Thursday, January 28, 2010

Shimano Direct Mount FD...fabrication

Yep, I know it's been too long since the last can hold my eyebrows in protest if ya like ;) 

I've been working away at finishing some final work before I can start on customer projects for the show.  Most of it has been fairly mundane work, hardly worthy of presenting and capturing your attention with, but I did snap a sequence of shots for one special project.

Today, I thought I'd share with you the Shimano Direct Mount Front Derailleur and what it takes to fabricate the necessary mount for the frame to utilize it.

The redesigned front derailleur is a boon for folks who like to run big wheels with short chainstays, odd shaped seat tube configurations, or desire the ability to creatively place a derailleur regardless of seat tube size or shape.  It can be used in a bottom or top pull configuration, mounts directly to a fabricated plate the framebuilder creates, and reduces the clamp and much of the garbage that extends towards the rear of the piece that reduces tire clearance and collects mud.

The interface on the rear of the derailleur is comprised of a flat plate with a projected ridge and a M6 slotted hole to allow up to 5mm of vertical adjustment.  The projected ridge allows the derailleur a secure interface to prevent from rotating on the frame mount.

To machine a mount, Shimano provides a tech document with most of the desired dimensions, though I found that I needed to modify a few for better performance and aesthetics.

To get started, I cut down a piece of stock 1/2" x 4" steel into two pieces that will eventually become four mounts.  I then face milled all the pieces to insure clean, square dimensions to begin working from.  Once machined to my desired starting dimensions, I grabbed the edge finder to establish a known reference point.

Next up, I positioned the mill to cut the support slot for the derailleur over the vertical length of the mount.

Multiple passes and a little patience helped me achieve the final depth necessary...nice and clean with a .01" tolerance.

After cutting the slot, I cut the two pieces into four and milled to the final dimensions. 

I then repositioned the pieces in the mill, reestablished my origin point, and found the center of the M6 bolt hole.  Creating the hole is a three step process; using a center drill to start, an undersized hardened drill bit follows, then machine tap the hole for the anchor bolt.

Tapping in the mill is a nice process and can be done easily with some care and due attention.
Once the holes were all created, some quick math helped me determine the center of bottom bracket to outside face dimension necessary for the bottom bracket witdth I was using.  I then determined where on the seat tube the mount would need to sit for proper alignment.  Armed with this knowledge, I was able to mill the back side to the appropriate depth and position.

The finished piece...

Holding it in place on the derailleur, you can see how the two pieces fit and the vertical adjustment that is possible.

Should make for a clean, custom touch on geary bikes.  A bit more time on this end to do it right, but well worth it for the benefits.




Experthasbeen said...

Hey Rody I changed my mind. I want to go with a 1x9!.........just kidding. That's some nice work there.

Easton Heights Blogger said...

shades of vintage Italian braze on front derailleurs! I hadn't realized Shimano came out w/ such a device. everything old is new again, I guess.

EdelBikes said...

Nice work ! It seems that your mounting plate is much closer to the seat-tube than what is specified by Shimano. Any reason for this ?

Rody said...


Not so my friend! The critical dimension is the distance from the face of the braze on to the centerline of the bottom bracket. This will change based on application; thicker/thinner tube diameters, bottom bracket width, chainring offsets, etc...

I took a pic for ya that I'll put up tomorrow to illustrate.