Gulmite Screws

Frequently, I am contacted by owners of Crown coaches and asked how to acquire a set of Gulmite drivers so that the fasteners holding their coaches together can be removed and/or replaced. Each time, I do my best to be helpful, but the fact is that these tools are elusive at best and unobtainable at worst. Therefore, I've decided to put everything I know about Crown Head screws and the associated driver tools down in one place so that I can refer inquiries to a central topic on the subject.

In the "Crown Advisor" on this site, I mention the following:

…without supplying any additional information. There was a reason for this, there is very little else to impart. My set was purchased through Eugene Fastener, 360 Wilson St. Eugene, Oregon, 97402. This was in 1995, and at the time, I knew everyone in the building by name, including the owner, Jeff. He put in a few calls after surveying the sample screws I provided, and eventually was told after describing them that he wanted "Crown Head drivers". The set that I received several weeks later looked like it had been picked out of all corners of a warehouse, as the photo later in this topic shows, nothing matches.

For a number of years, I used to refer people to West Coach of Chino, California to purchase drivers. I was once contacted by a representative of West Coach and told that sets of drivers were available for sale:

Hmmm, many of the fasteners in my bus were #8, and they weren't offering that size. Still, a partial set would be a start. Unfortunately, I recently found out the West Coach has gone out of business, leaving no forwarding address.

Here is my collection of Gulmite drivers, with a sample screw for each size:

From the left:

• #6 drivers (two)
  The far left hand diver is one that I had custom made, more on that later. The right hand one was a badly rusted driver that I found inside one of the window cavities of the bus while I was tearing it apart. A lucky find. It has a ¼" hexagonal shank that chucks up in a drill nicely.

• #8 driver, part of the set I ordered. It originally came with a plastic screwdriver handle that wasn't attached to the shaft very well. I got tired of using it by hand to remove the several thousand fasteners in the bus, and used a hacksaw to chop off the handle, turning it into a straight shank that could be chucked into an electric drill.

• #10 driver. This one also had a plastic screwdriver handle, but the driver tip kept falling off the shank and I was afraid I'd lose it, so I silver brazed it onto an old Phillips or square bit so I'd have the hexagonal shank.

• ¼" driver. This one came with an attached adaptor that engages with a ¼" square socket set bit. It's shown with the adaptor disengaged at the rear. There were only about a dozen ¼" Crown Head screws in my bus, I seem to remember most of them were in the emergency door hinges, and some had been used to attempt to repair some of the metal fatigue in my walls.

• #12 driver (not shown). I found this driver only after I took the photo partly because I couldn't find any samples of that size screw. I don't know that I've ever used this driver bit on my bus. It also has the ¼" square socket set drive end.

The #8 driver in the photo above contains an interesting artifact. Stamped into the metal shank is the following:

This patent number does appear to be valid, and a quick search of Google brought up some results referring to it as being a patent for a "security screw removing tool". Further research may turn up a patent holder who might be able to direct you to a manufacturer or drawings or plans that would allow the tools to be duplicated (assuming that the patent has expired).

So, if sets of drivers (or even individual drivers) aren't available for purchase, how about having some made?

The original tools I purchased had been broached in order to create the internal splines. This is not a process that can be duplicated at home, and while it might be possible to recreate the drivers with a metal lathe and properly formed cutter bits, it would be a laborious process, one that would be prone to trial and error until you got it right.

After broaching, metal is usually heat treated to increase it's hardness for tool usage, but my purchased tools apparently were not sufficiently hardened, because as I used them, the internal splines wore down, a process that was accelerated if I was not careful to prevent the driver bit from slipping on the screw heads due to misalignment or insufficient pressure. Several of my bits have had to have the ends ground down to expose more of the undamaged internal splines in order to continue to be useful.

The set that I purchased did not come with a #6 driver bit. Since my coach had quite a number of these size fasteners in the interior, I had one made so that I could remove the trim and panels that were attached using them.

At the time, one of my clients was a machine shop which had two EDM wire cutting machines. The older of the two machines was rather decrepit, and I was occasionally called in to troubleshoot its electronics.

I approached the operator of the machine and explained my need. (Rather than attempt to describe EDM machining, I'll refer you to the link above.) He used a very old optical scanner that looked like a giant view port from the Wizard of Oz to enlarge the profile of the head of my sample screws to fill the viewer, about two feet in diameter. Then, by some process I didn't witness, a program was written that directed the newer of the two machines (identical to the one pictured in the Wiki page) to cut a driver out of a billet of metal using the EDM process. The result was a hollow shaft that was splined all the way though. This tool is made from very hard tool steel metal, and will probably never wear out. I ground some flats on two sides so that I could put an end wrench on it to back out some stubborn screws.

If I was going to have another tool made, I think that I'd have the splined billet cut into wafers about ¼" thick, and weld those pieces to a shank of some sort. The long driver with the spline all the way through works well enough, but because the hole isn't "blind" there is nothing to prevent the screw from extending into the body of the bit. This makes putting screws into material difficult, as there is nothing to back up the screw head and give you a purchase to hold the screw against the material as you drive it in. All of the Crown machine screw have tapered self-tapping cutter threads at the tip, and are made of very tough material. They thread themselves into any material given the proper size pilot hole.

Another EDM process for making these tools called "sink cutting" was proposed by Gary, a Crown Coach owner who is very inventive. He supplied his machinist with several clean, non-damaged screws and those were used as the cutting electrode:

I mentioned to him that such tools might be marketable, to which he replied:

As far as I know, he never made any additional driver sets.

There you have it, EVERYTHING I know about Gulmite fasteners, including pictures, links, fabrication suggestions, and hints as to where to research out more info. If anyone has a source for these tools, or decides to have a few dozen sets made and wants to start selling them, go for it, I am easy to please, only a small royalty is due for my diligent research.