I want to thread aluminum and/or steel pipes/tubes of
diameters between 1.25" and 4" on both the inside
and outside in both metric and non-metric thread
sizes and pitches. What kind of tool do I need to
do this? I will only be making small numbers of
assorted adapters for astronomical applications,
but precision is important.
Alternatively, where could I get this sort of thing
done without paying a fortune for one-off parts?
Precision, 4" pipe, and cheap are not used in the same sentence.
I don't even want to think about dealing with a 4" pipe tap! This
calls for a lathe doing the various cuts.
Any small machine shop can do this for you at a semi reasonable
price. I'd suggest that you do a whole batch of different sizes
as one order so that the machinist can optimize the various setups.
Your cost might go down a lot if you could buy standard pipe
and/or couplings, cut them down close, and weld together. Your
application might not need to be fluid or pressure tight or even
particularly coaxial. Or at least look into standard couplings
and just machine one end.
Alan Wright wrote:
How much, in your mind, is a fortune? Precision is important, so you
think you are going to do this accurately, but don't have a clue what
you need to use for this. You are in a fantasy land. Get realistic.
Maybe a pipe threading machine will work, but you said precision is
important, so maybe not. That is if you want "pipe" threads. I imagine
you want machine threads. Start looking for a large lathe, and tooling
for it. Or just accept the fact that you can get a proper job done by a
professional or accomplished amateur, pay them so they can eat too, and
do something you would be more constructive doing yourself while that is
It depends on your usage. If you plan on using them in a non-commercial
setting (for instance, a teacher making telescope parts for student's use),
a lathe will do it. Check with your local tech school or college. But even
if they agree to do it for free, be prepared to come up with some sort of
donation. If nothing else, a free pizza lunch for the teacher and students
will get you a lot of good will. Here in Louisiana, the teacher would
accept several pounds of boudin, or anything grown fresh in a garden.
If you're planning on using these in a commercial setting, then the proper
tool would be a crow bar. Use it to pry open your wallet and pay a
machinist to do it :-) Seriously, draw up exactly what you want and get a
quote from the local machine shop. It may not be as expensive as you think,
and what you consider as 'precision' is SOP to these people. Keep in mind
that materials may run up the price. Depending on what you need made, if it
has to start out as 4" solid stock, that's not going to come cheap anyway
you look at it.
Thanks to you and the others for the replies.
Here are the basic economics:
I currently pay $100-300 for each part, and that's if they are
actually available at retail. I assume custom parts would be
much more. The stock is cheap (I know because I already
machine/drill/tap all kinds of parts so long as they are not
tubular). It seems that I can buy a decent metalworking lathe
for a couple of grand that would do the job, though I'm not
sure of the extra tooling needed. This would pay for itself
in about 2 weeks with my current backlog, and would pay
for itself 10 times over per year easily. Not to mention I
can easily sell parts which are not available at retail and
likely make a profit if I care to.
I would encourage machinists to get into the telescope
parts business. Take a look, for example, at the web site
and search on "adapter".
Look at the prices and then note that at least 90% of
all useful adapters are simply not available. Also note
that for most of us the high quality fit and finish of
the retail products is not needed. I just need to hold
product A to product B with spacing C. This involves
2 thread sizes and possibly a step up/down in diameter.
There are thousands of such combinations and products
come and go all the time. Also, there is also a ready made
place to market this stuff for little or no cost: astromart.com.
Recommendations of lathes suitable for machine
threading in metric and standard sizes on 1.25" to 4"
aluminum or stainless tubing would be appreciated.
Pointers to anyone who can make such parts for less
than $50 each would also be fine. :-)
You need a lathe that will handle fairly big stock and do both metric and
SAE threads. I would suggest at least a decent 12" lathe -- no so much
because you need the size, but for the stiffness. $2500 installed in your
shop -- assuming you handle the wiring.
1. Metric and SAE (i.e., "English") thread.
2. A 5-C collet set up and a bunch of good (big) pot collets. The pot
collets new will cost between $35 and $75 (2" to 4"). You machine these
collets to the right size as needed. Those are the "external collets" --
you will also need a matching set of similarly machinable internal collets.
The collet chuck will run you about $350 to $500 -- You want one that
can be adjusted for minimum runout. Costs more, but is well worth it.
If you find the collets used with enough meat on them to machine, figure
about $15 each and you'll buy about 10 of them (5 inside and 5 outside).
The inside collets can be machined to handle several different sizes. The
outside collets is a bit trickier for that.
3. A good 6-jaw chuck with two-part jaws. About $700 for one with
adjustable runout. You're dealing with thin wall stuff. A normal 3-jaw
chuck won't do the job without distortion. You make up aluminum jaws as
needed for various sizes. or buy them ready made for about $400/set.
4. A good toolpost -- $350. for an B sized Aloris clone with six or so
5. Outside threading tool -- varies -- from $30 to $250. Depends on how
much you want to fiddle. Figure you find a good one used but have to buy
a new bit -- $120 total.
6. Inside threading tool -- easy about $35.
7. A set of boring bars to go into the toolpost boring bar holder. About
8. An assortment of 1/2" tool bits for machining the ouside to size.
8. Dial calipers( $25) 1/10 dial indicator for adjusting runout ($125), 1,
2, 3, 4, 5," micrometers ($300), thread gauges $50, thread measuring wire
set ($25), Bench grinder ($150) , miscelaneous tools I forgot, ($115)
For a total tooling cost of $3000 + the lathe @ $2,500 is $5,500 -- which
is about right since the tooling costs more than the lathe -- which is the
I've got all that (except the 6 jaw, but I'll be real careful) and I
figured the above by looking around the shop and seeing what tools I would
use to make such adapters. The above prices are a mix between good (but
not best) quality used stuff and new only if I could not find the tool used.
For best quality tooling you can easily quadruple the above prices.
That's the good news. The even better news is that I won't offer to
do them. Even though made out of aluminum, they are a bitch to machine.
I've made a few (or tried to). Big diameter, soft material, fine pitch,
thin walls, tells the whole story. It is much easier to do a whole bunch at
a time of exactly the same size because then you can afford to invest the
time to make special mandrels, stops, etc. Doing them one off is fiddly --
just a hair too fast or too big a cut and your nice thin piece comes out of
the collet and turns into a moebus strip.
What I used to do for my camera gear when I wanted to make special
adapters is buy old filter rings and filters used. Then find a ring that
matches one thread and another right that matches the other thread. Machine
off the parts you don't need on both rings and glue them together with
epoxy. Also set some really fine screws (e.g., 3 to 5 00-96) for further
rigidity. I found that I could cobble up such filter ring adapters a lot
faster than making a new one with both threads.
If I were going to do this as a business, I would make all my
adapters two parts. One part has the one thread and an unmachined collar on
the other end. The other has the other thread and an unmachined collar on
the other end. This could be male-male, male-female, metric-sae,
metric-metric combinations. Then when I needed a particular adapter, I
would go through my stock of ready-made half adapters and find the two
halves that I needed to mate. Now machine off what you don't need to get
them to mate properly with the right depth. Out with the epoxy and little
screws. This semi-production approach will have a lot let wastage because
you have only one thread to bung up on the piece and never have a good
thread on one side only to bung it up with the second thread.
Think about it.
Anyone would be far better served to own a three jaw chuck capable of soft
jaws and learn to use them in place of all this. The cost would be FAR
less, and the flexibility far beyond that of the mentioned tooling.
Precision would not suffer, in fact it could easily be better. Properly
applied, soft jaws will hold extremely thin walled components without
distortion, including long pieces, something you'd be hard pressed to do
with a step chuck.
Thanks for the suggestion, though this is precisely what I already do
if I absolutely have to. The trouble is it is not at all easy to find used
parts cheap (often at 80% of retail), and you have to destroy the two
original parts to get the new one. Not really economical. The lathe
sounds better, and your "half adapter" approach is a good idea.
I'll try to get the cost a bit lower than your setup. The used equipment
around here appears to be much cheaper.
I should have been clearer -- correct, you don't need all three. Here are
the alternatives for chucking: In order of decreasing expense.
1. A good six-jaw chuck should be able to hold many different sizes, both
internal and external with very little distortion and probably no need to
machine the jaws to fit for each different diameter.
2. Collet set-up with appropriate inside and outside machineable collets.
Use the inside collets to machine the outside and the outside collets to
machine the inside. I favor (maybe because I have one) the Bison collet
with the adjustable run-out -- .e., an "adjust through" collet holder. It
can be tweaked to a runout of a 1/10,000. The inside collets can be
machined in steps for different diameters, so you will need fewer of them
than the outside collets. The outside collets can also be machined in steps
to hold various sizes, but then there is a problem with enough room to get a
boring bar in or a threading tool for such shallow rings. Theoretically,
you can argue that you don't need the adjust-through feature because you
machine the collet in place. That's true and the runout will be only the
headstock runout -- however, the next time you replace change the collet and
get back to the first collet, the runout has changed.
3. A three-jaw chuck with machinable jaws. The adjust-through issue
applies here again and therefore, an adjust-through chuck is preferable --
albeit more expensive. A three-jaw chuck with two-part jaws, especially if
you machine the jaws to be 120 degrees will hold perfectly -- for exactly
one diameter. The diameter it was machined for. In that respect, it is
the same issue as the collets above. You can step the jaws for different
sizes for internal holding, but external becomes an issue to accommodate
4. A four jaw chuck, with individually adjustable jaws -- the usual
four-jaw chuck. This is the cheapest solution -- especially if the jaws are
soft-two part jaws. It is the cheapest and in the hands of an old-time
machinist -- the best. But then you have to use an indicator and dial the
work in every time -- time consuming and tedious -- much easier if you use
two chuck wrenches simultaneously. I didn't recommend this because I
believe that it is too much to deal with for a beginner.
Ideally, you would do better with full coverage pie section top
jaws, especially with a three-jaw chuck -- just to distribute the
clamping force over the maximum of the circumference and thus minimize
[ ... ]
Aside from your customary use of "adjust through" instead of the
maker's intended "adjust-tru" (shortfor "adjust-true"), you are also
assuming that you need a collet chuck for your lathe. (I'm not sure
where the "through" comes from, but it sure sticks with you. :-)
Depending on the size of the lathe and the collets, you may well
not need such a chuck. As an example, my 12x24" Clausing has a 1-3/8"
bore through the spindle, and will accept a nosepiece to fit it to 5C
collets without the additional stickout (and loss of rigidity) of a
collet chuck. Add to that the lever-style collet closer mechanism and
you have something a lot faster to use (for repeated parts -- especially
when using stock fed through the spindle -- up to 1" with the collets),
and you have something much superior to the collet chuck -- assuming
that your spindle is in good enough shape so the runout is already at a
Exactly. I have yet to see any application for a 6 jaw chuck that wouldn't
have been dealt with better with wide jaws in a 3 jaw chuck, especially
with larger and thinner sections such as those described in making these
optical adapters. The only exception ould be when chucking small diameter
work, so small that the soft jaws may interfere with one another, even when
somewhat relieved. At that point I generally am running collets, so it is a
The real advantage with soft jaws is they are unlimited in application aside
from the physical limitations of the machine itself. That can't be said for
a 6 jaw chuck. Relatively long items can be well supported by making
longer jaws. For this I favor making the jaws from steel so they can be
welded for additional supports (gussets to increase rigidity when
necessary), or otherwise modified to hold strange configurations by the
addition of more metal where needed. Using aluminum (6061) works fine
until you weld, at which time they become quite soft, so I don't weld on
I'm suprised that the *one* item this guy is going to
need to make his telescope adapter tubes, has yet to
A steady rest!
Some of the tubing is going to be way too
large to fit inside the spindle bore, especially
on smaller machines.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
I thought some of them will be several inches
in diamter - which means he's going to be purchasing
aluminum tubing stock, probably a foot or so at a
time. The problem of trying to make an OD thread
and an ID thread on the same piece of large diameter,
long, stock, is best handled by extending the
raw stock out through a steady rest and working
on the end that protrudes through the rest.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
I stand corrected (got a private letter from him also). He indeed needs to
make some of these adapters longish and for that, he will need either a
lathe with a huge spindle bore (4+") or a good steady rest. Opt for the
better kind that has micrometer type finger feeds. They will be quite
expensive. Even simple ones go for $200+ used. Expect to pay $250+ for a
suitable, good, used steady rest. Then also, an investment in dial
indicators is a must.
The machining canb be tricky because if the work is not centered
properly the piece can flex enough so that the threads are cocked. You
can virtually eliminate that problem by spending more money -- a live bull
nosed center big enough to handle the work -- figure another $200 or so.
You chuck the work in the chuck and use the bull nose center on the other
end -- with the work through the steady rest, which isn't tied down.
Assuming your tailstock isn't offset, that's going to get the piece aligned
as well as you can expect. Check the runout with the indicator and adjust
the set up as needed. Now bring the steady rest as close to the working end
as you can and tighten the finger very gently (finger tips (of the steady,
not yours) should be lubed) -- you want the work to be free running but not
loose. Back the bull nose off and check for any play with the dial
Another approach for the external threads that doesn't use a steady
rest or a bullnose live center is to invest in a live tailstock chuck. I've
never seen any but a three-jaw chuck -- so all the issues of three-jaw, soft
jaws, etc. discussed before apply here also. Bison makes one. I think the
bigger ones have two-piece jaws, which would be essential. Probably the
combination of steady rest and bullnose comes to more than a live tailstock
But you still need the steady to the inside threads -- hmm -- how
about a dead bullnose with 1/4 cut out like a half center point -- some
tricky threading tools to go around the corner....