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Squareness of parallel bars matter?

T

turnworks

Cast Iron
Joined
Dec 12, 2018
Picked up some new .500 thick bars so I can face off a handful of parts at a time. Decided to check them before using them and they are flat and within .0003" in height to each other. The sides however have a .001-.003" crown to them on one side and off square .002-.004" on the taller bars. Not positive how much the crown is throwing off my squareness measuring though.

Used them anyway without pushing them against the jaws and the parts are coming out fine. Vise is the gerardi type.

Tried them up against the jaws and still no issues. Was always taught they should be flat and square so does it really matter?

If I used springs or keepers maybe it would show but I don't.

Curious of what others think.
 
It shouldn't matter a bit if they aren't touching the jaws. It might be a good idea to square them up for possible future setups just so you have them in case you need them. Also I much prefer keeping the parallels sprung tight against the jaws when doing more than a part or two. Keeps crap out of them and also pushes the jaws open as soon as you move the vise handle. That makes it easy to keep the handle set at the right angle and just give it a quick tweak to open and close the vise when changing parts. In theory the parallels should right themselves even when sprung against the jaws if they are out of square as long as you tap the part down, but why tempt fate?
 
It's good practice to do the best possible for initial ops. But it's most important when you have subsequent ops. If that's the only thing that needs to be done--fuck it.

R
 
Parallels are supposed to be precision tooling. The lack thereof may or may not be a problem in this situation, but they are frequently used in unconventional ways where these issues might cause problems. It's just not right. Send 'em back if you can. Otherwise, fix them. These things have a way of showing up at the worst times.
 
Parallel is the only thing you need them for, UNLESS you're wanting a setup where you need them to be square.
If you're just using them up against vice jaws, they can be out of square by 1/8" and it won't affect the part sitting in the vice because you're using the parallel-ness (for lack of a better term) of the parallel.

My old set has parallels that are bowed all to hell, but they're still parallel.
 
Thanks for the replies. I plan to fix them when I get time but have to get this job done.

My vise jaws move when tightening and that had me wondering about the squareness of the bars and if it played a role in the set up.
 
On a 1/2 wide I'd think not a problem as you have a decent seating surface. Hopefully the surface it seats on is also good with no nicks or high spots.
How many people stone the bottom rails of their vise for nicks and dings from usage?
On 1/8 or thinner .004 may be a problem as how to align.
I often use gauge blocks as sort of parallels. They are not square.

There is no "solid" jaw in a vise under pressure. As above they all move. Toolmaker vise's deflection is very small, mill vises certainly more.
Ideally you use the same pressure and your back jaw comes into zero at that pressure.
Knowing that sort of screws indicating its "tilt" in free space or unloaded.
Some people use torque wrenches to tighten a mill vise so that this can be controlled.

How fussy do you need to be? Microns, tenths, thousandths?
Bob
 
Thanks again for the replies.

The parts were 7” long 2” wide 1/2” thick 6061. First op was to face them down to 1.950” wide. I used the .500 parallels long ways so I could stack 7 pieces in at a time then mill flip and mill to size.

Tolerance is open but aimed for +.002 its more of a cosmetic thing after the parts get one side beveled with a .010” land.

The vise is the type with jaws that have an angle on the back side so it pulls the part down. I’m the lazy type and hated moving the table to get a good clear path for the hammer to smack down the part on the old vise. This style vise has stopped me from doing all that.

I did use a scrap piece to try holding the parallels close to the vise and still no issues was within .001” over a 6” piece milling both sides.
 
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