The trick to aligning the balance spring is to position the balance wheel so the Balance Wheel Post, that engages with the Fork Pins, is pointing directly at the center of the Fork shaft. I refer to this position as the ‘natural center position’ of the Balance Wheel. And the Fork Center Pin should be pointing directly at the center of the Balance Wheel Shaft.
Then, with the Balance Spring rotated to the position where it drops into the Balance Spring Adjuster mount on the L1 Frame 3, push the hex center of the Balance Spring onto the hex of the Balance Wheel. Then push the hex center of the Balance Wheel onto the hex of the Balance Shaft Note, you may have to file the hex’s before you start to make this a snug slip fit. I didn’t glue the Balance Shaft or the Balance Spring to the Balance Wheel, because the Balance Spring is the part most likely to fail, and I wanted to be able to easily replace it.
When I was testing my L1 Assembly, the Balance Wheel was regularly hanging at the same angle. Using the L1 Balance Spring Adjuster to rotate the Balance Spring so that the ‘natural center position’ of the Balance was better aligned with the Fork shaft, and it made the problem go away.
After connecting the balance spring to the balance wheel and the tourbillon frame, the balance wheel tab should point directly at the fork, when the balance wheel is at rest. See Figure 9.
It doesn’t really matter what angle the Balance wheel is at, relative to the L1 Balance Spring and the L1 Balance Shaft. But the L1 Balance Spring to L1 Balance Shaft relationship is critical.
Note: The Balance Wheel is ‘transparent’ in the drawing to allow the Balance Spring End Mount to be visible.
Getting it to Tick
This is the most critical part of the design. It is made easier if you have printer that generates accurate prints. With my printer, I needed to drill out the all parts so the shafts spun freely, but I did not need to file any of the parts.
There are 4 parts involved, the Balance Wheel, the Balance Wheel Spring, the Fork, and the Escape Wheel. The names in this section refer to Figure 9.
* Make sure that any surfaces that contact between the Balance Wheel, Fork, and Escape Wheel are free of burrs, bumps, or any other printing artifacts that may cause a surface not to be smooth. If not, then some filing or scraping with a knife may be necessary to smooth the parts.
* Make sure that the Balance Wheel, Fork, and Escape Wheel each rotate freely when installed by themselves. The Wheels should spin easily, and the Fork should flop back and forth as the assembly is rotated.
I ran a 2.5mm drill through the Fork and Escape Wheel shaft holes, and a 3.5mm drill through the Escape Wheel shaft hole to ensure that any printing artifacts were cleared out of the cavities.
· Note: Run the drill backwards in plastic at first, otherwise it may auger in at some weird angle, and ruin the part. Once the drill is running smoothly backwards, reverse it to clear out the plastic shards.
* All bearings need to fully seated, so that their top surface is flush with the respective part. You may need to pop them out and scratch out underneath them with a knife so they rest square with the shaft.
* With just the Fork and Escape Wheel installed:
· Turning the Escape Wheel backwards (clockwise in Figure 9), should cause the Fork to snap back and forth easily.
· And turning it counterclockwise should cause it snag against a Fork Tine. If the Fork snaps back and forth a little, it is OK. But if it never snags the Balance wheel when rotated counterclockwise, then the Fork Tines may be too short.
* With just the Balance Wheel and Fork installed (No balance Spring), spinning the Balance Wheel back and forth should cleanly engage the Fork. If there is any sign of a snag, or slowing down, then inspect where the two parts are rubbing, and file the offending part lightly. It is easy to take off too much. If you do, just print another part, and start again.
* Depending on the direction the Balance Wheel is spinning, one of the Fork Pins and the Fork Center Pin should slide along the surface of the Balance Wheel shaft, but not touch so much that they slow the Balance Wheel down. The two contact points formed by the Fork Pin and the Fork Center Pin act to hold the Fork at an angle where its Tines can snag/block an Escape Wheel tooth.
· When the Balance wheel is rotated in the opposite direction, the Balance Spring Post engages with the Fork Pins to swing the Fork in to its opposite position. The swinging action of the Fork causes the Escape Wheel to advance one tooth, and engage with the opposite Fork Tine.
· If there is any binding when the Fork swings, you will need to file the Center Pin a little shorter.
* When all the parts are assembled, a very light amount of torque on the Escape Wheel in the counterclockwise direction should cause the fork to swing, and the Balance wheel to rotate. Continuing to put torque on the Escape Wheel will cause the Fork to move to its opposite position when the Balance Wheel swings back, due to the Balance Spring. As long as you put consistent, light torque on the Escape Wheel, the assembly should continue to tick.
Other Troubleshooting Suggestions
If it is refusing to work, often the problem is with the basic alignment of the parts. In the ‘at rest’ position of the balance wheel/shaft with the balance spring attached and the Balance Spring End Mount screwed in, the ‘balance shaft post’ should point straight at the fork shaft. If it is way off, you have probably pressed the Balance Spring onto the wrong hex position of the Balance Shaft. If it is off just a little, you can try re-positioning the Balance Spring End Mount.
Sometimes I have either bent the Balance Spring installing it, or it has taken a ‘set’ (by sitting in a wound up or unwound position for too long) causing it to position the Balance Shaft Post at the wrong angle. The only solution in this case is to reprint the Balance Spring. I don’t use glue for the Balance Spring for two reasons; if I need to replace because of the problems mentioned above, and (according to A26) it is the normally the first thing to wear out.
The first time I tried to install it, I bent the Balance Spring when I was screwing the Balance Spring End Mount to it. Now I run a 2mm screw in and out of the end of the Balance Spring a couple of times before I try attaching the Balance Spring End Mount to it.
The bullets above basically say; make sure the escape wheel, fork, and balance wheel rotate freely as individual parts. Then combine them, 2 at a time, and make sure they don’t bind each other.
For instance, ensure that the Balance Shaft Post does not bind when it turns and pushes the Fork Pins back and forth. The slightest drag will make a difference. Sometimes I have had to either file off, or scrape off with an Exacto knife, the bottom of the Fork Center Pin, and/or the top of the Balance Shaft Post. And ideally the length of the Fork Tines only lets the escape wheel turn one tooth each time it is swung back or forth by the Balance Shaft Post.
The alternate forks are identical, except for the Fork Tines being longer on 2 and longest on 3. This allows you to file them down to get a better fit. The Tines of a freshly printed fork are rounded at the tip. Things work a little better if the tips are filed to a point. Also, as accurately as possible, make sure all the teeth of the balance wheel are the same length. Some elephant foot from printing can cause problems.