Vise size for 728-VT

[andrewgr]

How big is too big? How much of the vise can reasonably hang over the front edge of the mill bed? A 6" vise is so heavy, my intuition tells me that the weight of the overhang would twist the milling bed over time-- but I'm a complete novice, so I don't trust my intuition at all.

I purchased a used 6" Kurt vise, but I'm afraid to put it on-- the mill bed is 7" deep, whilst the vise is 17" deep! I've got a 4" vise, and it looks more appropriately sized (it's only 9" deep), but it's also pretty limiting-- I've done very little with my mill so far, but I've already run into multiple situations where I'd really, really like those extra 2".

Any advise would be appreciated.

 

[wrmiller]

No offense intended, but if you think you need a 6" vise, you may have bought too small of a mill. My mill table is 9x35, and I have a 5" Kurt on it that has 6" jaws. Works great for me, but I'm mostly into small(er) stuff like pistolsmithing and hobby stuff.

That 6" will eat into your Y axis range a bit too. Most guys like us with smaller mills run out of Y and Z axis travel quite a bit.

 

[mksj]

I often recommend looking at a CNC style which is more compact if you want a 6" on a smaller mill, so a bit more limited in the jaw opening (overhang is similar to a 5"). I do not see the front overhang is going to effect the mill bed, but it does obscure the Y axis dial if you do not use a DRO. Like Bill mentioned, the overhang in the rear is often a significant problem on smaller mills, and further limits the Y axis travel. I ran a 6" on my previous bench top mill (BF-30), note the mounting bolts for the vise, so it does overhang forward quite a bit. Having 6" Jaws makes a big difference in what you can hold, but it it has its tradeoffs. The BF-30 was around 700 lbs w/o the base, so a bit beefier than the 728, a full size 6" vise is a bit too big.

6" 660U CNC Milling Machine Vise 0.0004"

www.shars.com

 

[andrewgr]

No offense intended, but if you think you need a 6" vise, you may have bought too small of a mill. My mill table is 9x35, and I have a 5" Kurt on it that has 6" jaws. Works great for me, but I'm mostly into small(er) stuff like pistolsmithing and hobby stuff.

That 6" will eat into your Y axis range a bit too. Most guys like us with smaller mills run out of Y and Z axis travel quite a bit.

It's not that I need it, just that it would be convenient. (I bought the used vise off ebay because the seller didn't know what brand it was, but I was sure it was a Kurt, so I figured I could resell it at a profit if I couldn't use it.)

 

[SRay53TxTn]

Here a pic of my 728VT mill table with Shar's 440V 4" for size reference - so far has met all my project needs.

 

[yota]

I spoke to PM about this and they said to go with a 4" vise.

 

[addertooth]

I will share some pictures of what a 6 inch vice looks like on a PM-728.
One of the pictures is where the vice is using the T-slots closest to the operator. (second)
Another shot is where the vice is using the T-slot closest to the operator, and the other side is using the middle T-slot. (third)
There is also another shot of it where both sides are using the middle T-slot. (first)

The shot where both sides are using the middle T-Slot creates a 1 inch overhang towards the column.
Normally, I would REALLY hate that. However, the Digital Read Out for the X axis (when installed), will already make me sacrifice
1 inch of travel towards the column (Y axis travel). So that would bring up the rational question "am I really sacrificing an inch in this position?".

So another question would be, what else does a 6 inch vice cost me? Well, you tend to lose a bit of Z axis as well, because the vice is taller.

With the possible negative outcomes, then what is gained with a 6 inch vice? This is where there may be some disagreement. In the normal sense
you get more gripping surface (typically, but there are some WIDE 4/5 inch vices that are pretty good in this area). The other benefit is raw weight. You will see many people here discuss how "rigid" their bigger and heavier mills are. And to a large degree, what they say is true. But the factor
which ignored, is good old fashioned physics. A 60 pound ball bearing takes more force to make it move, than a 30 pound ball bearing. If you are trying to combat things like tool chatter, having more mass at the part you are working can help reduce it. (i.e. you have an aluminum part clamped securely in a 60 pound vice) I also realize that if you are a Mill pro-user, you are less likely to get feed and bit speed wrong, but many
who are buying their first Milling machine are still learning these things. (summary: novices have more problems with tool chatter.) This is why they tend to get better results with larger/stiffer/heavier machines. People more experienced with mills can get some rather phenomenal outcomes with lighter and more flexy mills.

A heavier vice can help a "little", with lighter machines. It is one of the two places where weight is good, with the second being the head. Although you may not like it in the Head, after cranking it up and down a few times.

 

[yota]

I went with a 4" Glacern. now I just need my back ordered mill LOL.

 

[petertha]

This question gets asked a lot. Here s another option to ponder. I have a 5" wide Bison (no longer made) which I love. I probably would have liked a 6" but the price was right & I'm happy. Anyways looks a lot like a GS vise.

SOWA - Homepage

Its very accurate, lends itself to any T-slot layout with side clamps in the rail. It can readily positioned at angles on the table without another rotary accessory. You gain quite a bit of precious headroom with this style of vise over a Kurt style. Nothing at all wrong with a Kurt but they are thicker.

Supposedly GS is a close copy/adaptation of the Italian Gerardi.

Standard Vises - Gerardi SPA

The most popular (and copied) vise in the world - The perfect mix: price, quality, versatility.

www.gerardispa.com

One downside is prismatic jaws don't lend themselves to the Kurt style (rectangular) jaw stops, but that is easily remedied with another solution.