cutter veering off circle

[bob_reda]

Just started doing this the past couple times. When cutting a circle, say 3/4" material. When the bit is getting toward max depth it suddenly veers off the circle and starts cutting into the material. I thought maybe I needed a new end mill, changed it out and it worked ok, then today did it again. I notice especially when cutting corian. Any ideas?

Bob

[Kyle Stapleton]

Need more info.

[robtown]

Need more info.
Agreed...
not sure how much “off circle” we’re talking here.

[bob_reda]

using a 1/4" em, either up or downcut, cuts straight across the wood. Like it catches a corner and goes haywire. Going 180ipm

Bob

[Brady Watson]

What happens if you run it at 90 IPM?

Use a piece of scrap. Extra points for pics or video...

Guessing this is a Standard and not Alpha.

-B

[bob_reda]

This is a prt with the RBK contol box and new motors. I will slow it down and hope that is it.

[Kyle Stapleton]

A downcut in corian is a bad idea, you should be using a "o" flute.

[robtown]

using a 1/4" em, either up or downcut, cuts straight across the wood. Like it catches a corner and goes haywire. Going 180ipm

Bob
the two descriptions you’ve provided are incongruent...
do you have a picture you can share?

[bob_reda]

I'll try and draw something to make it less confusing

[bob_reda]

http://www.talkshopbot.com/forum/attachment.php?attachmentid=31008&stc=1 Hope its understandable. It happened in both corian and in wood

Bob

[Brady Watson]

Hook yourself up with this: Windows Image Resizer Powertoy (http://www.bricelam.net/ImageResizer/), then right click on pics you want to post, choose 'Resize Pictures' and pick medium or large. THEN post your resized pic(s). The problem is the pic you attached is illegible and it is most likely because it was very large on disk when you uploaded it...Resized pics will appear larger than what you posted. I can't read a thing you wrote in VCP.

The problem with your machine is that you're probably machining too quickly with not enough RPM. When cutting a circle, there are a number of direction changes going on between the X & Y axes. Combined with a ramped step down, you could be right at the point where the machine needs more torque to follow through on the projected path, than is available.

Stepper motors are rated at holding torque. They have their most torque at 0 RPM. The faster you go, the less torque they have. The motors you have on your machine start to really fall off in the torque department at 3 IPS/180IPM. You need to account for this when cutting dense materials. Pull the move speed down, increase RPM & reduce step down/pass depth until you've lightened the cut enough not to lose position.

When cutting new or questionable materials, start slow. Set MS to 60 IPM and feather the speed up gradually. Look, listen and figure out where the machine is happiest. Corian isn't going to cut cleanly at high speeds on a Standard machine. You'll run out of RPM for proper chipload if using a single flute Spiral-O beyond 90 IPM. You say the issue also happens in 'wood' - not very specific...Solid maple has to be machined somewhere in the 60-120 range and softer woods can go faster if you have the RPM for a clean cut.

-B

[robtown]

Hook yourself up with this: Windows Image Resizer Powertoy (http://www.bricelam.net/ImageResizer/), then right click on pics you want to post, choose 'Resize Pictures' and pick medium or large. THEN post your resized pic(s). The problem is the pic you attached is illegible and it is most likely because it was very large on disk when you uploaded it...Resized pics will appear larger than what you posted. I can't read a thing you wrote in VCP.

The problem with your machine is that you're probably machining too quickly with not enough RPM. When cutting a circle, there are a number of direction changes going on between the X & Y axes. Combined with a ramped step down, you could be right at the point where the machine needs more torque to follow through on the projected path, than is available.

Stepper motors are rated at holding torque. They have their most torque at 0 RPM. The faster you go, the less torque they have. The motors you have on your machine start to really fall off in the torque department at 3 IPS/180IPM. You need to account for this when cutting dense materials. Pull the move speed down, increase RPM & reduce step down/pass depth until you've lightened the cut enough not to lose position.

When cutting new or questionable materials, start slow. Set MS to 60 IPM and feather the speed up gradually. Look, listen and figure out where the machine is happiest. Corian isn't going to cut cleanly at high speeds on a Standard machine. You'll run out of RPM for proper chipload if using a single flute Spiral-O beyond 90 IPM. You say the issue also happens in 'wood' - not very specific...Solid maple has to be machined somewhere in the 60-120 range and softer woods can go faster if you have the RPM for a clean cut.

-B
i have an older PRT with a 4g controller. I never cut anything but foam at 3ips.

[bob_reda]

Thank you everyone. I just thought that with the RBK control box, the newest motors, the hardened rails and the retro z I could push it a little faster, guess not.

Bob