Newbie problem

[donframbac@aol.com]

I'm sure that I'm doing something wrong. Can someone please tell me what. The following part file (using a 1/8" bit) cuts two horizontal lines. Unfortunately, the left of the top line is offset 1/8" from the bottom line. The right sides line up correctly.

statements are as follows:

Z2
MZ .25
MX 2
MZ -.25
MX 3
MZ .25
MY .125
MX 2
MZ -.25
MX 3
MZ .25


'end of statements

[bill.young]

Don,

You've got me stumped; these commands should first cut a 1" long by 1/8" wide horizontal line from x=2,y=0 to x=3,y=0. Then it should move in the y-axis an 1/8" and cut another line right above the first, making a 1" long by 1/4" wide by 1/4" deep groove.

Here are the same commands with comments added that tell what I think they OUGHT to do.


Z2 ' set x=0 and y=0
MZ .25 ' raise the z-axis to 1/4"
MX 2 ' move to x=2; y is still 0
MZ -.25 ' lower the z-axis to -1/4"
MX 3 ' move to x=3; y is still 0
MZ .25 ' lift the z-axis to +1/4"
MY .125 ' x is still 3; move y to .125
MX 2 ' move to x=2; y is now .125
MZ -.25 ' lower z to -1/4"
MX 3 ' move to x=3; y is still .125
MZ .25 ' lift z-axis to + 1/4"

Are you sure that there aren't some typing errors in your original part file? Have you tried typing in these commands from the keyboard? Does it do the same thing?

Bill

[Gerald D]

Mechanical backlash (freeplay) may be a cause. Things like loose grubscrews in the gears, router loose in mount, etc. can cause errors at a point when it is approached from different directions, or under different loads.

It might be interesting to know:
a. Model & age of your machine.
b. Can you feel backlash when you push/pull the router by hand, with motors switched on.
c. From which direction did the tool approach the first point.
d. Which line is the correct length.
e. Ever experience similar problems with any other files/cuts?

[bill.young]

Don,

Gerald has some very good thoughts. I thought your posting was saying that the two lines were not parallel; that the second cut was at an angle with the left ends an 1/8" further apart than the right ends. If however the lines are parallel but the lengths are different, with the left ends not lining up in the x-direction, then I'll bet that Gerald's on the right track.

Since you zero the x and the y with the Z2 command in the beginning of the file, the move to the start of the first cut is from left to right; x=0 to x=2. The move to the start of the second cut however is from right to left; x=3 to x=2. If you've got backlash or play somewhere in your tool then this is definately one place that it may show up.

Follow Gerald's suggestions and check over the tool thoroughly by hand with the motors turned on. Pay special attention to the pinion gears; if their setscrews are not tightened all the way they can rock a little on the flat spots of the shaft.

Bill

[donframbach]

Thanks for your comments. There appears to be no problems with backlash, etc because.
1) I can cut real nice circles
2) The problem only occurs at the beginning of part files.

Here is a part file that isolates the problem better:

MZ .25
MX 2
MZ -.25
MX 1.875
MZ .25

The cutter goes down and does NOT move left.

But when I enter:

MZ .25
MX 4 'or any other value to the right of 2
MX 2
MZ -.25
MX 1.875
MZ .25

The cutter goes down and moves left appropriately.

Would someone else please check this on their machine?

Thanks

Don Frambach

I have a brand new PRT-32.

[bill.young]

Don,

I've got a PR96 with the original belt-drive thrust boxes (software version 220) so I'm not sure my test will be all that much help to you, but your file works like it's supposed to for me. Are you using the newest verion of the software for the PRT, 221?

Just out of curiosity, how about trying the same file with the M2 command instead of MX; does it still do the same thing?

MZ .25
M2 2,0
MZ -.25
M2 1.875,0
MZ .25

Good luck,
Bill

[donframbach]

Bill,

I feel like a real dummy. It was backlash. Tightened set-screws on pinion gears on both X-motors and problem solved!

I'm a little concerned about these set-screws because I really tightened them down on both X and Y axis when I discovered backlash on the Y axis just after setting the machine up (due to the same problem!) Machine was working fine, making circles, etc until yesterday. Do you use more than just the Allen wrench to tighten the set screws?

Thanks for all your help.

Don

[jkforney]

Don
I just set up my new prt96 and the manual said that the set screws had a micro encapsulated lock tite on them and would be difficult to change after inital setting. I know on my old machine that I had to put lock tite on the set screws and really make sure they were tight. Maybe they forgot the lock tite. Or if the locktite was there and the set screws were not set properly, they may need to be completely removed and then reseated.
Hope that makes sense.

John Forney

[donframbach]

John,

Thanks John. That makes a whole lot of sense. Can I buy "lock tite" somewhere?


Don

[bill.young]

Don,

You should be able to get it at any auto parts store. It comes in a small squeeze bottle; buy the smallest one you can because you only use a drop at a time. Just back out the setscrew, put a drop of loc-tite on the threads, then tighten the setscrew back up.

Loc-tite is available in at least two formulations. The regular is all I ever use, but they make a permanent version that is supposed to be almost impossible to remove without heat, etc. My suggestion would be to use the regular stuff; I think it will be more than strong enough for what you want to do.

Bill

[donframbach]

Thanks Bill

[gdorrington@iafrica.com]

I am a little bushed after arriving back from Germany this morning, and glad to see that the problem was found.

The trick for tightening setscrews onto a shaft flat, is to make sure that the screw centerline is perfectly perpendicular to the flat. In practice this means that you first tighten the screw gently against the flat and then feel if you can "rock" the gear to a loose position. Tighten a little more and again feel for a loose spot. Final tighten only when you are sure that the setscrew is in the middle of the flat.