Problems with holding hardened blocks in vise.

PegroProX440 · Apr 30, 2020

Does anyone ever have the problem of holding a hardened block tight in a vise with hard jaws. Yes the part is parallel between the jaws. Vise is Kurt 3600V. Due to its shape I am holding about 1.5 inches in the X direction, and the part is sitting flat on the vise body. About 2 inches is above the jaws. The problem I am having is I can tap the part and move it around a little even with the vise tight.

My thinking is should I make up some jaws out of something softer like HH P-20. Will I get more gripping force.

I seem to be able to hold softer blocks very tight and rigid.

michiganbuck · Apr 30, 2020

Flat jaws dont hold very well and a vise closes with springing to the opendirection. even the best ones do this...
I would mahe an aluminum jaw on the solid side and use a hold down like used on a shaper.
berhaps 1/2 " on the jaw edge and 1/4 on the part side..the pounds per square inch go way up doing that.

You might even make a block-in-block to T bolt 9orvtwo bolt) down with it touching you vise at the high edge on the go side.

Try this somple test, vise the part with a little jaw open at the end... then JoBlock check the opening low and high..very ofter you will wider at top..they used to make hydralic vised hat weould only tightten to what would make the vise spring at top.

We did carbid-up some jaws with using DC current and a carbide sick to imbed carbide to one or bothe jaws but the would mark uo a part.

Did add a heavy duty C clamp ot two to a vise.

We had some diamond abrasive paper and set it to one side.

ripperj · Apr 30, 2020

If the part is only 1.5” in the vise and on the vise base, then it doesn’t sound centered, so the Jaws are deflecting in two directions. So hard jaws holding a hard part equals not much contact. A piece of paper on the moveable jaw might help.

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carlherrnstein · Apr 30, 2020

Clamp it in the vice using paper between the part and the vice jaws.

Richard Winn · Apr 30, 2020

Manila folder

emery cloth

roclinizer

Farmer Phil · Apr 30, 2020

+1 for paper

guest · Apr 30, 2020

Sounds like the jaw is cocking sideways from asymmetric clamping. Stick a spacer the same width as the part on the other side of the vise to act as a fulcrum. That's something you should always do when you're using only one side of the vise anyway.

+1 on paper also, I use time cards for that because they are handy and I have a box full of them...

dian · Apr 30, 2020

yes, probably asymmetric clamping. but also you have to know your vice. for example my hydraulic vice gets zero lift on the part if i just engage the hydraulic function, tap part down so parallels dont move and tighten to third mark out of four (probably 3 tons). anything else and part is not flat. it doesnt make much sence but thats how it is.

PegroProX440 · Apr 30, 2020

Nope not asymmetrical clamping..... part is off on one side of the vise but I have an identical part on the other side as a spacer. Parts are squared all around to a few tenths.

thomj · Apr 30, 2020

Richard Winn said:
Manila folder

emery cloth

roclinizer

Sounds like a old die sinker trick...

Thom J

John Garner · Apr 30, 2020

Have you tried the old "rod between workpiece and the clamping jaw" trick?

thermite · Apr 30, 2020

All good advice, brown "Kraft" paper the oldest .. and cheapest. "Bond" paper @ 25% or better "rag" content and highly consistent size works, too, when card stocks are too thick.

But have you adjusted the "aggression level" of the vise's "pull DOWN"?

Oh... wait... you'd have to have a Gerardi Modular.. or one of several equivalents - they have competition, and plenty OF it .. to DOO that wuddn' yah?

Cheaper than first appears once yah twig to how USEFUL that whole tribe can be.

thomj · Apr 30, 2020

John Garner said:
Have you tried the old "rod between workpiece and the clamping jaw" trick?

I keep a ejector pin and a flat 16 ga. x 1/4 strip on the bench for these situations. I think a flatter strip works better. Folded over narrow strip of fine grit emery works best but can wear out in long runs....

Thom J

Bobw · Apr 30, 2020

Toss in an aluminum softjaw on the moving side, or slide in a piece of aluminum.

I have a whole drawer full of aluminum bits that I use to hold stuff in the vise
when I need to.

EPAIII · Apr 30, 2020

The vise jaws are hardened and ground flat. Your part is hardened. Hard on hard will slip.

You need to have soft on hard to get a good grip. There are several ways to do this.

Soft jaws.

Soft jaw inserts over the hard jaws.

A thin sheet of a softer material. Many suggest paper. I would suggest aluminum foil because it is more uniform than paper so, in theory, will introduce less error.

thermite · Apr 30, 2020

EPAIII said:
I would suggest aluminum foil because it is more uniform than paper so, in theory, will introduce less error.

Meahh. Most days? "Theory" is just a fancy abbreviation for "this shit SUCKS"

NOT "foil", please!

"in extremis" .. where ignorant paper doesn't quite "get it", yah go thicker, grabbier, more readily deformable.

Sheet COPPER!

Salvaged 100 HP Dee Cee motor commutator bar Copper and a good quatah-inch thick would grasp the DAMNDEST of shapes in a big-old 4-Jaw.

Set it true by deforming the Copper with aid of a 12 or 16 lb sledge, grasped just back of the head, shaft under the armpit for "precise control"!!!

Ugly. Also effective. Sure kept a lot of coal mines running.

4GSR · Apr 30, 2020

I keep pieces of lead sheets robbed off of stand pipe roof flashings. Works perfectly for those things that move around in the vise.

michiganbuck · Apr 30, 2020

When a vise springs only the very bottom is houlding ...most all vises spring when tigheten..The Jo Block check tell all.

thermite · Apr 30, 2020

michiganbuck said:
When a vise springs only the very bottom is houlding ...most all vises spring when tigheten..The Jo Block check tell all.

Fair certain the several means to offset that were discovered multiple times in multiple locations deep in pre-history by SERIOUSLY annoyed craftsmen when a vise was still blocks of wood and driven wedges, not yet even Copper, let alone Bronze-age.

- raise the pressure point to tilt the "jaw" downward by "just the right amount" to make it ACT as if it was irresistably perfectly parallel.

- built the jaw in such a way that pressure SLIDES the jaw downward as clamping pressure goes up.

The best of modern "downforce" vises utilize one if not both.

Not all here have the best of modern vises for all applications under our respective roofs.

BFD.

So long as we recognize we then have a need to "fake it really well"?

LOTS of tricks can serve.

PegroProX440 · May 1, 2020

So will making jaws out of softer metal be worth it for doing precision hard parts?

Problems with holding hardened blocks in vise.

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