See the second photo. The screw mechanism in these assemblies wears easily. So does the plastic block that moves with the screw. The task is to build a new traveler block and a new screw, and make it all fit into the original case.
Step 1: Choosing a Key Part
- 1/4 inch tap and 1/4 inch die
- Electric drill and bits
- Dremel tool and cutting discs
- Wire feed welder
- Vise-Grip pliers
- 1/4 inch coupling nut
- 3/8 inch steel rod
- Threaded 1/4 inch rod
- Thin flat steel for making a shim
- Auto body adhesive
- Wood for a burnishing tool
- Motor oil
Step 2: Cut 3/8 Inch Rod
I decided to use a short piece of 3/8 inch steel rod in place of the old plastic follower block. Grind away any burrs after cutting. (Note: By the time I finish grinding, the rod looks like 5/16 inch rod. It may work as well, even better to use 5/16 inch rod and do less grinding to make the piece slide smoothly in the plastic case.)
Step 3: Cut the Coupling Nut Into Two Pieces
Step 4: Prepare to Weld
Step 5: Chase the Threads
Step 6: Grind and Smooth the Welded Assembly to Fit the Case
Step 7: Make a Cavity for the Cable End
Step 8: Attach the Cable Parts to the Case
Step 9: Threaded Rod
Step 10: Making the Screw Axle
Step 11: Retainer
When the adjustment knob is turned, the screw should not pull down into the case too far, nor should it back its way out of the case. The retaining pin keeps both of these from happening. I drilled an undersized washer to fit the 1/4 inch threaded rod and I welded it to the threaded rod. Then I ground it down until it would fit inside the plastic case for the assembly. The weld must be ground smooth so the retaining pin does not obstruct turning the knob. The screw has been cut to length in this photo. More detail about that is coming in the next steps.
(Later I drilled a washer so I could thread it for 1/4 x 20 threads. Then I used two or three spots of weld on the lower side of the washer. The threads kept it from moving. The weld needs only to keep it from turning. And, the length of the threaded portion from the upper side of the washer to the upper end of the threaded rod should be 9/16 inch.)
Step 12: Fitting the Rest of the Screw
A washer will help to keep the screw from going too far into the case. The length of the screw has been cut to accommodate the washer, and to feed part way into the piece of the coupling nut seen here. A bevel headed screw will fit into the coupling nut to keep the knob on the coupling nut. (The screw shown here is the original and it is a 10-32 screw. But, the coupling nut is 1/4 x 20 and a different screw will be used to retain the adjustment knob.) Notice the retaining pin from the previous step is in place here.
(Later I ground the screw before I put it into its place. Grind until the screwdriver slot is almost totally gone. Then use a Dremel with a cutting wheel to make a new slot. Grind away the threaded end of a 1/4 x 1/2 screw until the fit is right.)
Step 13: Secure the Coupling Nut on the Screw
The coupling nut needs to be "pinned" to the screw axle. I cut away part of the coupling nut for welding it to the screw. I removed the screw from the adjustment assembly for the actual welding. Otherwise, the plastic case would have been damaged. Be sure to put the washer onto the screw before welding the coupling nut to the screw (second photo).
The second photo shows the completed weld. Grind the sides of the coupling nut flat again. This is a good time to add a few drops of motor oil to the screw for smooth operation when finished.
Step 14: Make the Knob Fit
In step 1 the photo shows that the coupling nut fits too loosely in the hex socket in the knob. I used a caliper to determine how thick a piece of steel should be to fit around the coupling nut and fill the void. I used a Vise-Grip pliers to assist in bending the steel to fit. Even at that, the fit from such an operation is seldom perfect. As you can see in the second photo I did a little light grinding around the metal shim for a better fit.
(The shim material needs to be thick enough only to keep the knob from turning. It does not need to fill the space between the knob insides and the nut tightly.)
Step 15: Cut the Knob Screw to Length
I threaded a 1/4 x 20 bevel head screw into the top of the coupling nut and marked its depth with masking tape. Then I measured the distance from the masking tape's right edge (as per the photo) to the end of the screw. I measured this amount from the bottom of the bevel where it meets the threads and cut the screw to length. I ground away some burrs.
Step 16: Attach the Knob
I drilled the hole in the top of the knob to fit a 1/4 inch screw. The metal shim around the coupling nut does not fit perfectly, but I was able to push the knob onto it part of the way by hand. I used the screw to pull the knob onto the coupling nut the rest of the way. See the second photo. I used a grinding wheel to remove the excess from the head of the screw and make it flush for mounting the plate that goes over the top of the knob. I was careful not to grind away any of the plastic. The screw gets quite hot when grinding like this, so I stopped frequently and let the screw cool.
Step 17: Glue on the Top Plate
The plate that goes over the screw head on top of the knob is attached with adhesive, like auto body adhesive. Clean away any excess glue.
See the second photo. It is almost impossible to remove the thin aluminum plate from the knob without creases and wrinkles appearing. But, some burnishing with a piece of wood from both sides of the plate removes most of these so that no one notices them.
This knob adjustment assembly for a NordicTrack Achiever Ski Machine works very well again, and will last a long time. While this process is feasible and the cost in materials is very low, I spent almost six hours making and fitting all of the parts. Still, if one of these absolutely must work again, what I have done shows it is possible to make a repaired version that is probably better than the original.
Here is a link to an Instructable that describes a number of modifications I made to my NordicTrack Challenger, some of which would be helpful for any NordicTrack.