Hi,
I am looking at buying a lathe/drill/mill, but it has no automatic
thread driver, and I want to cut a few threads.
Is it possible (and reasonably cheap/easy) to do this?
I would be looking a making a screw on lid for a 50mm pipe to start
with.
Can you point me to some info on how to do this?
Thanks heaps!
Are the threads you intend to cut pipe threads, or are you simply trying to
cut a random thread on a pipe?
The typical engine lathe, without a taper attachment, can't chase a pipe
thread regardless of having, or not having, a lead screw. The taper
involved is beyond the ability of the machine. The sole exception to that
is if the piece is short enough that you can offset the tailstock the proper
amount. It wouldn't work for long pieces.
That being said, if you intend to use your proposed lathe for future
projects, do not buy a lathe than doesn't have a lead screw, or one without
change gears or a quick change.
There are other methods of chasing threads, but the machine must be so
built, and you must have masters from which you generate the lead. Threads
are precision items that can't, and should not be, generated randomly, not
if you want them to work properly.
No sense discussing how they're cut at this point, but it's something you
need to discuss and learn if and when you acquire a screw cutting lathe.
Good luck, (unless the pipe and lid are for a pipe bomb, that is)
Harold
According to :
Hmm ... does it have a turret?
Possible, with a turret (or some other way of holding and
feeding round-shanked tooling on the lathe centerline), and some
Geometric (or similar) die heads with the appropriate chasers.
However -- cheap doesn't match that. Even used Geometric die
heads on eBay are not cheap.
I've not seen a turret for a 3-in-1 tool (lathe/drill/mill), so
you would first have to make that. Also -- I haven't seen any 3-in-1
machines without a leadscrew and at least a basket of gears threading
setup, (certainly not a quick-change gearbox), unless you are talking
about tiny machines like the old Unimat SL-1000, which marginally
qualifies as a 3-in-1.
You mean that you not only want to make threads, but you want to
make female threads in a blind hole? (I presume that you are talking
about a cap for a pipe -- and those tend to have tapered threads, so you
would not only need a collapsing tap but a set of tapered chasers to
fit. I've gotten several sizes of Geometric die heads over the years
from eBay (since I have a bed turret for my lathe), but only two
collapsing taps, and very few chasers for them.
Single-point threading (instead of using a die) for a pipe
thread means that the machine would need a taper attachment -- which
also tends to not be available for a 3-in-1 machine. At least, not for
those which I have seen.
And very few 3-in-1 machines have a large enough spindle through
hole to allow feeding pipe through it for threading the end of the
pipe. (Which, I will admit, you did not ask to do.
It sounds as though you really need to consider buying a more
versatile lathe, not one with an afterthought of a milling machine
grafted onto it.
Beyond that, since you have given very little information on
what kind of machine you have (or intend to purchase), and not much on
the workpiece material as well, there is not much that I can add here.
From your 50mm pipe size and your domain, I see that you are not
in the US -- you are in Australia. You really should specify things
like this, as advice as to which machine is best is region specific.
What we have here in the US for not too much money could be quite
expensive in Australia -- and vice versa.
For example, the Geometric die heads are US made. I remember
that there is a similar die head in the UK, which I would expect to be
easier to find where you are.
Oh yes -- and a die head to thread a 50mm pipe is going to be a
bit too large for most 3-in-1 machines.
Premade pipe caps should be available from your neighborhood
hardware store. Buying a lathe to make your own is hardly cost
effective, unless you need something special about this.
Good Luck,
DoN.
Hmm. Lots of info.
Well, to start - here is the lathe I am looking at -
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a HQ-400 Multi Purpose Machine
One of the first things I want to make is a dive torch. Which is
essentially a 50mm (or so) tube with a thread on it, and a slightly
bigger tube with an internal thread on it to act as a 'lid'. The
thread depth would only have to be 10mm or so.
Do I need die heads for this? Or this only if it doesnt have a
leadscrew?
Is there any good reason not to just put a steppermotor on the control
to make an electricaly controlled powerfeed?
Its a HQ-400 Multi Purpose Machine
O.K. Without more details of the maker and model, and just
going by the photo shown, it appears to have a leadscrew (connected to
the hand crank at the right hand end), and it appears to go into the
gearing under the cover at the left-hand end. It looks as though the
control for forward or reverse feed is on the belt and gear cover, with
a yellow plate behind the knob.
That long column from the carriage to the toolpost will be a
problem when dealing with heavy cutting, because it is long enough to
both flex and to add leverage to flex other things. It is necessary
because of the large "swing" (maximum diameter of workpiece). The
actual reasonable size is probably suggested by the relatively small
3-jaw chuck on the spindle.
There *should* be a collection of gears to change under the
left-hand cover to set up for various threads.
UK "torch" is the same as US "flashlight" I believe?
By "depth" do you mean the actual depth of cut? If so, that
would leave you with only 30mm inside diameter (taking 10mm out of each
side of the pipe). I hope that you only mean the length of the threaded
section.
How deep do you need to take this? That will determine how
thick the walls need to be, and how good the seals. (And no -- *I*
can't give you the answers given the depth, but others probably can.)
I would suggest that the threads should be straight threads in
this case, with O-rings in grooves.
And the material is probably a bronze (for long term life in the
presence of seawater), or brass for infrequent immersion. Brass will be
easier to machine, FWIW.
The die heads are used for quick cutting of threads -- many
operations per workday. They (and a turret lathe) are production
machines.
You have a leadscrew on this -- and hopefully also have the
change gears (make sure before you bid, as Chinese replacement parts
become very hard to get after a few years, and I think that this has
seen a few years of service.
And to cut the threads, you would grip one end in the 3-jaw
chuck, and support the other end with a live center in the tailstock,
aided by a plug of some sort for the center to engage, as that one
appears to be tiny. The chuck (with the alternate set of jaws, which
are for gripping larger items) will probably handle your 50mm tube and
an appropriate cap. At least, I *think* so -- assuming that your
electrical plugs are a bit larger than the US standard ones, as there is
nothing which says how big this is, and the pointer to the ad from which
he bought it seems to not work. Reading that might give me more
information on what it might be able to do -- if it is complete.
Well ... if you want it for cutting threads, you need to have
information from the spindle as to how far it has rotated, and to step a
few steps to be in the right position. This is one of the functions of
a CNC conversion of a lathe. Until you do a full CNC conversion, you
really need to stick with using the gears inside the headstock covers
for your threading.
And based on experience with other such machines, I suspect that
you will need to add some extra belts and pulleys to slow the spindle
down, as the slowest spindle speed makes it difficult to enage the
half-nuts or the dog clutch (which I suspect this one has) to start the
thread at the right time for each pass. You can't cut the thread to
full depth in a single pass -- you need to make each one a little
deeper.
Stopping soon enough will be more of a problem for the cap which
you wish to thread on the inside, as you are threading towards a solid
piece of metal, so slower makes the chance to disengage it in time
somewhat better.
You'll have to spend quite a while learning the machine and the
operations before you start on your project, I fear. Plan to make
mistakes and to learn from them. And try to learn without breaking
parts of the lathe, as repair parts may be quite difficult to find.
And ideally, you need someone nearby who can help you to learn
to use the machine.
Good Luck,
DoN.
It's a waste of good money so I hope you didn't win it.
By the time you buy a lathe, the tooling, learn to use it etc etc you
could not only have bought a torch, you coulda bought a complete dive
outfit. Your dive torch threads have to be accurate and a good fit,
*and* you'll need O rings etc to keep the water out. Just go & buy one.
I wouldn't bother making one myself and I have a full workshop.
You can use die heads for cutting external threads on relatively small
dia workpieces. 50mm is not small by die head standards. I sold a small
die head some years ago for a couple hundred, IIRC. OTOH a reasonably
small lathe can thread both internally & externally at 50mm dia without
dramas.
Get a lathe first, then learn to cut metal, and only THEN start
modifying it. That's my advice. Also don't confuse a power feed with a
threadcutting feed. If you're thinking that you can take a piece of
crap, add steppers, DRO etc et and end up with a good machine, you're
dreaming.
Very little good used machinery, IMO, appears on the Australian Ebay
site. In fact I've been thinking of selling some of my surplus tooling.
You need to haunt the second hand machinery dealers. If you're in
Sydney or close, I can tell you a couple places to start at. Some of
the Chinese lathes aren't bad and are infinitely better than those 3 in
1 pieces of crap.
formatting link
is a more reasonable machine if the price doesn't go much higher
although the low speed is too high for my liking. Otherwise Hare &
Forbes in Sydney, Melbourne & Brisbane import Asian lathes. The AL-32G
would be worth a look if you want to spend $2K on a machine. It has a
low speed of 60 rpm, good for beginners threading, and a 38mm spindle
bore.
Can't afford new? Join the club, start hunting second hand machinery.
Trading Post is good but you need to know what you want and be prepared
to move fast. If your budget is less than $1000, look for a Hercus
lathe in good shape.
PDW
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