Peening the Underside of a Milling Machine Table. - Page 4
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  1. #61
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    I asked the professor the same thing and he said people should use long T-nuts. I have seen longer aprox 3" T-nuts. I was taught when I was an Apprentice to move the vise to the sides and not always mount it in the middle, make sense. I was just reading in the net about torque and found a reference on CNC forum and one guy wrote 110ft pounds. I suppose you need to stone the table top to remove the burrs on the table and raised spots above the T-Slots. I was thinking I'll call Kurt tomorrow and ask them if they have a spec sheet and cut and paste it here.

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  3. #62
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    What one would like to avoid is spreading metal (in essence peening) the underside of the tee slots by not applying metal-displacing point loads to the tee slots. Longer nut might help a little but still have two problems: they are case hardened and therefore can apply high point loads to whatever happens to be the high points under the footprint especially with the inevitable swarf, grit, and grime inherent in the milling process. The second problem is that although they may be long they are made of flexible metal and will still apply the great majority of their load in the area nearest the nut hole with little actual load applied at their end areas. So you will not be much ahead to use long nuts. Incidentally, I met Archie Cheda at his home and shop in San Luis Obispo something like 8 years ago. He is a very personable and bright fellow who “drug me” out to his shop for a lively discussion of his past, current, and future projects. It was a great and informative visit. For the record, he was not a professor at Cal Poly in SLO, but was a very capable lab/shop assistant if my memory serves. I do hope I am not doing a disservice to Archie.

    It would make sense to simply use aluminum tee-nuts. I suppose I’ll hear how that idea is ludicrous as aluminum would strip out quickly. Not really. I’ve used an aluminum tee-nut on my EE compound for 10years now and it gets torqued proper a hundred times a week on average. The day I purchased my lathe I made the nut out of a piece of 6061 that was right there at hand thinking I would make a proper nut when time permitted. Well, I’ve certainly had time to make a proper steel one and could have used a any of a variety of tool steels now laying in my stock rack. But I’ve had no need to do so. And since I had scraped the compound quite a few years ago, I had second thought about repeatedly point loading the tee slot with a hard nut. So, I left the aluminum one in place and it continues to works great. One reason it works well may be that, realizing the deform ability of even hardened steel, I relieved the central area of my tool post so as to avoid concentrating the load near the bolt and instead transferred the load peripherally where the same friction load has a lot more mechanical advantage to prevent tool post rotation.

    Using aluminum would allow the surface of the nut to deform to accommodate a bit of swarf or grit instead of deforming the tee slot surface and therefore reduce the peening effect tee nuts have on the table. Similarly, meticulous attention to cleaning the table top and the tool or part prior to clamping can help reduce inadvertent “peening” of the table top.

    Do I use aluminum tee nuts in my mill? No, as the tee slots in my mill had been somewhat abused by the previous owner prior to my buying it. So it is not too bad for flatness, but beyond aluminum tee nuts. On the other hand, if I had just spent the time putting my table back to factory spec or better, I would. As it is, I certainly am careful to avoid grit and grime in the slots and on the table and I am careful apply clamping forces that are best placed to avoid part movement and I nearly always put a piece of printer paper between the part/vise/rotation/indexer as the paper doubles the coefficient of friction for steel on steel and the paper can accommodate any minor dirt or the odd bit of swarf I don’t feel in that last sweep over the table prior to placing the work.

    FWIW,

    DENIS

    Edit: if you can’t bring yourself to use aluminum, maybe use 12L14 as it is at least not substantially harder than grey iron which usually comes in about Rc10.

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  5. #63
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    Quote Originally Posted by Richard King View Post
    I asked the professor the same thing and he said people should use long T-nuts. I have seen longer aprox 3" T-nuts. I was taught when I was an Apprentice to move the vise to the sides and not always mount it in the middle, make sense. I was just reading in the net about torque and found a reference on CNC forum and one guy wrote 110ft pounds. I suppose you need to stone the table top to remove the burrs on the table and raised spots above the T-Slots. I was thinking I'll call Kurt tomorrow and ask them if they have a spec sheet and cut and paste it here.
    Rich, you don’t hear of to many people moving the vise to the side of a knee mill table for reasons other making space for a dividing head or extra clamping space. We bought a new knee mill right after the Ashland scraping class, I mounted the vise to the extreme left side.

    Every year I move it over to the other side of the table. Two thoughts- even out wear on the tables dovetail and also keep the t slot peening
    spread out. I think we had the discussion when we were mapping Al’s Bport table.

    On bolt torque- machinists are apes when it comes to tightening bolts! I accuse a co worker of being engaged in a tightening contest with me. People will always tighten vise clamping nuts with the max force they can with a wrench.

    It would be awkward but you could always clamp your vise down on 4 corners and strap clamps. Forget the holes in the middle t slot.
    Then you could lower the bolt torque and spread the peening out some.

    On Archies idea of the long t nut. My thought is that it wouldn’t help much and you would be better off using non hardened steel. Or if you did make a longer nut, relive the center by the thread, that would help to spread the clamping forces.

    I just left the job with the new knee mill, I was planning on mapping the table after ten years of use. Oh well, hope the guys keep alternating the side the vise lives on.

    Has anyone heard from Archie?

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    Last time I heard when he retired from I think it was Penn State or some school out there., he moved to Southern CA. I have not heard from him in a few years. I did invite him meet the rebuilding crew at DFLE and here is what he wrote back.


    Rich,

    I would enjoy the opportunity to observe on Thursday morning -- you
    can tell them I am an Emeritus Professor of Manufacturing
    Engineering, retired from California Polytechnic State University.
    (That should look OK in their paperwork . . .)

    Just plan your day on what works best for you and I will provide you
    with transport. This could include picking you up at your hotel --
    coming a bit earlier will not be any problem.

    Archie

    I would tend to believe him and he was an Engineering professor. I met him in Minneapolis MN when he and his wife drove out here to get a part for a KT Mill from a PM member and then He stopped to say hello when I taught a class at Defense Logistics East in Mechanicsburg PA

    Heck I should try to track him down and invite him to be my special guest for my Nov. Burbank class.
    Last edited by Richard King; 10-08-2020 at 06:46 PM.

  7. #65
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    Another thing on moving the vise is screw wear.
    Leave your vise in the middle for decades of real use and the difference in lash is very noticeable and one can not split the nut to fix or the ends will not move.
    Over-torquing hold downs is a common problem and hard to make employees understand. For many it is "I do not want this to move" so big force that is new problem.
    Educating some on the torque multiplication and force of a bolt is helpful. When I break one free that is way over needed a slap on the knuckles with a steel rule is also helpful .
    I think most people trend to overtighten tee nuts.
    Bob

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    I was looking for a few emails I got from Archie and I got one he wrote to me from PA before he moved to CA.

    I did find this longggggg thread about how he rebuilt a Lucas for Tuckahoe Museum. I may be wrong where he was a professor. I Pm'ed Paolo as he probably knows him as Paolo is a volunteer at Tuckahoe.

    Lucas Horizontal Boring Mill going to Tuckahoe . . .

  9. #67
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    I emailed Archie yesterday and got a nice 700 word reply. He was indeed a full professor at Cal Poly. Ever the gentleman, he was very kind about my mistake saying that the title itself was not that big a deal. He taught for 20 years at Cal Poly and then retired at age 50 more than 20 years ago. Not bad. It was a friend and associate of his that was the lecturer at Cal Poly.

    Archie is still actively enjoying various aspects of machining and watch making. It was nice to hear from him. I always valued his detailed discussion of various aspects of machining, engineering and metallurgy.

    Denis

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    I know this thread is more or less finished up but I thought I might as well add this for posterity's sake.

    The first photo is a 1947 #2 Cincinnati table that is about 53” long from the Birmingham factory. It has 0.7mm bow, (my tenths indicator ran out of travel so I grabbed a metric dial. it is without a doubt the worse table I've seen in terms of bow, I Took three or so rough passes over the table with a 135mm rad blade with plently of stoning before I even put it on the plate for inspection

    The other table is a Dutch built Cincinnati tool master table from the Vlaardingen factory that is only 48” long but is 9/16” thicker in profile with extra ribs added to the underside. The stout Dutch table is also a odd grade of grey iron which a right bastard to scrape, closer to a ductile iron. It suffers only a few thou of bow. I have a second Toolmaster with the short table 42" or maybe 44" but it was about the thickness of the #2's table as well as being a soft grey iron and had 8 thou of bow.


    122776425_3309550709162476_5838271789899838454_o-1-.jpg

    122814497_3309550802495800_1272729816755536768_o.jpg

    I'll be taking the #2's table to a local shop with a huge elgamill to skim the underside T slots and will leave a camelback there to check the Progress as they are skimmed and Russell will also be taking a skim off the top to relieve as much stress as possible from the impact damage to the top face. I've never had a table this big skimmed before so I very keen to quantify the material removed to the change in bow.

    I'll also add that I helped a mate rough in the top of a Repco Plain cylindrical grinder this weekend not a universal table as I'm used but it has a inverted V way and a flat so inspection of the V way alignment to the Top face/flat wat is a dream as you can use Hoffman rollers to inspect the True centerline of the V way when the table is on the plate. the entire table top and bottom was bowed by 0.0004" but in roughing the top to flat (it was somewhat beaten up) a degree of stress was relieved and the bow was reduced to 0.0025" when inspecting the unworn portion of the flat way

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  13. #69
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    Thanks for you input Marcus, could you report back with your findings on how it relaxes after machining? The Cincinnati table is roughly the same length as mine although mine has slightly less bow.

    Lex.


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