@Aukai - Thanks. I read about fly cutters last night. That may make sense for me.
@erikmannie - Thanks. I hadn't though about being limited to my drill bit sizes which currently only go up to 1/2" for steel.
@Aaron_W,
@davidpbest,
@Jim F - Thanks. So the weight hanging off the front of the bed causes torque. Does that just result in wear, or also inaccuracy? I had no idea there were standards for the vices. (Don't most people with a lot of vices have no standards?
) I do see a few used Kurt 4" vices on Craigslist. They look a bit rough. I assume they can get worn out and damaged, and buying used would be a gamble? Dang, why are my lottery tickets always worthless.
The major issue you will encounter with a larger vise, is even on the furthest out set of T slots it will hang over the inside of the table reducing your Y travel. A 6" Kurt DX6 vise is 16" long, and the location of the hold down bolts to the front end is 6". It is also 7.4" wide.
Your T slots are probably located about 1-1/4" in from the edge so even using the outermost T slot that vise will extend at least 1" off the inside edge of the table limiting your ability to work in close to the column. Since the vise is also wider than your table you will be unable to mount it sideways (lengthwise with the table). Older Kurt vises and other brands may have the mounting point even further back making the inside overhang even more of an issue.
A 4" Kurt DX4 vise is 12-1/2" long and has its mounting point 4.4" from the front end, so mounted in the middle slot it will have the same, or possibly less overhang off the inside and mounted in the furthest slot there will be no overhang so you can work with the table right up against the column using the full range of the mills Y travel. The DX4 is only 4.9" wide so you can also secure it sideways if you need to. The DX4 can still hold a part 6-1/2" long using the jaws on the inside position and up to 12.4" in the outside position, so it is not a tiny vise.
There is also a height factor, the 6" vise is a bit over 4-1/4" tall, the 4" vise a bit under 3-3/8", the 728 has 16" of vertical travel, so not a huge issue on that mill, but if you need 3/4" more room under the spindle to fit your work piece and associated tooling it can make a difference.
I'm using the Kurt DX series because there is good dimensional data for it online.
On the Kurt DX4 I'll also note that it can hold a much larger part than most of the cheaper 4" vises. The Kurt DX4 opens up to 6-1/2" vs only 4-4-1/2" on most cheaper vises so you are getting more than just higher quality manufacturing for Kurt's prices.
A 5" vise may be a practical option for you, but I'd want good dimensional data for the exact vise before I bought it, just to make sure it will fit comfortably. Kurt does not currently offer 5" vises, but there are some quality 5" vises out there.
www.kurtworkholding.com
