NC Rick
Aluminum
- Joined
- Oct 7, 2007
- Location
- Asheville, NC
Hi folks,
While not at all inline with my regular gig, a customer/friend brought in a broken part from a rare old bike. Basically it is a simple shaft that connects the two peddle cranks and is supported by ball bearings that are pre-loadable in the bottom of the frame. The bike is old and strong. The bikes owner uses it in WWII reenactments. The shaft that sheared, clean half in two... is about 3/4” diameter and feels like heat treated medium carbon steel. The part is in good shape except for the issue of being sheared in half. No telling how it broke, my guess is it has to do with metal fatigue.
I could remake the part but for the weird left hand pitch thread. I don’t even have the thread pitch gauge that matches. The owner can’t find the part and will accept a repair that makes the bike a static display piece if necessary. I’d like to do better.
Unsurprisingly, the shaft sheared at the end of the threads which were finished without a relief. I have been noodleing on how to fix this. The “nut” includes the hardened and ground bearing race and that is not a part I am capable of making either. I don’t feel like there is room to go up a thread size although it isn’t out of the question as it is a very fine pitch thread. I suspect the nut is hard also. I am thinking of milling a pocket in the core of the threaded section and a coresponding slot in the other half of the shaft and make a 4140 or 1045 steel “key” to fit the shafts together before attempting a TIG weld or hard solder join.
I thought I’d share the problem here since most of you are far more knowledgeable than I. To me it is an interesting problem and I want to fix it because all the “machine shops” around have declined to deal with it. If I do fix it, I’m not going to charge for it, just do it with the intent of keeping an old bike alive and to give myself a little challenge that will push the envelope of my limited skills.
I hope others will se the project as something interesting and perhaps share experience and ideas with me. Thank you in advance, Rick.
While not at all inline with my regular gig, a customer/friend brought in a broken part from a rare old bike. Basically it is a simple shaft that connects the two peddle cranks and is supported by ball bearings that are pre-loadable in the bottom of the frame. The bike is old and strong. The bikes owner uses it in WWII reenactments. The shaft that sheared, clean half in two... is about 3/4” diameter and feels like heat treated medium carbon steel. The part is in good shape except for the issue of being sheared in half. No telling how it broke, my guess is it has to do with metal fatigue.
I could remake the part but for the weird left hand pitch thread. I don’t even have the thread pitch gauge that matches. The owner can’t find the part and will accept a repair that makes the bike a static display piece if necessary. I’d like to do better.
Unsurprisingly, the shaft sheared at the end of the threads which were finished without a relief. I have been noodleing on how to fix this. The “nut” includes the hardened and ground bearing race and that is not a part I am capable of making either. I don’t feel like there is room to go up a thread size although it isn’t out of the question as it is a very fine pitch thread. I suspect the nut is hard also. I am thinking of milling a pocket in the core of the threaded section and a coresponding slot in the other half of the shaft and make a 4140 or 1045 steel “key” to fit the shafts together before attempting a TIG weld or hard solder join.
I thought I’d share the problem here since most of you are far more knowledgeable than I. To me it is an interesting problem and I want to fix it because all the “machine shops” around have declined to deal with it. If I do fix it, I’m not going to charge for it, just do it with the intent of keeping an old bike alive and to give myself a little challenge that will push the envelope of my limited skills.
I hope others will se the project as something interesting and perhaps share experience and ideas with me. Thank you in advance, Rick.