I need to do some turning on a short piece of thick wall tubing; 14" OD, 8"
ID, 6" long. I estimate weight at 175 lb.
The part needs to be mounted in soft jaws and faced, with features, on one
end. Then flipped and faced with features on the other end. The two faces
have to be parallel within 0.002 in by measuring the length between faces at
several points near the OD, I'd prefer dead nuts here. No other tight
Can this heavy a part be turned in a conventional Leblond manual lathe with
a 16" swing? And not have real trouble with slipping/deflecting in a softjaw
three jaw chuck? I'd really HATE to have it come out and chase me around the
Just a thought, the finished part has a six hole bolt pattern at 10"
diameter. Should I build a special softjaw with a tapped hole and bolt the
part to the softjaw? This would add a lot of machining time, but I'm not
paying the help.
I'd like to know before I pick up the stock, the cost estimate is north of
$400. FWIW, this is a riser block for my CNC knee mill.
Before you get stuck on making the riser from tubing, you
might want to look at getting a piece of plate burned to
size and Blanchard ground. Based on a piece of similar
weight I purchased recently for a bolster plate, the price
would probably be less than what you're paying for the
tubing and would come with the ends already flat and
I've been treated well by American Grinding in Chicago,
even with shipping to Maine that last order showed up in
about a week. They'll Mattison grind if you want even
Cast iron would be the best possible choice for this job. Looks way beyond
your average hobbyist. The weight would still be at least 125 lbs.
There must be a reason they don't use AL for heavy duty machine frames, I
don't want to learn why.
This was plan A. Until I took the mill apart and seen that it won't
work -:( You'd have to see the part to understand. Could have got this
almost free as an "accident" scrap piece from my son's workplace.
I've shown the job to two lifetime experienced tool&die men. Both
(independently) told me to find this thickwall tubing.
Cast iron is actually slightly more dense than steel according to my data so
175 lbs is still the ballpark figure.
It's primarily a cost issue. When you're casting big lumps of stuff it's a lot
cheaper to use cast iron. Material cost, on the scrap market at least, is about
10 times as much for aluminium as it is for iron at the moment. In the UK you
can hardly find a buyer for scrap iron and steel anymore and they charge you to
take scrap cars away whereas you used to get a few quid or at least get the car
uplifted free of charge. Scrap values are about 50 pence/kilo for aluminium and
maybe 5 pence for iron and steel if you have large quantities. For small
quantities it costs more in petrol to take it to a scrap yard than you get
For a riser block I think aluminium would be an excellent choice. Rigidity of
such a large piece isn't an issue, aluminium damps vibrations very well and it
would be lighter and easier to machine. Approx 65 lbs for the finished piece.
Maybe 75 lbs for a casting with some machining tolerance built in on the length
and wall thickness. If you collected 4 or 5 old aluminium cylinder heads,
removed the valve seat inserts and other non alloy bits I'm sure a foundry
would melt it down and cast it for you. The mould is certainly straightforward
to make. You could do the wooden boxes yourself. You'd then need heat treatment
to improve the machinability and hardness but that wouldn't add much to the
cost. Pistons, as suggested, would also be a good choice. They are made from
higher silicon aluminium (approx 13%) which casts well, machines and wears well
and can be heat treated to a good hardness. Somewhat more abrasive to machine
but not really an issue.
I wouldn't mind a riser block for my Bridgeport clone. I've thought about it in
the past but don't have the roof height at present. I also have 10 or 15 scrap
cylinder heads plus boxes and boxes of old pistons lying around so this has got
If you prefer iron then find an iron foundry and take them a couple of old
engine blocks and do the same but aluminium would be my choice. Consider how
stiff an engine block is despite its thin walls and try and imagine how much
force it would take to deflect a riser block only 6" high with 3" wall
thickness. It just isn't going to happen. You could hang a 50 ton Chieftain
tank off something that sturdy.
Not really enough info to say for sure but I really don't see much
problem with this except for a few possible problems outlined below.
Why soft jaws. Is the chuck to small to take them with the hard
jaws? In this case possible problems though as long as you take it
easy you can probably get away with it. Personally I'd prefer hard
jaws or even better a four jaw chuck for a job like this. The four jaw
will hold the part much better than a three jaw.
You say Leblonde 16" lathe. Is that actual swing or is it nameplate?
If actual swing then you've not got much room for the chuck jaws (this
could be the reason for the soft jaws I suppose). In this case I might
consider making a face plate to mount the piece with or just use a
actual face plate.
To make a face plate or mounting ring take a ring or circle of plate
big enough to comfortably contain the bolt circle and thick enough to
stick past the jaws on your 4 jaw chuck. Turn the outside clean if
it's not already clean and then face one side. Hint if it's a full
piece of plate instead of a ring then tack weld another ring (can be
piece of pipe, another plate, etc) to the face with about 6 small
1/4"-3/8" long tacks. Lay out the bolt circle while in the lathe at
Remove from lathe (if you tacked a ring to it then remove at this
point) then drill and tap the bolt holes. Now remount in the lathe
with the already faced side to the chuck and chucking on the outside
of the ring with the four jaw chuck (there should be enough of the
plate sticking past the jaws for you to run a indicator on). From now
on you don't remove the mounting plate from the lathe. Take a facing
cut on the plate to true it up.
Now with the bolt holes in your work piece drilled and counter bored
for socket head cap screws (counter bore on both sides) you can bolt
the work to the mounting plate. You might need to do a little tapping
around to get the outside running like you want but I wouldn't go to
far since you're really wanting to machine to the bolt pattern at this
point. Face and turn your features on the first side. Remove from
mounting plate and then either check that the ring hasn't moved with a
indicator or even better face it and turn the mate to the features in
the ring. Now you can bolt up the work to the mounting ring and turn
your features in the other side. If you took care with the facing of
the mounting ring it should turn out as close to dead nuts on as
you're going to get.
I personally think that everybody should have a few rings of
different sizes around the shop for mounting work in this fashion.
It's a real good way of mounting some types of work without distortion
but then I worked a lot of years in a shop where we did work like this
a lot. For a picture of large work mounted in this fashion go to the
It's a really lousy shot. Back then I didn't have a digital camera
or scanner so I had them digitize the prints when I developed the
film. They did a really lousy job of it.
Anyway that shot is of a 20" rotary airlock barrel in a Leblonde
heavy duty lathe. In this shot the lathe doesn't have the riser blocks
in place so it's got 27" of swing. That's a 24" 4 jaw chuck which has
a mounting ring chucked up. The barrel has a finished bore of just
under 20" and is about 25" long. The barrel was rolled up from 1"
thick 316SS and then we cut the openings and welded the flanges to it.
The boring bar was over 5" dia (it's been so long that I can't
remember the exact size). You'll note the steady rest on the end of
the barrel. It ran on another ring which was bolted to the flange of
the barrel. It wasn't needed to support the piece so much as to reduce
the chatter and deflection. Many barrels got turned without it before
we got around to making it. It did speed up the work as did the larger
Wow that got long winded. Hopefully somebody will benefit from it at
The 3-jaw is not the best choice, but I assume you do not have a 4-jaw.
Some 'pie' jaws might be cool if the OD is round. If out of round, that
could make pie jaws not so good. Maybe you can just do this on your
mill. Just because a part is round does not mean it *has* to go in a
lathe. The weight of the piece will actually help it stay in place. And
if it should come loose, it won't go far or do the spinning top routine.
A friend of mine has some sizable equipment and told me a piece came out
of a VTL a couple weeks ago. It was about 40" OD and about 36" in
length. Said it bounced around like a top, and expended energy in some
unfriendly ways. Nobody hurt.
Karl, Cut a piece of bar stock. Say, 2" x 1/2" x 8" long. Grind or mill
a radius on each end to fit inside the tubing. Drill a 5/8" hole in the
middle of this piece then weld it inside the tubing about half way down.
Try to position it so it will not interfere with the mounting bolts on the
mill. If not, you can cutout this piece later.
Now, cut your soft jaws and mount the tubing. Get a piece of 1/2"
all-thread and run it thru the hole in the bar stock, down the spindle hole
and out the left side of the headstock. Place appropriate washers and nuts
on each end. This will give you the safety you need to keep the part in the
Machine one end of tubing, turn around and mount on other end.
Loosen the jaws slightly and tighten the all-thread, then retighten the
jaws. This will pull the tubing up tight against the jaws and should give
you the parallelism that you want.
First thing I'd do is round up 100# of old diesel engine pistons, and
cast me a hunka metal for the blank---Now, you've cut your weight WAY
down & the cost too---lotsa casters in this group--Mebby one of them
Karl Townsend wrote:
The weight is no problem. Can the part be held from the inside, with
the face of the part against the chuck body? You don't want any more
overhang than necessary. In fact, if you used a 6" chuck with inside
jaws, you could hold it with half of the tube OVER the chuck body,
reducing the overhang greatly. (Of course, to use this trick, you'd
need a hole in the part. Otherwise, I'd recommend a steady rest
to avoid shifting the tube on the chuck.
When mounting the part, if the chuck-side face was accessible (not
against the chuck body), you should be able to put an indicator on it,
and adjust for minimum wobble of that face. That will get the two faces
as parallel as you can measure.
Bolting the tube to a faceplate, or even a chuck backplate might be
reasonable. Don't think that the only way to turn something is with a
- Just shake it out of the mold early (start taking it apart after the glow
disappears, so you know it's solidifed). Then spray the hell out of it with
the biggest hose you have on hand. For something this size, you might even
need the fire department to lend a hand in cooling things...(having them
nearby wouldn't hurt anyway, considering! :-) )
356 alloy is pretty hard stuff as-is, but if you're willing to wait a few
months it will now age harden to T4.
For the furnace, a scaled up version of my large reverb. furnace would work
nicely, check sig. Dunno about refractory for something that size though,
unless you can get good stuff real cheap.
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
But couldn't you have the piece of plate cut out to the
same ID as the tubing? If I recall, you've got a 3" wall--I
expect that'd be doable in 6" plate.
(Don't you just love it when someone supplies an answer to
a question you didn't ask?)
Thanks, everybody, for all the tips. The job is definitely doable on my
equipment. I'll order the stock tomorrow, and spend the next week thinking
about the best way to mount it while I wait for the stock to arrive.
I think that your lathe can handle it, with a bit of support at
the tailstock end of the workpiece.
Let me tell you how I did something a bit smaller, but along the
same lines -- hollow, long enough so there would be a chance of it
walking out of the jaws without support. (It was about an 11" long
section of 4" OD, 3.5" ID aluminum pipe (Sched. 40).
I started with a 6-jaw chuck (because I had one, and six jaws
minimized the distortion compared to three jaws), and expanded the jaws
loosely inside one end. (Inside, because I needed to thread the OD on
each end, and gripping it by the already threaded portion was
potentially a problem.)
I then took a small chuck (happens to be a 3-jaw for an
Emco-Maier Compact-5, FWIW), and machined an adaptor to mount the chuck
in a changeable-point live center -- thus making a freely rotating chuck
for the tailstock. I fitted some un-machined soft jaws on the chuck,
and slid it far enough into the end of the workpiece so the jaws were
past the area which I needed to machine to clean up that end, but the
socket for the chuck key was just barely outside the end of the
workpiece. This left me clearance to true up that end.
I then used the tailstock handwheel to push the workpiece back
firmly against the jaws in the headstock chuck, and expanded those jaws
to firmly grip.
I then machined the end true and perpendicular to the axis.
FWIW, I was performing this on four workpieces -- two of one
length and two of the other.
I then took them to a surface plate, and using a height gauge, I
marked the desired final length on each (using layout dye).
Then back to the lathe, where I mounted the second end towards
the tailstock, and faced it to length, and turned the threads for that
end. Then reversed again, and threaded the first end.
Note that you can buy pre-mounted free chucks for the tailstock
in various sizes, so you may not need to make one, especially since you
have a much larger ID than I had. Remember that the whole diameter of
the chuck had to fit into the workpiece, with only the jaws touching, to
leave clear access for the tool which faced the end true. I saw a nice
free turning tailstock 3-jaw chuck made by Bison at the New England
Brass and Tool which might actually be a good size for your task. It
doesn't have to have much grip, as long as it expands to contact and
support the tailstock end and to provide some end thrust to hold the
workpiece against the headstock chuck.
I hope that this is some help to you,
If you're set on doing it in steel then holding it in a chuck should be a non
issue. The length/diameter ratio is very much in your favour and the weight
isn't much for a lathe with a 16" swing. Just push back with the tailstock
while you're clamping it up and it'll be fine. The cost sounds high for that
weight of steel though. We used to make crankshafts from billet EN40B. The
billets were about 20" x 6" and weighed 70kg. Cost was maybe £100 per billet
and that's a very high grade of steel. All you need is mild steel or similar I
presume. Might be cheaper to just buy it solid and bore it out than get tube.
It means starting out with a lump weighing 250 lbs though but the cost per lb
shouldn't be high. Mind you steel prices have gone up so much recently I'm out
of touch with it all.
I still think it would be much more fun and cheaper casting it in ally.
I am assuming that the tube ID does not have to be finished. If this
is the case, you may want to consider using a dog-driven fabricated
mandrel to support the tubing for turning. A mandrel could be made as
follows. Start with a round rod 2" or so in diameter and 12" or so in
length. Face and countersink both ends of the rod for mounting
between centers. Rough cut a couple of disks out of 1/4" plate with an
O.D. of a little over 8". Bore a 2" hole in the center of each disk.
Slide the disks on the 2" rod so they are separated by 5-1/2" (outside
to outside) and tack weld (large balanced tacks) in place. Mount the
assembly between centers in your lathe and turn the OD of the two
disks to fit the ID of the tubing. Insert your new fabricated mandrel
into the ID of the tubing and tack weld in place with very small
tacks. You probably don't need more than three or four small tacks on
each plate. Put the whole thing back in your lathe and start turning
your tube. The big advantage to this method is that you can
completely face both ends, turn the features and the OD of the tubing
without removing it from your lathe. Consequently, the ends of the
tubing will be perfectly parallel. When your turning is complete
grind out the tacks with a carbide burr and remove the mandrel.
Remember the smaller the tacks the less grinding required. Because of
the design the perimeter tacks can be very very small.
Man this NG is GREAT for coming up with ideas I would NEVER think of. Again,
thanks everybody for all the original thinking.
I really like the idea of turning this all at once. I'm afraid of this much
rotating mass just held between two centers. Anyone doing this all the time
with success or total failure? I've got no experience with huge massive
parts in the lathe. And, again, I'm just a bit afraid of eating 200 lbs of
steel real fast.
How about a variation of this approach? Make an arbor that mounts in the
four jaw and then is held in place with the tail stock? In this case, I'd
have the arbor maybe two foot long and put the part maybe 0.75" away from
the chuck. The chuck would hold all the weight, the tail stock to stop the
wobble and hold it in. I know I'd need extreme care to make sure the
tailstock part end is on center with the tailstock.
Ok, my two cents worth.
First, gray cast would be my first choice of material, I don't think
the machinery makers for the last 150 years have been wrong. Mass is
not the enemy here. Cast doesn't deform under heavy loads much, steel
would be the second choice. I would not consider aluminum if you
don't want to watch it slowly start to sag over time.
The faceplate, once you have one end finished or at least faced true
and flat, would probably give the face runout that you're looking for
with the least amount of hassle, assuming also that the faceplate is
flat, and if it isn't, facing a couple thou off to flatten it isn't a
big deal. IF you're using soft jaws, runout and parallelism shouldn't
be a problem. You might want to skin the OD and ID to eliminate the
variations in size that tubing is well known for. In other words,
tubing ain't round.
The weight, in a 16 inch lathe isn't really a factor. I have had much
heavier things in a 16" Colchester and didn't have any problem.
I'm assuming you're going to be turning a pilot on one end and a
matching counterbore in the other. Meaning that beyond the pilot and
the counterbore, most of the ID and OD mean nothing as far as
functionality goes. They're more of interest for "in process" than in
the finished part. A little time spent here will make the rest of it
go a lot easier.
With that wall thickness, deforming in the chuck wouldn't be a problem
either. I can't think of many people that would be ape enough to
deform it enough to hurt anything.
It would seem to me that facing, maybe even finishing one end in the
chuck and then going to a faceplate would probably give the best
results. Just make sure that you have witness turns to indicate from
and it shouldn't give any major problems.
Yeah. Aluminum has no fatigue limit, but it doesn't have any sag that I'm
aware of. So it'll only break after several billion heavy passes...
If it's of utmost concern, I heard CI has a lower modulus, i.e. is more
flexible than steel. Makes sense given steel is a solid material. And
the real reasons CI is used are 1. it's cheap, 2. it's heavy, 3. it damps
vibration. Flexibility is made up for by thick sections and weight.
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson