Reverse ratchet screw?

[Fleslie]

I am still very much a newbie, I have taken about 50 mechanical watches apart. Currently working on a Wittnaur 8K/1 movement where I snapped the head off the ratchet screw going into the arbor. I added some oil and tried to remove the rest of the screw and to my amazement it was reversed threaded like a crown screw. I was able to get it out but have never seen this before. I will try to find a reverse threaded ratchet screw (.65 by 1.31 mm) is this a common occurrence with wittnauers?

Frank

[mikepilk]

I have similar experience to you, and was recently nearly fooled by an ETA 984 movement which had reverse threaded screws on both crown and ratchet wheels. I've never seen it on the ratchet wheel before, and neither had the usual 3 slots in the head. So, it seems rare, but it does happen.

The ratchet screw was very tight: in such a situation I always try to turn it a bit the other way to break it free. That's how I discovered it was an anticlockwise thread.

[HectorLooi]

I had a similar experience with a Citizen 6501. And what's worse, the reverse threaded barrel screw keeps getting loose after a couple of months.

[anilv]

Citizen does this on their 0200 movements as well..Some had the three lines to denote a reverse thread.. some don't. Kinda stupid to use a reverse thread on a gear fitted to a square post (arbor) as it should never come undone on its own. The only reason I can imagine for specifying a reverse thread here is to prevent lazy folks (me!) from winding the barrel using this screw instead of getting the keyless stuff done first.

Anilv

[TimpanogosSlim]

Yeah. Some Unitas pocket watch movements were like this too. Guess how i know. 

[Fleslie]

Thanks to all that replied, now that I know that this is possible, I will proceed with caution on future watches.

Thanks

[Fleslie]

Can I use a reverse threaded crown screw to replace the reverse threaded ratchet screw which would be very difficult to find.

[mikepilk]

36 minutes ago, Fleslie said:

Can I use a reverse threaded crown screw to replace the reverse threaded ratchet screw which would be very difficult to find.

Yes, If they are the same size, as they are on the ETA 984 I recently serviced. 

[LittleWatchShop]

There is one on ebay for 25 bucks.

[LittleWatchShop]

According to my research the 8k is the same as an AS 1727.  Appears to me that one screw is RH and the other is LH.

Since you did not post a picture of the movement, there is no way to confirm, visually, that the movements are the same.

Edited January 28, 2022 by LittleWatchShop

[steaksauce]

Just put together a Ribaux that also had a reverse retched screw, with a right hand crown screw.  A bit backwards, I thought.

[mikepilk]

I serviced an AS where the ratchet screw on the crown was not reversed. Though it should have been. Someone had forced in a larger screw which had cut some sort of thread. Of course it kept coming loose, so I had to Loctite it.