Machining problem

[mike sr1]

I have a cosmetic problem with parts at the finishing point, I have tried different approaches, cutters 2 & 4 flute, light final cut etc.
anyone have any ideas on what might cause this? It is not as bad as the pics show it, but is cosmetically objectionable.

[ATTACH][/ATTACH]

The part size is only .3125 x 1" I just cropped the picture way back to show some detail.

[Steve Seebold]

What's the material? How fast are you running the spindle? How fast are you feeding?

When I first got my machine, I ran all cutters at 5,000 RPM and I couldn't get a decent finish to save my soul. Then one day I decided to call tech support to find out why it was doing that. I spoke with Greg and he told me it's just a harmonic in the spindle. Slow down to 4,500 and it should get better. It did, and now if I want a good finish, I run my finish pass at 4,000 RPM. It doesn't seem to matter how fast I feed, just the RPM. It seems that I can feed 8 IPM for every 1,000 RPM I run. But that depends on the size of the cutter too.

[mike sr1]

What's the material? How fast are you running the spindle? How fast are you feeding?

When I first got my machine, I ran all cutters at 5,000 RPM and I couldn't get a decent finish to save my soul. Then one day I decided to call tech support to find out why it was doing that. I spoke with Greg and he told me it's just a harmonic in the spindle. Slow down to 4,500 and it should get better. It did, and now if I want a good finish, I run my finish pass at 4,000 RPM. It doesn't seem to matter how fast I feed, just the RPM. It seems that I can feed 8 IPM for every 1,000 RPM I run. But that depends on the size of the cutter too.

Thanks Steve!

It is 6061 t6, I am running at 4500 now 20 ipm. That spot at the end of the cut can be polished out, it is noticeable to the naked eye though. I was just wondering what was causing it, the belt vibrates at 5000 so I back it off till that stops. I am going to look for a better belt, there was a suggestion on here a while back for another manufacturer that is better balanced belt.
I will try a slower travel and spindle speed for a finish cut and see what happens, I hadnt noticed the vibration in the finish till the photos.

thanks again..

[condor-machine]

I've seen this happen before. I asume your climb cutting (direction of mill cutter), as the tool comes in contact with the thicker (more material contact) part of the cut there is more tool pressure. The "mark" on the part is the cutter getting more tool pressure and hence picks up vibration and marks the part at that point. Does the mill have backlash on the axis the is perpendicular to the cut? Can you cut that cut before you have the step in it?

Don't know if this will help, good luck.

[mike sr1]

I just tried the arc in and out with a 600% radius, its better but still there. I would like it to finish the cut on a corner, but I havent figured out how to get Sprutcam to do that.
I have ran the program twice and its still there. It is just cosmetic and I think I am too concerned about it.
On the Bridgeport I always tried to never stop in the middle of a cut if it was the finish one just for that reason.

This will give me something to work on next week ha!

[TXFred]

Mike,

Are you using a contouring operation to make that cut? If so, if it's a closed contour, there is a little circle, flag and arrow symbol at the start point of the cut. You can manipulate that by dragging it to a new location or clicking it to reverse the direction of the cut.

Like many things in Sprut, it's easy once you know how.

Frederic

[tbaker2500]

What size cutter are you using? HSS or Carbide?
The feature you're asking about- is this the line at the transition from the thin to the thick portion? Do both the thin and thick portions have the same surface, it's just a line at the transition?

[mike sr1]

Mike,

Are you using a contouring operation to make that cut? If so, if it's a closed contour, there is a little circle, flag and arrow symbol at the start point of the cut. You can manipulate that by dragging it to a new location or clicking it to reverse the direction of the cut.

Like many things in Sprut, it's easy once you know how.

Frederic

I am using "finishing waterline"
I will try "conturing" and see what it does, thanks Fred.

Sprut is getting easier but I am only at about the 10 percent level!!

[Steve Seebold]

When I want a good finish, I will do a spring pass. That's an extra pass that doesn't seem like it's doing anything, but it will remove any cutter deflection if there is any. Your SprutCam should have that option somewhere in the toolpath selection. I will also make my program so the cutter begins and ends off the part.

I use GibbsCam to program my machine and when I define the tool path it has 4 boxes for the following: line in, circle in, circle out, line out.

This lets me make a line to a circle in, and a circle out to a line out. If I elimilate the circle in and circle out, I can make the line as long as necessary to begin the cut off the part and end the cut off the part.

Another thing I will do is, if I want sharp corners with no burrs, I will round the corners and tell the program to round the corners and use the same radius as the cutter radius.

[mike sr1]

What size cutter are you using? HSS or Carbide?
The feature you're asking about- is this the line at the transition from the thin to the thick portion? Do both the thin and thick portions have the same surface, it's just a line at the transition?

.250 carbide and high speed 2 and 4 flute, doesnt seem to make much difference.
The side is continuous, its not the transition between the upper and lower portions of it, its at the start end of the cut.
I made the finish sllower 10 ipm instead of 20 and slowed down the spindle to 4000. This helped on the finish of the cut but the mark is still there.
I am thinking it probably is cutter flex and in my thinking the cut needs to be stopped on a corner so its not as noticeabe.

This is one of my "learning parts"

Thanks for your input.......

[tbaker2500]

A 1/4" bit still has a surprising amount of flex in it. One thing we do naturally when manually machining, is to ease into and out of a cut. A CNC don't do that. :-) Therefore you need to carefully ramp in, or lead in and out. It's more a matter of trial and error at first to find out what works well in your software.

[mike sr1]

A 1/4" bit still has a surprising amount of flex in it. One thing we do naturally when manually machining, is to ease into and out of a cut. A CNC don't do that. :-) Therefore you need to carefully ramp in, or lead in and out. It's more a matter of trial and error at first to find out what works well in your software.

Yes they do! On a manual machine I try to finish the cut up to a corner without stopping or changing the speed of travel.

I think I may have found where to change the lead in lead out point, its in setup, I just need to figure out what coordiantes I need to get it to start outside the part........
I will post what I find out later, as it may be a benefit to another rookie.....