NordicDanny sent an adjustment knob assembly for a NordicTrack Achiever to me. He was curious about how to disassemble it. I covered that in a previous Instructable. This Instructable is also mostly for him, but covers how I rebuilt the stripped mechanism with common parts from a hardware store. I really hoped I could accomplish a rebuild with only a little cutting, drilling, and grinding; but, I found I needed to weld some pieces to finish the job.
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
The hex socket on the knob is 7/16 inch deep, too. Cut 7/16 inch from the coupling nut, which is just about half of it, including the width of the sawcut. Grind away any burrs.
Step 4: Prepare to Weld
I clamped the short piece of 3/8 inch rod and the piece I cut from the coupling nut to a piece of aluminum for welding the two together.
Step 5: Chase the Threads
Some weld spatter blocked the threads at one end of the coupling nut. I restored them with a 1/4 inch tap.
Step 6: Grind and Smooth the Welded Assembly to Fit the Case
I ground the welded assembly to make it fit and slide smoothly in the plastic case. Then I smoothed the grinding marks by hand on an oilstone. There may be marred surfaces inside the case that cause it to stick.
Step 7: Make a Cavity for the Cable End
A lead end on the cable needs to fit into the new welded assembly. (See the first photo.) Drill a hole into the side of the 3/8 inch rod portion of the welded assembly. Make the hole large enough to fit around the lead end on the cable. (See the second photo.) I used a cutting wheel on a Dremel tool to make a channel for the cable and to square the bottom and top of the hole I drilled. (See the third photo.) I had to make certain the lead end on the cable fits entirely inside the hole I made for it.
Step 8: Attach the Cable Parts to the Case
With the cable end in the welded assembly, push the other end of the cable through the hole for it at the bottom of the case. Feed the cable into its housing. Some twisting of the housing over the cable may be necessary to get the cable to go into its housing, especially if a strand or two have frayed. Snap the end of the cable housing into the case.
Step 9: Threaded Rod
A piece of 1/4 inch threaded rod (Redi-Bolt) will replace the cast screw shaft shown in the second photo of the Introduction. To my surprise, a 1/4 inch nut would not fit onto it. My calipers indicated the 1/4 inch threaded rod I bought is just a little larger in diameter than it should be. I had to improve the threads with a 1/4 inch die. Notice the curl of steel coming from the die.
Step 10: Making the Screw Axle
There is a hole in the bottom of the plastic case that anchors the end of the screw axle. Grind away the threads to leave a smooth section. This is not a high precision operation, but the smoothed round area should be on-center as much possible. I have also wrapped some masking tape around the screw to mark where the top of the case is on the screw. This will aid in determining where to cut the screw for length.
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.