Boss 5 Tool Cutter Compensation

[testertom]

Does anyone truly undewrstand how the Boss did cutter compensation. It doesn't appear one can write the program for the part and then tell what the cutter diameter is and let the machine alter the path. It appears one can program a path and then modify by a few thousandths and the path get changed. It doesn't appear there is really a cutter diameter stored but rather a cutter offset or diameter difference. Anyon e familiar?

[fredhh47]

I used cutter comp on my Boss 5 for many years. It takes a few tricks.
First, in order to use cutter comp successfully, you should write out every single G-code, and X, Y, and Z, I, J, and K entry that appears on every line, as if you were programming in incremental (another can of worms). Assume that no command or data is modal. If you move to an X and Y coordinate on one line, then change only the Y coordinate on the next line, you better reiterate the X coordinate anyway. Some post processors can be set up to do this sort of "verbose" output, some just do it by default. It WILL limit how much program you can stuff into your machine. (Remember only about 8k of actual program will fit. You CAN live without line numbers to save space).
Next, you should not make any rapid move while cutter comp is turned on. You should finish your compensated move, cancel C/C and then rapid. The Bridgeport manual says you can make one rapid move while compensation is turned on, but my advice is DON'T!
Third, you must make at least one, preferrably two NON-COMPENSATED moves before you ever touch where you want to be cutting. The non-comp moves should be AT LEAST as long as the amount of compensation you are using. I find that a cutter diameter's distance or more is good. The last non-comp move should be at as close to a right angle to the direction of your first compensated cut as possible. Here's what I do. Say you're going to start a compensated linear move at X0, Y0, going left to right, with a 1/2" cutter. I would position at about X-1. Y1, rapid down to the clearance plane, feed to my Z depth, TURN ON C/C (G41 for left comp, G42 for Right comp. For a climb cut, G41 is what you want). and make a move to X-.5, Y1., followed by a move to X-.5 Y0. Please be aware that the actual motion will be affected by the amount that you have put into the DIA parameter in your tool setting. It will NOT affect the first move, but WILL affect the second move. This is why I use two preparatory moves before beginning to cut the part. Yes, you can make less than right angle moves if necessary to avoid something you don't want to cut. Also, your first move may be a negative move away from the part. AS LONG AS YOU MAKE TWO MOVES. When you are setting your tool length offset, there is the opportunity to enter a diameter. If you enter a positive number, the compensation will be "away" from the part. You are telling the machine control that the cutter is larger than what you programmed. If you enter a negative number, it will behave as if the cutter is smaller. Don't put in the actual diameter. If you have a "one-half inch" cutter that has been reground to .460, then you would enter -.040 Actually, the decimal point is not entered, so it would look like -040 in the diameter setting for that tool. If you want to use a 13mm cutter instead of your programmed 1/2" cutter, the entry should be 012 (the difference between .500 and .5118, rounded to the nearest thou.) Be sure to make a move away from the part before cancelling cutter comp. It should be at least as much as the amount of compensation, more is better. This will prevent the control from cancelling the cutter comp too soon and gouging the part. I have seen it happen! It is a good idea to engage or cancel cutter comp on a separate line than on the same line as a linear move. Get to your start or end point, then program the comp command.
Last, be careful of "co-linear" moves. This is something that happens when you don't pay attention to how you are defining your cutter path. It involves a series of more than two moves along a line, for instance:
Start at X1.0 Y0.
move to X2.0 Y0.
move to X2.375 Y0
move to X3.2 Y0.
As you can see, these three moves define a straight line. The first move is legal, the second is legal, the third is NOT. There must be some change in the direction in order for the controller to look ahead for the purpose of maintaining the cutter comp. If you absolutely MUST program these moves, edit one of the intermediate moves so that the Y changes. Remember, you can "move" up to .0004 without affecting the actual position of the machine.
Last, one piece of advice, practice your cutter comp programming on something that is not important. Try machining a piece of plastic, wax, or wood first, to make sure you got it right. Cutter comp is tricky. I haven't used it in a while, so I may have said something wrong in the description. I have found over the long run that it is easier to modify a program in my computer and re-post it than to mess with cutter comp. The computer makes far fewer mistakes.
Good luck.