Newbie- What is causing this?

[Dstoddart]

Each time I run this file (and others) the bit deflects (if that is the correct word?) on the first pass of a profile cut. It only appears to happen at the beginning of the cut. I have moved the starting point and that does not clear up the problem. In the attached photo, I am cutting 1/2" mdf, 80 ips, 14000 rpms, climb cut. Thoughts?

[Daniel233]

Have you tried slowing it down to say 40 inches per minute, you might by pushing to hard for the rigidity of the machine.

[dertsap]

are you plunging in , the tool could be wandering upon the plunge and straightens itself out as to tool moves along

[fizzissist]

This is essentially slotting, and a cutter is climb on one side, conventional on the other side of the cut, so it's normal to see some deflection.

Milling a keyway in one pass in bar stock and looking at the end of the bar will reveal that the walls are skewed, and not parallel to the axis of the spindle.
In regular machining you'd come in with a tool slightly smaller, then take kiss cuts on the walls to square them up.

[slowlearner]

Try a carbide tool.

[louieatienza]

Is your bit bottom-cutting? If not, you may have to ramp in...

[Dstoddart]

I ran the file again, this time with a 1/8" carbide downshear bit, 35 ips. It did the same thing in the exact same places. It does not do this on each profile cut in the file--only a few and it is always in the same place, and on the first pass only. The other profile cuts are perfect. I will run the file again and ramp in.

Thanks for the replys!

[louieatienza]

Originally Posted by Dstoddart I ran the file again, this time with a 1/8" carbide downshear bit, 35 ips. It did the same thing in the exact same places. It does not do this on each profile cut in the file--only a few and it is always in the same place, and on the first pass only. The other profile cuts are perfect. I will run the file again and ramp in. Thanks for the replys!

Weird... though like an M&M, the MDF is harder on the outside and softer in the middle. If you can control the ramp-in speed I'd try to decrease it somewhat (maybe 25-50%), keeping your normal feeds. You might also try to do a radiused lead-in and lead-out into the profile, maybe that will help...

[Daniel233]

Is it happening on the outside edges of your table, if so it could be racking in the gantry which would go away as you get closer to the center of the table.

[kiwibrick]

Originally Posted by Dstoddart I ran the file again, this time with a 1/8" carbide downshear bit, 35 ips. It did the same thing in the exact same places. It does not do this on each profile cut in the file--only a few and it is always in the same place, and on the first pass only. The other profile cuts are perfect. I will run the file again and ramp in. Thanks for the replys!

Maybe it is a defect in your tool path in the file since it is doing it in the same place with different feeds and speeds and bits, check the tool path on screen (if you can) to see if it is the same as whats cut.

[Dstoddart]

It is not happening on the outside edges of the table. I ran it again, this time changing the starting point to the x axis. It fixed all but one, where it just moved the deflection area to the new starting point. (At least it's consistent...) I have looked at the G code on the screen and did not see any variation in the coordinates on the start of each pass. We also made sure the table is level/square--it is. I will try a radiused lead-in. I am stumped.