Converting Mrs. Grouch's Kettweisel to 27 speed is proving to be a challenge. I was able to pick up all of the big pieces pretty economically. It's acquiring the small parts that's generating all the fun.
I thought that I could just order a front derailleur mast from Hase. It turns out the derailleur mast is actually 3 parts - the CNC'd mast, a spring metal clamp, and a cone shaped part to hold the cable stop. The 3 parts were easily acquired for $128.00 which doesn't sound too bad to me unless one compares it to the cost of installing a front derailleur on a diamond frame bike. Also, the cable stop and fasteners weren't included but I had a cable stop in my spares and was able to buy an M5 flat head machine screw that fits perfectly from Home Depot.
The issue of the week is chain slack take up. The rear derailleur that I have won't take up all of the chain slack and installing one with a longer cage is iffy because, with 20" rear wheels, it would hang down too far in the middle of the rear axle. Hase uses an additional spring loaded slack take up device. Not the kind of part I'm likely to find at my LBS. I found a compression spring at Home Depot that looks like it will work, but I lack a hat shaped nylon bushing that would make the assembly a little more elegant. I'll see if I can order the "right" spring and nylon bushing this week from Hase.
My plan is to see if my grandson Tyler can come over next weekend to install the shifter and front derailleur with me and see if we can get it all to work. We also have two other trikes that would probably benefit from front derailleur adjustments. Derailleur mast - $128.00. Wrenching with my grandson - priceless. I love projects like this.