lathe work on heavy part

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
specs.
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
shop.
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.
Karl
Reply to
Karl Townsend
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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 parallel.
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 closer tolerances.
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(877)988-4343
Ned Simmons
Reply to
Ned Simmons
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.
Karl
Reply to
Karl Townsend
...
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.
Karl
Reply to
Karl Townsend
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 back.
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 me thinking.
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.
Reply to
Dave Baker
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 this point.
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 following URL.
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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 boring bar.
Wow that got long winded. Hopefully somebody will benefit from it at some point.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
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.
michael
Reply to
michael
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 jaws. 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. Chief
Reply to
Chief McGee
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 will help..
Karl Townsend wrote:
Reply to
jerry wass
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 chuck!
Jon
Reply to
Jon Elson
- 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.
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @
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Reply to
Tim Williams
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?)
Ned Simmons
Reply to
Ned Simmons
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.
Karl
Reply to
Karl Townsend
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, DoN.
Reply to
DoN. Nichols
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.
Reply to
Dave Baker
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.
Reply to
Ron Leap
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.
Karl
Reply to
Karl Townsend
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.
Reply to
Lennie the Lurker
Why do you suggest that aluminium would 'sag' over time? At ambient temerature and not excessively loaded it's a very stable material.
Reply to
Dave Baker
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.
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @
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Reply to
Tim Williams

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