Machine vices all flex when tightened - can't machine square - Page 2
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  1. #21
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    I had problems where the part sometimes slipped in the jaws of a shop made vice. I noticed when I tightened the movable jaw there was a gap at the top of about .004 . I removed the steel jaws and milled an aluminum jaw .006 out of parallel. This worked well. I then did the same with the steel jaw and replaced the aluminum jaw with the steel one. This vice is for a drill press, the store bought DP vice was removed and sits on a shelf. Shop made vice was from plans for a tool makers vice I saw online.

    mike

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    Chopper, With so many variables involved it may serve you well to determine what is out of square to start with and correct that. Then determine what exactly is flexing and where. After taking the vise off the machine and swivel base be sure there are no raised areas on any the surfaces. A nice flat stone rubbed at different directions will show the high spots. Clamp the swivel base to the table first and check it's flatness with an indicator. Take a skim cut if needed. Put the vise on and open it all the way then indicate the it's base to be sure it is parallel to the table. Then indicate up and down the solid jaw. Once you know how close both those are you can look for what happens when the vise is tightened. Put a wide parallel in the vise and tighten it leaving room to indicate the solid jaw up and down again and the base. What happens? Move the parallel higher in the vise and do it again. Any change? Most probably the solid jaw is not flexing nor is the base. If it is you probably need a better vise. So then if the movable jaw is the problem as was pointed out see if it's worn or can be adjusted. When squaring work always cut the wide side first by holding the edges shallow in the vise. Always put that side against the solid jaw. Then throw the welding rod in the trash and take a piece of about 1" round stock as long as the jaws and mill a flat about 1/8" deep along the entire length. Now put your machined side against the solid jaw as deep as you can and put the machined rod about half way up between the movable jaw and the part. Cut that edge. Turn it over and do the second edge. You could leave the part hang out of the vise a bit to indicate up and down to see if you are square, if not raise or lower the rod and check it again. Also sometimes the flat against the jaw and round against the part or the other way which ever gives the best results. After both edges are square to the wider flat it will be easier to make the last side parallel. Also keep in mind if you are working with cold rolled steel it will usually warp once you cut one side and that is no fault of the vise. The indicator is your best friend in locating what is going on here. Sounds like you have a very nice mill and do some way cool work. I hope this helps get things square.
    spaeth

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    You might make a couple of special fixtures that you can use with many different parts.

    One would be like a vise with very shallow jaws. The fixed jaw has a sharp edge the cuts into the work, top surface level and bevel on bottom, so as it bites it pulls down. The other jaw can be a standard toe clamp, that pulls down as it moves in.
    Another approach would be to place your workpiece on the vise bed and clamp it firmly down with one or more strap-clamps. Then tighten the vise, rap the work down and remove the strap clamp. Have an indicator on the work as you remove the strap-clamp to see if it lifts.

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    I had a quick go at milling a cube as per the solid rock machine shop video. I used my 4" abwood on a swivel as per op (gib was adjusted but the movable jaw still kicks .004" when torqued), chinese parallels and my less than perfect Milnes miller. Was high and low in the vice when appropriate and torqued the vice to 20lbft.
    Think I did ok considering my lack o mill skills.
    checking square
    checking parallel
    high.jpglow.jpgla-machine.jpg

  5. #25
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    -Your heavy vise is only heavy in all the wrong places.

    I suggest you buy some sort of quality angle lock vise. a kurt, orange, quad-I etc.... something with a LOT more thickness to the base.

    Here's a very nice vise. The base is thicker than the jaw height. Everything is ground just beautifully. You can fins similar features used.
    DX6 CrossOver Vise | 6” Manual Vise with 9” Opening

    Then, don't over tighten the hell out of it. Or if you must tighten it to unacceptable deflection, shim the fixed jaw.

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    I square up small blocks by the dozen weekly for mold inserts, that's why I use a rigid CNC and in a vise. But years ago we did it on a Bridgeport with mixed results. Getting any thing square on a manual mill takes skill and patience. There're so many variables that come into play you can chase your tail all day long if only only one of those variables is screwing with all the others. Such as if the head of the machine is not square. Or possibly loose gibbs. Or the vise is of an old design and not built to withstand normal clamping pressure without moving more than a couple tenths. The vise shown above is what I would call an old design and do what others recommend, remove the swivel base. Try moving the part lower in the vise for more contact with the rigid jaw. If the movable jaw kicks .004 then get rid of the vise or use another method such as a angle plate. That's my .02 cents so take it for what it's worth.

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    Ok thanks again for all the input, I had tried without the rotatable base but that didn't help. I was relieved to hear that this is generally something that many people experience. I have decided to go for fixtures general and specific particularly because I spent almost 2 days dicking about trying to get a square cut whereas I went into the shop just now and within 20 minutes I had machined a square onto some 2" ali that was only 2 tenths off - although I am very keen on that new Kurt DX6 vice thanks for the link

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    That's a nice looking vise. I would love to see some more photos of it, from different angles, if you have any.



    Quote Originally Posted by donie View Post
    This is a Stevens sub plate torque limiting vise mounted on a 2" thick steel plate, being used in an old jigborer. This vice has considerable less flex then a 6" Kurt.
    The repeatable torque setting is controlled by an adjustable multi plate clutch on closing, opening is done with a sprag clutch bypassing the settable clutch.


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    This makes me wonder if the fixed jaw of that vise is really square. First, check that the head is properly trammed, that is square to the table. Then put a DI in the quill and run it up and down the fixed jaw. Tighten the quill lock before each reading to eliminate any slop between it and the head. The reading should stay the same if the jaw is square.



    Quote Originally Posted by choppernigel View Post
    Ok thanks again for all the input, I had tried without the rotatable base but that didn't help. I was relieved to hear that this is generally something that many people experience. I have decided to go for fixtures general and specific particularly because I spent almost 2 days dicking about trying to get a square cut whereas I went into the shop just now and within 20 minutes I had machined a square onto some 2" ali that was only 2 tenths off - although I am very keen on that new Kurt DX6 vice thanks for the link

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    Demon 73
    I’m on my phone so I may be missing something, but your video shows a block that has top and bottom (surface plate side) surfaces flat and parallel to each other , the block could have 45 degree angles instead of 90 and still show the same


    Sent from my iPhone using Tapatalk Pro

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    Quote Originally Posted by ripperj View Post
    Demon 73
    I’m on my phone so I may be missing something, but your video shows a block that has top and bottom (surface plate side) surfaces flat and parallel to each other , the block could have 45 degree angles instead of 90 and still show the same


    Sent from my iPhone using Tapatalk Pro
    Ah there two videos in post 24, you want this one for overall squareness

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    Thank you, gonna ponder on that a bit , with regard to any delta in deflection. The parallel check first eliminates lots of possibilities.
    I always zeroed with a known good square, I now see it’s not needed, really just a extension of the three square method.
    Thanks again


    Sent from my iPhone using Tapatalk Pro

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    A few years ago there were vises made that had the screw operating so that it pulled the jaws together rather than pushing them apart. I couldn't find them in a quick search.

    Tapping a part down in a vise is an art. You can't just bang on it because the part will vibrate, which raises it. Use a dead blow plastic faced hammer, not a normal plastic one. The action is sort of like killing the baseball in a bunt. You swing the hammer down smoothly and not too hard and hold it against the part, don't let it bounce. If you don't believe me, put a block in the vise holding it down by hand and measure its height. The hit the block with your plastic hammer and measure it again. It will probably have bounced up higher than it started. After tapping, I check to see that both parallels are tight. If not, the part isn't square.

    Bill

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    Having read thro some good advice you have been given,and that you have clocked the fixed jaw in the vertical plane.Have to admit myself personally have never seen a back jaw flex.If your convinced that is what is happening I would put a shim behind the fixed jaw and lock the jaw back on.As for your worry about the different size blocks using the high and low method as described earlier should get you well in tolerance.For a temporary solution soft jaws can be made and skimmed with e/mill after they have been locked on.A lump of 2ins brass is better for tapping jobs down few light taps

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    Here is a side shot of the Stevens torque limiting sub plate vise.
    The notched collar tightens the multiplate plate clutch, the clutch can be set using a hydraulic scale between the jaws, from a few pounds to tons, when the jaws are opened, the clutch is by passed with a positive sprag clutch...similar to a starter Bendix.

    Being a sub plate vise, I have the two pieces bolted, and pinned to a piece of 2" thick ground tool steel. The traveling jaw moves about 1 1/2", so, the movable jaw, or the fixed jaw has to be unbolted and moved for major adjustment, both vise parts index into the same holes in the sub plates.

    The jaws are 5 1/2" wide, and deeper then a Kurt, made for ease of attachment of special jaws-fixtures.

    I bought this more then 20yrs ago, I remember it was expensive.

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    Those abwood vices are pretty much the worst machine vices you can get, in spite of being probably the most commonly found vice in any machineshop in the UK. The rear jaw is thin and flimsy and flexes when you tighten, and the front jaw with it's shitty keeper plate retention lifts so badly that it's difficult to even get a part to tap down onto parallels. Too springy.

    They are what I endured in the beginning of my career, not knowing any better. It was a glorious day when I discovered that better vices existed.

    Kurt vices (knock off and genuine) flex badly on the rear jaw, so even though they don't lift the part up off parallels they suck for squareness.

    If you have a very nice mill and want a very nice vice to match look at Gerardi, or any similar european style modular vices.

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    I got one of these as a cheap option for my 3 axis work. It's been working pretty well:

    6" 660U CNC Milling Machine Vise 0.0004"

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    Quote Originally Posted by 9100 View Post
    A few years ago there were vises made that had the screw operating so that it pulled the jaws together rather than pushing them apart. I couldn't find them in a quick search.
    ...

    Bill
    A vise that pulls the jaws closed where the screw is in tension is a shaper vise.
    A vise that pushes the jaws closed where the screw is in compression is a milling vise.
    The bad part about a milling vise is, because the screw force is carried through the
    body of the vise, it imparts flex into the body.
    With a shaper vise, the force is contained between the 2 jaws and the screw, and the
    body is kind of along for the ride.
    Kurt makes both milling and shaper style vises. You just have to know what you are
    looking at.

    -Doozer

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    Default toe clamps

    You could dispense with the vise and just hold the piece by its bottom edges.

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    Quote Originally Posted by TDegenhart View Post
    Out of curiosity, how does the classic solid base/jaw Bridgeport vise work?

    Tom
    Not very well - not compared to anything with pull-down, such as Kurt and decent clones, or the Gerardi modulars with selective pull-down.

    But WTH? Plenty of sound advice in-thread arredy. Vertical mill, head, table, all-else is - as already said - "rubber"

    First gain is to shed the swivel base on what is already there and paid-for.

    Only five parts each type? That ain't the vise's job. It's for the mill-hand to compensate like Hell.

    No Fine Way that mill can be lied-to well-enough to become convinced it is a surface-grinder, even if you get Adam Schiff to yammer at it.

    Getting to ONE thou not two thou is about all you can realistically goal for, even if real money is thrown at it. Justified? Dunno. First price-out a better choice of vise, or first-rate, not El Cheapo, clamping goods. Then "maybe not" with limited needs & budget?

    Up your skill, add determination, multiply by patience, run what you got. It's a mill, not an instant coffee machine or a standardized soft-drink vendor.

    Results are up to the man. Not the machine.

    'Twas ever thus...


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