Peening the Underside of a Milling Machine Table.
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    Default Peening the Underside of a Milling Machine Table.

    I have a Beaver Milling Machine made in England in the mid 70's with a 56 inch table that is suffering from the dreaded table sag. The ends of the table drop about .020" over 20 inches from each end although the center 16 inches or so is quite straight. I would like to try reducing the sag by peening underneath, maybe with a "pneumatic needle scaler", the question I have, for those with experience using this technique is, do I concentrate the peening around the badly bent areas or peen evenly over the full length of the table?

    Lex.

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    0.020 correction over 56" in a thick milling table is a bit much for peening in my judgement. Complicating matters is the surface of the dovetail boss (the surfaces parallel to the table (not the actual angle dovetails themselves) are a bit too narrow for several courses of heavy peening and the way surfaces too close to the table's XY plane of neutral axis to be effective.

    Cast iron is very slightly malleable. A very good pressman can possibly straighten the table but there is danger of cracking or breaking it. It's a major surgical risk but a good pressman can work wonders by a scientific over-straighten a careful trifle followed by a final back bend to straighten. This kind of presswork is beyond the capabilties of a limber automotive shop H-frame press powered by a bottle jack. What's needed is an industrial 100 ton press and a grizzled old pressman.

    Also a needle scaler is not a good selection. You want areas of deeply penetrating compressive stress. The ball peen of a 32 oz hammer would be well suited for this task had it not for the typical configuration of a milling machine's table end section.

    Peening works best if localized in areas needing correction.

    I suggest you take some careful readings and try peening a double row of correction. Check the result. An eyeball check of the area peened compared to the amount of correction attained compared to the peenable area remaining will tell you if you can straighten it out. This will take only a half hour.

    Some general remarks about peening machine tool castings:

    Since cast iron is brittle, peening blows near an edge may cause the corner to break off or crack especially where the edge overhangs a dovetail. Peening takes advantage of cast iron's very limited malleability by introducing compressive stresses in its surface, in effect, lengthening it to correct - straighten - a concavity. When peening cast iron, strike a given area only once. Repeated overlapping courses of peening promotes spalling. Leave little margins of undisturbed metal between each peening indentation.

    There is an esthetic consideration. A course of corrective peening consisting of random blows of a ball peen hammer is indistinguishable from deliberate abuse. A customer on seeing his precision casting looking maniacally battered probably won't be impressed by your remedy or expanations. However, neatly laid evenly spaced rows of uniform indentations looks tidy and professional and need take no longer than the random battering. Where peening was allowable, I used a strip of 1/8 door skin as a straight edge to guide the peen. I placed the ball peen on the surface and struck the face with the next size larger hammer moving briskly along making uniform equally spaced indentations. Thin items like gibs and retainer plates have to be solidly supported by something massive like a machine table. Make sure the interface is clean, otherwise whatever is between (like a chip) will be crushed into the abutting faces.

    If you have to peen a scraped face, remember some of the material you scrape off will be under compression. Removing it will cause the concavity to return. Plan ahead. Make allowances.

    Most important of all: scan the table reference faces to determine wear, distortion, etc. Map the error in a 3" grid and make sketches, photos. This gives a baseline for checking progress. Peening is a Black Art.; If you overshoot, it's tough to re-correct without peening BOTH sides. Start with not enough and add more correction as needed.
    Last edited by Forrest Addy; 09-16-2020 at 09:34 AM.

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    Quote Originally Posted by LexD View Post
    I have a Beaver Milling Machine made in England in the mid 70's with a 56 inch table that is suffering from the dreaded table sag. The ends of the table drop about .020" over 20 inches from each end although the center 16 inches or so is quite straight. I would like to try reducing the sag by peening underneath, maybe with a "pneumatic needle scaler", the question I have, for those with experience using this technique is, do I concentrate the peening around the badly bent areas or peen evenly over the full length of the table?

    Lex.
    Folks have been known to peen a gib for a mill's table Others may dispute the wisdom of it. Or agree. At least two sides to any gib, after all.

    But when it comes to a mill table, entire? Peening?

    For all the joy you are likely to find with the method outlined above, I'd suggest a time-saving modification:

    reducing the sag by peeing underneath and concentrate the pee around the badly bent areas ^^^ and ^^^ pee evenly over the full length of the table

    Takes about 13 seconds for the average human male, and DONE.

    No risk of cracking.

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    Quote Originally Posted by thermite View Post
    folks have been known to peen a gib for a mill's table others may dispute the wisdom of it. Or agree. At least two sides to any gib, after all.

    But when it comes to a mill table, entire? Peening?

    For all the joy you are likely to find with the method outlined above, i'd suggest a time-saving modification:

    reducing the sag by peeing underneath and concentrate the pee around the badly bent areas ^^^ and ^^^ pee evenly over the full length of the table

    takes about 13 seconds for the average human male, and done.

    No risk of cracking.
    wtf???????

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    Thanks for the detailed reply Forrest, a lot to think about there.

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    Quote Originally Posted by LexD View Post
    wtf???????
    If you missed the hint? Or Forrest's more in-depth, literally, "depth", given it is "deep" in section... explanation?

    Waste of time. It won't work. One cannot even deliver what it might respond to into the right places in the best way. Nor know in advance what would BE best..

    IF .. one persisted until it appeared straightened - by peening? It would not long retain the apparent improvement. Bending? Might do. Or not.

    The table is a complex shape, has thick and varying section, holds the complex accumulation of life stresses.

    It is not a flat, homogenous, featureless plate of uniform section and relaxed stress.

    THOSE, one CAN peen. As with gibs.

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    Seems to me a guy would want castings as free of stress as possible for long term stability of his machine. Peening introduces plenty of stress. While I have peened tables (not as big as the OP) during a course, it struck me as wrong. Kinda like putting a banana in a transmission before selling. It may sound good, but only for a short time.

    The biggest tables I’ve scraped (with no peening) since the course were 9x42 Bports, and with less sag than the OP.

    Were it me with a table as big and sagged as the OP, I’d plane or grind the table, then finess it with a scraper. No peening.

    Note: I’m not a pro scraper.

    L7

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    Prop up the table on the ends and put a sizeable weight on top in the middle. Place this in the Outback of Auzzi for about a month and the heat will straighten it back to straight again. Probably season the CI a bit, too.

    Seriously, if you have access to a oven big enough to place this table into, you could prestress the table and apply heat to bend it back to straight again. I'm no expert at this but have seen it done, especially with engine heads. Heat involved probably not over 500-600 degree F, guessing. This would get it closer than it is now and make it easier to scrape in flat, if you wish.

    My Index mill has a .0015" bend in the table toward one end where it was used for an anvil in another life. I just live with it. Had a old B & S mill many years ago that the table had about a .035" sag from end to end plus wear, dad borrowed a planer at work and re-planed it back to straight again. So from one extreme to another.

    Ken

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    Quote Originally Posted by 4GSR View Post
    Prop up the table on the ends and put a sizeable weight on top in the middle. Place this in the Outback of Auzzi for about a month and the heat will straighten it back to straight again. Probably season the CI a bit, too.
    That ain't just heat. It's the application of mass in calibrated increments.

    You'd have to know Bushflystan?


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    Quote Originally Posted by thermite View Post
    Folks have been known to peen a gib for a mill's table Others may dispute the wisdom of it. Or agree. At least two sides to any gib, after all.

    But when it comes to a mill table, entire? Peening?

    For all the joy you are likely to find with the method outlined above, I'd suggest a time-saving modification:

    reducing the sag by peeing underneath and concentrate the pee around the badly bent areas ^^^ and ^^^ pee evenly over the full length of the table

    Takes about 13 seconds for the average human male, and DONE.

    No risk of cracking.
    You're talking complete and utter nonsense. Again !!! Takes me MUCH longer than 13 secs with MY prostate !

    Otherwise, it's WAY too much for peening, not a good candidate. the machine is just a rubbish design and once "fixed" it'll come back.

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    Quote Originally Posted by 4GSR View Post
    Prop up the table on the ends and put a sizeable weight on top in the middle. Place this in the Outback of Auzzi for about a month and the heat will straighten it back to straight again. Probably season the CI a bit, too.

    Seriously, if you have access to a oven big enough to place this table into, you could prestress the table and apply heat to bend it back to straight again. I'm no expert at this but have seen it done, especially with engine heads. Heat involved probably not over 500-600 degree F, guessing. This would get it closer than it is now and make it easier to scrape in flat, if you wish.

    My Index mill has a .0015" bend in the table toward one end where it was used for an anvil in another life. I just live with it. Had a old B & S mill many years ago that the table had about a .035" sag from end to end plus wear, dad borrowed a planer at work and re-planed it back to straight again. So from one extreme to another.

    Ken
    Yes, you are no expert at this.

    Lots of things can happen once you place it in the oven and turn the hear up. Might end up looking like a propeller....

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    Quote Originally Posted by Orbital77 View Post
    You're talking complete and utter nonsense. Again !!! Takes me MUCH longer than 13 secs with MY prostate !
    Send yah a certificate, then. You are above average!

    Nah. Just takin' the piss..

    Weird trivia tripped over in travels.

    13 seconds applies to practically all major Mammals. Humans, horses, even Elephants.

    I did say "weird"?

    Just in case the OP thought his beaver was bent..

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    Curious why Orbital77 calls Beaver mills a rubbish design? I’ve never run one but have seen several. I do like the idea they use of two hardened pins to hold head nod and swivle in tram.

    L7

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    I have a beaver vbrp and there are a few things I am not fond about. First is the gib design, I much prefer a tapered gib over the flat one used in the beaver. Second is the quill depth scale. Whoever thought of this should have been kicked in the nuts. It confusing and its very easy to just push past the stop. Third is the x powerfeed handle, its about an inch long and something like 3/8" diameter. Way too small and after using it all day your hands hurt. Small problems I know but they wear on you after a while. The one thing I keep this machine for is the 18" Y travel.

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    Quote Originally Posted by Blazemaster View Post
    The one thing I keep this machine for is the 18" Y travel.
    There are days a desperate person would consider kneepadding for that extra six inches.

    Wait a minute... that don't sound good.

    Better to sub it out than put it out if yah got no beaver?

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    Quote Originally Posted by lucky7 View Post
    Curious why Orbital77 calls Beaver mills a rubbish design? I’ve never run one but have seen several. I do like the idea they use of two hardened pins to hold head nod and swivle in tram.

    L7
    Used to see them quite a bit here in Afreeka and always with hard to fix (if at all ) problems. In general, not the best materials and not the best workmanship. You want good mill ( or lathe ) buy French. Why do you think we visited France in 1940 ? Machine tools...
    No, really : if you want proper machine tool, buy French. You get TOP materials, proper weight, proper competent design, proper workmanship etc etc. On quite a few British mills the table is too long ( selling point ) for the width of the knee. I was told they were not accurate even when new.

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    When I rebuilt my Tree 2-UVR the table had some significant sag. It's been 4-5 years so I don't remember the exact amount but it might have been close to that.
    On Richard's advice I took a chance and peened the shit out of it using a 1/2" punch whose nose I rounded over and a big hammer.
    It was stress inducing (for me and the table) but it worked quite well and I was able to get within scraping range.

    Notes I remember:
    1. Stay off the thin sections (per Forrest's suggestions).
    2. Measure frequently to be sure you not twisting things.
    3. Stop before you go too far (see #2).

    I have not seen any major changes in the last few years, but by the time I die I expect it will be a pretzel again.
    Tree mill condition assessment and advice

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    Quote Originally Posted by Orbital77 View Post
    Yes, you are no expert at this.

    Lots of things can happen once you place it in the oven and turn the hear up. Might end up looking like a propeller....
    Careful with your words there, I have been around the block many times in my past dealing with stuff like this. Far as I'm concern, you can go back from where you came from and join the ranks with termite!

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    Thanks to those with experience in this type of work for all the suggestions.

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    Quote Originally Posted by Orbital77 View Post
    Used to see them quite a bit here in Afreeka and always with hard to fix (if at all ) problems. In general, not the best materials and not the best workmanship. You want good mill ( or lathe ) buy French. Why do you think we visited France in 1940 ? Machine tools...
    No, really : if you want proper machine tool, buy French. You get TOP materials, proper weight, proper competent design, proper workmanship etc etc. On quite a few British mills the table is too long ( selling point ) for the width of the knee. I was told they were not accurate even when new.
    Maybe Orbital77 can list the items that were "Not the best Materials and Workmanship" and "Not Accurate from New" that he saw when he walked past a Beaver Mill in Africa.


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