Handy Aluminum Scribe!

Hi all! I've decided to come back from my years of hiatus to bring you this beautiful beginner project that can teach various lathe operations and fundamentals! Here we have the Handy Aluminum Scribe! A scribe is a super useful tool for woodworking, machining, or just poking and prodding! Here's a little background information: I was starting to see a lot of good material being tossed into the metal recycling bins at a shop I frequent. I thought that maybe if I developed a little project, I might be able to salvage that useable scrap and also possibly turn it into a teaching tool for anyone wanting to learn machining over there!

DISCLAIMER!

I am NOT a professional machinist and I would caution anyone using machine tools. THESE ARE DANGEROUS. Never get too comfortable and always remember that they are stronger than you. Use all safety measures and be careful! I am not responsible for any injuries or damage from the result of this project.

The first step in any project is to gather your work pieces. I was lucky enough to find a drop of 3/4" diameter aluminum bar that was about 7" long. My first thought was "why would someone throw away such a nice stick of material?!" Anyways, I measured it out and it was just the perfect size. At this point I was still wondering what I would use as my point... the story behind that will come later! I will say this, if you are able to acquire 1/2" diameter aluminum bar, use that! It will save you a lot of time by not having to machine down so much, although it is very good practice and you can adjust your feeds and speeds while working to get the perfect cuts.

Since this is an on the fly, work with what you've got project, I didn't really see the need to do a 3D CAD model to plan it out. Also, many people don't have access to systems that can handle 3D CAD so I decided to try out hand drafting this project! If there is a lot of requests for a 3D CAD, I could draw it up in SolidWorks and post the Part Files later on (I can export to a lot of different software like Fusion as well). Here's the gist of what my paper and pencil draft means:

6.000" Length of the Body

0.400" Diameter

3/4" 6-Degree Taper at the Front End

60-Degree Chamfer at the Back End

5-Plunge Cuts to Identify the Back End (0.125" Apart, 0.040" Deep)

10-Plunge Cuts to Identify the Front End (0.125" Apart, 0.040" Deep)

REMEMBER... all of these dimensions can be changed by you! I have fairly small hands so this is what felt comfortable for me. I would suggest holding a bunch of screwdrivers, dowels, and pencils/pens in order to feel what is comfortable for you. After all, you're making it!

One of the most basic operations on a Lathe is the Face-Cut. The purpose of this operation is to cut a nice straight surface to work off of. By doing this cut, you are essentially setting up the work piece to be perfectly parallel to the cutting edge of the tool, with respect to the carriage. To do this cut, you just barely want to touch off of the flat face of the workpiece (while the machine is running), set your zeroes, and then take about 0.025" off the face. I'm assuming if you're this far, you might have access to a lathe and know how to use it (I hope).

I was cutting at about 1100RPM. Because this is aluminum, you want to cut at a faster speed because any slowness can cause buildup on the cutting tool from melting chips. I had a power feed rate of about 0.030" on all my cuts.

Here comes the fun! This is probably the most time consuming part of this build. First things first, safety and material handling. A simple rule of thumb for working on the lathe is that if your workpiece is sticking out of the chuck 3x more than the diameter, you need a live center. This not only keeps the workpiece from extreme chattering when cutting, but also reduces the stress on the headstock from a workpiece flapping around spinning at 1000+ RPM.

An easy way to work your piece down is to take 0.025" passes for rough cuts, and 0.010"-0.015" for your finishing cuts (in order to get a slick, almost mirror-like surface). Remember to machine back enough to compensate for your parting tool and the depth of your hole when you set up the live center! I worked it back a total of 6.400" to account for any mishaps. You can also machine the diameter a little oversize, .405"-.415" for any sanding/finishing operations. I had my settings dialed in so I was happy with the machine finish.

Soon you'll be able to get the rough feel of your scribe! As stated in the Step before, make sure you have enough room for your parting tool and removal of that hole you drilled for the live center. Make sure to use cutting fluid and be nice and easy! I would suggest putting a cushion or some paper towels under the workpiece to keep it from marring once it falls off after the cut. DONT TRY TO HOLD IT WHILE THE WORKPIECE IS SPINNING! This is very dangerous because there could be an uncut burr somewhere along the part, these are very sharp and will fillet your fingers at the speed we're working at! Once the part is free, give it a once over and see how you feel about it.

Now this part is a little tricky and requires some setup. Because we are going to be doing a 6-Degree Taper, we are actually going to set the machine's compound miter to 3-Degrees. This will give us a total included angle of 6-Degrees. I chose a 6-Degree angle because it is not too in your face, and it adds a very nice aesthetic to the piece. I took around 0.100" off with this setting. Be sure to work slowly on this stage. The compound is moved manually so a nice steady pace will give you the best finish!

If you don't know how to set up your lathe to run tapers, here is an excellent YouTube Video by ToolHugger.com: Turning Tapers on a Manual Lathe

NOTE: Don't forget to face the part to get rid of your live center hole!

I had two criteria for my scribe needle: A material that is hard and wont lose it's point easily, and a material with a diameter that fit the aspect ratio perfectly. I searched around the shop and on the ground, I found a bent up 3/32" Tungsten Electrode! This would be perfect for this project. I used a triangular file to cut a groove into the straight piece of tungsten and broke it free from the bent part with a pair of needle nose pliers (1" Length). I drilled a 1/16" Hole using the drill chuck about 1/2" Deep. To make the final fitment, I ground a spade point on the tungsten and used that as a ream for the perfect fit. You see this makeshift drill bit in the second photo!

NOTE: Make sure you center drill the first hole for proper alignment and use lots of cutting oil. Smaller drill bits are prone to breaking and you DO NOT want to get one stuck in your scribe!

Now that all the main body parts are done, the only operations left to do are the cosmetic ones. I used a 60-Degree Threading Tool for the rest of the build. To cut the chamfer, all I did was run the edge of the tool (the one with the angle) into the corner of the work-piece and cut it down to what I thought looked good. This is subjective to the builder! Some may like a very subtle chamfer, some may like a very pronounced one. I did mine on the pronounced side. Be careful not to go too far or else you will form a point!

Remember... Be sure to face the back edge, the parting tool leaves a little material left over on the cut!

We're on the home stretch! To do these plunge cuts, you're going to want to lightly touch off in the X-Direction of the carriage (Forward/Backward) and set your zero. Then you want to go to the edge of your chamfer and move over 0.125". You can make as many plunges as you want! I found that a 0.040" Depth gave a very nice looking cut with the 60-Degree Threading Tool. I decided to do five on the back and ten on the front.

Note: Don't forget the live center rule! If you want to add a lot more grooves to the front end, you can use the hole drilled for the scribe point (tungsten electrode) to hold the body while you work.

Now that we are done with all the cosmetics, it's time to finish everything up! Once you push in your scribe point (you may need to do this on the lathe if it's really tight), you can now take it to a grinding wheel and sharpen your point. I held it at about a 30-Degree Angle and just rotated until I liked the depth and pointiness of the scribe. I didn't use any glue to set the tungsten electrode because of how tight of a fit we have! Also, if we need to replace it, the process will be a lot easier.

Congratulations! You just made yourself a super awesome scribe that you can pass down for generations to come! I'm planning on being more active on Instructables so if you have ANY QUESTIONS leave them in the comments and I will find time to answer! Also I am planning on entering this Instructable into the Trash to Treasure Challenge please don't be afraid to show your support!

PLEASE DON'T FORGET TO VOTE!

MORE PROJECTS COMING SOON!