Originally posted by: MARIÁN MIHOK Dear all Sony DD fans. There are many posts explaining various methods of fixing the cracked center gear. It's hard to say, which method is the best. Here I would like to present my method, with which I have very good results - it works like new and it should not be just temporary solution. Here are some of the methods: 1. Form the missing tooth - it's good solution, but it will not last long. The glued area is very small and no glue will bond to this kind of plastics, well. The plastic gear will continue shrinking, causing new crack on it's weakiest point, i.e where the tooth was formed. 2. Reduce the center metal disc size - it will not always work - the walkman will probably have problem with FF and during PLAY, w/f may be increased 3. Split gear into two parts and glue them to the metal disc leaving one-tooth width gap on each side. In this case, it may produce clicking sound as well, but it's not bad solution. My method is the combination of the above mentioned methods, taking advantages of each of them. The main prerequisite is, that you have to have one more gear, for example some from your previous unsuccessful repair attempts. You can use this one gear to repair many other gears. If not, buy any DD, DDII, DDIII, DD30, DD22 or DD100, DC2 walkman sold cheap or the one "for parts". And of course, you have to have right tools. Also, you have to work very precisely. 1. Adjust the crack gap width to be the multiple of one tooth width. If the gap width is 1 1/4 of the single tooth width, you simply cannot add 1 1/4 tooth because the gears wouldn't fit. You also cannot add two teeth and extend the gear size because it would be eccentric on one side and the result would be audible. Extending size about 1/4 or 2/4 tooth width is acceptable, but 3/4 is too much. First, split the gear from metal disc and then put it back. Second, measure the gap width using the second gear Now we have to decide, how to proceed. If the gap width is exactly the same as the width of single tooth, then we have to reduce metal disc diameter by 0.1 mm - to leave some space for further gear shrinking If the gap width is between 1/2 and 1 of single tooth width, then we're happy - we do not need to do anything, for now. If the gap width is between 1 and 1 1/2 of single tooth width, we have to reduce the metal disc diameter by 0.1mm to obtain the gap width of about 1 tooth. If the gap width is between 1 1/2 and 2 of single tooth width, then we're happy - we do not need to do anything, for now. If the gap width is between 2 and 2 1/2 of single tooth width, we have to reduce the metal disc diameter by 0.1mm to obtain the gap width of about 2 teeth. 2. Reduce the metal disc size, if necessary (see above) In order to do it, attach the disc to the upper side of 1.6 mm drill. Reduce the size by using sandpaper and high-speed grinder 3. Increase the gap width Later, we will insert several teeth into the gap. If we insert just one or two, they will not fit well. Their width will be so small, that they will not fit precisely to the metal disc (they will twist). Therefore we have to insert at least 4 new teeth. We have to increase the gap width accordingly. Cut the gear as displayed on the image. Do the cut on the place, where the teeth begin. In my case, I removed 3 teeth: Very good method of widening the gap is to use the following tool:
4. Insert new teeth into the gap I removed 3 teeth, so I have to cut 4 to be inserted into the gap. Use razor blade to cut them. Again, cut them where the teeth begin. Now, form them to be cone-shaped. Now, insert them into the gap You can notice two gaps, between inserted teeth and gear itself. These are very important for two reasons: - later we will fill them with the glue. Glue will bond perfectly to the metal inside these gaps, however it will not bond to the plastics. We will apply glue to both sides of the gear, both layers will be joined together via these gaps - we must have free space to be able to position the inserted teeth very precisely. It is key to the success On the image above, you can notice additional hole drilled. This one is also important, as the epoxy glue layers on both sides of the gear will be joined through it. Use 1.2mm drill to make this hole 5. Position the teeth precisely Use the second gear to position added teeth with very high accuracy. 6. Apply the glue Apply the glue to the both sides of gear, as displayed on the image. Do not forget to fill the gaps and additional hole that we created. From the top side, apply the glue around one side of the socket, as displayed on the following image. Leave the thinner part of the socket untouched. Also, do not touch the metal disc with glue. The epoxy glue layer cannot be thicker than the thickness of socket. From the bottom side, apply as thin layer as possible. Fill all gaps and also join plastic gear with the metal disc: After the glue hardens, reduce the layer width on the bottom side with the file. I have very good experiences with this method. If done precisely, the result functionality is indistinguishable from original. And I think it will last longer. Epoxy glue is not the best to use for this kind of plastics, but in this case it is not important. Marian
4. Insert new teeth into the gap I removed 3 teeth, so I have to cut 4 to be inserted into the gap. Use razor blade to cut them. Again, cut them where the teeth begin. Now, form them to be cone-shaped. Now, insert them into the gap You can notice two gaps, between inserted teeth and gear itself. These are very important for two reasons: - later we will fill them with the glue. Glue will bond perfectly to the metal inside these gaps, however it will not bond to the plastics. We will apply glue to both sides of the gear, both layers will be joined together via these gaps - we must have free space to be able to position the inserted teeth very precisely. It is key to the success On the image above, you can notice additional hole drilled. This one is also important, as the epoxy glue layers on both sides of the gear will be joined through it. Use 1.2mm drill to make this hole 5. Position the teeth precisely Use the second gear to position added teeth with very high accuracy. 6. Apply the glue Apply the glue to the both sides of gear, as displayed on the image. Do not forget to fill the gaps and additional hole that we created. From the top side, apply the glue around one side of the socket, as displayed on the following image. Leave the thinner part of the socket untouched. Also, do not touch the metal disc with glue. The epoxy glue layer cannot be thicker than the thickness of socket. From the bottom side, apply as thin layer as possible. Fill all gaps and also join plastic gear with the metal disc: After the glue hardens, reduce the layer width on the bottom side with the file. I have very good experiences with this method. If done precisely, the result functionality is indistinguishable from original. And I think it will last longer. Epoxy glue is not the best to use for this kind of plastics, but in this case it is not important. Marian
