Custom License Plate Screws

After finishing the rotary broach, and having a 5/32" broach ready to go (the size of hex for my other 1/4"-20 socket machine screws), I was ready to rumble on my machine screws.

I first tried to make it head first so I could punch the hex hole in it.

While this worked in getting the basic profile, getting the thread in there would have absolutely wasted brass material.  Additionally, once threaded, and parted, I had a bad bolt - it didn't even seat into the washer, indicating that I had the angle completely off that I'd measured.  I could not check the fit of the screw while in the part was still in the lathe.  (The angle was measured as a 90-degree bevel.  Apparently, even though I did my best, I did not get it proper.)

I did this twice before I realized I was wasting more material because I could not test it, and concentric surface on the other side was inconsequential.

Third try is the charm.  I used some aluminum and realized that all I need to do is get the angle less than the washer so that the upper edge would seat.  I just wanted it close enough.  Truth be told, it is nearly half way between 45 and 60 degrees, but since 60 degrees would have given me the outside seat, I went with that with the tool squared up.

On my next try, I opted to reverse the construction - turn the outside diameter (0.600", then cut the 60-degree, large chamfer for the bottom of the head to the 1/4" diameter, then thread it on).

Once that was ready, it was time to part it off.

Now, I have two bolts, with no way to grip them yet.  I used a chunk of 9/16 aluminum bar stock and drilled and tapped it to 1/4"-20.  I then cut a number of slots into it so that I could chuck this little tiny bar into the lathe to get "close enough" on the concentric nature of these bolts.

In the previous photos, I had not yet cut two other slots (not all the way through) on the chucking nut in order to properly grip the screws.  Set in the chuck after the cuts, I proceeded to drill a 5/32" hole as a start, re-chamfer the entry point on the drill, then broach it through.

And that is now two license plate bolts complete.  I need to fabricate the light bracket and install the lower plate before I can install these, but two more parts have been completed.

Fancy Hex-Shaped Drill Bits

 On one of my projects (the drafting kit), I had a beam compass that I needed to increase the radii on.  I bought a rod to match what it had, and then promptly realized I needed to drill a hex-shaped hole lengthwise.  Nearly any machinist who has been around for a while (I have to say nearly, because it took me a long time to find this out) will be familiar with tools to cut holes in shapes that are not round.  These tools are called "rotary broaches", and they can get pricey (e.g. the bit itself comes in cheaply around $61 from some random supplier found on the ol' Internet).

So, I found a build-it-yourself rotary broach kit and ordered it from Hemingway Kits.  It uses a designation for "FCMS" (or something similar), which is essentially "cold rolled steel".

The tools required for this are a milling machine (the Harbor Freight special will do), and a lathe, along with an M3x0.5 tap.

First is to face, bore and turn the locking lug.  Then thread it (the measured drawings have measurements in metric and imperial, so it was threaded at 52 TPI).

Once done, make the shank.  It is essentially a part made on the lathe, but the mill is used to cut a flat groove 4mm wide for alignment.

Next comes the body - face it, bore it (different sizes to different depths, then turn the outside of it (this is exact).  Once this is done, you will need to cut an internal thread to match your locking lug.

This comes after the lug itself because you want a good, secure fit, and the locking lug can be used to ensure you don't cut threads too deeply on the inside.  In other words, you will fit this to your lug.  Once done, the part is parted (no pun intended) off, and taken to the milling machine where it is set up at a 1-degree angle.  I used a collet block to hold it, so I set a 0.017" lift 1" from one side to give me exactly a 1-degree angle.

Then the back (parted area) is milled flat there, and then a boss is completed flat along that angle to match the groove in the shank.  You have to drill the two holes to bolt the shank and the body together, and then you can tap those holes.  I milled small flats on the sides on opposite ends using the boss as a horizontal index.  Those two flats allowed me to get a solid grip on the body when threading.  Hint - use tapping fluid with an M3 tap.  It makes it much easier.

You might notice the appearance of the aluminum bar with pins and a hole - I quickly realized in a previous step (when fitting the locking lug to the body) that I needed a spanner wrench to match, so I whipped one up.

The next part required is the broach's "spindle".  This is the part that actually holds the rotary broach itself.  Following the specs, I slapped it together.  Now, I know I am supposed to wait until I have an actual broach, because angles and math, but I wanted this complete.  Here is the parts, followed by assembly.

After the spindle, I measured, and re-did the math for how long broaches are going to be based on the angles of everything.  After recalculations (and making tools along the way to measure how far I am when I am really close to the lathe spindle), I whipped a broach up.  Quite fun using a hex collet block in the mill at an angle.  It was a bit sketchy - it was a tool makers vise, in a tilting vise.  But, once I got the feel for taking cuts, it went pretty quickly.  This is a 5/32" for what I assume to be a 1/4"-20 drive.

Once shaped, I needed a slight cone.  Most people seem to use a Dremel to grind, but I opted to chuck in a small hollowing wood carbide holder because of it's diameter, and then just used it like a normal tool in the South Bend.

With that, all I need to do is harden the broach and then I can start making car parts again!  I grabbed some brick and a torch, and a jar filled with ice water, and heated it up to red hot (actually, orange hot).  Then just a quick dunk, agitating (shaking it to prevent steam from creating too much of a barrier) it the whole time until it is cool to the touch.

I scraped it against some aluminum, and it definitely scored it.  This thing is, in theory, ready to rumble.  I will to a test cut just to make sure this is going to work before I proceed, but this tool is DONE!

Dial Indicator Adapters for the South Bend

I've been working on a rotary broach kit from Hemingway.  As I started the phase of making the first broach, I encountered a bit of a problem.  The collet set I'm using requires me to get fairly close to the headstock, and the micrometer doesn't actually fit in the space I have to subsist in.

I need a new way to measure.

I grabbed some cut-off chunks (and "scrap parts") I had laying around and built two of them.  One of them connects to the V-ways like we normally see, but the other one uses two 1/4"-20 holes right above the gear box.  This would allow me to offset a dial indicator much farther away.  I had a gits oiler right there, so I needed to mill around it.

First was getting the parts to square.  Then, machining out a slope and the v on the moveable indicator holder.  I then drilled and tapped 1/4"-20 holes in two directions for the dial indicators (specifically so I could orient the dial indicators as either facing upward or facing outward), and cut grooves so that the indicators can nestle down in and be secure.  At that point, I drilled (and counter bored) a 3/8"-16 through hole in the middle, and machined the bottom clamping jaw out of a scrap bin part.

Once that one was complete, I ran a cut-off block through the mill to square it up as well as notch for the gits, and used transfer screws to set the drill points for this new block.  I did have to make a few tweaks, but I also drilled and tapped two 1/4"-20 holes to hold the dial indicator.  This dial indicator was only going to face upward.  Here they are without the indicators attached.

Here they are with dial indicators on them.

These will be absolutely sufficient for my next steps on the broach - cutting the broaches to exact length.  Here is the micrometer attachment, showing the length (which is how much it obstructed the carriage movement).

This is a win, and allowed me to continue on the broach project.