Single Point Threading

[willofiam]

Hey guys, I want to make a new screw because I cannot find a straight slot screw head to match, only phillips. this is for the g-clock I am working on, the bolt thread would be a 10-32. I farted around last night and had pretty good success cutting the threads on the lathe (first time and thanks for the information David and Tom) BUT I was not able to support the end of the steel only because I could not get near enough with the tail-stock and still function, this caused flexing and therefore I didnt get a good cut at the end of the piece. could I use a drill chuck with a center to gain length in the tail-stock for supporting the end of my piece? use a longer piece between centers and thread from the center of the piece inward? or is there a better way to do this, I know I could use a die and could save some hair but I would like to figure this out on the lathe. Thank you, William

[Bob Tascione]

Hi William,
Yes you can use a dead center in a chuck which in this case should work fine for you although it’s much more secure to use a center that fits into the taper in your tailstock or into one or more step up sleeves. This screw is so tiny though for your large lathe that the amount of pressure being exerted against the chuck should be negligible. For tool clearance you can grind a flat on your dead center shank for clearance.
Taking a series of really light cleanup cuts with a very sharp threading tool can sometimes solve the problem without using a center but you’ve most likely already tried that. Another thing that works very well and helps reduce deflection is to thread from the headstock out toward the tailstock. The tool is placed upside down in the tool post with the cutting edge set at center line and the lathe run in reverse. By cutting a relief a little less than the minor diameter of the thread into the stock just under the screw head you will be able to start the cut from the same point without digging into the steel. You would then run the lathe spindle in reverse. The result will be the same right hand thread. This is a technique used often in machining and is the way I usually do single point work. Without a mechanical disengage or kick out stop it is a less stressful way to thread (at least for me) as it almost eliminates the possibility of crashing into the headstock. I say almost because if an operator isn’t paying attention after stopping the lathe for a thread depth test and then re-starts the lathe in forward rather than reverse and kicks the thread feed in…well, surprise! There are other techniques that work well too but using a center is always a good way to go if you can swing it. This technique may seem complicated but thought I would throw it out there to show that there are other ways to do the same job. If you decide to experiment with this your tool post will need enough clearance to allow your threading tool to be raised enough to bring the cutting edge ‘up’ to the stock center.

Hope this helps William,
Have fun!
Bob

[willofiam]

Hey Bob, thank you, it does make sense, I will try from the headstock out without support first, thinking about it I like that idea, I will post my results. have a great day, William

[Bob Tascione]

You’re welcome William,
I don’t want you to think that I’m saying that it’s a better way to thread just another way and one that I prefer (for me). Another way to do it is by bringing the cutter from behind or the rather the other side of the part. This way you don’t need to turn the cutter upside down but can still feed out toward the tailstock by running the spindle in reverse. You will need a boring bar type of tool though. Kinda hard to visualize so I’ll try to locate a demo up on YouTube for you and will post it up here. There are times when feeding out isn’t a good or doable option.
A few words of CAUTION!! Something you may want to consider with your Atlas is, if I remember correctly, that it has a screw on chuck. If so then running the spindle backwards while applying cutting pressure can sometimes cause the chuck to spin off! With Cam lock type chucks this isn’t a problem. Working with that tiny screw might not be a problem (be careful if you do decide to try it though) but definitely something to think about if you plan on taking heavy cuts in the future. Reversing or just starting up in reverse can sometimes cause these chucks to loosen up!

Bob

EDIT: Here’s a link to a video cutting from the back of the part.
http://www.youtube.com/watch?v=L4MH0gqPUDI

[willofiam]

Bob, thank you, I like that cutter in the video. thanks for the warning about the thread on chuck, I forgot….. I do have a milling drawbar (whatever its called), I can turn my stock to fit and chuck it up with that (should do that as a lesson so I remember in the future). Maybe someday santa will send me a collet closer (if thats what its called) for this lathe, right Paul, David or Tom?

[david pierce]

William,
One idea that might work to support the end of your screw is to remove the point from a carbide scribe and put it in a drill chuck. A #10 screw is about .190 inches so the scribe tip will fit inside that diameter and give you a little more working room. A threaded screw is not usually a high precision item so you will not need an ultra precision center support. Hopefully the scribe tip will be strong enough to support the cutter pressure. One way to find out. Are you threading up to the head of the screw or is there a gap between the thread and the head of the screw? What is the length of the screw? If it is short, a center support at the end should be all you need. If it is long then you will have additional problems from the cutter pushing the part in the middle. One trick I used was to mount a dial indicator to monitor the carriage movement. With that I could flip the half nut lever up within a couple of thousandths at the end of my thread cut. If you do that stay on top of the situation.
david

[willofiam]

Hey David, thank you, the screw is 1 1/2 inches long. If I am catching you right I could use just about anything in the tail-stock jacobs chuck, I think what you are saying is even something a bit smaller in diameter at the tail-stock would stay out of the way at the same time as giving just enough support. I could turn a point on some stock that would probably be precise enough. I was also thinking in conjunction of what Bob was saying @Bob Tascione wrote:

By cutting a relief a little less than the minor diameter of the thread into the stock just under the screw head

, I should have cut a relief at the end of the screw also, bonehead me I had only faced it off, the cutter had to struggle to get started and cause all kinds of flexing. Yes David I can have some space at the head for stopping, it will be a tapered head that fit into a tapper brass washer and then thru the seat-board, the screw is for mounting the movement to the seat-board, not something terribly precise or has to be pretty. just needs to function. this is why I decided it would be a good idea to figure out the threading on a lathe with this piece, thanks guys with each idea my knowledge on threading increases 100%. William

[Bob Tascione]

Hey William,
Good that you’re tackling this job on your lathe rather than using a die. This type of practice will pay off big time in the future. Getting to know that Craftsman (Atlas) is always a good thing. I know you had doubts about that lathe being good enough for clock work. This video should convince you that your machine is capable of doing a lot! Only thing that I remember that was a problem with my Craftsman was that I couldn’t slow the feed down enough to get a great finish. There’s a video that TubalCain put out covering a modification to slow down the feed on his craftsman. He actually disengages the gear box and runs a separate motor off the back of the lead screw. I’ll try to find it and will post it up here. If it’s something you would like to do with your machine then I’m sure David could help with choosing a suitable drive motor and controller. He’s really up on that stuff.
Enjoy that machine
Life before the half nut & thread dial: Cool machine though. http://www.youtube.com/watch?v=65sWv212kqo

Bob

[Bob Tascione]

William,
Here’s the feed modification upgrade for your Craftsman lathe. Good ‘ole Tubalcain!!!
http://www.youtube.com/watch?v=3DlPDr4f6xQ
Enjoy,
Bob

[david pierce]

F.Y.I.,
A number of years ago ATLAS purchased CLAUSING-COULCHESTER then dropped the ATLAS name. The company is in business and may still be able to supply items for the ATLAS-CRAFTSMAN machines.

[willofiam]

Thanks David, that is handy information, now that you mentioned it I did hear that but had forgot. William

[willofiam]

Well, I made my first real screw, took several tries but I learned alot and feel much more confident in making screws. the hardest part seemed to be parting it off, need more practice on that, a good feeling of accomplishment, now I can bore the kids and grand-kids about the screw I made for the family clock.

have a great day, William

[david pierce]

William,
That is a nice looking part. This type of machining is where an engine lathe is hard to beat. On Novermer 11 you asked what single point threading was. Now look what you can do; excellent
david

[willofiam]

Thank you David, your encouragement means alot to me Have a wonderful night, William

[david pierce]

William,
How about putting up a new post showing how you did it. This would include:
A description of your lathe
How you ground the cutter
How the cutter was held in the lathe
The angle of the compound
How you used the threading dial
How much metal you removed with each pass
Which slide you used to change the depth of cut
The orientation of the screw in the chuck
The direction of feed
How you tested the thread when you were finished
This would have a lot of meaning to others coming from someone who just did it and fought their way through the process.
david

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