Instructions

The g89 command
G89 is intended for boring and uses a p value, where p specifies the number of seconds
to dwell at the end of the hole. The problem with dwelling at the bottom of a bored hole,
especially with a machine as light as a Sherline, is that tools have a tendency to chatter. I
usually don’t bore a hole to the exact bottom unless it is absolutely necessary. Remember
that in the Sherline general instructions, which I hope you have read, chatter is usually
cause by taking too heavy a cut, but it can also be caused by having a cut so light that the
tool skips around on the surface. Also consider the fact that chatter can damage the hole,
because as the chatter occurs at the bottom of the hole, the tool will usually remove
material from the sides and cause it to be oversize.
1. Move the z-axis only at the current feed rate to the z position
2. Dwell for given number of seconds p1 (1 second)
3. Retract the z-axis at the current feed rate to clear z. This cycle is like G82
except that the tool is drawn back at feed rate rather than rapid.
Example:
%
g90 g40 g80 g00 z2
x0 y0
g89 x1 y1 z-0.50 r0.010 p0.5 f3
g00 g80 x0 y0
%
For boring more than one hole, add the needed x, y positions for each hole.
The L and the g91 command
NOTE: Although I recommend using lower case letters in your programs because I
believe it makes the code easier to read, the letter l is a special case because it is easily
mistaken for the number one; therefore, I use the upper case letter L. (You might also
want to consider this for the letter Q.)
It’s time to learn about drilling a series of holes without writing any unnecessary lines of
code. The L command will allow you to drill or bore many holes on either the x- or y-
axis with a single line of code, but it can be tricky to use at times. Unless this is
something your need to be doing I’d skip it for the time being.
The reason confusion can quickly develop is you have to be in g91 (incremental) in order
to implement this function and many things change. When you’re in g90 (absolute) the r
value is given as a point; however, in g91 you use the actual distance the r point is from
where you are located, and this will always be a negative number. The z programmed
distance in the canned cycle g-code is now given as the distance in incremental from the
r-point. This will also be a negative number and many times the number will be less of a
negative number than the r number as in the example below. Note that we are using the
g98 command in this series of examples.
(Note: The letter “L” is capitalized in the following example so it is not confused with a
number “1”.)
71