Ski ramps on rectangles

[daski]

I've been part wizard to draw the squares, then cut them on the BOT. Some of the rectangles have little ski jumps in the corner where the cut begins. Any one ever have this issue?

[jhicks]

Dave, do you have a "ramp" command checked?

[daski]

Where would I find this command?

[Brady Watson]

Ramping the cutter in the XZ or YZ plane is disabled in PartWizard. This feature is only available in Insignia, ArtCAM Pro & VCarve Pro.

It would be most helpful if you posted a picture showing the problem. Also, tell us what bit you are using (size, up or dn spiral, straight etc) and what speed & RPM you were cutting. The most important question is, how was the material being held down while you were cutting?

-B

[richards]

You might have "Add Lead In / Out Moves" checked in PartWizard. You'll find that checkbox in Toolpaths, Profiling just under the cut direction Radio Button.

[daski]

Brady,we are using 1/4" compression bit, 10 000RPM at 2"/sec on 3/4 melamine. We have an old version of Part wizard (ver 1) so no real options to turn on/off. we cut the melamine in two passes at 3/8" per pass. It's held down with two fiens. I even have it happen on the first cut, and with that much hold down the sheet is not moving. it's always located in the corner where the cut starts. we are using a conventional cut, so if the bit was defecting it would be into the piece, but our ski ramp is out of the piece. I thought about lash in the machine, but given the cut direction it seems to eliminate that. i'd like to send you a copy of the toolpath and you could try it on your machine.

[weslambe]

Hey Dave,

Since you are cutting this part out in two passes, cut the first pass of the path then stop the machine. Cut it again. If this got rid of the ramp then it's all machine flex. Is your machine a PRT by chance? My old prt flexed enough to make me have to cut a the vbit path twice every time on door jobs.

[Brady Watson]

Dave,
It sounds to me like it might be a mechanical problem. Check to make sure that ALL of the v-roller bearings are correctly contacting all of the rails. Also make sure the the horizonal ones that ride on the lower rails of the X car are centered with the rail. If not, shim & tighten them. It is possible that the Y car is lifting in the corners due to a change in direction or there is enough slop in the bearing adjustment to allow it to move. Be sure to check the Z axis t-rail bearing adjustments too. Grab your router and try to move it in all directions.

-B

[daski]

BIT DEFLECTION!!!!

well after some experimenting I have found that my problem is bit deflection. As the bit gets to the end of the cut it starts cutiing into an area that has already been cut and so the bit starts to relax and causes the ski jump. I'll post pictures soon. I tried starting the cut along an edge of the rectangle and got the same result. Anywhere that the bit cut that had been preiously cut, an adjacent rectangle, there was no defection and the cutout was perfect.

The defelction is only 20 thou but it shows up. Any ideas on how to solve this.

[harryball]

As Brady suggested, make sure all the vrollers are fully engaged.

Also, some general tips...
Slow down the rate of cut
Make the cut in multiple passes
Make a larger cut than the part then come back with a clean up pass
Change the direction of your cutting (climb to conventional or vice versa)
Place your parts so you leave waste around them all
Use a larger bit

Robert