How do you screw a ratchet wheel on tightly and securely?

[VWatchie]

Image from here: https://www.sellita.ch/scripts/calibres/images/DocTec_SW200-1_7.pdf

I wonder if there is a safe and effective way to screw in the screw for the ratchet tightly and securely.

This question has arisen because I am servicing my very first Sellita movement, the SW 200-1 calibre, and have therefore studied the technical documentation in detail. As shown in the image, Sellita recommends that the screw should be tightened to 16 Newton millimetres. I don't know exactly what that is and don't think it's critical. What is critical is that I don't know how to even get close to tightening the screw properly.

As we all know, when we screw in the screw, what happens is that it starts to turn the ratchet wheel and wind the mainspring and therefore sits very loosely. One method is to lock the ratchet wheel by driving a screwdriver blade between two teeth, but I generally think this is a very bad idea as it could damage or even break a tooth, especially if the ratchet wheel is made of brass, which I believe it is in this case.

I have to say that I feel lost. On one hand, we know that screws, in general, should be tightened very tightly, as @nickelsilver described in this post, but on the other hand, that seems impossible for the ratchet wheel and is possibly not even desirable as indicated in this post, also by nickelsilver.

It would be very helpful and interesting to receive feedback and practical advice on how to tighten the ratchet wheel screw tightly and securely.

Edited January 19 by VWatchie

[HectorLooi]

I usually jam a homemade brass oiler into the teeth of the ratchet wheel and crown wheel. Brass is softer than the steel teeth, so it is less likely to damage the wheels.

[RichardHarris123]

Very interesting question.  Although I understand the concept of torque, what 2l16N.mm feels like, I  have no concept.  Once the ratchet wheel starts to turn, I  use a chisel edged piece of peg wood too hold the wheel and tighten by guesstimate. 

[Neverenoughwatches]

We just develop a feel over time of how tight screws should be, I generally pause momentarily when the screws reach the end of their threads and then an extra little nip up. The same method I've used for the last 45 years but on a much smaller scale. 

Whereas the average wood screw or machined screw takes the driving force of our wrist, forearm and upper arm even our shoulders come into play with heavy gauge long screws to send them home. Watch screws only have to deal with the torque we can apply through our fingers. I would say the size difference is comparable. 

Edited January 19 by Neverenoughwatches

[GPrideaux]

I generally hold the ratchet wheel with a finger. Appropriately covered, of course.

As for visualising 16 N.mm ... that's a torque of one Newton at a radius of 16mm ... roughly a 32mm cotton reel being turned on a pivot with enough force to winch a 100g mass. Or a 6mm diameter screwdriver handle turned with sufficient force to winch a mass of about 270g. (I am a Maths teacher.) To be slightly less mathematical, "good and tight but don't overdo it" would seem to be what is called for.

[caseback]

This makes me think back on a HD liberator motorcycle engine I overhauled some 40 years ago. The workshop manual we had only specified 3 torques: tight, very tight and extremely tight .

For watch repair however, we have " extremely light".

As already mentioned, you develop a feeling for it (which I'm sure you already have yourself) safely staying away from any breaking point.

I use an old pair of brass tweezers to hold the ratchet wheel while tightening.

[VWatchie]

56 minutes ago, RichardHarris123 said:

I  use a chisel edged piece of peg wood too hold the wheel and tighten by guesstimate.

So do you press it down on the flat top of the ratchet wheel or do you jam it in between the teeth?

14 minutes ago, GPrideaux said:

I generally hold the ratchet wheel with a finger. Appropriately covered, of course.

That sounds like a safe method, and since the finger will cover a rather large portion of the area I guess it will give enough counterforce. I'd be happy to try that.

Even if we were to tighten the screw a bit too loosely, I assume the risk of it coming off is small since it continuously rotates and is tightened in the clockwise direction of the ratchet. Still, it would feel safer to tighten it a bit harder than I usually manage.

 

[RichardHarris123]

Pressed onto the flat top but using a finger seams like a better option.  

[VWatchie]

3 minutes ago, caseback said:

For watch repair however, we have " extremely light".

I don't think so as expressed by one of our most experienced friends:

"In school, if your screws aren't tight, like you think they might snap, you get your movement tossed in the sawdust box!"
~ @nickelsilver

("tossed in the sawdust box!" roughly meaning "failed")

[caseback]

4 minutes ago, VWatchie said:

I don't think so as expressed by one of our most experienced friends:

Well, for my XL sized fingers, 16N.mm is extremely light. 

[Neverenoughwatches]

2 hours ago, VWatchie said:

So do you press it down on the flat top of the ratchet wheel or do you jam it in between the teeth?

That sounds like a safe method, and since the finger will cover a rather large portion of the area I guess it will give enough counterforce. I'd be happy to try that.

Even if we were to tighten the screw a bit too loosely, I assume the risk of it coming off is small since it continuously rotates and is tightened in the clockwise direction of the ratchet. Still, it would feel safer to tighten it a bit harder than I usually manage.

 

Tight but not over, the ratchet screw is one that you really dont want to snap....we've all been there

[Malocchio]

For a reason I don't remember anymore I once tightened the screw without the ratchet wheel. I ended up filing a wrench out of a spare ratchet wheel to get the screw loosened. 

[mikepilk]

I just hold it still with a bit of brass rod - see below.

The torque of 16 N.mm is the effect of a force of 16 N acting at 1 mm. Hard to visualise as we don't tend to think in Newtons. But 16 N is about 1.6 KG, or 1600g at 1mm. Still not easy to imagine.

But consider it acting over a distance of about 150mm (that's about 6 inches to use oldies).  Then the force to give a torque of 16N.mm is about 10g.  So if you were tightening a bolt and had a 6" spanner, you would put 10g force on the end.  (Not a lot, my Bergeon 4040 movement holder weighs 32g)

Problem is, that doesn't really help as we are using a screwdriver 

BTW, one of my most useful tools is just a bit of brass rod I filed to a point at one end, and to a sharp shovel at the other - useful to prizing bridges apart, holding things in place etc without scratching.

Edited January 19 by mikepilk

[Neverenoughwatches]

@VWatchieLook what this " Tool Junkie " just found in a watchmaker's lot, and check out the range on the scale

[nevenbekriev]

I also use my finger to block the wheel. Apply the same torque as on bridge screws

[SwissSeiko]

I use a plastic pointer stick between the teeth and the bridge. I rarely use my fingers to hold stuff, as they obstruct my view.

[Neverenoughwatches]

1 minute ago, SwissSeiko said:

I use a plastic pointer stick between the teeth and the bridge. I rarely use my fingers to hold stuff, as they obstruct my view.

I use a plastic probe as well, pegwood tends to have crumbs break off sometimes. Bamboo is harder and breaks less, now we get into the discussion of bamboo contains a high percentage of silica which can scratch watch parts I think that may not be entirely true, silica has more than one form. Holly or boxwood is a hard uniformed tight grained timber that won't break up like the pegwood thats most available today. Why do we use pegwood ? It readily soaks up naptha.

And easily forms to a shape.

Using a brass or copper probe might be a good idea instead of wood or plastic.