lathe

metal

109 lathe

One of my projects is fixing up an antique Craftsman Model 80 6" lathe, usually just called a "109" lathe. Built by AA for Sears in 1949, its model number is 109.21270, sometimes listed as 109-21270. It has a capacity of 6" swing over bed and 18" between centers.  Many machinists consider them toy lathes since they were inexpensive, common and easy to break.  But I've found it to be reliable if treated with care.

Sears Craftsman 109 Lathe before restoration
Sears Craftsman 109 Lathe before restoration

I slowly removed rust and grime from all the components. It was taken almost fully apart to it's basic parts. Rust was removed with a phosphoric acid solution. I would have used an electrolytic process if the rust was worse, but it's only a surface coating with little to no pitting. I degreased the parts with Simple Green, I wanted to stay away from difficult to dispose of degreasers.  I then repainted with a color close to the original dark gray, I couldn't save the original Craftsman label though.

I built a backsplash to keep the chips and oils from getting everywhere.  Then I mounted the lathe to a solid base.  The lathe came with a couple missing change gears for setting threading and feeds.  I ended up finding the two I needed on E-bay.

Sears Craftsman 109 Lathe change gears
Sears Craftsman 109 Lathe change gears

The lathe must not have been used too harshly, most of it shows very little wear, just neglect.  The 4-jaw chuck shows the most problems, the jaw screw threads show either rust damage, or poor quality manufacturing.  The screws hold, but the threads are missing in many places.  Even so, it holds stock tightly and squarely.

Backsplash for Sears Craftsman 109 Lathe
Backsplash for Sears Craftsman 109 Lathe

 

Resources

The threading chart in my lathe was a little worn in spots, I've reproduced the chart in a few formats.  On my old website I had charts posted that included metric thread setups; but most of the setups were impossible to mesh using the 109.  I've changed my setup calculations to include gear meshing, so the two vertical charts now include metric threads.

The look of the original Threading Chart (no metric threads):

Sears Craftsman 109 Lathe Threading Chart
Sears Craftsman 109 Lathe Threading Chart

Sears_109_Lathe_threading_chart_original(PDF)

Or, as a vertical 11x17 sheet, including metric threads in either white or black backgrounds:

Sears Craftsman 109 Lathe Threading Chart
Sears Craftsman 109 Lathe inch / metric Threading Chart

Sears Craftsman 109 Lathe Threading Chart
Sears Craftsman 109 Lathe inch / metric Threading Chart

 

 

 

 

 

 

 

 

 

Sears_109_Lathe_threads_w-on-b (PDF)

Sears_109_Lathe_threads_b-on-w (PDF)


Now I have RPM speed charts for belt and back gear combinations:

Sears Craftsman 109 Lathe RPM Speed Chart
Sears Craftsman 109 Lathe RPM Speed Chart

Sears Craftsman 109 Lathe RPM Speed Chart
Sears Craftsman 109 Lathe RPM Speed Chart

Sears_109_Lathe_speeds_w-on-b (PDF)

Sears_109_Lathe_speeds_b-on-w (PDF)


All of the above charts, and the formulas used for generating thread pitches and feeds can be found in this Excel file: Sears_109_Lathe-charts.

The charts are free to use and modify, but if you share it with others please give me credit for it.  I put a lot of effort into making these charts.


I found a copy of the original Operating Instructions for the 109 Craftsman Lathe:

 

 

15 Replies to “lathe”

  1. Thank you for the information on the 109 lathe. I have a 109.21270 lathe. I cracked the banjo. It seemed a bit loose so I tighted the screw and then it cracked. Am I doing something wrong? Thanks for your help.

    1. Hi Phillip. Sorry to hear about your banjo. It’s my guess that the banjo already may have had the start of a crack and that’s why it was loose. The metal used in the castings for the banjo was sometimes called “pot metal”, an alloy mixture of various quality depending on what was put int he pot that day. It’s possible the banjo was just not made well. I don’t think you were doing anything wrong.

  2. These are beautiful charts.

    I do have a question about the metric charts–Are the errors correct? I looked at two and the errors seemd to be numerically equal to the error per thread in mm * 100. For instance:

    0.9mm pitch : (25.4/(32/64*46/44*54)) = 0.899839mm — error of -0.000161mm or -0.01789229%

    1.5mm pitch : (25.4/(32/64*40/52*44)) = 1.500909mm — error of 0.000909mm or +0.06060606 %

    3.0mm pitch: (25.4/(32/64*20/52*44)) = 3.001818 — error of 0.001818mm or +0.06060606 %

    Are you positive the units and signs are right on the error column?

  3. Replacing the values in the error% column with excel formulas like this and formatting them as percentages will correct the column:

    =(G44-ROUND(G44,2))/ROUND(G44,2)

    1. Hi Dave, you’re absolutely right. The errors were calculated wrong. That’s one reason I posted the spreadsheets, in case anyone had improvements. I’ll try to add your changes and generate new graphics.

      I’m glad you like the charts. I keep improving the metric conversions, it took a while to calculate tooth collisions. On my old charts, the gears would never be able to mesh on some of the arrangements.

  4. thanks for taking the time to calculate the pulley speeds, and sharing them. that was on my to do list, now i can laminate a copy and keep it on the wall,
    thanks again

    1. I’m glad to help. Depending on your motor and the step pulley on the motor, the speeds may be different. As long as you’re using a 1700 to 1800 RPM motor, the table should be close enough.

  5. just read the operating instructions for the first time, and seen the pulley speeds on the last page, it was good to finally read them. there is always something to learn

  6. I have a sister 21270 to your Lathe , I had been looking for one on Craigslist and the right one came on and I pulled the trigger and got it. The old Gent was so happy I was buying it to use he threw in all kinds of stuff, A cute little Dunlap drill press that uses the same motor, and all the accessories that went with both, plus a bunch more ! I wanted a smaller lathe for little parts that I make, and for about the same price as a smaller chuck for my 10 inch Atlas I got the complete machine. I have printed your beautiful charts and am going to laminate them for the shop, Thanks TJ

    1. Thanks TJ, I appreciate hearing that the charts are useful. I’m still impressed with the quality of wok that can be done with these old small lathes.

      Hope you enjoy your 21270!

      -Joe

  7. Hi, Based the pix on your website, I believe I have a nos 109. It was never used – I found this lathe in my wife’s father’s basement with all the gears in a box unused. I have little knoledge of lathes since high school 50 years ago. The lathe has a 4 jaw chuck and I would like to get a 3 jaw chuck that would fit this lathe – or get an easier to operate used metal lathe to help me in my hoby of building ford model A cars. Any help in obtaining a 3 jaw chuck or a lathe that be easier to use would be greatly appreciated.

    1. Hi Richard,

      I still don’t have a 3-jaw chuck for mine. I just use a pin-dial and take my time centering pieces in my 4-jaw. I’ve seen 3-jaw chucks, but they typically run around $150. Just search for “1/2-20 3-jaw chuck”. By searching for that, one of the first hits was for a 2.5″ Sherline 1070 chuck on Amazon for $154. As an alternative you could buy a 1/2-20 threaded 3″ chuck back plate and true it, then mount a standard 3″ 3-jaw chuck to it. A 4″ chuck may work, but it’s hard to find a 1/2-20 4″ back plate.

      As far as suggestions for other lathes, I’m not the best source. I enjoy using the 109, partly because it’s old and finicky. I just have to take my time with it.

  8. Hi Joe. Thanks for all this – it is very needed. I am just starting out and got a 50s vintage 109 off craigslist. Like you, I specifically wanted a lathe that is old, finicky and solid. I’ve disassembled it, cleaned it thoroughly and have made a few improvements, including adding a variable speed-controlled 2HP DC motor with a tachometer. I didn’t repaint is because I like to old used patina it has. My real problem is that I can’t get the teeth to engage well between the 32T spindle gear and the smallest gear on the selector (I think that is a 20T). I have tried all kinds of things including switching out the 20T for another one. The only thing I can think of is that the teeth on the spindle gear have worn out “just enough” even though they don’t appear to be. Do you have any ideas/solutions? Also, what are your thoughts on accurately measuring tool travel since there are no markings on the compound/slide? Right now I plan on using my magnetic mount dial gauge as I work, but that doesn’t seem like the best solution. Thanks.

    1. Hi Lawrence,

      It sounds like the forward/reverse selector is loose or, like you said, the gears may have worn enough that they don’t fully engage. If the teeth are worn I’d look into ways to adapt the selector to position the gears closer together.

      For cross-slide travel you can measure the tpi of the cross-slide screw; I don’t remember off hand what it is. From that make a chart of movement per number of turns. You’d have to factor in backlash when changing directions though. The dial gauge would be more accurate though.

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