Adam Savage Stumped by This Mystery Lathe Problem

While working on a powered hacksaw build, Adam runs into a problem with his lathe's ability to cut bolt threads, with the machine not cutting the desired threads per inch. It's a bit of a head scratcher as Adam attempts to problem-solve and understand this unexpected behavior before making his fix!

Shot by Adam Savage and edited by Joey Fameli
Music by Jinglepunks

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[gregolson]

On the left of the threading chart there is a diagram of the gear mesh for cutting standard threads and another mesh for cutting modified threads (the chart with the yellow screw at the top). Your gears are set to cut the mod chart not the standard chart. Open the door on the left side of the machine, flip the middle gear so the larger diameter gear (56t) is in mesh with the bottom (57t) gear. Then put your dial back on the correct way.

[hectorrenesegovia]

Imagine... WE ARE NOT THERE WITH HIM! He is alone in his workshop talking to himself... to an inanimate object (the camera) with no feedback nor emotion (not even a crew) - and STILL he is able to maintain - without feeling insane - an actively engaging personality and demeanor as he works his way through this... alone. Adam, you are a national treasure!

[positronalpha]

As a software developer, this process is very familiar and I actually find this kind of troubleshooting quite comforting.

[Evan-e-cent]

Adam, Check the gear train. It should be set up using the diagram at the top left of your gear table. There is a second gear train diagram, but it has the diagram of a yellow thread beside it. That one is used only for the column which also shows a yellow thread ie for modulus and Diametric Pitches for cutting gears. For threads you should use the top gear train diagram. 
Specifically: stud gear 24T (teeth), idler gear 56T and leadscrew gear 57 T. In this setup the middle gear is an 'idler gear' which does not affect the gear ratio. I suspect your lathe has been set up for gear cutting, using the bottom gear train. In that case it includes a pair of compound gears with a 56 T gear connected to a 44T gear by a keyway. This introduces a ratio of 56/44=1.272727 which approximates 1.27 with 0.21% error.
Why would we want a ratio of 1.27? Well, we can easily use gears to multiply by 2, and then 2 x 1.27 = 2.54 and there are exactly 2.54 cm in one inch. So this gives you conversion between metric and imperial threads. 
I have written a free online computer program called RideTheGearTrain for doing gear train calculations. Just put dot com after the name! This will work for any lathe without a gearbox. But for a lathe with a gearbox (like yours) it needs to know the gear ratios in the gearbox. The program contains gearboxes for many different brands of lathes. I could add your lathe to the list, but need to know the pitch or TPI of the leadscrew. Unfortunately it is not shown on the table.

[RonShore-vc]

If you open the door on the left side of your lathes headstock you will find a 127 tooth gear and a few other gears with likely a diagram of at least 2 configurations that the gears can be arranged in. This is how lathes are designed to be configured for odd thread sizes and sometimes metric sizes .This is a likely might be the source of the gearing problem. I am a machinist and have seen similar problems on my equipment when someone has rearranged the gear's to cut a special thread. The side of your lathe opens up for this purpose.

[supralapsarian]

Was I the only one screaming “Don’t change all the numbers on the dial; just move the index mark on the panel!” 🤣 Thanks for welcoming us into your shop. We always learn something!

[jdwtf]

These kind of "informational/learning journey" videos are my favorite. Everyone makes mistakes. Learning from them is paramount. Edit: Only 1/4 way through the video. I'm betting someone rebuilt the gearbox and misplaced one of the gears on the selector trees. Edit2: After watching the entire video I'm betting that the other end of that shaft, that the selector knob " does not" have an offset pin or key and is 180 degrees out of phase. As a field service person I'm good with the "quick" fix just to get it done. I'm also going to think about this issue every time you use this lathe now. I look forward to the day where you completely disassemble this and determine once and for all the "actual" cause. Amazing content as always!

[DidItForDale]

I just watched 45 minutes of solving a problem on a lathe i'll never known but LEARNED A TON! Grateful.

[jvanbelle]

It could probably have been diagnosed much faster by looking at the setting for the thread you actually cut. When you wanted to cut the 18TPI you set it to LB3P, but got 16TPI, which is LB7P, which immediately tells you your number dial is off (by 4) without the trial and error, though you'd obviously still want to confirm with a few more tests.

[RelUnrelated]

About thirty years ago I worked as security in a large factory. Some of the coolest people I knew there were machinists, and this reminds me so much of all of the times they allowed me to watch as they cut custom threads on a project. Thanks for being real with us, Adam, and letting us in on the problem-solving!

[tommcd]

There is nothing more satisfying than troubleshooting and remedying the problem after a solution has been determined. Also, I really like the warning sticker on the lathe. "This machine has no brain, so use your own". That is such a good reminder that in order to do something to be in the moment when making anything in a shop setting.

[Esteb]

I'm and ISP/Telecom field tech. Troubleshooting is what we do all day. Watching someone troubleshoot, and isolate a problem in itself is interesting. To then watch someone come up with a way to fix the problem is the cherry on top. A terrific way of gaining knowledge is by viewing someone else resolve problems in systems different than yours, because it gives you a different perspective, and allows you to always keep an open mind when encountering issues.

[SweDownhill]

This is one of the best episodes I've seen in years. I loved the fact that Adam speaks through and explain the troubleshooting process.

[erikpeterson]

These episodes are what make me really appreciate Adam, I love the insight into the problem solving rationale. His whole approach is built on probabilities.

[TheAmericanDane]

I’ve never used a lathe in my life, although I know what one is… I think it speaks volumes to Adams character that I just know I will enjoy watching this before it’s even started. Such a relatable man, no ego, no front and down to Earth just a man being himself.
Much love from England brother 🇬🇧

[Nyghtprowler]

It's an internal issue. As they grow older, that "rough" engagement you are dealing with can hop out of phase and engage 180 degrees from the intended engagement. They are always whacky and you have to wiggle the spindel to get it to slip into gear. You can probably google that model lathe and get the schematics for the threading mechanism setup and you'll understand what I'm saying when you see the layout of how that scales the feed lengths based on that dial. I don't doubt that you had it working at some point, and later it slipped out while trying to engage it and now you are 180 off. It's also very possible for you to get it slipped back in and you will be back to normal the your dial mod will be wrong :) Those lathes are old and worn, it's probably due for some much needed maintenance or a rebuild.

[ceaselessshadow]

i realize problems like this aren’t planned obviously, but seeing this kind of real time problem solving from adam is so fascinating. i love watching the process, seeing him not know the solution and experimenting and troubleshooting to find it. this is just as interesting to me as any one day build. love seeing stuff like this

[flatulentdragon]

Adam, the honesty you bring to your content is what makes you one of my all time favorite content creators. When you show your pain and frustration, when you're willing to show your humiliation (for want of a better word) - like with the thumb injury video or your story about screwing up your friend's college project - that picture of your humanity is an amazing gift. Beyond priceless. Especially to amateur, ham-fisted makers like myself, to see that the "great Adam Savage" has those moments helps me on my own journeys. To err is human. To make an honest YouTube video about erring reassures us that it's OK to be human.

[jlconway]

Honestly my favorite thing about watching Adam Savage work is that he does all the same weird stuff I do when I'm and I feel so seen. The pauses and the tapping and the random singing and noises and drumming tunes and patterns, staring at the lathe and having it click "the knob is 180 out!" within moments of one another. Then the horror of realizing the knob only goes on one way, pausing, and exclaiming "the handle is on the shaft right, the shaft is in the machine wrong!" how do I fix this without taking the machine apart DRILL ANOTHER HOLE anyway thank you Adam Savage for being yourself unfiltered on camera.