[PhoenixMetal]

I just bought a brand new Kurt D688 vise, and when I put a workpiece in using parallels and tighten the vise, the parallels become loose enough to slide out. I have been removing the parallels at that point so they don't fall out.

I'm new to machining, but I get the idea that the parallels are supposed to stay in during machining, and that they're supposed to stay snug.

The vise came with two little o-rings and some cryptic instructions that say that the o-rings are for use with parallels and that they will help create downward pressure onto the parallels. Here is a link to those instructions.

Their o-ring instructions and diagrams are terrible and I can't understand what I'm supposed to do... Am I supposed to disassemble the vise before putting the o-rings in? And if so, what is the procedure? Of course I could figure out how to take the vise apart on my own, but before I mess with it, I'd like to know whether I really need to do this.

Also, where is that adjustment screw they're talking about? Is it accessible from the rear of the moving jaw or is it hidden behind the jaw plate?

Kurt may have a reputation for making a good product, but they sure are remiss in not providing any instructions (in the box or on their website) for how to use and adjust their product. That's just really not acceptable in my opinion.

Anyhow, does anybody have any experience with using these o-rings?

Thanks!

[One of Many]

The set screw is on the rear face of the moving jaw pointed at you. Right in the center. This set screw pushes the moving jaw back so that the ball swivel is pulled/seated into the ball socket. The ball swivel joint in combination with the wedge on the screw casting is what gives the moving jaw its pull down action. Just loosen this set screw a ways to remove the moving jaw. Remeber to grease the swivel with a dab of moly grease, first to keep it from fretting and second to keep the swivel in the seat while putting it back together. The set screw should not be tightened. Just snug and back off a wee bit, so the swivel can still move. The intructions advise to tighten the set screw so that a .002 feeler gage will just slip under the moving jaw.

The purpose of the O-rings is like a spring under the moving jaw. They lift it up when the vice is unclamped leaving a .002 gap under the moving jaw. Supposedly as you clamp a work piece, the jaw pulls the work piece down onto the parallels.

IMHO that is what a deadblow hammer is for. To tap the part solid, seating the work piece down onto the parallels. I wouldn't trust anything to cut parallel, square or otherwise without seating the part manually.

Secondarily, if there is an open gap under the moving jaw, it can and will collect crud under it, thereby when the jaw does pull down, it is also seating on crud. There goes the parallelism between the jaw faces and additional wear from that crude lapping those surfaces.

Simplistic solution at first glance, but impractical in use!



DC

[Geof]

Some people will probably be horrified at the thought of doing this; hold the part down with the spindle while you tighten the vise.

I have used a tool holder with a piece of Delrin plastic in it that is tapered down to about 0.3" dia at the end. You just tighten the vise up to grip the part and then slightly loosen it, then bring the Delrin down until it is just touching with a bit of pressure and fully tighten the vise.

[One of Many]

Some people will probably be horrified at the thought of doing this; hold the part down with the spindle while you tighten the vise.

G-code a pattern and some Z rapids to thunk it in place against the parallels!

Now I'd have to admit I have used the quill on mine similarly in setup. I have also used the Z on others (without a quill) as a press to hold a large spring down while installing a C-clip.

DC

[Geof]

G-code a pattern and some Z rapids to thunk it in place against the parallels! ....DC

This I have done unintentionally.

[ckirchen]

A urethane pad also works. The 'overtravel' provided by the flexing of the pad would eliminate most of the risk of moving the quill down too far or fast on a CNC.

Chris Kirchen

[PhoenixMetal]

Thanks guys - thanks for the advice. I think I'll try seating the part onto the parallels with a rubber mallet next time. I definitely don't want to use the z axis to hold the part down because that just doesn't sound healthy for the machine. I have tried pushing the part down with my hand while tightening (which didn't help), so I wonder whether the z-axis trick would work anyway.

[MachEng]

We use a rubber band around each jaw to keep them in place.
It works great.

[One of Many]

We use a rubber band around each jaw to keep them in place.
It works great.

The specific issue here was that the parts were not actually seated to the parallels when clamping. Loose parallels were the indication as a result.

Using something to retain them would keep the parallels from floating around, but it won't help in seating the part against them. We used stock compression springs, old sections of bandsaw blades(teeth ground off) or that black metal banding strap, bent into a Z shape as a spring between the parallels to retain them. Double back tape can also work. Never thought about rubber bands I guess. Either that or the shop owner was too cheap to buy them when there was plenty of free scrap around to fit the need.

DC

[mc-motorsports]

Use your parallels like a flatness gauge, if you can slide them out, your part isn't sitting flat.

Kurt vices are about as good as it gets. Your right, the instructions weren't very clear, but you got what you paid for, a quality machined precision vice that should last longer than your machine.

[carbidecraters]

Some people will probably be horrified at the thought of doing this; hold the part down with the spindle while you tighten the vise.

I have used a tool holder with a piece of Delrin plastic in it that is tapered down to about 0.3" dia at the end. You just tighten the vise up to grip the part and then slightly loosen it, then bring the Delrin down until it is just touching with a bit of pressure and fully tighten the vise.

I am officially horrified!

Havent you guys heard of dead blow hammers?

[Geof]

I am officially horrified!

Havent you guys heard of dead blow hammers?

Sure I have; I also know there is absolutely no risk to the machine doing what I describe.

[hawkburger]

A swiss Mallet. Gehring I think is the name. They are by far the world's best for mill. They are really expensive, like kurt vise, but worth it. The are black rubber grip molded on grey metal with White plastic knobs That strike your matrial. When they get old you can just barely jear the little pellets moving in the head when you shke it. Don't get a solid rubber Black or especially orange, they will just bounce off and not "DEAD" blow the material. (No bounce back) Let the mallet drop onto the part, just give it momentum to start as you strike your piece, don't swing at it. or through it. Learn how to love that smack, like learning to kiss, it takes practice.

[PhoenixMetal]

Original poster here... I just installed the o-rings and tightened the set screw down so that it has the specified 0.002" gap under the movable jaw. I'm not sure if it really made any difference at all, although using a rubber mallet I have been able to successfully keep the part clamped down onto the parallels (tighten the vise a little bit, hammer the part down, then tighten completely).

I think I'll invest in a dead-blow hammer now as it sounds like that is the preferred tool over a rubber mallet.

[One of Many]

Use your parallels like a flatness gauge, if you can slide them out, your part isn't sitting flat.

Kurt vices are about as good as it gets. Your right, the instructions weren't very clear, but you got what you paid for, a quality machined precision vice that should last longer than your machine.

Sure this could indicate many issues for investigation if it is warranted. Anything from a chip behind the jaw, stress relief in a prior or during the current operation, to simple happenstance as the first surface to register against either jaw is not perfectly square to the bottom of the part.

This is an elementary but important portion of the production learning curve early on seasoning an operator that it is very common where the part lifts/shifts slightly as it is clamped. Seating it with a dead blow is one form of persuasion.

As long as there is enough clamping there to hold it for the current operation. Raising it higher in the jaws so not so much is influencing its clamping surfaces over its seating surface is another option. It still should be seated with a thud, and more likely to stay there.

Make sure the part doesn't flex when clamping or flex from clamping forces during the cut where material loses strength as it is removed.

The instructions linked to were busy with no step by step introductions for the uninitiated.

Something one must get accustom to, just like the machinist trade and resolving things like proper vise usage. Reading with peripheral visualization, comprehension comes with exposure to subtle hints-an instant connection to past experiences, concepts and lessons learned. Had you taken apart a Kurt vise before, you'd know within a scan what the instruction were describing.

It's all part of patience and becoming a talented well seasoned silverback.......like.....uh....well....Geof.


DC

[masonbcaldwell4]

Hey, if the dead blow doesn't work, get a babbit hammer! that'll always work, providing your work is square...

[PhoenixMetal]

Thanks guys - I've taken a number of your suggestions. The movable jaw now really does clamp down on the workpiece and hold the parallel (only the close one) down. I think maybe the o-rings and setscrew setting needed to work in, but it really does clamp down properly now.

However, I am still having trouble seating the part onto the parallel on the FIXED JAW side. Even with hammering (I still don't have a dead blow, so I am using a rubber mallet), the fixed-jaw side parallel comes loose once the vise is put under pressure. I have taken to keeping a rubber band on it as I learned here, but it doesn't make me feel good to know that my part isn't sitting flat.

Using a dial indicator, I found that the fixed jaw lifts up 0.002" when the vise was clamped with a part up on 1-1/8" parallels. If the fixed jaw is going to lift up under pressure, I'm not sure if any amount of hammering will get the workpiece seated flat. Is this normal? It doesn't seem like it to me, but I don't have prior experience with these things. Is my vise out of tolerance?

Thanks again for your help!

[One of Many]

Use a feeler gage and check if a gap of .002 or less is forming under the fixed jaw under clamping pressure. I wouldn't imagine it is arch deflection of the main body casting, but I have never verified it.

The fixed jaw is keyed and the bolts run up from under the vise to hold the fixed jaw down. I'd speculate if the key were high centering the jaw or the threads up in the jaw were not deep enough to fasten it down solid, it would rock. You could shorten the key or the bolts a tad if either were the issue.

DC

[Geof]

...Using a dial indicator, I found that the fixed jaw lifts up 0.002" when the vise was clamped...

That, to put it mildly, is a bit excessive.

Take the vise off and check that the big bolts holding the fixed jaw down are really tight.

I have dozens of Kurt vises and none of them move that much. Maybe up to half a thou when I pretend I am a gorilla hauling on the handle but 2 thou???

Come to think of it; take the fixed jaw off and make sure everything is nice and clean then reassemble it.

[PhoenixMetal]

I have dozens of Kurt vises and none of them move that much. Maybe up to half a thou when I pretend I am a gorilla hauling on the handle but 2 thou???

Thanks for the input - its good to know at least that my vise is not within tolerance. I have not yet had the opportunity to disassemble the fixed jaw to inspect it, however I did take it off and check that the bolts were good and tight. Using a 2 foot long breaker bar, I couldn't get it any tighter.

I'll call Kurt about it this coming week to see what they have to say about it, since the vise is brand new. If the solution involves re-grinding any of the mating surfaces (other than to shorten the key height), that's something that I wouldn't want to do myself because I don't think my equipment is capable of achieving the necessary precision tolerances needed to fully rely on the vise as a precision work surface - so I would be looking to Kurt to replace it if needed.

Thanks for your help!