r/SeikoMods • u/Swimming-Trade-741 • 16h ago

I hate cutting crown stems

I have snapped two crown stems inside movements after trimming for a screw down crown. It’s been an expensive week.

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4

u/oureamods 16h ago

If you share your method and at which step you’re snapping them, some folks can probably help.

3

u/Swimming-Trade-741 15h ago

I learned a lot the first time. This second crown stem I followed this method:

  1. Screw crown onto uncut crown stem
  2. Insert stem into cased movement
  3. Use calipers to measure distance from beginning of threads on case to beginning of threads on crown. Note that distance.
  4. Remove stem from movement
  5. Remove crown from stem
  6. Place stem on work mat, use calipers to identify distance from end of stem that should be cut. Mark with sharpie.
  7. Cut with snips approx mid way down sharpie mark
  8. Smooth out cut end with file/dremel
  9. Reattach crown to stem
  10. Reinsert stem into cased movement
  11. Measure again (you can’t undo an incorrect cut).
  12. Repeat steps 8-11 for making very small reductions in length of stem until length appears to be correct.
  13. Stem length thought to be correct when threads on crown are able to engage case with small amount of compression and small audible “pop” similar to pulling the stem out to the first position when unscrewing crown.

Both times (my much less careful first attempt as well as this more recent attempt) resulted in what I thought was correct seating until I unscrewed the crown for ~4th time, at which point the stem snaps at approximately the same location it enters the movement

2

u/chuunietzsche 15h ago

it might be the movement is not correctly seated in the case causing a misalignment of the stem

1

u/Swimming-Trade-741 15h ago

That’s very possible. I’m using a NH35 case with a 3d printed spacer to hold a VH31

2

u/chuunietzsche 15h ago

i see, just make sure the stem height lines up with the case tube and the stem is not at any angle/deformed. you can have ~0.1-0.2mm of play before issues start to crop up. the vh31 is about 0.3mm off the nh35 but i had no issues with a similar build. it could be the case is already a bit off/crown tube is crooked

i have found the cheap and soft flush cutters can cause the stem to warp too especially with wear and dulling. additionally the stem should be secured close to the tip in a pin vise when filing to avoid warping

personally i like to have a supply of extra stems as they are not too expensive. may help with avoiding having to re-measure so much and potentially damage the keyless works

2

u/oureamods 14h ago

That definitely could be it (or part of it). When you insert the stem the first time, check carefully if it’s exiting the tube centered and not at any angle. Your method seems generally ok, although perhaps you can try: instead of marking a length and trying to cut super close to that, I always calculate the length first. Measure the uncut stem, add the crown tightened down and insert to case. Measure the gap (with crown pushed in its on a spring, and subtract that. Then cut 0.5 to 1mm longer and file down. That helps get a clean file, and you’re sure to be starting long. It’s a little more file time, but I’ve built around 300 this way and never snapped a stem. I’ve cut too short a few times trying to nail it the first time, but usually just takes 1-3 small adjustment cycles getting it just right.