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Thread: Meehanite and the unflat table...

  1. #1
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    Meehanite and the unflat table...

    There has been quite a bit said lately about unflat and warped tables in various machines both new and used. Once again, its up to the old timers in this racket to remind a few folks about this issue and to let you know the ugly truth.

    1). Alloy is Everything. Machine tool builders of the past, (1935 to Present), used Meehanite Iron to make machine tools. This is not your run of the mill pig iron melted in coal fired cupuloas! It is a complex alloy with complex rules for melting and pouring it. You can learn more about the metalurgy of meehanite iron at www.meehanite.com. The powematic foundary which poured castings for powermatic machines prior to the jet buy out was certified as a meehanite foundary. So is the foundary used by canadian made general machines. Delta has outsourced its foudary operations to a foundary in Brazil which is not meehanite certified and many of the foundaries used in asia are also not meehanite certified.

    2). Its Hard to Recycle Meehanite. The brake drums and discs on your automobile are often a meehanite alloy of which there are a few. Again, check the meehanite website for more information. When its made, it is made in batches and these are not small. Its hard to brew up a batch of say a few hundred pounds with any economy. Just prior to the pour, additional ingredients in the form of "nodules" are added to the melt like alka-setzer tablets. When these melt and the drouse is skimmed off, the castings are poured. If you remelt or blend these castings, you loose some of the metalurgy through dilution and burn off making recycling not an easy proposition for this alloy. It can be recycled into other products to make things like drain pipes and the like.

    3). Its greatest claim to fame in machine tool use is the fact that it is stable and does not warp wildly over time. Machine tools costing hundreds of thousands of dollars were made from this alloy along with machine tools like bridgeport milling machines and your better woodworking machines. Woodworking machines may be crude by metalworking standards; however, they often have large, ribbed cast iron tables with thin wall sections and accurate flatness requirements. This is a meehanite application!!!!

    4). When cast iron cools, it does not cool uniformly. Differnent sections cool at different rates depending on the mold used and the thickness of the item. In certain cases, large steel sections are used in the mold to force rapid cooling and hardening of certain surfaces. Railroad wheels are done like this. But you do not wish to have to machine a quick cool cast iron part! At any rate, this all leaves non uniform internal residual stresses in the part. Now, the modern way to get rid of this stress is to go through a thermal stress reduction process. Although this process works, it does not work with 100 percent certainty. The old way is what rolls royce used and what northfield calls Minnesota Stress Relief. You toss the rough castings outside for a couple of years to get exposed to rain, snow, heat, cold etc. These cycles of heating and cooling under adeverse conditions works the stress out. Rolls would season their engine blocks, prior to BMW affiliation, for one year before any machining was started. Modern makers do not have the time to go to this extreme.

    5). Machine work must be done in stages: When a seasoned casting is first brought into the shop to build a new woodworking machine, it must first be sand blasted and then the bottom must be ground flat. There are a few spots on the bottom of the casting which must be machined to form a reference plane for the ensueing machine work to take place.

    The new casting, a table for example, is then mounted in say a planer. These bottom tabs are lined up and the table is clamped down. The planer then takes its first set of initial cuts by cutting through the crust or foundary film on the top of the table. This crust which contains hardened iron, pores, residual casting sand etc. is nastly and must first be removed in this intial phase. This **WILL** relieve any left over stress and cause the casting to move a bit. This work in progess table is then taken and stored on a shelf for a period of time to allow for this last bit of movement to settle out. After a couple of months or so, this table is then remounted in the planer and the planer takes its final and finishing cuts leaving a table like that shown in my belated gloat posting of my shaper. See the stripes left behind by the planer? Many older woodworking machines and many european machines have these stripes suggesting the planer process. IT is time consuming and a real pain to go to this extreme but you will not find many warped tables done this way.

    6). In an attempt to reduce the time and cost of the planer process, many companies resorted to linear grinders and blanchard grinders. The blanchard grinder is the most popular and it leaves behind those swirl marks that many of us have seen on tables from delta and powermatic. Many tables on jointers such as the DJ-20 were done using a linear grinder. Now there is nothing wrong with using grinders and todays grinders can produce a surface as good if not better than planers. In fact, grinders today are the most accurate machine tools made. But not all of them fall into this last statement and it also assumes that the process is done correctly.

    Here is where life becomes unpleasant. Many grinders produce lots of heat during the grind process even with flood coolant. You need to allow the item being ground to normalize before continuing the process. Some of these machines have a dwell setting to allow you to do this. When metal heats up, it expands and if you keep grinding away, you will not have what you expect when it cools down. This is esp. true in light of holes or areas were you have varying web thickness. So if you take rough castings with quickie stress relief and do all the grinding at once and do not allow it to cool or normalize during the grind process, you will have issues later on with your flatness and warp.

    Now the problem is which tables will warp and which will not. Will they warp today or tonight after the grind process or will it take time? Does the warp or out of flat condition happen in one month or 6 months or 2 years? This is the issue that I have found with many modern woodworking machines. When schlosser was still in business, one of the most pressing issues for delta jointers and some of the, then, powermatic artisan line were warped jointer tables. Many had to to be sent back. In the grizzly catalogs of a few years back, they actually brag about haveing a thompson style linear grinder for grinding out of flat tables flat again. Folks, if you follow the rules of the old timers, you dont need to worry about having to have a 10,000 pound thompson linear grinder in your back room when your selling imported machines!

    So this is the truth about warped tables, meehanite, minnesota stress relief and the reason the germans are using 80 year old, rebuilt planers to build woodworking machines. Northfield at least has a hydraulic open side Rockford 10 foot planer in their shop.

    The good news is that this warpage or out of flat does not continue for ever. In time, the majority of this stress relief happens and then the table becomes stable unless its involved in a fire or someone heats it up with a gas torch etc. If you have an out of flat or warped table and the mahine is a few years old, then getting it ground at a reputable machine shop will most likely resolve your issues for life. Better yet, find a machine shop with a planer and have them plane it. Your not taking much off as well. You should not have to take more than 5 thou off. You can go more if you have to but try not to unless its really really needed.

    For those who are curious, I hope to have some photos illustrating the planer process as soon as I get to it. I plan to plane the table on my Y-20 when I tear it down. If I need it for the summer season, then it will be a while. If not, I should have some photos in a month or two, etc. Just remember, that even if you have warpage, most of it can be fixed with a planer so all is not lost. Just ask some questions before you buy and pick your vendors based on how they build things. If they only OEM the machine and cannot give you the skinny about these issues, I personally would walk.

    Good Luck...
    Last edited by Ken Salisbury; 05-02-2005 at 7:27 AM.
    Had the dog not stopped to go to the bathroom, he would have caught the rabbit.

  2. #2
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    hi dev

    thanks for the info. It was quite informative. A few of my machines have "planed" tables, and as you say, are dead flat. I also have a machine with a blanchard ground table and it is also flat. It seems to me that price pressures and such just force a lot of the manufactures to cut out some of the seasoning of the iron and just run it through the factory.

    My rockwell rt-40 has a "neglected table" that someone allowed to get rusty. It does not effect the saw, just looks bad. I know that you have a martin TS. How about some pictures of it. I have thought about getting one to replace the rt-40.

    lou

  3. #3
    That was really interesting Dev. You sound like you've been in the industry pretty deep. Very educational. So...If my TS top hasn't moved over the last 10 years, then chance are, it ain't gonna?
    ~john
    "There's nothing wrong with Quiet" ` Jeremiah Johnson

  4. #4
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    Dev---Thanks for that very interesting explanation of why my New Delta Unisaw has a hump in the top.

    Dan
    Eternity is an awfully long time, especially toward the end.

    -Woody Allen-

    Critiques on works posted are always welcome

  5. #5
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    Very, very good article. I learned a lot

    Please have someone place this information in the "articles" section of SMC so others can reference it in the future.

    BTW, you need to add an "e" to the Meehanite website link
    Best Regards, Ken

  6. #6
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    Thanks Bill for pointing out that the link in my orig. posting was misspelled.

    I edited the link and corrected it; however, the software still wants to route me to the wrong URL. This is the correct URL:

    www.meehanite.com

    Again, thanks.
    Had the dog not stopped to go to the bathroom, he would have caught the rabbit.

  7. #7
    Join Date
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    Quote Originally Posted by Dev Emch
    Thanks Bill for pointing out that the link in my orig. posting was misspelled.

    I edited the link and corrected it; however, the software still wants to route me to the wrong URL. This is the correct URL:

    www.meehanite.com

    Again, thanks.
    Thats OK Dev - I fixed the coding in the original post

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