I found that I didn't have enough torque as I would have liked with the 130mm cranks, so I'm going to run some140mm cranks for a while and see if I like the power production better.

07 Feb 2007

     I mounted up the 62/40 oval rings I made and gave them a good test at the Brantford ice races.  The cranks worked great, there was no flex in the modified spider and the holes were good enough that I couldn't notice any pedal wobble or misalignment.  My daughter raced the trike they were on so I didn't get to use them enough to see what a difference the 140's made comapred to the 130mm cranks I'm used to.  Lots of time for testing later and I have a 48/38/28 triple with a stripped pedal hole to shorten to 140mm as well.

Update:  While the chainrings both worked fine, the pattern I cut seems to have weakened the big ring a little more than I would like and it feels to me like it might be too easy to bend if it was cranked on hard.  So, I'll take another ring of AL and make some kind of stiffener ring and rivet it to the 62T ring and that should solve the problems.  More on that when it's done.

28 Feb 2007

     These are the cranks that I used on the delta instead of the big oval set above.  These 170's had nice fat arms and one of the pedal holes was completely cross threaded and stripped.  A perfect candidate for shortening, yes? :)  Anyway, the shortening went off fine and in some test drives, they feel great. Smooth, no apparent alignment issues, and a perfectly good pair of cranks is brought back to life.

10 Apr 2008

     Took two sets of 160mm 53/39 double Dino cranksets and chopped them down to 140mm.  I would have liked them to be at least 25mm longer than the shortened final length, but they were all I could get on short notice.  The reduced torque and power output should still make them last every bit as long even though the thickness at the end is not as much as I would have liked.  They'll come in handy on any bent with a 24" or larger rear wheel.

1 May 2008

     For the Raptor 44, I took a pair of inexpensive MTB cranks with the intent of shortening them down to 145mm and replacing the rings with 59/48/32 10% oval rings.  To the right is the drilled cranks with the unfinished rings, just prior to trimming them down.  At the bottom is the finished cranks with the rings mounted.

21 Sept 2006

     Here's an '06 Catrike Road with a 20" 350 Bionx on it and a 60/40 double with another 110 to 130 BCD adapter plate.