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Thread: I didn't bend it, but I wanna straighten it

  1. #1
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    Default I didn't bend it, but I wanna straighten it

    The solid, rectangular section shaft affixed to the moveable side, that slides into the channel in the fixed side, is bent, where it meets the body of the cast jaw.

    What would be a satisfactory way to straighten it? If I heat it, will it make it weak. I suspect it would break if I pounded it, and there is no good way to get purchase on it to lever it back with a long section of pipe. It is held in the other vise just for the pic.


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  2. #2
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    Default Re: I didn't bend it, but I wanna straighten it

    Pass a sharp file over it to see how hard it is,then you'll know if heating it will be harmful.
    It's probably mild steel since you could actually bend it.
    R
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    Default Re: I didn't bend it, but I wanna straighten it

    If it's mild steel your local mechanic's hydraulic press will likely straighten it. Mild steel bends easily. If it's cast iron (unlikely) do not try to bend it, it will break.
    '' You ain't gonna learn what you don't want to know. ''
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  4. #4
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    Default Re: I didn't bend it, but I wanna straighten it

    Looks like mild steel that bent under very heavy clamping pressure.

    Can you remove it, flip it over and reverse the process?

    Can you put it in a receiver hitch and jack it back into shape?

    I do like Peter's suggestion.

    If it's hollow perhaps once it's straight enough maybe you can hammer in a straight piece of rod to reinforce it. That might even straighten it some.

  5. #5
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    Default Re: I didn't bend it, but I wanna straighten it

    The steel has become work hardened right at the bend. So any effort to bend it back will only create another bend next to the original one unless it's heated to red hot. And I don't think you could heat it enough as long as the cast iron clamp head is attached because it's too great of a heat sink. Removing and replacement is the best option.

    How on earth was it bent in the first place? That is a very large section and you stated it is solid!

    Jeff

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    Default Re: I didn't bend it, but I wanna straighten it

    I would probably just put it in the press and straighten it or break it. Most likely it will straighten easily, supporting it correctly will be the most difficult bit. That bar might even be removed and replaced.

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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by jpatrick View Post
    The steel has become work hardened right at the bend. So any effort to bend it back will only create another bend next to the original one unless it's heated to red hot. And I don't think you could heat it enough as long as the cast iron clamp head is attached because it's too great of a heat sink. Removing and replacement is the best option.

    How on earth was it bent in the first place? That is a very large section and you stated it is solid!

    Jeff
    I would be suspicious about the overall quality of the vise. I don't work with metal, but that does not seem like something that should bend during normal use. Maybe someone tried to use the vise like a press and put a long extension the vise handle?

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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by Canoeyawl View Post
    I would probably just put it in the press and straighten it or break it. Most likely it will straighten easily, supporting it correctly will be the most difficult bit. That bar might even be removed and replaced.
    I would start with Canoeyawl's advise.

    Quote Originally Posted by jpatrick View Post
    The steel has become work hardened right at the bend. So any effort to bend it back will only create another bend next to the original one unless it's heated to red hot. And I don't think you could heat it enough as long as the cast iron clamp head is attached because it's too great of a heat sink. Removing and replacement is the best option.

    How on earth was it bent in the first place? That is a very large section and you stated it is solid!

    Jeff
    As long as the bar is mild steel, the work hardening will not be that much, the metal has not deformed more than one or two percent. Cast iron does not bend well. While it isn't important in this case, the Bauschinger effect is your friend here. when steel is stretched, it work hardens, i.e., gets stronger in tension. At the same time is has not been strengthened as much in compression. It is more of a problem with higher carbon steels. A fan of 'Big Bang Theory' will recognize this as one of Sheldon's irritating fun facts.

    This is very unlikely to be a high hardness quenched and tempered steel, so some heat will not be a problem. There are tricks with heating one side and cooling that can do a lot to bend or straighten steel, but I don't have a good working knowledge or the experience to describe the process adequately. I looked up a few references that might give you enough information to try it. The process is called flame straightening. I think that if you heat the outside of the bend with a torch to 7-800°F, it will straighten a little as it cools. It will take several cycles of heating and cooling to do the job. Bottom line: I think it can be done, and I only know enough to look for someone else to do the work for me.

    Basic principals: https://www.youtube.com/watch?v=IxzV9VeUpLY But this is using red heat, which might be too much.
    For lower temperatures, this might help: https://www.fhwa.dot.gov/bridge/steel/heat_guide.pdf


    How was it bent? 'Brute force and stupidity', which is always a good solution to a mechanical problem where things are stuck, buggered up and rusty. Sometimes it works.
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    Default Re: I didn't bend it, but I wanna straighten it

    That ACME thread was not cut in hardened steel, I've straightened many quills on a press between v-blocks. You'll need a dial gauge indicator.
    PaulF

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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by MN Dave View Post

    As long as the bar is mild steel, the work hardening will not be that much, the metal has not deformed more than one or two percent.
    That sounds good in theory but I've never found it to be true in practice. I've bent many a chunk of steel a bit more than I intended. Trying to unbend it has always resulted in a slightly different curve. Perhaps an almost straight bar will still serve the OP.

    Jeff

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    Default Re: I didn't bend it, but I wanna straighten it

    Remove the screw and press it straight. Your local automotive machine shop, a shop that repairs hydraulic cylinders, or even a competent motorcycle shop that can straighten a fork tube can do this in the blink of an eye. I might go just slightly beyond where you think it originated so that the jaw will clamp square under pressure.
    Or put it in the mail (flat rate) and send it to me, I'm less than a hundred miles from you and will do it gratis...

    (I have often straightened steel using heat and cold, but don't think this is a candidate for that technique.
    The lincoln welders manual (bible) has a section on this for straightening or curving steel beams) It wants to be red hot, bright red preferably, and the shrink wants to be cold, a running hose is good, a CO2 fire extinguisher is better!

    Edit; Here you go, You need one of these, don't take up much space and will a lot of work. He'll take a little less!
    https://sacramento.craigslist.org/pt...708411146.html
    Last edited by Canoeyawl; 09-30-2018 at 03:55 PM.

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    Default Re: I didn't bend it, but I wanna straighten it

    Is the bar able to be removed from the casting (forging?) that it is set in? Have a look at that possibility and take it from there.
    I would be very careful of trying to bend it straight where some of the force will be transferred to the casting.
    There is nothing quite as permanent as a good temporary repair.

  13. #13
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    Default Re: I didn't bend it, but I wanna straighten it

    Maybe heat and a press? #14 [EDIT: this is a link]
    https://www.garagejournal.com/forum/showthread.php?p=2312630#post2312630
    Edit: Does anybody ever click the link? So these are the pictures from the link. It looks like the heat was applied to the channel next to the jaw. The blue heat tint shows where the heat was applied at he top of the channel adjacent to the jaw. This vise was bent in the same place as the OP's vice. The press restrained the part more than bent it. When the heat was applied, the metal expanded, softened and was compressed. As it cooled, the thermal expansion (contraction) pulled the part straight. When I say softened, I mean at temperature, so the stretched metal was compressed with a lot less force than if it was cold.

    Last edited by MN Dave; 10-01-2018 at 12:59 PM.
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    Default Re: I didn't bend it, but I wanna straighten it

    I believe the “steel” bar was set in the mold and the “cast” steel or iron was poured over the bar. I suspect the cast portion is cast iron and may well break if you apply enough force to straighten the steel bar.
    You can try, but I would consider the vice to be pretty much done.

    or,... you can use heat on the bar until it starts to glow and can be straightened easily. However, unless it is re-hardened the bar will rebend even more easily.

  15. #15
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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by nedL View Post
    I believe the “steel” bar was set in the mold and the “cast” steel or iron was poured over the bar. I suspect the cast portion is cast iron and may well break if you apply enough force to straighten the steel bar.
    You can try, but I would consider the vice to be pretty much done.

    or,... you can use heat on the bar until it starts to glow and can be straightened easily. However, unless it is re-hardened the bar will rebend even more easily.
    That is not the case. This is a ACME thread Vice screw. It is not hardened and can be "carefully" bent back into service. They are tougher than Chinese arithmetic and made to be repaired.
    PaulF

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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by paulf View Post
    That is not the case. This is a ACME thread Vice screw. It is not hardened and can be "carefully" bent back into service. They are tougher than Chinese arithmetic and made to be repaired.

    The OP said that the shaft, not the screw, is bent.

    Jeff

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    Default Re: I didn't bend it, but I wanna straighten it

    I may have misled; By "remove the screw" I meant "get it out of the way" so you can press the bar straight.

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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by jpatrick View Post
    The OP said that the shaft, not the screw, is bent.

    Jeff
    The shaft and screw are one piece, the ACME thread and shaft was cut from a single bar, it bent at the bearing surface. It can be straightened in place with a press enough to be removed and trued up.
    EDIT

    Excuse me, Do you mean the rectangular guide is bent? It still can be repaired with a press. get the acme screw out of the way.

    I was mistaken that the round bearing shaft was bent...my bad!
    Last edited by paulf; 09-30-2018 at 10:59 PM.
    PaulF

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    Default Re: I didn't bend it, but I wanna straighten it

    So, just how did you bend that thing Jim?
    Simpler is better, except when complicated looks really cool.

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    Default Re: I didn't bend it, but I wanna straighten it

    I think Jim is not the culprit. I have seen them bent. Just progressive overuse over decades of time.

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    Default Re: I didn't bend it, but I wanna straighten it

    It was here before I arrived, and in the same shape. I put the yellow paint on it. I have other vises, it just bothers me that the jaw faces are not parallel.

    I find that vises are like tablesaws, in that the really good ones deserve their reputation and that is reflected in prices of used items. Big vises, with recognized names like Wilton, go for huge prices, several hundred bucks, while a perfectly good item with lesser reputation goes for a song. And they're like boats and cars, everybody thinks theirs is worth more than it probably is based on the premise that it's worth what someone will pay for it. The big machinist vice is either a Wilton five inch that is missing the name plate, but matches all the rest of the details I can see. I got mine at a yard sale for about ten bucks. I put walnut sacrificial jaw faces on it and use for woodwork because it is massive enough to hold some chunk to be pounded with gouges. The no-name Taiwanese four incher is for holding metal stuff. The little one I want to straighten will get used for something else.

    Thanks for all the info and input. WBF is better than google for these things.

    Pron-King, it's in the thread title. I'm pretty sure nedL has it correct. I might have to move this post to the 'ever been falsely accused' thread in the bilge.
    I don't care to know what the tough do when the going gets tough.

    I am interested in what the enlightened do.

  22. #22
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    Default Re: I didn't bend it, but I wanna straighten it

    Yes, get the screw out of the way, put in shop press and press. Spread force over a few inches with a thick plate, so tubing doesn't 'dent'. If you want it to be stronger, press a sliding-fit tube inside it once it's straight.

    This is trailer-hitch level stuff -- mild steel square tube sections. You'll want to preserve the attachment to the front jaw, though you could drill and thru-bolt it if needed. That may tighten the joint, but make it weaker overall.

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    Default Re: I didn't bend it, but I wanna straighten it

    If you have an oxyacetylene torch, you might not even need a press. Just don't heat the screw.
    vise.jpg
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    Default Re: I didn't bend it, but I wanna straighten it

    Alternatively, take an angle grinder and file to the clamping face until it is parallel to the fixed clamping face.
    Whist you are at it, file in a grove for clamping round bar.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: I didn't bend it, but I wanna straighten it

    Quote Originally Posted by paulf View Post
    That is not the case. This is a ACME thread Vice screw. It is not hardened and can be "carefully" bent back into service. They are tougher than Chinese arithmetic and made to be repaired.
    I don't think it's the Acme thread that's bent, Paul. It's the rectangular guide shaft.

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