A Work-Holding Thingamajig

This thingamajig actually has a real name, but I didn't put it in the title because nobody would know what it is. The official name is a "finger plate," and its mission in life is to hold small and awkwardly-shaped things for drilling or shaping. In the staged photo below of my completed plate, it's holding a scrap of aluminum I picked specifically because it is not square (parallel) in any plane. Holding it in a vise would be hopeless, holding it in your hand would be dangerous, but holding it in the finger plate just works:

The brass bit that looks like an arrow is the finger, and I'm sure you can guess which part is the plate. The adjustable nut on the screw in the middle merely provides a fulcrum point, and you adjust it for clearance equal to the part being clamped. The large knob in the back is tightened to provide the clamping force. You can move that one to the other end, so you can clamp with the single point when that's appropriate.

I had read about the finger plate in a totally geeky book called "The Machinist's Bedside Reader." That book is an out-of-print cult classic, and I recently paid $75 for the pleasure of owning it. It was the first copy I had found under $100, so I'll definitely get my money back after I'm done reading it.

Then, I stumbled upon an amazing video source on YouTube. The guy's library of pro-quality videos is called "Clickspring," and it's really well done. His two-part video series on making a finger plate inspired me to make one. Seriously, if you have any interest whatsoever in this machinist stuff, invest 20 minutes to watch these two brief videos. You'll learn a lot about how it's done, and appreciate a master at work. Click these links: Part 1 , Part 2

My project started with a chunk of scrap aluminum I had picked up at Cabin Fever for a couple of bucks. Not bad, since a brand new piece that size might be 20 bucks once shipping is added. Of course, it already had a slot in the end, a couple of random threaded holes, and another slot across the face of one side. No problem - this is a shop tool, and existing features just add character. Here, I'm using the height gauge to precisely mark spots to drill.

I had already deviated from the plan, because my plate was significantly larger than Clickspring's. I just couldn't see cutting it down, so I modified all the plan dimensions to compensate. The other problem is that on my small mill, I didn't have a nearly large enough "work envelope" to hold the plate in my vise. My first task was to make a removable "foot" to hold it in the vise. I accomplished that by clamping the plate directly to my mill table. Here's a photo taken later in the process. You can see the four very precisely located holes that let me put the foot in either direction, and the threaded hole in the center where it attaches. The pins exactly match the location of the holes. You can see that the hole at the top had to be elongated a bit, because in rotating the plate to drill the hole, my alignment was off a bit. That would never happen on a larger mill, coming soon to the Grant St. Garage...

In that photo, you can also see that I've filled the two existing threaded holes with threaded rod, held forever and ever with red Loctite, and the slot has now been turned into a V-slot with the band saw and sander.

Once the foot was done, I could hold the plate in my vise and erase that annoying slot across the top. That operation also leveled the screws filling the old threaded holes with the base.

Now it was time to make the thumbscrew for the center post, and by happy coincidence, the most beautiful object I've ever managed on my lathe lined up with the most in-focus photo I've ever taken on my cell phone - click it and look at the close-up!

I also made the larger screw for the back. I didn't have brass in sufficient diameter for that, so I made the head in aluminum and used a brass screw.

Now, time for the finger. I made it from brass, and the first step was to carefully lay out the shape and the center point of four holes. It's blue because I coated the top surface with "machinist's blue", a special dye that's easy to remove later. The lines were scribed by hand, as were the locations for the holes.

The outer two holes were threaded for the clamping screw, and the inner ones made the end points for the slot, which was finished with an end mill:

The slot was a little rough - I cleaned it up later with a hand file. Then it was over to the band saw to rough out the shape:

The final shape was refined with a vertical belt sander and a spindle sander:

The final result is the lead photo in this post. If you've watched the videos, you might note two deviations from the plan. First, there should be chamfers on the edges of the finger. I spent some time trying to duplicate Clickspring's methodology, but in the end my mill and vise were just too small. And, since my finger is thinner than his and brass instead of steel, maybe I'm better off without then.

The other variance was for a fixture to precisely drill holes in the center of round stock. I actually made it, but I didn't feel all that comfortable with it, so I made a test piece first. The V-groove in the test plate was cut with a router bit in the mill, and the complex round piece fits precisely in the groove, and holds a 9/16" drill guide, with a separate guide made for each hole size:

It fits together like the photo below, and then you put the round stock in the V-groove and clamp it down. Somehow I didn't take a picture of that, but I'm sure you get the idea.

I tested it, and was not impressed. The drill cut slowly, and there was nowhere for the chips to go. It stalled, and I finally finished the hole without the guide. It did indeed bisect the small rod I was testing. I had made the template with the tap drill size for 8-32, so I tapped the hole. That showed the other problem - no support for the tap, so it was difficult to get it started straight.

The picture below tells the story - a nice tapped hole in the center of a rod, but crooked! Not good.

That operation is easy to do in the mill, and the results are very precise, so I left that feature off my finger plate. I'm pleased with my new thingamajig - not a tool I'll use every day, but essential in some cases for safety, and I learned a lot making it!