Tuesday, January 15, 2008

Replacing the plastic key head with a wooden one


Recently, the black plastic head for my key finally tore completely off. After using the key without it for a couple of weeks, I decided it was time to do something about it. While perusing my favorite Mercedes wrenching site, I found this thread http://www.mercedesshop.com/shopforum/showthread.php?t=208913,, where one of the members had replaced the plastic head with some wood. A suggestion was made that some nice zebra wood to match the interior trim would be nice. Since my head needed replacing anyway, I embarked on the following project to replace it with a nice wooden one. With replacement heads being only about $3 I didn’t save any money, but that wasn’t why I did this project.

All in all, I think the key turned out rather nicely, pretty much just like I wanted it to turn out.

Picture 1: Finished key

First I’m going to outline the steps I took. After that I’ll point out all the mistakes I made and what I did, or could have done, to correct them. Lastly, I’ll include a few woodworking tips for those non-woodworker gearheads that might be interested in trying this project themselves.

The entire project probably cost me about $80 since I had to buy all the supplies and didn't cut corners to get the desired result (the mirror finish epoxy, for example, was ~$30 alone). I did it anyway because I wanted experience with the materials and finishes, I thought I’d like the result, and I wanted to practice my dormant woodworking skills.


  • Dremel tool with tear-drop shaped burr.
  • Jewelers saw (or fretsaw, jigsaw, or even a hacksaw).
  • Drill, at least ¼”.
  • Rattail file or small riffling files.
  • Coarse flat file.
  • Two small disposable artists brush.
  • A small chisel.
  • A vise.


  • 1/8" thick wood.
  • Thick gap-filling, two-part epoxy that isn't runny when mixed.
  • Finish. I chose a two-part mirror finish bar coating epoxy.
  • Denatured alcohol, used to clean epoxy off surfaces, even once cured.
  • Some paper. Thick, brown paper or several layers of newspaper will do nicely.
  • Sandpaper. I used just a single grit of 320 and found that it sanded the wood plenty fast enough.


This project isn’t a quick one, mainly because of my use of epoxies for glue and the finish. I compressed the timeline into just under a week and it was half as long as I should have taken.


The overall process is to cut some key-head blanks from some thin wood and sandwich the key between them. We carve out a mortise (pocket) between the blanks for the key to fit into, epoxy the laminations together with the key inside, and then finish it. Sounds pretty simple.

STEP 1: Select the wood

Picture 2: 1/8” thick Bolovian Rosewood

My local woodworkers store sells dimensional, surfaced, exotic hardwoods, including zebra wood (what Mercedes calls zebrano). The pieces come in 3" x 24" and varying thicknesses -- I chose the 1/8" thickness because two layers of it were a pretty close match to the thickness of the plastic head, eliminating the need to plane it thinner. They were out of the 1/8” thick surfaced zebra wood when I went, and not wanting to wait, I selected some Bolivian Rosewood because it had a fairly strong grain and I liked the warm tone of it. The exotic hardwoods run about $13, but they also had some really nice figured “domestic” hardwoods that I almost chose.

STEP 2: Layout Key Head Blanks

Picture 3: laying the key head on the wood

Picture 4: Four blanks laid out on the board. Two will be needed for the project.

Lay out some key head blanks on the wood, and cut them out with the jewelers saw. Do the layout so the grain runs sideways along the key (perpendicular to the key shank) like shown for strength. Use the plastic head to size the blanks, but make them a little oversize.

STEP 3: Cut Out the Blanks

Picture 5: Rip cut first

Picture 6: Cross cut next

Cut out the blanks. Make one edge straight as a reference edge for laying out the mortise.

Picture 7: The two blanks that will be used

The two blanks that will sandwich this key.

STEP 4: Mark the Key Shank

Next put the key into the plastic head and mark a line across the shank, then pull the plastic head off the key shank. We’ll need it again for later steps, so don’t mangle it too badly getting it off (assuming getting the plastic head off will require any effort anyway).

STEP 5: Lay Out the Mortise

Picture 8: Laying out the location of the mortise

Use the line across the shank and the straight edge on the blank to lay out the mortises in the blanks.

STEP 6: Carve Out the Mortises

Picture 9: Test fitting the key in the mortise. Not quite deep enough yet.

Use the Dremel tool with the burr to carve out the mortise in each blank. Make sure that the two blanks fit together flush with the key between them.

STEP 6: Glue the Lamination Together

Glue the laminations together with some of the gap-filling epoxy so the key is held tight in the head. Spread the epoxy into every cranny of the mortises and over the entire faces to be glued together, then embed the key in it.

Picture 10: Clamping the laminations together

Gently clamp the laminations together with some paper between the lamination and the blocks of wood to keep the squeezed out glue from gluing the key head to them. Pictured here is the key, shank sticking up, clamped in the vise.

STEP 7: Clean Off Excess Glue and Test Fit in the Locks

Picture 11: Fresh out of the vise. There’s a big glub of glue to be removed.

And here’s the key with wood head after letting it cure overnight. Trim of any excess glubs of glue using the file or chisel and test the key in all the locks of the car – some locks (especially the trunk lock on my car) need more clearance than others.

STEP 8: Layout the Desired Head

Picture 12: Desired head laid out and marked for visibility.

Next, position the plastic head on the blank and trace the outside to get the shape of the head.

STEP 9: Make the Keychain Hole

Picture 13: Drilling out the ends of the keyring hole.

Picture 14: Sawing out the remaining wood between the holes.

Drill and saw out the wood from the interior of the hole through the head.

Picture 15: The rough keyring hole.

STEP 10: Shape, Round Off and Sand

Shape the outside with the flat file and the inside of the hole with the rattail file. When you have the desired shape, sand the wood smooth with the 320 grit sandpaper.

Picture 16: The shaped, smoothed and sanded key head.

STEP 11: Finishing

Mix up a small amount of the bar-finish epoxy and paint it on the wood.

Picture 17: The key immediately after painting the expoy finish on.

STEP 12: Let the Finish Cure

Picture 18: The finished key after the finish has cured.

And here is the finished coating. It still has that extra glossy look that matches the interior wood trim in the car.

Once the finish is cured, check that the key fits in all the locks of the car again and remove any excess.


Since I had to buy all the materials I certainly didn’t save any money, and my choice of materials and finishes made the cost quite a bit more than it could have otherwise been. However, I think my key turned out rather nicely and I enjoyed learning some new woodworking techniques and materials, which was pretty much the point of this project for me. I now have a nice conversation piece and enjoy the tactile feel of the smooth finish whenever I use it.


I’m certainly no master woodworker and my finished key shows it. I made mistakes nearly every step of the way, some of which I expected and planned for, but others I didn’t and had to correct for along the way. In this section I’ll point out all the mistakes I made and how I corrected them as I went along as my way of illustrating that one does not need to be terribly skilled at woodworking to end up with a nice looking key head.


When I laid out the key head blanks, I knew I needed a straight edge to reference the key shank position against. I decided to use the straight edge of the surfaced wood for this, but didn’t notice that it had been dyed a dark color. Luckily, my key shank ended up deep in the wooden head and I had to file down the wood on that edge for clearance in the locks, thus removing most of the dyed wood. Also luckily, the remaining dyed wood is in the least visible part of the head, the one facing the key shank, and because of the curve of the key head, dyed wood only remains close to the shank where it is least visible.


I went through a couple of false starts trying to get the mortise formed in the blanks. First, I tried putting the sandwich in a vise and crushing it together.

Picture 19: Attempting to crush the mortises into the blanks.

Here is the sandwich being crushed. This didn’t work at all. If I had used thick blocks of recently harvested, soft pine, it would have worked. I put a fair amount of pressure on the sandwich and the key barely made a dent in the blanks because the wood is just so hard.

Next, I got out my smallest chisel and figured I chisel out a mortise like you see in the woodworker shows on TV. I proceeded to score the outline with the chisel by tapping straight down into the blank, and all went well until I tried to score an edge with the grain. Then the chisel just split the wood along the grain and popped the small piece into two. I cut four blanks in the beginning because I figured I’d break a few trying to cut the mortises, so I just grabbed another and tried a different way. If I had to make this method work, I’d use some glue and paper to stick the blank to a larger block of wood to keep it from splitting.


When I finally got the mortise carved out with the Dremel tool, I did such a poor job that the key slopped around a lot.

Picture 20: Blurry picture. See how my mortise extends beyond the key.

Sorry for the blurry picture, but I wanted to show how sloppy of a job my mortise was. It got even worse because I had to grind it more so the reference line on the key shank fit all the way to the edge of the blank. This isn’t really a mistake as such since I expected I’d do a sloppy job. This is why I chose to use two-part gap-filling epoxy to glue the halves together. I knew my mortise would be sloppy but that the epoxy could fill the gaps and be stronger than the wood itself. I just had to make sure the epoxy was well spread into all the crevices of the mortise before embedding the key in it.


When I made my mortises, there was so much slop that the key shank could move every which way – side to side, tilt and rotate and even in and out of the head. As I mentioned earlier, in mistake 3, I did plan for this and chose gap-filling epoxy for my glue. As shown in step 6, I braced the key into position in the vise with some cardboard. So far, all was expected and planned for. My mistake was that I forgot that the key shank could slide around in the mortise so that the reference line on it slides inside the key head. When I clamped it in the vise with the shank pointing up, this is exactly what it did. I later caught and corrected this when I test fit the key in the locks of my car and had to trim down the edge with the shank sticking out with a file.


In step 7, the photo shows the key shank sticking out of the head at an angle. This is another place where I didn’t intend for this mistake, but had expected something like it might happen. Back in step 2, where I laid out the blanks, I purposefully made them a bit oversize, just in case the key shanks didn’t end up perfectly centered in the head. In a more perfect world, I’d have made the blanks just a little larger, but it turned out I had just enough extra room so I was OK. To fix this mistake I rotated the plastic key head as I laid it out on the new head in step 8.


In step 9 where I made the keychain hole, I made a mistake in judgment that caused me to make a whole series of mistakes – I decided to try to duplicate the oval hole in the plastic head. This resulted in the wood head being thin on the sides of the keychain hole, right where it is across the grain and the wood is weakest to begin with.

Choosing to do the oval hole also caused me to decide to drill two holes at the sides. I figured I’d get a nice round curve from the drill at those ends and could cut out the middle with the jewelers saw. For some reason, despite using a drill press and a cross sliding vise, I didn’t quite get the two holes exactly where I wanted. Then I had to use the rattail file to clean up the hole. I’m not very good with a rattail file and ended up going too deep and having to repeatedly enlarge the hole, further making the sides of the hole weaker.

So far the head hasn’t broken. Yet.

I didn’t fix this mistake. I’ve given some thought about it and come up with two solutions. The first would be to not try to replicate the oval hole and instead just use a large round one. This would have been easy to make with a larger drill and then I wouldn’t have a rough hole to clean up and smooth out. It is too late for my key, but I’ll do this on the next one.

The second solution is to reinforce the sides of the key head with some brass. I can apply this to my key and am considering it. As I see it, the basic idea would be to cut a slot in the edge of the key from top to bottom with the jewelers saw. Then epoxy a piece of brass in the kerf and file it to match the profile of the key head. There will be a tradeoff with the saw – a wider kerf will allow a thicker piece of brass and strengthen the head more, but it will also weaken the head while trying to make the kerf, possibly to the point of causing it to break right when there’s very little wood to piece back together.


This is a minor mistake, but when I went to finish the key, I mixed up enough epoxy to coat about 10 keys, and then ended up throwing the extra away. Six to nine drops would be more than enough.


I applied too thick of a coating of the finish epoxy and it dripped off, and even cured with some drips. This happened partly because I mixed up so much epoxy, and partly because epoxy, even the fluid kind I selected, is thicker than paint. It may have been thick, but it flowed for an extraordinarily long time (hours) because it was designed to be a self-leveling, pourable finish.

I don’t have any pictures of the back side of the head, but it has some drips of epoxy in it. I haven’t fixed it yet because they are not large and don’t bother me, and I just show the other side to people J. If I wanted to fix it now that the epoxy has fully cured, I could file or sand the bumps off and then either try to polish the finish by wet sanding up through 1500 grit and then polishing with compounds, or put a very thin second coat of epoxy over the entire key.

Better yet would have been to only put a thin coating on the entire head the first time, then, once it was cured enough to put on a second coating (about 2 days), then flip it over and put another thin coating on the entire head. This is why I suggested two brushes in the materials list. You might be able to clean them out with denatured alcohol before the epoxy cures if you want to try.


This is probably the worst mistake I made on the entire project because I made it after everything was done. What was so horrible? After letting the finish epoxy cure for only two days, the finish felt hard to the touch, so I picked up the key and pocketed it. Oops, big mistake. My body heat warmed the finish and made it soft enough to allow the fabric of my pocket to make an imprint in it as shown in the picture (notice the bumpiness of the reflection in the picture below). I had to set the key aside for another 2-3 days for the finish to cure the rest of the way.

Picture 21: I ruined the finish by not waiting long enough for the finish to cure
Like the drips, I’d repair this by either sanding smooth and polishing or just putting on a second coating of finish.


The project is done and ready for use but I still found one last mistake to make. I put a big scratch in the finish while putting it on my keyring. It is one of those split rings, and I didn’t think to protect the key as I worked it around and onto the ring. Next time I’ll wrap some paper or something around the top edge of the keyring hole to prevent this.


I’ve certainly not a master woodworker so none of my tips will be new to fellow woodworkers, but I’m going to provide a few woodworking tips for those non-woodworking gearheads out there that might be interested in doing this project.

So, straight from a barely competent woodworker (me)…
  • Make sure the tooks are oil and grease free. The oils will soak into the wood while it’s being worked and prevent the glue and finish from sticking to it. I use many of my tools for both woodworking and automotive work, so I just make sure they are cleaned off before they touch wood again.
  • Account for the width of the saw kerf when laying out the blanks.
  • The size of the teeth of the saw is critical for this project because of the thin wood used. The rule of thumb is to have at least three teeth engaged in the wood all the time. The support of the other teeth helps keep the saw from catching on the wood and jumping around. If you don’t have a saw with fine enough teeth, cut through the wood at a slant so more teeth are in contact with the wood at any given time.
  • When using the flat file for creating the straight, reference edge on the blank and for shaping, I had a lot more control by holding the file perpendicular to my body with the handle in my stomach, then pulling the small pieces of wood toward me along the file.
  • Some woods, especially exotic hardwoods, have natural oils in them that hinders glue and finish adhesion. Wipe them off with denatured alcohol before applying glue or finish.
  • This is probably just me being paranoid, but denatured alcohol absorbs water over time which is left behind when the alcohol evaporates. Glues and finishes won’t adhere to wet wood so give the wood a good while after wiping it down.
  • Denatured alcohol is a solvent for epoxy. So it can be used to clean up remaining films of epoxy when trimming it away from the key shank. Doing this is a good idea because it might otherwise scrape off in the lock and make it stick.
  • I’m not very good with a rattail file, but I finally figured out that filing at an angle to the face of the head rather than perpendicular it caused the file to not make grooves so easily and also allowed me to change the angle of the strokes to remove the high spots.
  • When mixing epoxy, use the two pot method. Put the components together into one “pot” and mix them thoroughly, then move the mixed epoxy to a clean “pot” and mix it thoroughly again. This helps eliminate there from being any resin that has no hardener at all mixed in as happens along the sides of the first pot. The resin remains sticky for a lot longer if there isn’t enough hardener mixed in and may even never harden. It is recommended to mix the finish epoxy this way so it all hardens at the same time.

That's it.


Anonymous said...

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Cody-wankenobi Gibson said...

This is beautiful! Would you like to sell any of the excess rosewood you most likely have left-over? I'm interested in this project, and will be checking out other amazing remedies you've posted on your blog!


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