One of the things we were most worried about as we looked at starting this restoration is how we could replace the bolts that held the wings on since they had been lost in California. We lucked out when Steve Stavrakakis had a spare he was willing to loan us and we found a machine shop that does quality work and isn’t afraid to make things for aviation use.

At first glance, this looks like it shouldn’t be too difficult to find. It looks to be just another shoulder bolt drilled for a cotter pin. Nope! We were able to use the manual to find that the tolerances are tiny. Just 1/1000 of an inch can be the difference between the bolt working as intended and wearing in an unsafe way. They also have to fit the holes in the attach fitting. Not easy to find and doing it wrong could mean the wings falling off in flight.

I spent time talking with Glenn at Limited Productions in Bellevue, WA and showing him this bolt along with the manual. We were able to find the specs for the material in the manual and it matched 4140H. Glenn compared the strength properties of that to the strength requirements called out in the manual to be extra sure it would hold. All we needed to do was provide him the dimensions needed.

How do you measure a hole to 0.001″ accuracy? You try the micrometer that works great for most of what we are doing and notice that you can’t get the same number twice and then you decide you need to find the right tool for the job. After all, the wings need to stay where they are supposed to! There are lots of options for inside micrometers out there and they get more expensive as you get more accurate. We decided that a two point option with 0.0001″ accuracy was plenty for what we are doing.

This thing is awesome. It comes with a disc so you can check the calibration. It does need to be calibrated once per year to ensure it stays within tolerances, but I can live with that. This thing even specifies what temperature it was calibrated in. I ordered from MSC Industrial Direct and would happily buy from them again. Here is a link to this one: https://www.mscdirect.com/product/details/38170874?rItem=38170874

Being able to measure helped. We also discovered that the holes in the attach fitting are not perfectly round. Great. We will be honing the holes to precisely match the custom made bolts. I’ll post on that as we actually do the work and I can give pictures and information other than what we plan. (Since things on this project seldom go exactly as planned!) The general idea is that we will hone the holes out to fit the brand new bolts. then hold them in place with unthreaded bolts (essentially pins) that Glenn also made for us while we carefully place each bolt.

I’m sure you noticed that one is pretty and shiny while the other is dull and sort of yellow. That is because the pins were left as Glenn made them and the bolts just came back from being cadmium plated to prevent corrosion. The dull finish is because they had to be baked as part of the plating process since they are hardened steel. The team at Metal Tech in Monroe, WA were great to work with. I dropped these bolts off to them on a Tuesday and was able to pick up that same Friday. They also took great care tagging each bolt and returning them to their correct bags so that we can identify them. (We do have that cool inside micrometer but I still don’t want to have to sit and decide with 100% certainty exactly which bolt is which since some are just 0.002″ or less difference in size.) Link to Metal Tech: https://metaltechfinish.com/

One thing the pictures don’t show is that Glenn made the awesome suggestion that the threaded part of each bolt be made to a standard size. Brilliant! the part of the shank that goes through the hole is exactly the size of the hole in the fitting (well, what we will hone it to be) but the threaded section is just a tiny bit smaller so that it works with AN standard nuts and washers that I can just buy off the shelf at Spencer Aviation. He also made the head a standard size so they work perfectly with our tools!

I’ll be mentioning Glenn often in this blog. He and his wife are nice people who run their company machining pieces to exact specifications. He knows what he is doing and is genuinely a pleasure to work with. http://limitedproductions.net/5001.html