M3 Threading problems.

[rerod]

I'm not a machinist. But I enjoy R/C boating and building what I can on my old atlas lathe.

Today I finally found the Hanson 3mm .5 die I needed to thread a 1/8" steel rod. I bought both items at Ace hardware. I know the die was intended to thread a 3mm rod, but I need a .125 shoulder for the project. This part replaces the glow engine propeller screw so that I may mount a flywheel and flex hex on the engine so its important that it is very true and centered.

My first attempt, the die started wrong and was off center. So I placed the die in the lathe and turned it by hand slowly. I used oil and backed off every few threads. It seemed to be going well until the rod broke. After a few choice words I removed the broken threaded rod from the die and tried to thread it into the engine crank. The die had worn so badly in the 2" I had used it I could not thread it in. The die was junk after only 2" of threading

What did I do wrong? And how do I go about making this part? Do I need a titanium nitride coated die? And who makes one?

Thanks before hand.

[star-turn]

is ypu die a 'split die' (button) of a solid die?

if solid then i suspect it is just poor quality.

if it's a split die (button) you will need a holder to adjust the die - on the o/d of the die are 2 drill points either side of the slot the holder has 3 screws - 2 of which close the die to get a smaller diametr thread the centre one locks everything it place so the size does not wander. therefore your first pass creates a thread hen you can die again slightly smaller for good finish and size.

Die holders are easy to make and you could make one to fit into the tailstock of your lathewhich would make the die engage sq. to the rod.

Remeber, All threads have various limits and fits

Lastly are you sure your tapped hole is M3 x 0.5 ?

[mactec54]

Hi rerod
First you should turn the rod down to the right size to .118 before threading
.125 would be to big for the button die to thread very well

[rerod]

Thanks mactec54 and star-turn. It "was" a solid Hanson Die. And yes Im sure M3 .5

Can someone recommend a good die? A TiN coated.

[star-turn]

You should not need a coated die HSS should be fine, as its solid you will need to find 3mm dia. bar Or turn down your 1/8" bar

[mattstawicki]

rerod,

2" worth of 3mm thread will be a trick. Like Mactech54 said, you need to turn the 1/8" bar down to .118. The OD of the thread you made was probably torn up because the root of the die was doing all the work (trying to cut down the OD). Chances are the part you made may have worked, but the diameter of the thread was too big. You had 100% thread, and that won't work. The major diameter of the OD thread was most likely rubbing on the major diameter of the ID thread. You basically had a press fit thread.

To turn and thread a 2" long part, you can't expect to hang the 1/8" material 2" out of the chuck (collet) and turn it (or thread it, for that matter). You need to do it in sections. Generally, you can only hang the material out of the chuck 3 times the diameter, and still have enough strength to turn it accurately (no taper). You'll need to stick the 1/8" material about 3/8" out of the chuck, turn it, then thread it. Remove the die, move the material out another 3/8", turn it and thread it. Repeat until you get the thread length you need.

As Star-Turn said, a High Speed Steel die will work just fine (chances are, Ace Hardware sells carbon steel dies). You just need to make sure you're cutting the proper diameter, and you're not exceeding the length to diameter ratio (especially when you're trying to do this by hand).

Matt

[ctate2000]

Can you cut 50 TPI on the atlas. If so cut the threads with the lathe and finish with the die. Leave .005 or so for finish. M3 x .5 is close enough to 50 tpi to work. You will get to practice your vocabulary trying to cut 2 inches worth of thread on a .125 diameter. Good learning exercise though.

[mattstawicki]

Originally Posted by ctate2000 Can you cut 50 TPI on the atlas. If so cut the threads with the lathe and finish with the die. Leave .005 or so for finish. M3 x .5 is close enough to 50 tpi to work. You will get to practice your vocabulary trying to cut 2 inches worth of thread on a .125 diameter. Good learning exercise though.

You can't do that. By the time you cut 2" worth of thread, you'll be 1.6002 threads off. Depending on the depth/length of the thread in the piece he's threading it into, it will most likely begin to bind about 1/4 of the way in.

That .000315" difference between a .5mm and a 20 tpi thread may not seem like much, but it starts to add up quickly. In fact, by the time you get 15 threads into the part, it's already off by almost .005"! (.004725 to be exact). And that's only the first .300" of the part!

Also, you can't hang 2" worth of 1/8" material out of the chuck and expect it to hold still while you cut it. Unless you can do like we do on Swiss screw machines, and that is to rig up a half-round support, opposite the cutting tool, that will support the material while you're trying to cut it. Alignment has to be prefect, or you'll get a taper, and you have to take pretty light cuts, or it will try to hop out of the support.

Matt

[star-turn]

MAtt, Altho you are correct with the pitch, you would need a metric dial added to the lathe you could cut 2" of thread in one go...

1. centre the bar and support in r/centre while s/cutting.

2. hold die in a carrier with thro hole and feed die onto job ( die held in chuck in tailstock ) once startrd th die will pull itself down the bar - so tailstock should not be clamped.

This works the same way as threading with coventy dies.

ST

[vulcom1]

If you have an old Atlas like I do(TH54) then you may have the threading capability on it then you don't need a die. I have done 6/32 which is comparable but have not tried M3 but sooner or later probably will.
It is in the Atlas book the setup for the gears and says it is accurate to 1 in 3000 which is a lot closer than I could achieve. If you have the Atlas Pickomatic and not the book let me know and I will get you the gear ratio's.
I have a few 1/4" carbide bits that I have made for cutting things like this. It will need to be the right profile, sharp and set dead on. I would also centre drill the shaft and use a good pointed centre in the tail stock. I also use a
1/2" drill chuck mounted in my 4 jaw to get it on centre. A 3 jaw would be a waste of time even if it would fit. You also may be able to use the follow rest mounted on the cross slide if you are equipped.
If you need more info especially on the Atlas let me know. Had mine for years and still cutting well.
John (also an RC modeler)