[tikka308]

I'm a *relatively* experienced hobby mill user. Now that I finally have enough space, I'm researching which Lathe to purchase. I'm learning towards the LatheMaster 8x14 (http://www.lathemaster.com/LATHEMASTER8x14Lathe.htm or http://tinyurl.com/7sedb) based on quality, size, etc.

However, I have a "beginner" question: How can you cut threads on one of these small lathes without powerfeed? How does that work?!?

[Geof]

....However, I have a "beginner" question: How can you cut threads on one of these small mills without powerfeed? How does that work?!?

I assume you mean small lathe?

Both the links you gave show a small lathe with a leadscrew and change gears so they can be used for threading.

The leadscrew is driven by the spindle through the change gears. On the carriage there is a lever that locks a split nut down onto the thread of the leadscrew so that the carriage moves forward as the spindle turns. The distance the carriage moves depends on the lead of the leadscrew and the drive ratio of the change gears. If the leadscrew is 8 turns per inch, a lead of 0.125", and the drive ratio is 1:1 the carriage moves 0.125" for every turn of the spindle; if the drive ratio is 2.5:1 the carriage moves forward 0.05" for every turn of the spindle, etc.

[tikka308]

Geof - I see. I figured it was related to the gears. So, said in other words, when you're cutting gears, the lathe gears are turning the leadscrew, thus indexing the tool/carriage automatically. So the lathe operator sets everything up, then steps back while it's cutting? Sounds nice!

[HuFlungDung]

He steps back while its cutting then steps right back up when its at the end, hastily grabs the half nuts lever and tries to disengage before the tool runs into the chuck. Then, he winds the carriage back to the other end..whoops forgot to withdraw the tool... and frantically tries to engage the half nuts at the right mark on the thread dial.....whoops forgot to set the tool in for the next depth of cut......

You get the idea. There is no 'stepping back time' involved in anything but cnc lathe threading

[Geof]

.... So the lathe operator sets everything up, then steps back while it's cutting? Sounds nice!

No, the lathe operator is very definitely involved. Have you ever tried the trick of rubbing your stomach and simultaneously patting the top of your head; threading on a manual lathe is about as difficult, you need good coordination.

You set up the tool and set up the change gears for the correct threads per inch. Your workpiece having previously be turned to the correct size.

You line the tool up a small distance ahead of the end of the workpiece and adjust the cross slide so the tool is cutting a few thou deep.

Now you are ready to engage the split nut, but you need to know when the thread on the leadscrew is correctly aligned with the thread inside the split nut so the two halves can close.

There is a dial called a 'chasing dial' that has a worm gear engaged with the leadscrew and a graduated disc that rotates when the leadscrew rotates. When any of the marks on this dial are lined up with a little index mark beside the dial then the threads are lined up so you can engage the nut.

So you watch the chasing dial rotate, did I say you have the spindle running very slowly? Just before a dial mark lines up with the index mark you start closing the split nut by pulling on the engagement lever. You do this a whole bunch of times for practise well clear of your work piece until you have it down pat.

Now your nut is engaged and your carriage and tool are rocketing toward the chuck cutting the thread, eventually you want to disengage the nut to stop the carriage motion. Which you do at the correct point; having previously practiced this also well clear of everything.

You are doing this with the spindle turning very slowly because at sometime you are bound to crash the tool or toolholder or carriage or something into the chuck and you want to minimize the damage.

Were am I?

You have taken one threading passand stopped the carriage. Now your tool is just cutting a groove in one spot because I forgot to tell you that at exactly the same time as you disengage the split nut you spin the cross slide handwheel backwards to retract the tool. (I did say you should be able to pat your tummy and rub your head simultaneously to do this.)

If you want to chicken out on the first threads you cut you can cut a groove at the end of the thread to stop the tool in; this is called an undercut.

Now you retract the tool, move it back to the beginning and bring it back in to take off a few thou more, and this is where the fun starts. You want your second cut to line up with the first and the easiest way to do that is make sure it is the same dial mark lined up with the index mark when you engage the split nut for all cuts.

So away you go, cut after cut.

[tikka308]

Geof - I'm not sure whether to say "thanks" for the thorough post or just to crawl back to my what-seems-to-be-relatively-simple Mill!!!! I have ordered the Darrell Holland Lathe DVD's, so hopefully that will compliment your explanation.

Thanks!

[Geof]

Geof - I'm not sure whether to say "thanks" for the thorough post or just to crawl back to my what-seems-to-be-relatively-simple Mill!!!!......Thanks!

Thread cutting on a manual lathe certainly is a challenge the first few times, but once you have a bit of practise it is not bad. When you are proficient it is really handy and rather than being difficult it just becomes tedious, and it makes you appreciate how convenient CNC is for threading.

[Al_The_Man]

...and when you have that first part down, the next addition is to use the compound rest to advance the tool slightly in both the Z & X so the the the tool always cuts on one edge.
For a non-machinist like me, I picked up an older book that can be bought on ebay cheap.
It is the South Bend Lathe Works book aptly titled, 'How to Run a Lathe'
First published 1914!
It has all the details of all the above and much more.
Al.

[tikka308]

Can't wait to order one! I think I'm going to go ahead with the 8x14 by Lathemasters; I have an email into them with a few questions but it seems the best balance of quality, size & functionality.

I'm really excited for the Lathe also because my mill is CNC, so I never had the chance to push/force myself on a manual mill. While I don't regret that decision because the CNC mill was required for some parts I had to make, I'm really excited for what will almost certainly prove to be a humbling learning experience. Cheers.

[Thumpper-14]

I have a little 9 x 20 and for the few times I have threaded, I found ti faster and easier to just use a tap. but I have done it on the little one. Just to show my son how to do it as I was teaching him how to thread. I did a search on south bend once, and ran across a web site with videos from an old training class that showed some threading. you might find that online and save some time.

Thumpper

[dareposte]

The previously mentioned South Bend lathe book is a good one, but I would recommend the book "Technology of Machine Tools", ISBN #0070353832.

You can get it for $1.00 + $3.95 shipping from used book sellers online, and it is an excellent reference. I think it was originally a textbook of some sort back in the 1980's. Try abebooks.com or amazon if you are feeling brave, I know for a fact abe's has several copies for $1.00 + shipping.

Best of luck,

[gmac]

just as the tapping and die- operations ont he lathe and the drill press can eb done by turning the machine spindle by hand, so also can the singlepoint threading. it is NOT as beneficial as the finish that one gets by using the machine motor to evenly turn things but its a great way to learn whats going on and what to do at various times. especially when you have your machine spindle speed turned down WAY slow so you can grab all the handles in tiem to stop it from munching up the parts thay you really want to keep, like the chuck and the toolpost etc.

the spindle-handle is a GOOD device to use but its best buddy is the powerplug. when you get the spindle handle out- you pull the powerplug out of the wall socket- nochance of power and no forgetting that you didnt do it. that stops you from turning the machine ON when the spindle handle is still in place and spanking yourself REALLY hard with that handle when the spindle starts flailing it around or throws it off.

its probably a really good thing to set up the first few singlepoint threading operations with the spindle handle so one can see what the effects of various th ings are. I have ( horrors) actually made up a sharp HSS tool and threaded some fittings etc. using hand power, as well as the normal operations- using the lathe axis to hold true when I was threading with tap or die on a larger bore but needed some beef to hold true axis on the part and the tools.

think of it as a tool first, and a POWER tool second. there is a LOT that you can do with it and not all of it takes power to do.

btw, if you get good at it and want to play with some artsy stuff and trix, and if you can set your machine up to turn VERY slowly ( this might take some selective gearing changes there, the basic machine does NOT go real slow with any reasonable amount of power available ) )
and then you can use a turret or crosslide mounted tool to engage special areas in the part and cut recesses, spirals ( including basketweave-looking and reversed spirals) on curved surfaces, and lots of fun things. I tried using a marking crayon to get the hang of the motion operations before using a cutting tool and it still took some practice. no respouts worth showing but the technique is available there.

now if you had a froggy or similar single-axis controller that could move ( switch a solenoid) a tool back and forth while sensing the rotational position of the spindle ( like using a magnet or a photocell, or even a limit switch tripped by the chuck jaws, or a point device screwed or clamped onto the chuck , wow, there are hundreds of possibilities there) , then you could really start whipping up some neat looking finishes on your parts. hammered designs, cut and sculpted finishes and patterns. the works!!

the basic lesson here is - slow speed work can demonstrate to us things we cant do with speedy power-operated tools. slow speed work is the province of HUMAN integration. with a bit of eye-opening we can see how power-operated speed has increased the amount of things we can do with any given tool like this, not decreased it by limiting us to power uses only.