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​​​​​​​​Lathe Info by Boots Obermeyer

I would like to pass on some of my thoughts on lathes.  The lathe is the most important machine for your shop.  It can do more things than other machines can do.  Now of course you should know it is used to turn a piece of metal round but much more can be done with a lathe.

One of the most important things that can be done with a lathe is the cutting of threads.  This in fact is the “bread & butter” of lathe work.  There are many different sizes and styles of threads that are done on a lathe.  Threads are usually a 60 degree V-form, as are found on typical machine screws, but there are many other forms like simple square ones, double lead and many more.  Dies for many of these that are used to twist onto the stock to cut the threads are not available.  Even when these dies are available, they are much more expensive than standard machine screw dies.  Threading of larger diameter holes, usually ½” or larger, can be done on the lathe as well with a boring bar.  The smallest boring bars are 3/8” in diameter.  If you have a taper attachment for your lathe you can also cut pipe threads, which are tapered.  The lathe can duplicate what some hand tools do and you save money by not having to invest in a lot of extra tooling.

You can also make special reamers and taps by first turning the basic tool and then cutting the flutes. When I started my own shop I did not have a mill.  I made a vertical holder for an index fixture that I had made at TSJC gunsmith school.  I mounted this on my 9" South Bend and cut the flutes.  I used O-1 tool steel, which can be oil hardened.  Once you have the tool made, heat it until it is red hot and then quench it vertically in oil. This may not be perfect but you can save time and money and in some cases have a tool that's not available.  I once made a large tap from 4150 barrel steel to thread a small engine for an exhaust pipe. I did this by first turning the stock to the major diameter then I cut the threads and then the flutes.  Most dies have a tapered end to facilitate starting the die in a hole.  You can perform this step last.  After all of the machining is done then coat your die with case hardening powder, heat it red hot and quench it in water.  It worked for the repair job.  A new tap would have been about $130 at the time plus I would have had to order it which would have been another time delay because it wasn’t something that was stocked in a local store.  Also, I cut the threads on the die to match the job which were not a standard pipe size.

Another item of growing importance is metric threads.  Many of the new lathes come with gearing built in or added on to cut metric threads.  I recall when I had an Atlas with a quick-change gear box, I bought a set of metric change gears.  That is one of the beauties of the old Atlas lathes.  While most of the new lathes have quick-change gear boxes, they are limited to the number of thread pitches that can be cut with them.  With the Atlas and two sets of change-gears, any thread pitch from 4 to 96 per inch can be cut.    The metric gears also allowed me to cut a number of special inch threads.

I have an old Milwaukee loose change 16" lathe which is much like the Atlas.  Back in the 60's a number of barrel jobs required metric threading.  I had to cut a 1.5mm thread pitch for a barrel. Checking it against what it would be in inches, I found it was 16.9+ threads per inch approx.  So, I bought the gear necessary to cut 17 threads per inch and it worked very well.  Also you can cheat some special threads by using your feed rate that matches the pitch you need.  This can be done on lathes with a feed clutch system, (not a split nut) by moving the carriage for normal turning at an inch feed per revolution as listed on the quick-change gear box.  Just pull the tool out at the end of the cut and run it back in reverse and then start the next cut.  Keep the feed clutch locked so the tool stays in time.

When you cut threads on a bar on centers with a bar locked to a drive dog, you can take the bar out of the machine to check the threads to insure that the threads fit.  As long as the drive dog is locked on to the piece you are working on and you put the dog in the same slot on the face-plate it's still in time. With a bar on centers you can offset the tailstock and cut a long taper.  The long taper like those on rifle barrels are much longer than can be done with the taper attachment.

Suppose you have to make a gear.  You then have to bore a hole in that gear you need with a boring bar.  Now you need to cut a keyway slot to lock the gear on the shaft that the gear is to be installed onto.  The slot can be cut with a cutter that can be ground for the boring bar.  Once you have the cutter made and mounted on the boring bar, push it through the hole in the gear by cranking the carriage hand wheel back and forth; with the lathe off.  This will have to be done by making light cuts and will take time but again you can make a repair and save a lot of money.

Now the lathe can also be used as a mill.  You can get a vise type attachment that mounts on the compound.  Some lathe companies called these attachments milling attachments.  The attachment can be hand cranked up or down as needed to make the cut.  An end mill cutter is held in the lathe chuck and you move the slides by hand.  Some lathes have power cross feeds that can be used to move the attachment to make the cuts.

Now, to start out, I recommend a small bench lathe like a 9" South Bend. This is a good way to go to make small parts.  One with a 4’ bed works well for sporting barrels. The 9” South Bend has a ¾” spindle-hole so you are limited as to what diameter barrel that can be held in the head stock; but, if you are working on a sporter barrel hold the muzzle end in the chuck.  The best way to chamber is with the muzzle end held in a chuck and the breech end in a steady-rest after it has been centered using a center on the tailstock to align the barrel in the steady-rest.  Some say it is easier with a large spindle hole with the barrel centered on each end.  I think this is a much slower method.  For example: the Pratt & Whitney chambering machines work with muzzle chucked and the breech end in a steady-rest.

So, a longer bed lathe for barrel work is the way to go.  The 9" SB with a 4 ½’ bed is seldom seen.  The Craftsman lathes as sold by Sears (which were made by Atlas) are often found with a long bed; these work well for chambering.  The Logan is another good lathe and can often be found with long beds too.  Some Logan lathes were sold by Montgomery Ward's; possibly with Ward’s name on them.  Of course today there are many imported lathes.  I have a lathe made in Taiwan and sold by a New York supplier in the 90's.  It's a very good lathe.  I think the same lathes are also sold by Grizzly.

An extremely good lathe is a Sheldon.  I have a 13" and it's as sensitive to hand work as the 9" SB. Another option is an older lathe run by line shaft.  They can be found for very low prices but can be in very good condition.  My main barrel chambering lathe is a 13" SB made in 1926.  The fellow I bought it from had a machine shop and bought it just before the big depression crash.  He had to shut down his shop but moved the lathe to his home and put it in his basement.  He made a line shaft drive and used it for some work and kept it almost like new.  This 13” SB lathe, even though fairly large, was easy to disassemble and move.  I added a converter drive system from another used machine to the 13" SB.  I still think it's one of my best lathes.

These older machines may be rejected by many because they don't understand the real basics of machining.  After all CNC is everywhere now and has been for some time.  Anything that can be done on CNC can also be done manually.  It just may take longer.  You can get quality, size, and a machine that is easily moved for less money with an older machine; as long as it is not totally worn out.

Additional Lathe info
By Tim Siewert

When you buy a new lathe, or any new piece of machinery for that matter, generally it will come with everything that you need to start running it.  If you buy a used machine many times this is not the case.  For example: In the last few years I have purchased two lathes from Boot’s machine list.  The first lathe I purchased is an Atlas/Craftsman, 10 x 36.  As a matter of fact, Boots personally turned me on to this lathe because he knew what was on my wish list.  It is a very good machine and I got it for a very reasonable price.  I knew what I was buying when I bought it.  The second lathe I bought is a 13 x 40 Jet.  This is another very good machine.  I got the Jet for a song, literally.  My point being, that there was a caveat with both machines.  The Atlas came with only one chuck; a chuck that is commonly referred to as a “speed chuck";  A speed chuck has no provision for tightening with a chuck key therefore I had to get another chuck for the Atlas.  I bought a new chuck from Tools for cheap.com.  For those who do not know, most lathe chucks are mounted on a back-plate which is mounted to the spindle shaft.  The reason why I bought a chuck from Tools for cheap was because the chuck came with a matched back-plate from the factory, unlike most other chucks available;  most of the time, the option is buying a new chuck and a plain-back back-plate.  This option requires a considerable amount of machining to mount a new chuck on a machine.  Not that it is that difficult, it is just more time involved before you can run your machine with the new chuck.  Then, there is the possibility that the register on the back-plate may be too small.  The only thing that I had to do was to turn the register on the back-plate about .060 because the register from the factory comes oversized.  This is a good thing because then your new chuck is matched to your machine.  I ended up turning the register about .003 oversized and then using the mounting screws that came with the chuck and back-plate to pull the chuck onto the back-plate.  This makes for a nice, tight, accurate fit.  When you do this don’t think that you will be able to get the chuck and back-plate separated at some time in the future.  Once you have this done, it is one solid unit for life.  There are chucks available that mount directly onto the spindle without a back-plate.  Generally, those chucks are designed for a D1-4 spindle or similar spindle.  The Atlas has a 1 ½ x 8 threaded spindle so the back-plate is the way to go.

The reason why I decided to buy a new chuck for the Atlas instead of trying to find a used one is that you want the chuck matched to your machine.  This insures an accurate set-up.  A used chuck will have been matched to the original machine that it was mounted on.  There are variations between machines by the same manufacturers.  If you try putting a chuck from a different machine on your machine, there may be too much run-out.  The first thing I did before I got the new chuck was to check the run-out on the spindle of my machine.  The run-out on my spindle was less than .0005 which is very good.  I did this to make sure that the spindle bearings did not need to be replaced before I mounted the new chuck and then also I had a reference for mounting the chuck.

One other thing I would like to add about the Atlas.  As Boots wrote in his article about lathes, it is possible to cut any thread pitch from 4 to 96 with an Atlas or Logan or a few other older lathes that are equipped with change gears as opposed to a quick-change gear box.  The thing is that you must have two sets of gears because some thread pitch set-ups require two gears of the same size.  For example: Most lathes that have quick-change gear boxes do not have the capability to cut 50 T.P.I.  This can be done on an Atlas but you have to have two 40 tooth gears.  Other thread pitches require other duplicate sizes.

Now for the Jet: I got it for such a reasonable price because it did not have everything to start running it.  There was no chuck, tail-stock, tool-post, and it was missing parts in the head stock.  Also, the brake shaft was bent which Boots was able to straighten for me.  That was a significant savings for me and I really appreciate his friendship and effort with it.  Fortunately, I already did some homework before I agreed to buy the machine and determined that all the parts to get it running were still available.  I learned that this particular machine had been used for parts to repair another identical machine.  This machine had never been run.  Now, eight months later, I have all of the parts that I need to get my machine running.  The rest of the story is this; when I get this machine back together I will have a virtually brand new lathe for less than half the cost of a new one with the investment of some time, effort, and patience.

I add these as examples of what Boots has written.  With a little effort you can save a lot of money and learn things in the process.  As far as the example of my Jet lathe goes, it is always a good thing to know all the parts of your machine, and how it works, in case something breaks and you have to fix it.  Finally, I like the idea that I will be able to save a top quality machine because the guy I bought the Jet from told me that he was considering selling it for scrap.

Boots has told me a few times that your lathe is the only machine in your shop that can “rebuild itself”.  By this he means that every part on a lathe can be made on a lathe; as long as you have the knowledge and the right stuff.  That is another reason why he wrote that it is the most important and versatile machine in your shop.  So I am with Boots, if you want to get into machining and have your own shop, buy a lathe first and learn how to use it.  When I had my machine shop training, we started on the lathe.  Much of what you initially learn on the lathe can be applied to other

machines.​​​​​​

MACHINIST'S CORNER