So here is a small job I did for an automotive shop that was in need of some replacement knobs for their tire changing machine. The knobs the machine came with were plastic and the threads eventually gave out over time. The only replacement knobs available were the OEM ones. The stub thread for the knobs to screw onto was an odd ball 5mm x .80 pitch so buying better replacement knobs were hard to find. I spun 4 knobs out of aluminum in hopes that they will last longer. For those of you who may have struggled with the title of this posting I am using DOB as “date of birth”. Was that one stetching it? Hey give me a break ok? It rhymes.

My main motivation for machining them was purely selfish. I had recently upgraded some lathe tooling and was now the owner of a new indexable cutter. I shelled out some dough for a Sowa .500” SCLCR tool holder part #146-784 and outfitted it with a CCGT-AP 146-024 carbide cutter. I was itching to give it a go. The cutter cuts like a hot knife through butter. I was giggling the whole time I was using it.

Anyway…I thought I would do this post up as a play by play and throw my methods out to the masses for criticism. The following is a picture post showing the steps I use to machine knobs. Please remember I AM NOT A MACHINIST, I figure things out as I go. If I am doing something wrong I am not surprised however I would love to hear about it.

Keep in mind that on this blog posting, as it is with all my postings, you can click on the images to get a full size view.

Let the show begin.

My new Sowa tool holder with an AP CCGT carbide tip for aluminum

Starting off with .625 6061 Aluminum round stock trimmed to 1.400" lengths. Four in total

Step 1: Face the end to clean it up

Step 2: Turn down the circumference just enough to clean up. Lathe speed of 265 SFM (1620 RPM)

Step 3: Chamfer the edge at 45 degrees to give the knob a smooth edge

Step 4: Remount knob in the chuck in order to machine the lower half and then face the end to clean up

Step 5: Using the part off tool make a cut .350" from the bottom to a depth of .075" reducing the overall diameter by .150". Lathe speed set to 19 SFM (115 RPM)

Step 6: Turn lower half of knob's circumference down to equal diameter of the part line

Step 7: Performing the trig. calculation an angle of 12 degrees is required to join the upper and lower halves of the knob. Set the compound angle to 12 degrees and cut down until the upper and lower circumferences join flush

Step 8: Using a number 2 center drill bore a starter hole in the bottom of the knob at a lathe sped of 350 RPM

STEP 9: Drill a .500" deep hole using a #19 (.166") drill bit

Step 10: Chamfer bottom hole to allow for clean thread starts

Step 11: Tap the .166 hole with a 5mm x .80 metric bottoming tap. Tapping was done manually and not under machine power

Step 12: Put a 45 degree chamfer on the outside of the bottom edge to give it a more clean look

Step 13: Cleaned up the finish by first using 320 grit sandpape, then Scothbrite, and then finishing it off with 0000 steel wool

Step 14: Flipped the knob around in the chuck and then cleaned up the top half

Set of completed knobs


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