Flattening a table larger than your straight edge
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    Default Flattening a table larger than your straight edge

    So I was just wondering if its possible to scrape in a mill table that is larger than your SE? I have a k&t 2h with a table in relatively good shape that I plan to rebuild. I plan on buying a 24" SE and have a 24x36 surface plate but the table on this mill is 50 inches. Would I be able to flatten the table on my own or would it need to be shipped out and done professionally? If it has to go out I wouldn't even bother, it's far too expensive for me and I really dont need a table that flat, but if it can be done manually I'd be willing to put the time into doing it myself, more for value of the learning experience than the value of a flat table.


    Also I'd be lying if I said this isn't because I love the look of a scraped table and dont want to "fake" scrape it.

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    Why is it I'm reminded of a mouse looking at an elephant with rape on its mind?

    It is possible to straighten the table with a short straightedge but you're a long, long, long ways away from that. For the foreseeable future just put that out of your mind. You want to rebuild a machine tool and you're still dickering about getting a straightedge. If you like the looks of a scraped finish on the table, just go over the whole thing with a scraper so it looks good and call that enough. If the machine really needs a rebuild, it's the way surfaces you need to focus on, and by the time you're deep into that you'll have a five foot straightedge in your kit and you can do the table top.

    Yes, the table could be done with a short reference but it takes some experience and insight and a lot of time. And a bonus hint - learn how to map a surface with a precision level.

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    Quote Originally Posted by TGTool View Post
    Why is it I'm reminded of a mouse looking at an elephant with rape on its mind?
    That'd be daft. Mice don't even DATE elephants. Giraffe's, rather.

    Elephant's backside is too steep to make the run for the French kissing to warm 'em up, and the run BACK to kiss 'em goodnight, afterwards.

    It is possible to straighten the table with a short straightedge but you're a long, long, long ways away from that. For the foreseeable future just put that out of your mind. You want to rebuild a machine tool and you're still dickering about getting a straightedge. If you like the looks of a scraped finish on the table, just go over the whole thing with a scraper so it looks good and call that enough. If the machine really needs a rebuild, it's the way surfaces you need to focus on, and by the time you're deep into that you'll have a five foot straightedge in your kit and you can do the table top.

    Yes, the table could be done with a short reference but it takes some experience and insight and a lot of time. And a bonus hint - learn how to map a surface with a precision level.
    What he said.

    Table that long, I wouldn't be using an SE, anyway. My four-footer is all I care to lift.

    Optics, rather.

    Basics: Using a D600 Comparison Autocollimator

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    A K&T 2H table is not that different than a Bridgeport. Have done several Bports and other tables. Call me lazy, but there’s no way I’d do a table top with just a straight edge. Surface plate of greater size than table (and known quality) or send it out for grinding. I’m sure it can be done by using a level or auto-collimator, but a mill table is so easy to scrape in using a surface plate!

    Doing the table top is easy. Then comes dovetail ways. And how bout the rest of the machine. A K&T isn’t the easiest machine for a first project.

    If all the OP wants to learn is how to scrape a larger area flat (and this is a good practical lesson) then suggest a cast iron surface plate. I find a portable 10x30 inch plate very useful for spotting on bigger machine parts I don’t want to put on the big surface plate. And cast iron plates this size are cheap- mine was a deeply webbed worn out plate that I put a little sweat into. This plate is now flat, at least 40 ppi, and easy to touch up when it gets worn.

    L7

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    Can you imagine how much time it would take to step scrape the top and the bottom flats and dovetails and get everything co-planar? I would guess never or 50 to a 100 times longer in time and frustration then doing it the professional way using a straightedge longer then the part in the first place. I will not try to teach this method as it is nuts in my opinion. If you want to waste time, get a migraine, if you have lots of money do this hard back breaking work and get a lousy job go for it. The forum was set up to explain the correct professional way to do things. What your asking, is not.

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    Quote Originally Posted by Richard King View Post
    Can you imagine how much time it would take to step scrape the top and the bottom flats and dovetails and get everything co-planar? I would guess never or 50 to a 100 times longer in time and frustration then doing it the professional way using a straightedge longer then the part in the first place. I will not try to teach this method as it is nuts in my opinion. If you want to waste time, get a migraine, if you have lots of money do this hard back breaking work and get a lousy job go for it. The forum was set up to explain the correct professional way to do things. What your asking, is not.
    So theres no way of measuring and setting it up for flatness? I was asking because I didn't know if there was an actual way if doing this or if the only method was massive surface plates. I figured there be some sort of way to measure it and find the high spots but if not then I guess it's a lost cause

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    Quote Originally Posted by marino1310 View Post
    So theres no way of measuring and setting it up for flatness? I was asking because I didn't know if there was an actual way if doing this or if the only method was massive surface plates. I figured there be some sort of way to measure it and find the high spots but if not then I guess it's a lost cause

    Sent from my SM-N950U using Tapatalk
    Surely there is BUT. Richard is not wrong.

    Gernoff.. and others.. meself included... "mess with" the opticals - and the precision electronic levels for the fun of it and "because we CAN"!

    "Thout getting into the details, figure whatever Richard's way costs in large surface plate and SE...?

    Now add a zero to the dollar figure. Or stick a "1" in front of it.
    And the scraping part STILL need's doin'. Well. I cheat. Been hiring that part done!

    If yah have 30 -40 years at workin', 20 years or so of 'em with "Managing Director" or "Chairman" or "President" on yer resume? This is "playtoys" budget for bored old farts once the house - or several of them - be long-since paid-for..

    Collitch STUDENT didja say?

    "Run what you got and be glad you got it, because you'll get the rest when you get it, not a minute before!!!"


    Age-old human challenge. Young guy has an "I want it NOW bone" in his head as stiff as the dick in his shorts.

    Old guy finally gets what he got when he gets it, but... he's either down to just the one bone. Or having to rest one or other other by turns.

    Run what you got while you got it!



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    Quote Originally Posted by thermite View Post
    Surely there is BUT. Richard is not wrong.

    Gernoff.. and others.. meself included... "mess with" the opticals - and the precision electronic levels for the fun of it and "because we CAN"!

    "Thout getting into the details, figure whatever Richard's way costs in large surface plate and SE...?

    Now add a zero to the dollar figure. Or stick a "1" in front of it.
    And the scraping part STILL need's doin'. Well. I cheat. Been hiring that part done!

    If yah have 30 -40 years at workin', 20 years or so of 'em with "Managing Director" or "Chairman" or "President" on yer resume? This is "playtoys" budget for bored old farts once the house - or several of them - be long-since paid-for..

    Collitch STUDENT didja say?

    "Run what you got and be glad you got it, because you'll get the rest when you get it, not a minute before!!!"


    Age-old human challenge. Young guy has an "I want it NOW bone" in his head as stiff as the dick in his shorts.

    Old guy finally gets what he got when he gets it, but... he's either down to just the one bone. Or having to rest one or other other by turns.

    Run what you got while you got it!


    You got a good point, but I rarely settle for what I got. If I did my k&t would still be a rust pile sitting in an old garage. Every problem has a solution, the issue is how much you want to look for that solution. I'm sure theres a way to do this but it would be far too much for what its worth. I'll probably just settle for what I got, maybe check what I can and remove material where doable, but I wont be making a surface plate of it for sure.

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    Quote Originally Posted by marino1310 View Post
    You got a good point, but I rarely settle for what I got. If I did my k&t would still be a rust pile sitting in an old garage. Every problem has a solution, the issue is how much you want to look for that solution. I'm sure theres a way to do this but it would be far too much for what its worth. I'll probably just settle for what I got, maybe check what I can and remove material where doable, but I wont be making a surface plate of it for sure.
    You don't YET even have 20 percent of the goods it would take to survey and determine what it MIGHT need!

    You want to maximize the value a(ny) old K&T has?

    Hit the dam' table with a "jitterbug" sander to knock the raised burrs TF off it, take a cut, measure the sag onto a graph and as columns of figures along the axis and keep that handy, going forward.

    Get you some shim stock, and let the Mark One human brain learn to "compensate" for what it IS rather than what you WISHED it could be.

    Old mill made parts right up to the last hour it was asked to make parts.

    Takin' a long nap in between then and now ain't changed the plane of the table by enough to matter. BirdPort tables sag like wax on a hot summer day. They are THIN!

    K&T? Some. Gravity is a patient bitch. But so is a heavy-boned K&T.

    May as well try to arm-wrestle a Polar Bear.

    She'll do.

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    Quote Originally Posted by thermite View Post
    You don't YET even have 20 percent of the goods it would take to survey and determine what it MIGHT need!

    You want to maximize the value a(ny) old K&T has?

    Hit the dam' table with a "jitterbug" sander to knock the raised burrs TF off it, take a cut, measure the sag onto a graph and as columns of figures along the axis and keep that handy, going forward.

    Get you some shim stock, and let the Mark One human brain learn to "compensate" for what it IS rather than what you WISHED it could be.

    Old mill made parts right up to the last hour it was asked to make parts.

    Takin' a long nap in between then and now ain't changed the plane of the table by enough to matter. BirdPort tables sag like wax on a hot summer day. They are THIN!

    K&T? Some. Gravity is a patient bitch. But so is a heavy-boned K&T.

    May as well try to arm-wrestle a Polar Bear.

    She'll do.
    True. This monster has done nothing but made me happy since I first "rebuilt" it (remove all old grime, cleaned and replaced anything broken, fresh coat of paint, etc). Nothing I can throw at it has managed to slow it down. It can even throw an 8" facemill 1/8" deep into iron like nothing. Shes stout all right.

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    Quote Originally Posted by marino1310 View Post
    True. This monster has done nothing but made me happy since I first "rebuilt" it (remove all old grime, cleaned and replaced anything broken, fresh coat of paint, etc). Nothing I can throw at it has managed to slow it down. It can even throw an 8" facemill 1/8" deep into iron like nothing. Shes stout all right.
    Well... f'f**ks SAKE? Quicher-bitchin', plotting, and scheming, and go do sumthin' more productive, then!

    Y'all remind me of a "Smother's Brothers" skit!

    You don't know the rules. If you borrow it, bring it back!

    I do TOO know the rules! If you borrow it. .......??? ... BREAK IT!

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    Quote Originally Posted by thermite View Post
    Well... f'f**ks SAKE? Quicher-bitchin', plotting, and scheming, and go do sumthin' more productive, then!

    Y'all remind me of a "Smother's Brothers" skit!



    Hey man theres no such thing as good enough when it comes to this shit! Half of what I do can be done on a drill press with an XY table but that ain't no fun!

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    If you don’t mind an opinion- a K&T 2H is a small to medium sized older horizontal mill with a dubious lubrication system and mostly unavailable parts. If similar to the K&T 3H I have some time on, it is a useful mill, relatively easy to work on, but no monster. Yes, much more rigid than a Bridgeport. IMHO a K&T is significantly more involved to repair/work on than a Bridgeport.

    Re-scrape a simple machine first.

    L7

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    Quote Originally Posted by lucky7 View Post
    If you don’t mind an opinion- a K&T 2H is a small to medium sized older horizontal mill with a dubious lubrication system and mostly unavailable parts. If similar to the K&T 3H I have some time on, it is a useful mill, relatively easy to work on, but no monster. Yes, much more rigid than a Bridgeport. IMHO a K&T is significantly more involved to repair/work on than a Bridgeport.

    Re-scrape a simple machine first.

    L7
    Oh yeah it's just big for a hobby machine. Way more rigid than any BP I've used. But yeah, I pray nothing breaks on this thing because theres a 98% chance I'd have to make the replacement myself

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    I would put money on it that the center of your table is bowed up a good .010-.015 from peening. Usually on Bridgeport's you can bank on at least. 007-.009 hump on a 30 year old machine. A K&T is a rather heavy industrial machine, even a small one like you have. Generally the peening is much worse on something like that. I have personally seen tables on our #6 and #5 mills at work out as much as .060-.070, these tables are 107 X 21" and 96 X 18" respectively. When it comes time to re-plane or mill them it's a minimum three step process, top, ways, top again and sometimes ways once more. As you start cutting the hump from the top it removes the peening stresses and it will slowly start laying down and before you know it, it's only hitting the ends and it takes a while to get back to the center. Flip over and start cutting the flats, again work hardened stresses are being relieved and it does it all over again ruining your top which "was" done. It's like performing an exorcism releasing all that stress. Send it out to be machined.

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    Ironsmith89, curious, on the bigger mill tables, do you also send them out for a stress relieving cycle in the oven at some point in the rebuild?

    Lucky7

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    Quote Originally Posted by marino1310 View Post
    Hey man theres no such thing as good enough when it comes to this shit! Half of what I do can be done on a drill press with an XY table but that ain't no fun!

    Sent from my SM-N950U using Tapatalk
    My "drillpress with an X-Y table" is not gonna dooo ANY millin'!

    Adapting a salvaged B&S #1 "Universal" table is only 'coz an AB5/S can drill s**t FAR too damned heavy to POSITION easily, my age.

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    Quote Originally Posted by marino1310 View Post
    So I was just wondering if its possible to scrape in a mill table that is larger than your SE? I have a k&t 2h with a table in relatively good shape that I plan to rebuild. I plan on buying a 24" SE and have a 24x36 surface plate but the table on this mill is 50 inches. Would I be able to flatten the table on my own or would it need to be shipped out and done professionally? If it has to go out I wouldn't even bother, it's far too expensive for me and I really dont need a table that flat, but if it can be done manually I'd be willing to put the time into doing it myself, more for value of the learning experience than the value of a flat table.


    Also I'd be lying if I said this isn't because I love the look of a scraped table and dont want to "fake" scrape it.

    Sent from my SM-N950U using Tapatalk

    To get something flat you need two things: one is to check the local flatness and two is to check the overall straightness. If you have a surface larger than the table, it is a piece of cake, rub it and scrape off the highs. if your surface is shorter and narrower than the target, things get interesting. you can introduce cups, bows, and twist without being able to detect them. Theoretically, and I mean it, you could flatten the tabletop one half at the time, but it will not be an easy task. if you flip the table on your stone you will have 14" hanging off, and that will impact your spotting. You need even pressure to get a realistic transfer and the imbalance will make the transfer heavier near the unsupported end. Once you have the top flat you can measure the ways from that reference. At that point, a short SE may be sufficient to assess local flatness, and judicious measurements from the top can assure straightness. With experience, you can compensate for these things, but this sounds like this is your first rodeo. if you embark on this, I would suggest getting a larger stone and longer SE. Taking off CI is the easy part, figuring out where is more complex. Good luck.


    dee
    ;-d

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    Getting it right down to what you might have to actually DO.....

    1) Assume you have a 30" surface, and a 24" SE. OK, you could scrape 24" of it to the SE (takes some care), and then overlap the SE 6" to get the rest, scraping THAT until the SE prints OK in that position. A pain, not impossible.

    2) now, you have your little 24", and you are looking at a 48" table. Leaving aside the sheer surface area to be scraped, and just looking at the width of the SE..... what would you have to do? Just as above, you'd have to scrape part, then overlap, scrape that, overlap, scrape that, etc.

    Fine.... Now, how do you know you are dead-on the direction that gets you to the other end where there is metal, and not generating a surface that sticks into the air at that end? You have to measure to a straight surface somewhere on the ways, but they are not known straight. If they were, you could do a pretty good scraping job just on measurements.

    And, assuming you get that right, you are still doing a lot of overlapping, and by the end of that (4 steps), you are only as sure of your straightness as your spotting technique can detect, and that is over only 24", so you could be double that "out", and not know it. Your last overlap will have no connection to the first checked surface, because the SE will not even overlap onto it.

    If you wanted to do 48" with a 36" SE, well that would be a nuisance, but do-able, because you would still have 2/3 of the SE on the first surface.

    None of the above is a viable commercial way to do the job efficiently. A 48" SE is large but not the largest. Much over that and optical is more practical. Optical, taut wire, even water level can be done with a decent-to-quite-good accuracy over longer distances, But using a short SE is like doing a flat patio by using a level on each individual brick, one at a time.

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    what i would do with more time than money:

    assuming the bed is convex, as most are due to peening stresses:

    machine 5 rods to the same length, from 3/4 or 1" steel. they need to be about 9" long. drill and tap one end of them for whatever you use for T nuts, tighten them up against 5 ground washers, such that they are all the same height on your table. one in the center, 2 at each end. if you have an even number of T slots, you need 6 posts. two in the center off set from each other such that they match the same straight edge.

    build a straight edge long enough to measure the diagonal:

    you only have to measure ~50 inches so i would marginally suggest the 2" square steel square tubing with pre-existing holes, the stuff they use for road signs.

    make 6, 1/2-20 bolts that are all exactly.. say 4 inches long, with the ends ground square to the thread. you can grind them by eye if you have a v block to rotate them in next to a grinding wheel. .0005" tolerance on the length is probably good enough for you.


    find the holes in the beam that are closest to the diagonal of the posts you bolted to the bed, or move the diagonals to match the straight edge. if you have an even number of T slots you need to move the middle post in the straight edge towards one end, and offset the two middle posts in the bed to match the straight edge across both diagonals. i tried drawing an ascii image but it failed miserably, i think you can figure it out.


    pre-set the 1/2-20 bolts to the same height off the steel tubing, one at each end, one in the middle. tighten the nuts but not very tight, weld the nuts to each side of the beam with a tiny tack weld. if you drill and tap regular square steel, use a lock washer, or a nylock nut.. you want friction but not the hassle of jam nuts where you have to lossen them to rotate the bolt.

    lay the two beams next to each other on a reasonably flat surface (a good sheet of plywood is good enough, or use your surface plate, and adjust the center bolts of each beam such that flipping either of the beams over doesn't result in much difference. you now have two identical straight edges each with 3 points in a straight line. you can add more bolts to get more points, but the effort in adjusting them grows significantly.


    now measure the diagonal of your bed. using shims measure how much its curved. you will want to average the measurements using both sides of both straight edges that you made. or, don't worry about it and just use one of them and note which side you are using.


    now take the bed off the mill, support it on three points. one in the middle of one end, and the other end at two corners. i would weld 3 posts, about 2 feet high, to a somewhat rigid frame, but i don't think it matters. you want something that won't get knocked over.... then set the bed on those posts.

    get 2 oven heating elements (3500 watts each typically) and straighten them out, they are typically as long as 8 feet and you should be able to get 2 of them to fit down in the T slots in a U configuration. run them on 120 vac not 240, each will generate a fourth of their nominal wattage.

    wrap the bed in 3 or 4 layers of regular r-13 fiberglass insulation, and heat it up, you should be able to reach 1200F with 1750 watts of heat. I was able to hit 1000F on an 8 foot long, 9 inch by 9 inch square beam wrapped up in 2 layers of shitty fiberglass, but with 3500 watts of heat.

    you should have already noticed the bed sag, under its own weight, how much did it sag, keep that in mind....

    as it gets hotter it will sag more. and more quickly. it will take a long time to get up to temperature, 6 hours perhaps or more. you will want to check and recheck how much its sagging, and also how quickly. as it gets up past 1000F you are in the danger territory where you want to cut the power and unwrap the outerlayer of fiberglass insulation to let it cool off quicker.

    you could try a couple cycles. take it up to 800F and let it cool and see if it sagged any.. i am curious to know.


    instead of using shims and the straight edge you made to verify if its straight as you are heating it.. you can can use just any old piece of steel and rest it on the diagonals (with a strut to stabilize it against the other corner) and use a dial indicator to watch how much the middle post is sagging under the heat. if you trust your measurements with the straight edge you made, just note how much the table sagged under its own weight and add that to the amount you need to wait for the table to sag as the stress is removed. yes, the beam you've got your dial indicator clamped to is going to get warm might bend a bit, but that's why i suggested make the posts 9 inches long and use 3 or 4 layers of fiberglass.. or set up a fan to blow air on it to cool it off. or use a piece of aluminum which has better thermal conductivity

    the only reason to use the straight edge you made to measure how much it is sagging under its own weight is if you're paranoid that you're going to end up with a table bent in a helix.. personally i am not worried about that.. i think that the stress its under, under its own weight will dominate and you don't need to worry about it bending into a helix.

    now there is a problem with applying all the stress to the middle of the bed.. this isn't ideal. but, in the real world where most of the peening stresses were probably applied to the middle 2/3rds of the bed it is probably a good compromise.

    moving the 3 points you rest the bed on.. moving them in just a little bit like say 5 inches will make a pretty significant difference to how much stress the center of the bed is under.

    on a 50" bed moving the points in 12" from the ends will reduce the stress in the middle of the bed to zero and you will actaully droop both the middle and the ends an equal amount.

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