On my square column Lux style mill I replaced the screw adjustment system completely with a simple D section rod having plain collar sliding up and down it. A wing headed screw locked the collar onto the column once set. The machine already had a simple ruler scale with 1/8" and 1 mm graduations printed on the front face of the head.

Theoretically less accurate than the screw system but the implementation on my mill was so bad that any accuracy gain from the screw was swamped by general flippity-flopping about. If I really needed accuracy I used to measure the actual travel and lock the collar hard up aganst the stop. Good excuse to get one of the cheap vertical digital scales.

I have seen devices where the collar is in two parts with a screw device for fine adjustment. The collar has a number of preset positions on the rod, a dimple for the screw tip would probably work here, and the calibrated screw device covers the intervals. Perhaps 1/4" to 3/8" or 5 to 10 mm on the screwed part. Overcomplication for little benifit here in my view but it can work well.

Clive.

Perhaps you want something like this. Could use the existing threaded rod.

This one's for a Bridgeport but the principle is fairly obvious – spring loaded half nut. The BP has a sensitive feed trip arrangement requiring little force to trip so you'd need to either fit a beefier spring or lock it with a threaded element such as a wing nut for a machine like yours that requires a solid stop.

Clive's suggestion is similar – but without any teeth to grip, the (split?) clamp needs to be pretty strong. Depends how much force you think it needs to withstand.

PS – seems I was telling porcupines. In fact this Grizzly accessory seems to be for a Sieg(?) 6"x21"  mill, so perhaps more beefy than I gave it credit for.

Edited By Muzzer on 16/03/2016 19:16:34

A bit too late now, but was going to suggest a 1/2" or 12mm round with a short thread on the lower end, for fixing, and a moveable stop. But you've just done that with the M8 studding!

Howard