Smoothing Broaches

[Curare]

Hi All

Now that I have a staking set, I want to purchase some smoothing broaches specifically for barrel arbour holes in plates and mainspring barrels.

I mainly work on Seiko movement and the average measurements are around 1mm plate hole to 2mm barrel hole.

And are all broaches tapered ??

I was thinking of this set from Cousins?

https://www.cousinsuk.com/product/0070-to-300mm-german1?code=B36688

Appreciate your advice and comments

Regards CJ

Edited June 3, 2024 by Curare

[Neverenoughwatches]

21 minutes ago, Curare said:

Hi All

Now that I have a staking set, I want to purchase some smoothing broaches specifically for barrel arbour holes in plates and mainspring barrels.

I mainly work on Seiko movement and the average measurements are around 1mm plate hole to 2mm barrel hole.

And are all broaches tapered ??

I was thinking of this set from Cousins?

https://www.cousinsuk.com/product/0070-to-300mm-german1?code=B36688

Appreciate your advice and comments

Regards CJ

Yes all broaches are tapered, without the tapered length they would not broach evenly and the tapering does vary. Minimum to maximum broaching out sizes are quoted per broach.

[Knebo]

21 hours ago, Curare said:

was thinking of this set from Cousins?

https://www.cousinsuk.com/product/0070-to-300mm-german1?code=B36688

Appreciate your advice and comments

I have a very similar one (also Cousins, also German, but 0.6 to 2.0mm). I'm happy with it and I once did a decent job (I think! time will tell..) on a barrel bridge to reduce sideshake of the barrel.

Sure, if you are an extreme perfectionist, you could argue that holes get better=straighter by having smoothing broaches with the least possible taper. That means, to have many! 

But really, for Seikos you will be fine with that set from Cousins. 

PS: have fun! It can be quite a bit of back and forth until you get the right hole size. Take it slow and don't get frustrated. But when you do get it right, it's a great feeling. 

 

 

OH, a tip!! 

What I did to help me get the hole size right was to measure the barrel arbor (at the respective position for barrel or bridge) and then use a sharpie to draw a line on the smoothing broach where it had the correct width. That saved me a lot of time. 

Edited June 4, 2024 by Knebo

[Neverenoughwatches]

4 hours ago, Knebo said:

I have a very similar one (also Cousins, also German, but 0.6 to 2.0mm). I'm happy with it and I once did a decent job (I think! time will tell..) on a barrel bridge to reduce sideshake of the barrel.

Sure, if you are an extreme perfectionist, you could argue that holes get better=straighter by having smoothing broaches with the least possible taper. That means, to have many! 

But really, for Seikos you will be fine with that set from Cousins. 

PS: have fun! It can be quite a bit of back and forth until you get the right hole size. Take it slow and don't get frustrated. But when you do get it right, it's a great feeling. 

 

 

OH, a tip!! 

What I did to help me get the hole size right was to measure the barrel arbor (at the respective position for barrel or bridge) and then use a sharpie to draw a line on the smoothing broach where it had the correct width. That saved me a lot of time. 

You can always broach from both sides to make the hole more even. The plate and brigde holes i broach for a tighter fit than the barrel and lid.  These are not part of the unwinding only the winding as the arbor is fixed by the click and only moves when winding up.  As long as they aren't so tight as to stress the winding mechanism, the important bit is to get the friction right in the barrel so as not to rob power right at the source.

[Waggy]

2 hours ago, Neverenoughwatches said:

You can always broach from both sides

I tend to do the same, but I'm not very strict about it, given the very shallow taper of the broach from end-to-end and the 1 or 2 mm of hole you are broaching the height difference of the broach over that plate thickness is vanishingly small, I could do the trigonometry, but haven't had enough coffee  yet this morning, therefore in reality I don't think it really matters if you do from one side or do 50:50..or...? I tend to do from one side, and if it needs more I try and remember to do the next bit from the other side, if I can't remember which side's turn it is I don't worry about it using the reasoning above.

[Neverenoughwatches]

3 hours ago, Waggy said:

I tend to do the same, but I'm not very strict about it, given the very shallow taper of the broach from end-to-end and the 1 or 2 mm of hole you are broaching the height difference of the broach over that plate thickness is vanishingly small, I could do the trigonometry, but haven't had enough coffee  yet this morning, therefore in reality I don't think it really matters if you do from one side or do 50:50..or...? I tend to do from one side, and if it needs more I try and remember to do the next bit from the other side, if I can't remember which side's turn it is I don't worry about it using the reasoning above.

The difference is likely insignificant, on a thicker material than a lid a bit more so. Theoretically you would end up with a peak in the center of the hole if you broached from both sides, which i suppose once that had worn away would leave a cylindrical hole. That possibly could be taken into account of when to stop widening the hole. In all circumstances the the finished fit is the narrowest part of the hole and will eventually wear to the widest part of the hole which is one reason why its not a lasting repair. Dont be tempted to polish up the opening as the soft brass can potentially be charged up from any compound used. Ideally a broach with as shallow taper and smoothest cut as possible to finish with.