Troul 

looking to mount something on the back side of a crank arm, and was searching for a pedal extension or alike that might work. Only need to protrude 1/2" at best. Or a hollow threaded hole could work too.

dedhed

I'd probably just weld a short piece of round bar stock (or whatever shape you're looking for) on to the pedal spindle in a smaller diameter than the threads so it fits through the crank. You'd have to use pedals with wrench flats and not allen on the spindle.

Troul 

If I go through all that, I'd rather create a flat area on the back of a crank arm & tap in a couple of shallow small bolts. Trying to not mod the crank arm, as that might bring about stress areas.

fietsbob

Challange is heat treated steel ... will take some better than shade tree mechanics to drill, tap and put a small stud or bolt in .

Have a Machine shop to ask to do this?

maybe tack weld a nut on?







....

Dinen1986

Thank you for the details.

Dinen1986

This type of infromation is really cool.

Dinen1986

Thank you for sharing this wonderful post here.

Dinen1986

Details are always available for anyone who want to get it.

Dinen1986

good to see the page.

Milton Keynes

If I may ask, what is it you plan on putting on the back side of a crank arm?

jadocs

What does mounting something on the back side (inside?) of a crank have to do with extending your pedal?

Troul 

Surem no problem in asking!

The cadance sensor doesn't clear the chainstay when using the oem sensor mount. The adhesive the OEM gives as an alt doesn't hold on for long due to the irregular surface on the crank arm... Already nearly lost the sensor. Zipties allow it to slip down & causes it to interfere with the pedal/my foot. Worst case, I change the BB to allow a wider position, but that isn't something I want to do when the BB is not a problem.

Troul 

Im not trying to extend out the pedal, I'm trying to lengthen the stud to poke thru the otherside to use its threads for a small fabricated bracket.

coupster

Having a hard time visualizing your setup, so I may be way off base. I've got a bike whose crank arm barely clears the chainstay by itself. I've got a cadence sensor mounted to the bottom of the chainstay angled as close to the crank arm as possible. Then on the crank arm, I've got a very thin rare earth magnet attached by magnetism to the pedal axle through the hole in the crank arm. Clearance between everything is about the thickness of a thin piece of cardboard and everything works as it should. In all of my years, I have never seen a cadence sensor that attached to the crank arm, just the triggering magnet. But I've also learned that anything is possible, not matter how improbable. Or just maybe your crank arm is solid on the inside and you can't use my setup, but it was worth mentioning.

jadocs

Gotcha…… What are you planning on mounting there? I'm only asking because there may be a simpler solution.

Troul 

the sensor.

jadocs

What kind of sensor and from who?

For example a Wahoo cadence sensor comes with a mount that allows you to attach it to your shoe.

BlazingPedals

You already tried my go-to: zip ties. Does adding 2-sided tape help? (Be sure to keep the knuckle part of the zip tie toward the frame.)

Troul 

Wahoo sensor. I'd much rather it be affixed to the crank arm.
The cradle that Wahoo supplies increases the thickness, which causes it to bind. Even the rubber "boot" they supply makes it too thick. The sensor itself barely clears the chainstay.

fietsbob

Or the triggering magnet?

Barry2 

3M VHB tape is amazing stuff.
They use this stuff to put windows into high rise buildings!

Clean the Sensor and Crank with rubbing alcohol and let them dry (5-10mins).
Attach tape to Sensor, attach sensor to crank in the exact place you want it. Don't plan on being able to move it.
GENTLY clamp the sensor to the crank overnight. Even a tight rubber band will do the trick.
Done. It's not coming off.... honest !

If you decide you want the sensor off, DO NOT pull on the Sensor...... cut the tape by sawing it with dental floss.

All the best

Barry

BlazingPedals

Things were simpler when the wheel sensor and the cadence sensor were separate. The currently-popular all-in-one sensor works great, if it works. If it doesn't, you're stuck.

Troul 

speed sensor is on the hub, cad is on the crank arm.

Troul 

The arm surface is not flat to allow for full contact adhesion.

Troul 

Once my foot makes contact with the sensor, it loses the battle & drops towards the pedal.