How much jaw lift is expected on a D675 Kurt Milling Vice?

[Junkmaster]

Hello All,

I've been a hobbist for a while and have always struggled to get a block squared up. I would get close and call it done and move on. Which really means I had to compensate later on the project to deal with the out of square stock.
I decided that I'm tired of that routine and wanted to be closer to getting it right. I watched a few You Tube video's about squaring up stock (Tom's Techniques was pretty good). I was practicing squaring up a block of aluminum. I wasn't getting things square. I could get things flat, but getting the sides square wasn't happening.

I checked the spindle was trammed
I checked the vice was trammed to the table
I checked the ways of the vice were parallel to the travel of the table.

I put a 1-2-3 block on parallels in the vice but did not clamp it down. Put the indicator on the spindle and ran the tip around edge on top of the block by moving the table.
Found one of my cheap parallels is taller than the other by 0.0003. I got what I paid for ;^) Switched to some nice adjustable parallels adjusted then measured with a micrometer.
Did the 1-2-3 block trick again and found everything was in the same plane +/- 0.00025, this is way better than I expected.

Then I put the dial indicator on the end of the 1-2-3 block near the movable jaw and clamped down. The jaw lifted up about 0.0015. If I went ape, could make it rise a bit more.

Is 1.5 thou expected? If so, how do you compensate? If not, any guidance on how to tune up a Kurt vice?

Evan R.

 

[JimDawson]

The short answer is Dead Blow Hammer. Drive the part down onto the parallels.

I tend to be a little heavy handed so one thing I did was to replace the 1/2 inch cap screws in the fixed jaw with 5/8 cap screws, and torqued them to almost yield. (about all I could pull on a 30 inch breaker bar, 250-300 ftlb?) That pretty much held the the fixed jaw in position.

Check the adjustment on the lock down ball on the movable jaw. This is accessed via the screw hole in the back of the movable jaw. It should be tightened pretty tight, but not hinder smooth operation of the movable jaw.

If I need to get pretty accurate, I place a strip of paper at each corner between the work and the parallel, then smack the high side with a dead blow hammer until all four corners are seated.

 

[dsh1001]

One thing to remember is that the kurt vises have a ball mount behind the movable jaw. this is designed to pull the stock (material to be machined) down against the parallels but it will only work if your stock is deep enough into the vise. Always use the shortest parallels you can get away with to keep the pivot point of that ball above the center of your stock . This will put more stock in contact with the vise jaws and help to pull it down onto the parallels. If your stock is above the pivot point created by the ball then your stock will be pushed up instead of down. A dead blow helps too. You don't need to pound the material like you are driving nails. In most cases a single solid whack will seat it just fine. Once you have smacked it with the dead blow do not tighten the vise any further or it will lift the stock again.

When you are squaring a block it is even more important to put the stock on the shortest parallels you can. In a lot of cases, you can use the bottom of the vise as your solid base instead of using parallels at all. It also helps to use a round pin n the movable jaw when squaring up the first side of a peice of stock. I am guessing there must be a youtube video that shows this technique. On the first side that you square up, you only use one parallel and the round pin. The single parallel goes against the solid jaw. If you don't find the info on youtube, let me know and I will post a few pages from an old textbook that explain the technique in finer detail.

 

[larry2c]

One thing to consider is, if your initial block is rough (sawed or other uneven surface) you can put a piece of thick cardboard between your block and the movable jaw to help distribute the load across the whole block. This helps with a little bit of roughness & out of square condition, but not great amount.

 

[Junkmaster]

Thanks for the point about keeping the stock as low as possible. I suspect that is my issue. I will try again tonight with the short parallels

I've been using a piece of 10 gauge copper wire between the movable jaw and the material. I use the wire until the surface facing the movable jaw has been finished (i.e. parallel to the surface facing the fixed jaw)

Tom Griffin, has posted a Youtube video: http://www.youtube.com/watch?v=igfqYZPdQ78
I thought this was a good video.

He also posted it somewhere in this forum but I've lost the link.

Evan R.

 

[Bruce_Mowbray]

A few things you can check on Kurt vises, especially if you're not the first owner.

Make sure there are no chips or any dings or burrs on your vice jaws or on the fixed and movable sub jaws (the ones that hold the actual jaws.

Make sure the bolts that hold the rear base jaw are tight. You might want to remove this rear base jaw to make sure there are no chips or burrs around the bolt holes and that the slot for the key is not burred up or has any raised areas around it to prevent the base jaw from sitting down tight.

Make sure the holes around the actual jaws are not bulged out around the face of the holes that are against the base jaws. This often happens from over - over tightening.

Make sure the way surfaces that the movable jaw slides on is clean. I take my vises apart now and then just to clean things up. It's amazing how much gunk and crud gets where it doesn't belong.

Bruce
Springville, PA

 

[Ebel440]

I find most people over tighten the vise when they are not used to them. You should also clean and grease the ball inside. You may want to use a torque wrench to tighten the vise to get repeatable clamping. You may also need to adjust the screw that holds the movable jaw down

 

[Junkmaster]

Thanks for all the input. I am using all of it. I am getting very close to being square. Well within my acceptable range.

To prove to myself it wasn't just luck I made 6 rectangle chunks 1.5 by 1.5 by 3.0 inches.
All of them were better than did in the past. I am pleased with the results.

There were a small number test blocks that were sacrificed, before I started getting acceptable results.

Evan R.