How do you cut small threads?

[V22]

Recently I cut an M6 thread on my lathe (12x36 - AL960b/G4003G). Unfortunately the part was deflecting and I ended up with a thread that the bolt wobbles down. It does not seat flat. I figure that there are a lot of people working successfully here with fine small diameter threads. There must be a trick I am missing (besides cheating and using a die)?

I did some spring cuts but likely not enough. I wonder if I should be using a traveling rest or a tiny live center?

I was thinking of cutting some M4's but I cannot see how that is possible. How do you prevent deflection on these small threads?

 

[Swifty]

I would definitely be using a live centre, but of course it depends on the length of the part. If the length of the part was less than 12mm for an M6 thread, I would not use the centre. For smaller threads, it may be advisable to get some good dies.

Paul.

 

[V22]

I would definitely be using a live centre, but of course it depends on the length of the part. If the length of the part was less than 12mm for an M6 thread, I would not use the centre. For smaller threads, it may be advisable to get some good dies.

Paul.

One of the issues is that I do not know of a live center small enough. I can't get the single point tool in to start the thread with the center in. There is simply not enough room with my standard sized MT3 live center and BXA tool post. There is not enough room with a dead center.

I thought there must be some trick (supporting tool) that Model Engineers use to do these threads outside of a die.

 

[abby]

Use a half centre !

 

[Swifty]

We used half centres on cylindrical grinders, well they were not quite half, but of course they are dead centres. I use a live centre set with different tips, I have a few tips that I have made myself to suit smaller work. Here is a link to a set (not the one I have).http://www.machineryhouse.com.au/C063

I made a couple of tips with fairly long shafts, this allows me to get in close without the tooling interfering.

Paul.

 

[Lakc]

When the cutting forces are greater then the stiffness of the part, a die is not cheating.
Single point threading is a useful skill and a point of pride for many, but when it comes down to making the part you need correctly, the proper solution is set up a screw machine to make it, and to my knowledge they all use dies.
Another solution, I have seen on the forums somewhere but a link escapes me right now, is a special tool that in concept is essentially a travelling center and toolbit holder in one. Mainly made to cut long thin diameters, it fits in the toolpost and the part fits through the center of it, while the cutting bit slides along inside of it.

 

[mcostello]

Box tool is possibly what Your were thinking of, but He still needs to put some threads on.

 

[kvom]

M6 is a little smaller than 1/4", and I've had not trouble getting the threading tool at the end of the part using a live center and a AXA QCTP. I almost always just single point part way to get the threads straight and finish with a die. M4 is slightly larger than 1/8"; I use dies for these using a tailstock die holder to get the threads straight.

 

[Mechanicboy]

Keep the tool sharp and handrotate the chuck to be sure the treads is not flexing or be damaged by power of the lathe. Take small cut each time, and take a test with nut to be sure the size of treads is correct (no sloppy nut on treads).

 

[Fabrickator]

I recently had to cut a double ended M5 thread stud in brass. I sized the stud and then cut the threads with a die in a tail stock die holder. I made it long on both ends and then finished it to size on my belt sander.

 

[Tin Falcon]

remember the 2 1/2 rule do not turn or work on a piece more than 2 1/2 time longer than the diameter of the material without supporting it.

Tin

 

[barnesrickw]

remember the 2 1/2 rule do not turn or work on a piece more than 2 1/2 time longer than the diameter of the material with supporting it.



Tin

Didn't know that rule, but it's easy to remember, and sounds like a good guideline.


Sent from my iPad using Model Engines

 

[MachineTom]

A company called Concentric makes spring loaded live centers, the purpose of the springs is to limit the load on the small bearings in use. Also buy a mt-3 - mt2 sleeve or extender. There are center drills small enough to pop a center point on a #3 screw.

A die head is great if doing 1 or many, but the die sets are $$$ even on ebay. I have one and it works great, but not cheap.
Using a die holder is the next best thing to a die head. And you can make one yourself.

 

[Tony Wells]

One thing I did not see mentioned is that it is possible to reverse the roles in this situation, provided you don't mind working with a dead center. Since most people thread at relatively slow speed, dead centers generally don't give any problems.

To do this, simply turn a 60° point on the end of the screw-to-be (allowing length for this to be removed later), and use a tap or similar HSS tool that has a grinding center in the butt end of it and put it in a drill chuck in the tailstock. Naturally, the shorter that HSS tool is, the more rigid will be the support. I have used a broken tap and was able to chuck fairly close to the driving square and this gave good support.

 

[Krutch]

You could turn a dead center to use for your small diameter threading. Make it like the CNC centers with a long reach cone to allow your tooling to get in for the job. If you can use a drill chuck in the tailstock, make the dead center shank to fit into the chuck like a drill shank.
Even a rod of the same or smaller diameter with a 60 degree point should work. Don't take any deep cuts
For threading you won't be turning fast and you'll need to lube the "center", otherwise it will work OK.

 

[V22]

One thing I did not see mentioned is that it is possible to reverse the roles in this situation, provided you don't mind working with a dead center. Since most people thread at relatively slow speed, dead centers generally don't give any problems.

This is a great ingenious idea. I really like making the center on the part and running the dimple from a tap in the drill chuck via the tailstock.

That all being said, I purchased a new live center.The type with interchangeable centers. I plan in turning a longer small center (to fit the new live center) out of 4140 to support small parts without interfering with the compound or toolpost.