Francisco Posted June 30, 2009 Report Share Posted June 30, 2009 The “ratchet wheel driving wheel”, reference 32.033, is a gear of the automatic winding system of the 7750. In some cases this gear will finish with some teeth damaged, as seen on this picture took by Zigmeister: This failure can be produced by frequently manually winding a watch with a 7750 movement. If this failure happens the watch will show a poor power reserve. The ETA 7750 replacement is not compatible with the Asian 7750. The difference is the size of the two pivots of this ratchet wheel. The Swiss spare will not fit in the jewels, as the diameter of the pivots is larger. Here a picture of the Asian ratchet wheel: Next picture shows one of the two pivots that are different: This is a picture of the another wheel face and of the pivot that has smaller diameter in the Asian wheel. The marked pivots have the following dimensions: Asian 7750: 0.19 mm Swiss 7750: 0.27 mm Therefore, the is a difference of 0.08 mm, 8 cents of mm. This difference is large enough to not to use the Swiss replacement, as the pivot cannot fit the jewel. There are three options to use the Swiss part: 1.- To exchange the central part of the ratchet wheel (steel, silver) that it is fitted on the wheel (brass, golden). That means using the central part of the Asian, fitting this part in the Swiss. This task is explained here: http://www.replica-watch.info/phpBB3/viewt...=59&t=53355 2.- To fit the ETA jewels in the Asian plates. I have not research if these jewels are available. Anyway, this is not an easy task. 3.- Modifying the pivots of the ETA ratchet wheel, to reduce the diameter. This task is shown in this tuto. This task requires an extreme precision. It is difficult to show you how small these pivots are. I try ii in the following pictures: First, the size of the gear. The pivot is not visible in the next picture, due to its very small size. On this zoomed image it is possible to see the pivot. A watchmaker lathe will be employed to reduce the pivot diameter. With a good watchmaker lathe a precision better than 0.02 mm is possible, so we can do this task. First step is to measure the ratchet wheel, as shown, it has a diameter of 6.76 mm. Therefore, a collet of 6.8 mm is used: Next picture shows the wheel fastened by the collet in the head-stock of the lathe: Another image to show the vey small size of the pivot: To reduce the diameter a precision milling disk will be employed: The disk is connected to the milling attachment of the lathe: Next step is adjusting the lathe. The milling disk only has to polish the pivot, not other parts of the wheel. We move the disk closer to the pivot until they are touching. In this moment we know we have to polish 0.04 mm, because the total reduction will be 0.08 mm in the pivot diameter. As this task requires so high precision, the scales of the lathe has not enough precision. One of these scales is shown in this picture: We need an external indicator, which has a real precision of 0.01 mm. Next picture shows the indicator, located to measure the distance we move the disc to the pivot. Once the disk is brushing the pivot when it is rotating, the dial is set to 0. Then we are ready to turn. However, the motor is not employed. Just turning by hand as this video shows, to be more precise: Quote Link to comment Share on other sites More sharing options...
valerian Posted June 30, 2009 Report Share Posted June 30, 2009 That is very impressive, Francisco! Thank you very much for the creativity and for showing. Val. Quote Link to comment Share on other sites More sharing options...
Francisco Posted July 1, 2009 Author Report Share Posted July 1, 2009 That is very impressive, Francisco! Thank you very much for the creativity and for showing. Val. Thanks! It is a mod that requieres expensive tools... but I think it is interesting to show how these mods are done. Francisco Quote Link to comment Share on other sites More sharing options...
sander Posted July 1, 2009 Report Share Posted July 1, 2009 Thanks! It is a mod that requieres expensive tools... but I think it is interesting to show how these mods are done. Francisco How about selling them? Quote Link to comment Share on other sites More sharing options...
Francisco Posted July 1, 2009 Author Report Share Posted July 1, 2009 How about selling them? why not? Quote Link to comment Share on other sites More sharing options...
RWG Technical Posted July 1, 2009 Report Share Posted July 1, 2009 Well documented Francisco. I did the same project a while back to see if I could get the gear to work in the Asian 7750. Only problem was the cost of the gear and the time to do the modifications (I only have a watchmaker's lathe, so all is done by hand). I would have to charge $75 for the gear to only break even...not worth it... Thanks for taking the time to document the process, your lathe is much BIGGER than mine... Quote Link to comment Share on other sites More sharing options...
sander Posted July 1, 2009 Report Share Posted July 1, 2009 your lathe is much BIGGER than mine... Well....as long as it's only his lathe..... Quote Link to comment Share on other sites More sharing options...
bwhitesox Posted July 1, 2009 Report Share Posted July 1, 2009 Lathe envy indeed. Thanks Francisco very informative post. Quote Link to comment Share on other sites More sharing options...
FxrAndy Posted July 1, 2009 Report Share Posted July 1, 2009 Thanks francisco Quote Link to comment Share on other sites More sharing options...
Guest avitt Posted July 1, 2009 Report Share Posted July 1, 2009 Nice work, Francisco! You have a fantastic setup! May I ask what is the primary use of your milling equipment? Quote Link to comment Share on other sites More sharing options...
Francisco Posted July 1, 2009 Author Report Share Posted July 1, 2009 Nice work, Francisco! You have a fantastic setup! May I ask what is the primary use of your milling equipment? milling, making gears, cutting, polishing... Quote Link to comment Share on other sites More sharing options...
Guest avitt Posted July 1, 2009 Report Share Posted July 1, 2009 milling, making gears, cutting, polishing... All for watchmaking? Quote Link to comment Share on other sites More sharing options...
specialvat Posted July 1, 2009 Report Share Posted July 1, 2009 Love to see this detail work. Thank you. Quote Link to comment Share on other sites More sharing options...
Francisco Posted July 1, 2009 Author Report Share Posted July 1, 2009 All for watchmaking? no. a watchmaker lathe means a precision lathe. It can do the same as a bigger lathe, with more precision and, as it is smaller, with smaler pieces. Francisco Quote Link to comment Share on other sites More sharing options...
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