Now you have a plastic case, and you have printed out your dial and hands on photo paper. To complete your prototype, pickup a mineral glass crystal (only a couple of bucks) and mount a strap, and see how it has all come together. Obviously, plastic cases are only so strong, so springbars can pull out rather easily. So strapping on plastic prototypes is something to be done carefully. And ABS seems to be stronger than PLA.
If you need to make a running prototype, you need have one of your designated movements, a prototype dial, and some hands which will fit the posts of the movement. I have a laser engraving machine at home (doesn’t everyone?) so for this Mark Carson Ka La Ladies watch, I laser engraved and laser cut a prototype dial from plastic. I had to sand it down to 0.40mm, but then it was a good fit for the plastic prototype case. My watchmaker had some hands laying around which fit the target Ronda 763 movement, so we were able to create a running prototype. While visually not exactly like the production watch, it did confirm dimensions and ergonomics.
If you need to work on ergonomics, now is the time to make revisions, not after you send your design off to have cases made. While your cases are being made, you need to have hands and dials manufactured if you are assembling the watches yourself. If you have a manufacturing partner make the entire watch for you, then you just pay your money and wait for their pre-production prototype to arrive. But you are fully committed at this point.
If you are going to do assembly yourself (as I do with my Ka La men’s watches via watchmakers here in Hawaii), you can have cases, dials, and hands all produced by separate companies. But try to keep the number of vendors down whenever possible, so compatibility problems are avoided, and you have an accountability trail.
Using a manufacturing partner (as I plan to do with the ladies watch) for complete watch production makes life much easier. The downside is that you will have stock of however many references you decided to make in fixed quantities. In contrast, for my men’s Ka La watches, I have 3 case finishes, 6 dials, and 3 hand colors, so I can assemble a variable number of each reference based on demand using the collection of parts I have. Also, by having parts on hand, repairs will be easy in years to come. Another reason my men’s watches are assembled here in Hawaii is that we can regulate the mechanical movements as needed during assembly. But to be honest, brand new ETA movements are very well regulated, and so far, none have required adjustment during assembly. But having the ability to regulate mechanical movements is a plus. The ladies watch will utilize a Swiss Ronda quartz 763 movement, so regulation will not be an issue. And to be able to offer this ladies watch at this price, it made sense to have the entire watch made by a manufacturing partner.
What’s left, now that production is going on (for a number of months)? Well you will need straps and packaging (boxes or travel cases) and stuff for supporting sales, like manuals, a website, etc.
Assuming you are happy with readily available (not custom designed) straps, you just need to find a vendor and get some samples before making quantity purchases. If you are doing a metal bracelet, this should have been designed along with the case, and ideally is made by your case maker, so the fit and finish will match the watch case. Custom bracelets are like cases in that the MOQ (minimum order quantity) will be in the hundreds and will often be another 50% of what a nice case costs. So you will have a large capital investment with custom bracelets. If you can live with readily available metal bracelets, then this is no harder to source than straps and may even come from your strap vendor.
You will need boxes or some sort of packaging. I use travel cases for my Ka La men’s watches, but I plan to use boxes for the Mark Carson Ka La Ladies watches of this Kickstarter project. Boxes with your brand name imprinted on them are usually subject to MOQ in the hundreds (500 units being typical). There will be production time measured in months, so as soon as your watches are in production, you need to make some decisions regarding boxes or other packaging.