Measuring a M.S. Barrel

[Hank7421]

I have a Waltham 16s 1908 7j Hntg. SN 16215159. The M.S. is missing. How can I measure the M.S. Barrel to get the right thickness M.S.?
I tried measuring the depth of the barrel with the stick end of the calipers and come up with 2.49 mm. When I pull up the SN on the P.W. Database, There is only 2.80 listed for a hole end M.S. Am I measuring it wrong? 2.80 would make the M.S. stick out beyond the lip of the barrel.

[Bob Tascione]

Hi Hank,
Not sure if you're going to be able to measure the internal depth with your caliper that way. You need to measure from the cap 'seat' down to the bottom of the inside of the barrel. I would just measure the thickness of the barrel cap and the thickness of the bottom of the barrel and then insert the cap into the barrel (might want to put the arbor in to help get the cap back out),measure the thickness of the barrel from the outside and then subtract the cap and barrel thickness from your measurement. You can then subtract a tiny bit (.1 mm or so) from that to give a tiny bit of clearance for the spring width.
If you would like I can figure out the strength and length for a 30 hour run. I would need the exact inside diameter of the barrel (not across the cap seat diameter but the internal space where the mainspring sits and also the diameter of the arbor.
Note that if the top of the cap sits below the barrel edge then you'll need to measure from the top of the cap and NOT the edge of the barrel. I think it probably sits flush or a little above but just in case.

Please let me know if I can help Hank,
Bob

[Hank7421]

Thanks Bob. I went on Dave's Watch Parts website and sent him my question. Dave replied that it is normal for the mainspring to extend past the edge of the barrel and that 2.80 is the right width. He is sending me the right mainspring. I will let you know if it works.

[Bob Tascione]

Oh ok Hank,
You must have a safety barrel there. Is the main wheel resting right above the mainspring with no cap on the barrel?

Bob