Plate Crown Fork

This was a fun beginning to a much bigger project that came about when the man behind Dapper Dre Enterprises mentioned that he liked the look of bikes that were more classic and angular.  He mentioned  liking a bike I made some years ago, so after our conversation I revisited that bike and the blog entry I posted about it, HERE.  It was a traditional level top tube touring bike, but the plate crown fork stood out, so why not revisit that.  I re-read that post and at the time had concluded not to make one of those for a good long while, or until I have a mill.  Yeah, I remember now why, drilling out matching holes in plates with a drill press and then filing them to round sounds like a terrible idea.  At least I raked the blades to achieve offset rather than angling the holes at the crown...you can probably see where this is going.  Anyway, fork now complete, my favorite comment about it so far came in the form of "How the f^@k did you make that."  Well it took a while but here are the basic steps.

Lots of time went into the working drawing and pre-planning and angles were calculated rather than measured.  I periodically have to recall those high school trig classes out there in the shop and this fork required several of those old formulas...really practical math, folks.  As well I cut a new die for the crush bender to form the lower plate; the upper is the railroad track die used to bend the yoke on Joe's Murray in the last post. 

This thing came in handy for once.  The Palmgren 400 lathe milling attachment.  I picked it up at my local machine supply, Quality Tool, about a year ago in serviceable condition for $100 and haven't touched it other than to clean up and oil.  I bought it initially thinking it would be the tube mitering station, but quickly thought better of it, things just didn't quite compute.  And yes, Flagstaff has a machine tool store even though it doesn't really have too many machines, and I won't bother linking you to it because the guy that runs it is even more of a techno-luddite than I am, so you can find him in the yellow pages, or just drop by, he is there, tucked into the corner by the beauty college with barely even a sign.  Yesterday I picked up a Kennedy tool box loaded up to the gills for not too bad either.

Steerer hole cut into plates and tacked against the crown race seat.  The top plate will actually serve as the crown race seat the sleeve is just to give the proper O.D for the race's press fit.  This whole sub assembly is then sweated with brass and cleaned up. 

Time to make the holes for the legs.  Calculations for rake and crown to hub widening are programmed on the Palmgren and the compound slide respectively.  Then marks are centered before cutting.

 

Holes cut....I almost lost it here.  The expansive angle to the hub was set for the other side so my cut went the wrong way.  Luckily, the metal to the inside (steerer tube side) of the hole was all still there and the 1.625 degree angle of cut was not enough to drastically affect my canvas.  At this point I still didn't have much of an idea of how the fork was going to look in the end, but with the mis-cut I started getting the idea.  I would have to close that gap in at the outside, just like any old lug point.

The rounding cuts were added while in the lathe followed by much manual sculpting.  The closed holes were carved into lug points and made for some fun tight quarters brazing.  

Looking forward to seeing this with a layer of paint and then all done up on the bike which is in process as I type this.  Lots of work into this one!  

The Trade

Steel for Steel.  A nicely equipped, tough as nails, American made touring mountain bike frame built for long travel forks and plus sized tires....and in exchange....a nicely equipped, tough as nails, American made metal munching machine.  

I got wind last fall that in the garage of a notable Flagstaff mountain bike personality sat a Bridgeport mill, collecting dust, taking up space, no longer needed in shop operations, not even five miles from here.  I was immediately interested, but with winter approaching and side jobs waning for the season, had little money to afford such a hunk of metal.  I tracked down the owner of said machinery and arranged to head over for an inspection anyway thinking maybe an arrangement could be made.  Save for a little dust it seemed quite clean, minimally used, included a fair assemblage of attachments, an adjustable boring bar, a swivel vise, and perhaps most importantly a phase converter for the variable frequency drive.  You mean I don't have to climb a ladder to change speeds on the belt and pulley drive?!?....OK, I want!, but how?  Then out of the man's mouth whose name is worn on more bicycle frames than I can imagine...."I'd be willing to trade you the value of one of your frames toward it."  Joe Murray, you sir have a deal.  

I mentioned that I would like to make the bike on the machine and arranged to pull it out of there as soon as possible.  The Viking crew was wrangled on a slushy Saturday last December.  One Kubota tractor with fork attachment, two three quarter ton Chevys, two two-axle trailers, the standard arrangement of carpentry tools and rigging, one hour of time at each shop, lunch at Satchmo's.  Done.  What would a guy do without the Neffs?  

I rounded up all the scrap metal I could and spent few months learning this machine.  Old metal was repurposed; fixtures made from scrap, bolt patterns, Tee-slots, Tee-nuts, tapped holes, boring!!!   So many possibilities.  I do love me some recycling!  Joe stopped by on a ride with a sweaty folded computer print out in hand.  A scale CAD drawing of the bike he wanted me to build.  It was time to pay the debt.

The bike to be wanted 29+ wheels and 150mm of Fox 36 fork.  We discussed some specifics which included a dropper post, a granny gear (YESSS!), thru axle rear with offset for good chain line, and rack mounts (YESSS!).  A properly sturdy bike with timeless accommodations.  I must say that of all the production bikes I ever owned, my favorite, and the only one that ever really fit me was the one of Joe's design.  I took the dimensions from his print out to full scale on my drawing board to double check clearances and setup the jig.  The seat tube would need to be bent and some serious tire/chainring clearances would need to be resolved as always.  It was time to make my own plate bender (see back a few posts: Yoked).  Commence mill work. Working with a 30.9 seat post and a bent seat tube required a call to Solid bikes for one of their seat tube plugs, a real nice piece of turned and internally relieved 4130.  This piece comes as a press fit to be stitch welded, but would be reduced to accommodate brass flow into the joint.  The seat tube is the pre-bent True Temper Chromag downtube with the lower (actually in this case the upper) butt cut completely off.

Now building offset rear end bikes for large tires presents a new set of problems to solve, especially when considering it is not likely a bike I will ever own myself.  Finding the center line on the jig is no problem but confirming the accuracy of your work without actually having a 142 thru axle wheel dished so the hub sits 6.5 mm to the drive side is a little bit more complicated.  I did however have a freshly laced 29er wheel with a 135mm XT threaded axle hub at my disposal, so I devised some concentric end caps and spacers to make up the offset dish.  

The cones fit thru the dropout and thread to the 10mm axle.  The one on the right is longer since it has to accommodate the additional 7mm of spacers making up the difference in outer locknut dimension.  Now this regular old school 135mm center dished wheel sits on the centerline of this offset bike allowing me to visually confirm that this monster truck won't have an unwanted rear wheel steering issue.  Thank goodness.

Onto final frame prep.  I went with an 83 mm bottom bracket shell to accommodate a granny gear without having to use some oddball crank like a Mr. Whirley.  The shells come .5 mm over width to allow for facing after getting distorted in the heat cycle....and they do.  

So now she waits in a high gloss orange waiting for some unmarked parts to be slung on and abused.  

Thanks for the project and the trade, Joe!  I hope you like your bike.