# HWN/Hawina BPH?

#### JeffG

NAWCC Member
Good day!
Could someone please help me understand how to calculate BPH for this time train?
The two wheels on T2 are confusing me.
-Jeff

#### new2clocks

NAWCC Member
Is there any information on the backplate? Some German manufacturers will stamp the backplate with the BPM.

Also, your title does not distinguish between a HWN marked movement and a Hawina marked movement. Although they were made by the same company, they are different movements.

Can we see a picture of the backplate?

Regards.

#### JeffG

NAWCC Member
Is there any information on the backplate? Some German manufacturers will stamp the backplate with the BPM.

Also, your title does not distinguish between a HWN marked movement and a Hawina marked movement. Although they were made by the same company, they are different movements.

Can we see a picture of the backplate?
Sure!

#### disciple_dan

NAWCC Member
Donor
Isn't that upper wheel part of the motion works?

#### JeffG

NAWCC Member
Isn't that upper wheel part of the motion works?
The upper wheel on T2 is clutched, and drives the 30-toothed wheel on the center arbor. The same wheel on the center arbor also drives the intermediate wheel which drives the hour cannon.
-Jeff

#### Willie X

##### Registered User
Only thing different will be the 30 to 72 gear down to the 2nd wheel pinion, all else is the normal gear up to the escapement. Willie X

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#### JeffG

NAWCC Member
Only thing different will be the 30 to 72 gear down to the 2nd wheel pinion, all else is the normal gear up to the escapement. Willie X
I don't understand. There is no 72 gear. The 30 teeth on the center arbor mesh with a 48 toothed wheel on T2's arbor, but a 75 toothed wheel drives the rest of the train. Maybe my poor penmanship has thrown you off?

My confusion stems from that smaller extra wheel driving the center. I know that on an American-style auxiliary driven center you disregard T2 altogether in the BPH formula, but in those cases the same wheel is driving both the center arbor and the T3 pinion.
I know that, due to the pendulum length, BPH should be between 3,800~4,000.
-Jeff

Last edited:

Corrected.
Willie X

#### JeffG

NAWCC Member
Holy cow I might be onto something!
If I assume that the 48 toothed wheel on T2 is acting as a pinion in the train between the EW and center arbor, the math works out to 3,984.4. That's about right for this 33-ish" pendulum setup.
I don't know for sure if I'm correct, but I'll be able to sleep tonight.
Ultimately, I suppose the clock will tell me if Im wrong.
-Jeff

#### David Hill

NAWCC Member
theindex.nawcc.org

#### dickstorer

##### Registered User
Jeffg, I think your BPH is going to be 4080. That works out to be a pendulum of approximately 30.5 inches.

#### JeffG

NAWCC Member
Jeffg, I think your BPH is going to be 4080.
Thank you for working that out. Would you mind telling me how you got to that number?
-Jeff

#### shutterbug

##### Moderator
Staff member
NAWCC Member
That upper wheel in not involved in the calculation.

#### dickstorer

##### Registered User
I may be wrong but I think the upper wheel on T2 serves the same purpose as it would if on the center wheel arbor. So it is 48 x 68/8 x 40/8 x 2 =261120/64 = 4080 BPH To go farther find BPM square that and divide that number into a constant of 141120. 4080/60 = 68 BPM. 68 squared is 4624 So 141120/4624 = 30.519 inches Theoretical pendulum length

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