Peening a bent gib

My brother and I have been scraping in a lathe, and had to make a new gib, taper type. It's for the compound rest so is only 7 inches long and maybe 3/8" thick at the thick end. We noticed that it was bent, so I peened the low end to straighten it, worked like a champ. I was afraid to try to bend a thin piece of cast iron, concerned that it might break.

Well, we found we were beating a dead horse as we tried to scrape it to final coverage as the thick end was about .002" too thick, which we discovered doing a shake test, so I lengthened the stroke and ruthlessly destroyed much earlier work on the thick end so we would stop wasting time.
The work went fast after that but I kept having to scrape the ends, and an alarm ell went off in my head because it was straight, wasn't it? A knife edged straight edge revealed a wow and in the end I straightened it by bopping it with my palm with one end in the vise.

Anyway, I reason that the hard scraping actually went below the peened compressed layer, and as we kept scraping it just got worse and worse. Anyway, I wanted to ask if anyone else had had the same experience, and if bending it the scary way of straightening a gib is therefore considered the answer.
parts.

We covered this about 6 months ago. But i never peen a gib...some like it, but i never would do it or teach someone to do it. Take your straight-edge and check the positive side where the gib rests. If you have not checked that, I bet it's high in the middle. I bend gibs and step scrape big ends. Google peening gibs and you will read all you need on the subjects in the PM archives. Rich

I was taught by my dad to peen gibs back to straight, too. But I've learned, Richard's influence me, that this is not the way to do it. Most will straighten by hand easily, larger ones a small shop press works, too. Kirk vise is handy, too! Once a while, I will re-machine one back to straight, if it's in bad shape and needs a fairly thick shim added to it. I rarely make new ones, but have done so.

The only machine component I really peen is mill tables in the hollow relief of the bottom where the leadscrew passes through. As parts mentioned, if you scrape off the peening you remove it's effect. I like to use the bridgeport for straightening gibs. Most short gibs fit across the kurt vise jaws spread open as two end supports. I use the quill to apply the force and the machines DRO keeps track of my progress serving as a gauge to let me know how far I'm bending it, then I let up and see how much the gib moved in it's free state. Obviously a sticky quill won't work here, and for the concerned, the minor force involved in bending a gib is not harmful to the spindle bearings.
Chris German

Here is a picture of the set up I use to bend gibs during the classes on left front of granite table. I use a dial indicator and feeler gages to measure the bend the set the indicator on a steel plate and the gib on 2 tool bits or cast iron blocks and put the indicator on the gib and use a C- Clamp to have a controlled bend. This is Stu at the Portland class testing his box parallels he scraped for a project. Rich

No one's mentioned it yet, but if you're making a new gib, rather than re-lifing an old one, stress relieve the cast iron before you machine it or at least after you rough machine it. Get it to a dull red heat for 20 minutes or so and cool it in air and it is very unlikely to move after further work. Continuously cast bar has a fair amount of stress in it unless the piece is cut from the inside of a large block.

When I built my dovetail straightedge many years ago I made it from continuous cast ductile iron, roughed it first, then put it in my wife's oven at full heat, then out into the snow outside until ambient outside temp, then back to the oven again. I did that 20-30 times. It's still pretty straight today, I checked it against a granite SE a while ago.

It was mentiioned above that this subject was covered previously and that is true but no link has been given. I used peening to straighten a gib I was making and found it to work very well. It was very quick and it allowed very precise and localized straightness adjustments. http://www.practicalmachinist.com/v...ted-ci-warping-when-sawed-282453/#post2258824
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The first protion of the cited thread has the information directly related to peening and you will find a link in the thread to a process called needle peening which is a refinement of hand peening and used in industry to straighten or precisely curve parts.
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Snce I learned about peening I have used it to intentionally curve flat parts as well as straighten others. It is a method worth considering.
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Denis

Yes DG, the only "Problem" comes if and when you scrape below the effected region. I suppose we could have straightened it using peening again and done final finish scraping, but I'd had it with peening by that time, so I bent it straighter. Weird though, after straightening by peening, after scraping through it it was bent far worse than when I peened it.

partsproduction said:

Yes DG, the only "Problem" comes if and when you scrape below the effected region. I suppose we could have straightened it using peening again and done final finish scraping, but I'd had it with peening by that time, so I bent it straighter. Weird though, after straightening by peening, after scraping through it it was bent far worse than when I peened it.

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That is weird. You were peening on the concavve side to lengthen that side---right? The peening affected area of metal runs much deeper than you would ordinarily scrape. So, in my case, even though the peening marks were scraped away the straightening was not adversely affected. I would like to actually see how that worked in your case.

As I did it, if I was able to tell the bend was localized to a certain area of the gib, it was quite easy to peen that area only to straighten that area only.

Denis

Bending gibs straight was quick and easy, Richard King demonstrated this at his St Paul class
Last fall. If you can find a straight peen hand sledge you can straighten stock quite well but this
usually is used for fabrication not machine rebuilding.

That is weird. You were peening on the concavve side to lengthen that side---right?

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Yes, and it worked like a charm, however, later after heavy scraping it scraped through. If the peening was very light with many strikes the effect is the same as a few harder strikes but the effected compression depth much thinner. That's my theory at least. After looking over R.King's method I like that a lot, and it can't break the gib because it is limited movement, the only way one might break a gib would be by bending it beyond it's elastic limits, which would not be very far with CI.

Hell when I am demoing bending a old Bridgeport gib I carry in my kit..or tools I demonstrate in the classes I will bend it .250 or 1/4" and it doesn't break. Everyone thinks it will break, but I have never - let me say it again I have never - broke a gib in 40 + years of bending gibs. Do it yourself if you have an old Bridgeport gib. Not one off a Chinese junk cast iron. Good Iron! Rich

Richard King said:

Hell when I am demoing bending a old Bridgeport gib I carry in my kit..or tools I demonstrate in the classes I will bend it .250 or 1/4" and it doesn't break. Everyone thinks it will break, but I have never - let me say it again I have never - broke a gib in 40 + years of bending gibs. Do it yourself if you have an old Bridgeport gib. Not one off a Chinese junk cast iron. Good Iron! Rich

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Rich, as you will remember, you asked me to take a gib and bend it "good" at the Dallas class back in 2012. You didn't specify just how "good". I bent it into almost a U shape and it did not break, but sure gave the next guys in line something to work hard at to straighten back with the blocks, indicator and C-clamp. Good times !!!

I don't remember that. It was so hot there then my mind was fried down there......lol....It was the year it stayed above 100 degree's for what 8 weeks..?

Yeah these guys who are afraid of a gib breaking have never broken one I think. bahh Bahhhh Baahhhhk. LOL... Hopefully you can drop by to the Swap meet we are having at the Houston class and sell some of your straight-edges. You mentioned in your email that your selling other scraping items now?? What else are you selling ?? bed time....good night...Rich

Don't forget that the OP was making a new gib, not straightening an old one. In that case, it's worth trying to make sure that there's no stress locked up in the iron to start with.

Mark Rand said:

Don't forget that the OP was making a new gib, not straightening an old one. In that case, it's worth trying to make sure that there's no stress locked up in the iron to start with.

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That's a good point Mark. Could make a difference in whether it breaks if it's not stress relieved, but would also be good to know if we are working with DUCTILE cast iron for the new gib.

Richard King said:

I don't remember that. It was so hot there then my mind was fried down there......lol....It was the year it stayed above 100 degree's for what 8 weeks..?

Yeah these guys who are afraid of a gib breaking have never broken one I think. bahh Bahhhh Baahhhhk. LOL... Hopefully you can drop by to the Swap meet we are having at the Houston class and sell some of your straight-edges. You mentioned in your email that your selling other scraping items now?? What else are you selling ?? bed time....good night...Rich

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Rich, I am hoping to make it to the swap meet. I currently have the small lathe faceplates, drive plates, and tailstock wrenches in addition to the Camelbacks. I have patterns for a small shaper vise, lathe radius turners (large and small). I have currently 1 large radius turner, but I'm hanging on to it hoping to do a Youtube video of finishing the casting and putting it to use. I feel like having videos to see how to finish the castings will help get some folks over the hump and get their projects going. There are many people who buy castings and never get around to machining them and putting them to use. Some don't know where to start and others just need a little motivation from seeing others progress to get them in gear. Similar to monkey-see-monkey-do.

Last year, when I was shopping for a DRO for my 14x40 lathe, DRO-PROS had an excellent series of videos showing every single installation step with lots of tips and that really sold me on their product and made my installation simple and fun. None of that standing around trying to figure out how to get around the next issue, then saying to self, o.k. self we'll put this project on hold for a day or two and 2 months later, it's still not done.

As you and I have discussed back and forth, there is not much incentive to go through the trouble of getting things cast for such a small pittance in return on the effort. It's just a labor of love of cast iron and restoring machines. I will eventually cast more of the items I don't have for sale presently, but don't nobody hold your breath, it could be a good while yet.

Mr. King is very right about Chinese iron being junk. Here locally there is a an oil well supply firm that purchased four Harley hollow spindle threaders that were poor copies of the old tried and true Landis machines. They were always breaking the tool holder slider plates, on all the chinese machines. The fractured iron resembled a broken up concrete sidewalk.......big grainy shit. At first we would braze them back together, and remachine the dovetails, but soon gave this up and fabbed ones of steel to replace the crappy iron. Years ago the Harleys were junked as hopeless cases.

The gib was for (and from) my 2000 Jet 1440W I bought recently, I had to make a new gib for the compound as the previous owner had crashed it bad enough to pull the T nuts through the cross slide, both the cross slide and the compound base are new parts and the old gibs would not work. I took the old CS gib and made it into the new compound gib. The iron seems good to me, I've just never known cast iron to bend very far without breaking is all. Perhaps the gibs are made of continuous cast bar, the ones you can bend that far.
Had I expected to scrape through the peening I'd have done it differently, often a small shaft can be straightened in a controlled way in the lathe, bend with the cross slide screw, check, bend check, etc. I do it there because then I have a convenient fast controlled travel for a dial indicator to check progress, the force needed being small and not enough to strain anything. A gib might be done that way held in a 4 jaw chuck. By the time we started scraping the location had changed to a borrowed shop, and the jig I used to machine it was two hours away.

I made a jig to hold the gib for both milling and surface grinding, the jig is a long piece of 1 1/4" key stock with a rectangular slot about 1.5 times as wide as the over all widest part of the gib, and slightly longer. Holding the gib in place with weights I then poured fixturing metal around it, which held very well during both milling and surface grinding.
I used the surface grinder to "find" the taper to a close degree, my jig has setscrews that allow me to raise or lower one end to adjust that taper. Oh, and the longest part of the time was spent heating and cooling the fixturing alloy to take the gib out, check it, and put it back in for adjustment grinding.

I took the gib out several times to check fit until it was very close, before beginning the scraping. Before we started scraping the gib was surprisingly straight, and Jet had only scraped one side of the original, the other side was surface ground at the factory.

So now everyone will tell me all the mistakes I made.