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Thread: cast iron and memory
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9th Sep 2013, 08:47 PM #1
cast iron and memory
Hi
I have heard of cast iron lathe beds that have developed a permanent built in twist in the bed as a result of being stored on a uneven floor . Is this possible - Or is it just a furphy ? Mike Thanks in advance
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9th Sep 2013, 09:22 PM #2Most Valued Member
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Hi Mike,
I vaguely remember people mentioning something similar in a thread some years ago. From memory the lathe was left for a prolonged period of time in an non-level state (with twist) and when they attempted to level it under it's own weight, a leg lifted off the ground. Think there was mention of using masonry anchors to pull it down to the ground and re-level.
Then again I could have just dreamt it!
I would have thought that it would have to be stored in a very uneven state for this to happen.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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9th Sep 2013, 09:28 PM #3Golden Member
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Mike,
I think the relevant term is "creep". Not (only) the person who bolted it to an uneven floor, but "the flow or plastic deformation of metals held for long periods of time at stresses lower than the normal yield strength". Creep does happen in CI, and the extent seems to be subject to several variables. I have encountered two lathes with a twist in the bed (one very severe) which I suspect resulted from uneven mounting.
Cheers,
Bill
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9th Sep 2013, 09:46 PM #4
Have known lathes to develop twisted beds during delivery to the first purchaser, or in use if not properly levelled and alligned. Fairly common in beds that are lightweight, if there has been neglect along the way. I always wince when I see what would be a decent lathe advertised with an included trolley bench to make it easy to move. Either it will rock on three castors or always be out of allignment as it gets moved around and never gets back to the exact same spot.
We had a Chinese lathe at work at one stage that would not hold allignment over a weekend while mounted on it's flimsy 1.2mm sheetmetal stand. Once we had the boys weld up a decent stand, bolted it down, then mounted the lathe, got it properly shimmed, levelled and alligned, it held it for about 18months till sold when the business wound up. Despite the calibration chart supplied with it, it was twisted from time of manufacture or had some sort of casting void in the bed that allowed it to twist.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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9th Sep 2013, 10:37 PM #5Most Valued Member
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The cast iron base of horizontal steam engines do this when they have been mounted on timbers instead of proper footings.
Phil
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10th Sep 2013, 02:40 AM #6
I think the answer is yes... if you twist it past the elastic limit it will be permanently twisted. Unless of course you can twist it back the other way and try to straighten it.. but go too far and it will probably crack at some point.
Of course if you crack it you'll want a "cast iron alibi", in that case there is no "cast iron guarantee" you'll ever fix it.
Regards
Ray
PS Google "cast iron elastic limit" for better information..
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10th Sep 2013, 02:58 AM #7Banned
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That
That Chinese case hardened plasticine Cast Iron - made from recycled sardine cans, is de debbil I tell you!
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11th Sep 2013, 02:04 PM #8Most Valued Member
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Could another cause be from cheap, careless manufacturers who do not "rest" the castings before they machine them. In which case they will warp soon after dispatch?
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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11th Sep 2013, 10:21 PM #9Cba
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I think large lathes are likely to be heavy enough to twist, if stored on a twisted floor. But not bench lathes, these really need to be bolted down onto a twisted surface to twist enough for the deformation to become permanent. Just from their own weight it will not happen.
Of course, some lathe beds will twist all by themselves, without needing to be helped by bolting down or bad storage. In the old days all lathe bed castings were first roughly finished, then carefully stacked and seasoned for up to six months before final machining and grinding. That was to relieve stresses from the casting. The cheaper lathes now days are maybe stored for a week or two between roughing an finishing. They will relieve the stresses at sea in the shipping container. Chris
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14th Sep 2013, 10:36 PM #10Chief Swarf Maker
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What is the go with machining cast iron and warpage? I have had this issue on long, small diameter parts in the past, as you release the surface tension they bend like a bananna (relatively speaking)
I have to, er, add a relief to the apron/saddle on my milling machine (not on the ways of course, just for some clearance under the table, mostly in rough cast areas). This will be done on another milling machine, with my apron clamped down onto its table.
Do I need to worry about it warping and my ways not being flat anymore? It is a pretty big lump of cast iron, i estimate around 70kg. The bottom surface where it is clamped onto the table is pretty large and was already machined flat.
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15th Sep 2013, 12:06 AM #11Cba
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The problem with warpage of cast iron is mostly during the first year after being cast. But it is hard to predict what may or not happen in your case. Disturbing one side of a table is not unlikely to have some effect on the flatness of the other side. Particularly if it is a precisely ground surface. I would be careful and remove only as little material as absolutely necessary for whatever your purpose is. Chris
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15th Sep 2013, 12:17 AM #12
This subject is full of myths.
Much research has been done and stress relieving in cast iron only happens above certain temperatures, time has little or no effect as far as stress relieving is concerned.
This pdf covers most of the questions raised.
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD620556
Regards
Ray
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15th Sep 2013, 12:24 AM #13
So i can dive into the slides for the Rivett with no fear of them moving.....Great.
Interesting article Ray, thanks for sharing.
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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15th Sep 2013, 12:29 AM #14
Umm no, maybe not...they will be stressed and machining will release the built in stresses in some way, ideally for long term stability you should stress relieve them by heating.
I don't know if flocast as supplied has already been through a stress relieving cycle?
Regards
Ray
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15th Sep 2013, 12:32 AM #15
Yeah i was about to edit that......I can machine them now knowing that waiting will make no difference to how they may move. But since i have roughed them out before doing anything accurate i hope all will be well. I've cursed missing out on that heat treatment oven a few times already, here's another time.....
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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