Peening the Underside of a Milling Machine Table. - Page 3
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  1. #41
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    It is a miracle then! Several of the fellows here seem to have done it and had it work.

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    I have no doubt that a serious peening will change a worktable.
    The question I pose is how long does this induced stress last?
    1 year, 5 years, 20 years, forever?
    As a machine ages are such stresses gradually removed and you go back to where you started?
    I know that if you peen straighten HSS cutting tools they come back a bit after 6 months on the shelf but machine tables are not little long skinny round pieces of HSS.
    Bob

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    Probably depends on the material and its hardness. I'd expect softer materials that are lower yield strength like (non-hardened) cast iron to stay put pretty well as long as no other stresses are induced.

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    Quote Originally Posted by eKretz View Post
    Probably depends on the material and its hardness. I'd expect softer materials that are lower yield strength like (non-hardened) cast iron to stay put pretty well as long as no other stresses are induced.
    Why do I not trust induced stress holding and aging in soft cast iron? Say crankshafts or engine blocks?
    Problem here time frame. All nice today who checks it again 5-10 years out?

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    It is done for crankshafts all the time. Peening in the fillet radius area of the main journals is (or used to be) standard procedure for tweaking a crank. If the iron is stress relieved it shouldn't move much anymore on its own. The old school way to do that was to leave it outside in the weather for a while. Not sure if anyone still does such things.

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    Quote Originally Posted by eKretz View Post
    It is done for crankshafts all the time. Peening in the fillet radius area of the main journals is (or used to be) standard procedure for tweaking a crank. If the iron is stress relieved it shouldn't move much anymore on its own. The old school way to do that was to leave it outside in the weather for a while. Not sure if anyone still does such things.
    Always new things to be learned so thanks but still I wonder. Does one stress relive after peening?

    Not sure what old school qualifies as. I only know close to 100 years of production auto engine making on both sides of the family.
    Blocks and cranks are no longer left outside to age as in the past. It is a JIT world and now AL so different.
    Hit a truckload of too "green" brake discs or cranks and life not so fun. Eat tools and do not stay put.
    Peening a crank as said not so great an idea, Like pissing down your leg. Warm and fuzzy at the start.

    I see this as a temp fix and can not help but think so long term.
    I just question it but I could be all so wrong.
    Bob

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    No stress relief after peening. Peening adds stresses. If you then relieve them, definitely going to get movement. I'm sure they sometimes don't stay put, but better than starting with a bent crank... I have peened cranks and taken them back out years later and they were still pretty straight - straight enough that they didn't take up the existing clearance in the bearings and still spun freely. Not saying that's always the case, but it has been my experience in the 7 or 8 that I've actually taken back apart. Also remember that sometimes even cast iron that is not peened moves too.

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    Quote Originally Posted by Hbjj View Post
    I've peened two Bridgeport tables
    And straightened many a propeller shaft with peening i find it to be a slow and precise process

    It sounds like you're table has alot of bow to it it might not be feasible to get that much movement do you have any photos of it?

    As far as where to peen on a mill table it's going to be more in the middle tapering to less at the ends


    Attachment 299588
    I don't have a photo to post and I doubt it would show much anyway, I just sat a long straight edge on 1mm gauge blocks at each end of the table and measured the gap in the middle with feeler gauges.

    Would you mind briefly explaining the procedure that you used on the Bridgeport tables and the tools used?

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    The two bp tables I worked on are still in service several years on and I have reinspected several pump drive shafts after peening and a stint in service and all was well.
    I did set both tables up at .001+ concave as future proofing (IMHO it's folly to not build in a little cushion on machine tools)

    I haven't and can't measure them again (I'm a homeschool teacher now...) but all was well when I left.

    I used a standard 16 oz ball-peen hammer and a punch to get in the tight places

    The underside of a bp table is a waffle pattern of raised ribs in between the ways.I worked these and the areas near but not the way itself. I didn't want to make a problem there

    I used a standard machinist level to measure twist (all measurements were on 3 points of course) and a indicator set up to measure flat.

    the flat way of there best lathe was my flat reference surface (it's all I had)
    Both machines cut flatter after this work but still convex

    Both tables were out about.008 on a 42 inch and a 36 inch and it took some serious peening to make it happen

    When I do this again I will (help) things along by pushing on the table with a screw jack setup

    20151113_111103.jpg

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    Thanks for the information Hbjj. What are you actually checking with bar and indicator setup?

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    Thats measuring the bow or crown of the table
    I set that to zero on the best flat reference surface I had. The wide flat way of there best lathe
    I had checked that way surface with a sensitive level and i stepped it off with a strait edge when I installed the lathe and it was nice.

    The gauge would sit on the lathe until needed
    In use I would check the zero then measure the table then verify that the zero was good when i put it back

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    We have been talking about this for years on here. It works as Glen writes about it in the following old post. I use a cold roll 1" rounded end shaft about 6" long and use a 5 pound sledge. Hammer the ribs near the middle Have to lay the table on a 1/2 piece of plywood on a concrete floor. No Bounce. Be careful not to hit above the dovetails.
    Can you bend a warped BP table?

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    Here is a great post done by Engineering Professor Archie Cheda who taught me how overtightening the Tee slots will peen or bend the tables/

    Lucas Horizontal Boring Mill going to Tuckahoe . . .

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    Thanks for the information Richard, the only thing that I haven't read in any article about peening is the layout and spacing of the "hits", are these done at random all over the underside or as you mentioned, only around the ribs in the middle of the table?

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    I had a student bring a Bridgeport table to a class that was tested on 3 points at 30% and the table was off bent .012". We took the table down and layed it on the concrete slab outside the shop on the plywood. We then made a punch with a large radius on a 1" cold roll shaft aprx. 8" long. He put on some gloves and started to hit the punch with a 5 pound short handled sledge hammer on the center of the table bottom on the ribs. There are ribs under there for support. I was busy with the class and he came back in and point it back on 3 points and checked it again and it was only out .002" His name is Steven Isherwood. I'll see if I can find his email and send it to you. He was a member here a while ago. Oh the class was in the Netherlands and he was an Englishman living in Norway.

    I found it and will message you his email address. I do know he laughed at how many times it took. Maybe he can come here and tell the group. Rich :-)
    Last edited by Richard King; 10-02-2020 at 02:32 PM.

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    I heard back he said he stopped writing on the forums and has been rebuilding a lot of machines. Here is what he said in his letter

    "Yes thats is all correct

    The process of peening worked very well. After peening the table had a very slight m shape with the very center and ends being low compared to two high areas in between.

    I don't know if that is a typical outcome but if it is then I strongly recommend to peen prior to any scraping."
    Last edited by CBlair; 10-15-2020 at 08:00 AM.

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    I heard back from redacted in Norway and he attached a photo.
    He wrote Lex and copied me:

    Hi Lex,

    I've CC Richard in case the picture is of use to him when helping others.

    no problem. Ask away.

    find a picture of the underside of the table attached. You can see the peening marks. I had to hit the table pretty hard. The process works and saves on a lot of scraping but you need to be careful you don't crack and damage the casting. So hit it hard but not too hard....

    Thanks,

    _underside of table and fellow from Finland checking the table after peening. If you look at the last pic, you can see we were crammed into a small shop without a lot of tables. using a blued camelback on floor he was bluing the table with. He was using the vertical board in vise to the right to keep the table and King-Way shaded from the sun shinning in a window. Also he has the table is sitting on 3 points. 2 sets on King-Way straight-edges. 12", 18", 24" 36" and 48" as you can see the non angled camelback on the right of the 48" camelback with an angle.
    Last edited by CBlair; 10-15-2020 at 07:09 AM. Reason: removing photo

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  23. #58
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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
    What kinda index mill do you have? And how do you go about measuring the sag in a “bent” table like what you described? My tables all have factory scrapping but I never thought about some bonehead needing an anvil while Looking at my machine in a past life!! Scares me

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    The table does not sag from overhang as I originally thought too. Then I talked to the Engineering professor Archie C. who said a friend had done a paper on it in university and discovered it was not hang over sag it was from over tightening the vise and stretching the Tee slots. I had a rebuilder tell me at the IMTS show shocked and could not believe him. I was at a SME event and met Axel Fors from Salt Lake City who also told me how re runs a T-slot cutter through the T-slots and peens the bottom before he planed the tales. I tried it on an old beater Bridgeport years ago and was shocked how well it worked. I had also tried to bend it with a chain and hydraulic jack, parking a 5 ton fork lift on a table that was sitting on 2 x 4's on the ends that never helped.

    Finally peening it. It took a while to figure out how to do it. Using a big diameter shaft and rounded nose as you can see in the photo's did the job as Steve tells us. It is your machine and you can machine, grind or scrape off top and bottom .015"....you can.

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  26. #60
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    Quote Originally Posted by Richard King View Post
    The table does not sag from overhang as I originally thought too. Then I talked to the Engineering professor Archie C. who said a friend had done a paper on it in university and discovered it was not hang over sag it was from over tightening the vise and stretching the Tee slots. I had a rebuilder tell me at the IMTS show shocked and could not believe him. I was at a SME event and met Axel Fors from Salt Lake City who also told me how re runs a T-slot cutter through the T-slots and peens the bottom before he planed the tales. I tried it on an old beater Bridgeport years ago and was shocked how well it worked. I had also tried to bend it with a chain and hydraulic jack, parking a 5 ton fork lift on a table that was sitting on 2 x 4's on the ends that never helped.

    Finally peening it. It took a while to figure out how to do it. Using a big diameter shaft and rounded nose as you can see in the photo's did the job as Steve tells us. It is your machine and you can machine, grind or scrape off top and bottom .015"....you can.
    Nice info rich! So how does one prevent over-tighting the tee nuts and t slots, A Torque wrench? If so what is an acceptable torque on t bolts/slots?


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