Poor Chip Clearance in Slots

[verhoevc]

Hey y'all! I'm finding that I'm getting pretty poor chip clearance when running profile paths that are more than 1x DOC that are essentially slots. For example cutting out the body shape of a guitar from a big square wood blank. Even with upcut bits (1/4" going 1.5IPM, 12k, .17" DOC). The first path seems to work fine, but then subsequent passes leave more and more until I see things like:
- bit deflecting and gauging the edge
- lost steps from the bit binding
- bad noise from the bit
The machine is obviously struggling and therefore I have to stop and until I figure this out I'll have to not do these operations.
Thoughts? Should I slow the feed each step down? Should I do two profiles making a wider slot each pass? (Both of those require a lot more paths and programming...) Am I just going too fast overall for slots up to 1" deep after all the passes are finished?
Thanks,
Chris

[Gary Campbell]

Chris....
Try a 3/8 compression with a 1 1/8" LOC and try multiple feeds to see which ejects chips better. You may also need to use an air blower to remove chips from the slot

[paul_z]

You might try a single flute bit.

Paul Z

[Burkhardt]

When cutting such deep slots I tend to get similar clogging. Things that help as mentioned in the previous posts
- single o-flute or at least a steep flute helix angle
- a directed air jet (I have such a nozzle now as a permanent fixture next to the spindle)]
- strong dust collection air flow to prevent flying chips from settling somewhere else in the groove
- making a wider slot than the bit
- less depth of cut per pass (if you can afford the time) makes it easier for the bit to clear the produced chips

[bobmoore]

I would use a 3/8 bit with .015-.020 offset for the cut outs so that chatter doesn't reach into the finished part. Follow up with a full depth of cut in a single pass to clean up to the vectors (climb or conventional doesn't seem to matter. Make sure to blow all the chips out of the kerf before that final cut to eliminate deflection.
Bob

[verhoevc]

Thanks guys. I have a single O that I'll give it a try with. I'll admit my dust collection likely leaves a bit to be desired. The CNC is in the house as I didn't fancy leaving it out in the non-humidity/AC controlled barn shop... where all the real dust collection is. So right now it runs on a shop vac. Looks like I should look into an air jet.
As of right now I always do a .020" offset and then finish up with a full depth pass for cleanliness. I just usually don't get that far before running into clogging issues haha.
Thanks, time to experiment!
Chris

[verhoevc]

Burkhardt do you know of an easy way in VCarve to do a slot wider than the bit? The only way I could think of is to:
- make a path with a large offset to the first DOC
- repeat that path without the offset
- repeat both paths to second DOC
- repeat both as needed for total depth
- finish with onion-skin full depth pass
This seems like a LOT of paths. So if there's some secret I don't know about I'd love to hear it.
Chris

[verhoevc]

OMG that single flute Super O bit test I just did is like night and day! I did three 0.75" deep slots:
Top: 1/4" 2 flute upcut at 1.5ips 12k
Middle: 1/4" 2 flute upcut at 1ips 12k
Bottom: 1/4" upcut super O at 1.33ips 12k

http://i95.photobucket.com/albums/l139/verhoevc/CAD/66625A84-2992-482D-99A7-D4BF5CA444D8_zpsb81fzwph.jpg (http://s95.photobucket.com/user/verhoevc/media/CAD/66625A84-2992-482D-99A7-D4BF5CA444D8_zpsb81fzwph.jpg.html)
http://i95.photobucket.com/albums/l139/verhoevc/CAD/9778025C-C94C-4C77-9E16-659DAE97EA17_zpsbqgrflvi.jpg (http://s95.photobucket.com/user/verhoevc/media/CAD/9778025C-C94C-4C77-9E16-659DAE97EA17_zpsbqgrflvi.jpg.html)

Here's what I noticed:
1- the super O had more "chip" looking results while the 2 flute bit had thinner shaving type chips
2- the super O had much better chip evacuation
3- when the super O path ran I was surprised by how quiet it was! I was used to the other bits having this sharp high pitch noise as they ran through material and there was none of that with the super O!
4- Look that the surface quality that the super O left!!! It's gorgeous! The other two slots have little "hairs" hanging off the sides.
Chris

[Kyle Stapleton]

You are cutting too slow with the 2 flute bits.
With your feeds and speeds almost the same for the 1 and 2 flute bit, that means your chip load is double for the o flute.
That is why it sounds better, cutting slow does not mean you are getting a better cut.

[verhoevc]

I used to run them faster Kyle, but ran into the problems I discussed in this thread: http://www.talkshopbot.com/forum/showthread.php?23276-Drifting-Skipping-Axis
It seems when I ran them at the speeds that I should have to get good chiploads I encountered other problems.
Chris

[Kyle Stapleton]

Oh ya, I remember now running a desktop with bad bearings.
Have you tried push it after you got it fixed?

[verhoevc]

Luckily, most of the CNC-centric stuff on my current set of builds got done, so I haven't had much to throw on there and try and push it. Once I knock out all this stupid sanding work I have to do I'll hopefully find more time to get back to it and mess around.
Chris

[verhoevc]

Alright, so new tests running 2-flute bits faster. Not apples-to-apples since I snapped my only up-cut straight bit at the very start of this test (don't ask). So this was a down-cut 2-flute that came in the Desktop Starter package. However, seeing as it's downcut that explains why the chips in this .75" slot, even on the faster runs with better chipload, aren't very large... they got re-churned up on subsequent passes. That said, watching them come off they looked nicer in the faster passes.

http://i95.photobucket.com/albums/l139/verhoevc/CAD/47408268-FD7F-4814-8835-9C64E5516924_zpsdbeonyr1.jpg (http://s95.photobucket.com/user/verhoevc/media/CAD/47408268-FD7F-4814-8835-9C64E5516924_zpsdbeonyr1.jpg.html)
http://i95.photobucket.com/albums/l139/verhoevc/CAD/4E6A7785-F53B-4C86-AF16-CD31F03C2DC9_zpsfpw0fxsg.jpg (http://s95.photobucket.com/user/verhoevc/media/CAD/4E6A7785-F53B-4C86-AF16-CD31F03C2DC9_zpsfpw0fxsg.jpg.html)

Top: 2 ips (.005 chip)
Middle: 2.5ips (.00625 chip)
Bottom: 3ips (.0075 chip)

I wouldn't call any of the resulting channels as nice as the super O single flute... but you can definitely see a reduction in "hairs" in the channel as things went faster.
Chris