a couple G76 questions

[hackmeister]

Whenever I use a G76 I always need to rerun it after the 1st time in order to adjust the offset and get the right pitch diameter. The offset change could be anywhere from about -.007 up to -.025 depending on how big the thread is. What do you do so that the numbers in the G76 will put the correct pitch diameter on the part the first time?
Lets say I need to cut a 1"- 8 UNC thread 2 inches long. What would the G76 lines look like?

G00 X? Z.400(start position)
G76 P020030
G76 X? Z-2.1 U F.125
I may have forgotten something in the lines, but you get the idea, right?

When turning an ACME thread what angle do you plunge it at, 0 or 29deg?
I was just turning some acme threads yesterday. The part I was making needed a left hand thread on one end and a right hand on the other end. I used the same tool to cut both ends.I cut one end , moved the tool over, cut the other end, and then parted off. The insert was a ER10ACME . The right hand thread looked fine , but the left had a burr. I thought that the insert would remove that burr. I cut them plunging at 0 deg.
Any thoughts?
Thanks so much, Hacky

[Geof]

Can't answer your G76 question because I use G92.

Second question answer is that you need to use left and right inserts. I have found that acme is less forgiving than unified thread form; the 60 degree angle on unified gives more clearance to the cutting edge so you can run the insert either way but the acme 29 degrees does not allow this without rubbing in the wrong direction for the insert.

[CNCRim]

Good question y you keep offset - cause the threading tool has cosine error. Normal threading tool is 60deg and which mean 30deg/per side, look in machinist handbook and you see how the thread gage is, on the machine when you are move down .001/tan30 ........ it's not complete .001. Second question the bur on the part is cause be wrong hand threading, you need right hand tool for right hand threading, left for left. Otherwise the trick for used right hand tool for lefthand threading is start point opposite the right hand.

[lyfordln]

Look in the machinist handbook and program the minor dia..Run the part, measure with pitch diameter micrometer or thread wires and change your minor dia. so the next time you setup. it will cut correctly. The problem is that the tip of the insert has different radii depending on brand and style. There is no way to be exact with out using some way of setting the angle instead of the tip. However, it takes very little time to re-run the part after changing the minor diameter in the program.