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-   -   Screaming bit (http://www.camheads.org/showthread.php?t=9998)

Clayton.Lott 07-01-2019 07:46 PM

Screaming bit
 
Need some help for the new guy. Cutting 1/2 5x5 birch with 1/4 in upcut and it screams unbearably. I've tried rpm ranges of 10000 to 16000 and Ipm ranges of 50 to 150 with no changes. Also tried a second brand new bit. Throw some knowledge out there for me guys. Thanks

Jim Becker 07-01-2019 08:36 PM

Honestly...nature of the beast. Cuts like that require hearing protection.

Clayton.Lott 07-01-2019 09:18 PM

So this is something I should expect on all my cuts or is there something I'm doing to cause it? Such as bit size, material, etc

Ken Rychlik 07-01-2019 09:48 PM

Try bumping your cut speed up to 250 or 300. In my experience a screaming bit is under worked. Need slower spindle speed or faster travel speed. Another thing to watch for is chips. If your making dust, your going to slow. You need to make chips.

Compression bits are the worst for screaming. I still use a lot of straight bits just for this reason.

bmilam 07-01-2019 11:58 PM

Quote:

Originally Posted by Clayton.Lott (Post 81514)
So this is something I should expect on all my cuts or is there something I'm doing to cause it? Such as bit size, material, etc

Not necessarily. I really haven't pushed my machine and cut thru in one pass so mine makes little noise compared to dust collector. Other bits I'm sometimes wondering if the bit broke because they are so quiet. Every once in a while I get one that screams like you are talking about.

Xray 07-02-2019 01:17 AM

A screaming bit usually indicates a dull bit, and/or one with improper RPM's/feedrate for the job at hand. Could be that you are taking too much of a bite as well, try reducing cut depth if practical.

The real JP 07-02-2019 04:45 AM

Download a chipload calculator to help you get a starting point with speeds and feeds.

You want chips, not dust. try 13,000-300 you can bump the feed or rpm up or down with the keyboard.

I have the "us tools" app on my iphone. ( red square with chrome US )
It gets me close enough to get cutting.

Think of it like when you use a skillsaw. Go too slow and it burns and shrieks. Go too fast and it gives a splintery cut. Same deal with the router, you'll get used to the sound of it when it is cutting good. Any change will draw your attention.

guitarwes 07-02-2019 09:58 AM

50-150 ipm is WAY too slow for those rpms (10k-16k). Try 12000rpm at 240-300ipm full depth pass. A screaming bit wants to be fed (use slower rpms or faster feed rate).

Clayton.Lott 07-02-2019 12:17 PM

Thanks. I will try out some of this. Does everyone use two flute bits? Ever try three flutes? Straight bits?

tmouse 07-02-2019 01:13 PM

Three flute would need even more speed and slower RPM

BradyWatson 07-02-2019 03:39 PM

Quote:

You're cutting too slow.

You're cutting too fast.

That's just how 1/4" bits sound.

The bit is dull.
You're ALL right at one point or another.

If the design can handle it, swap the 1/4" out for a 3/8" dia. It's 2X the volume of a 1/4" bit with only an 1/8" penalty in kerf width. Makes a huge difference in edge quality on a number of materials & doesn't have the harmonics of a 1/4" tool...and you can run faster if you have the hp. Unless you do something dumb, you'll never snap off a 3/8 solid carbide cutter.

You want 2-flute if you are stuck on 1/4". FYI - 2 flute end mills/upcut spiral are stronger than 4-flute ones because of the cross section. (same w/3-flute) Besides...2-flute is what you want for chip clearance. 4-flute doesn't allow wood chips to flow as freely as a 2-flute. As I mentioned, and your design internal radii can handle it, go with a 3/8. You'll get more meat in the center web of the tool and less or no screaming at comparable speeds. All that 'screaming' telegraphs into the cut...and you don't want to put your name on that.

There are a number of decent 3/8" compression spiral cutters out there that are perfect for what you are doing. Centurion tool comes to mind...and of course Onsrud.

TimPa 07-03-2019 07:05 AM

very enlightening thread, thank you all!

Carbidetooth 07-03-2019 08:59 AM

Quote:

Originally Posted by BradyWatson (Post 81531)
Unless you do something dumb, you'll never snap off a 3/8 solid carbide cutter.

You mean like forgetting to turn spindle power on?
Right out of the chute, first time cutting panels, first time using compresssion bit. Was kinda nervous, dust shoe concealed bit. Drove it right into table...tink! Lesson learned.

Jim Becker 07-03-2019 09:09 AM

Quote:

Originally Posted by Carbidetooth (Post 81541)
You mean like forgetting to turn spindle power on?
Right out of the chute, first time cutting panels, first time using compresssion bit. Was kinda nervous, dust shoe concealed bit. Drove it right into table...tink! Lesson learned.

https://qaf05a.sn.files.1drv.com/y4m...&cropmode=none

drummerjg 07-03-2019 09:56 AM

Quote:

Originally Posted by Carbidetooth (Post 81541)
You mean like forgetting to turn spindle power on?
Right out of the chute, first time cutting panels, first time using compresssion bit. Was kinda nervous, dust shoe concealed bit. Drove it right into table...tink! Lesson learned.

Experience.....what we get when we didn't get what we originally wanted!

Been there...dumb that [lol]

TimPa 07-03-2019 12:33 PM

i already have learned 2 "bit lessons" (i hope they are still making lots of bits!!!).

this is why i don't play golf, they don't make enough golf balls! that and i am really bad![embar]

Clayton.Lott 07-03-2019 06:32 PM

So glad for all this helpful knowledge since I'm a newby, however I will add that cutting conventional instead of climb made all the difference I was looking for. And yes I felt like an idiot when I realized what I had been doing. This forum has already been worth the price of admission.

BradyWatson 07-03-2019 07:20 PM

Quote:

Originally Posted by Clayton.Lott (Post 81556)
So glad for all this helpful knowledge since I'm a newby, however I will add that cutting conventional instead of climb made all the difference I was looking for. And yes I felt like an idiot when I realized what I had been doing. This forum has already been worth the price of admission.

"Don't throw away your best edge."

Meaning...if the scrap looks better than the part, reverse cutting direction.

Your powers of observation at the tool when your mind is on the work and not the phone/FacePlant or other distractions - is precisely what separates the pros from the shmoes. If you take any advice, let it be to observe and think about cause and effect at the machine. All will be revealed if you're quiet enough to listen.

SteveNelson46 07-03-2019 07:43 PM

Not me! I've never broken a bit. And if you believe that you'll believe there'll be a Richard Simmons Jr.

drummerjg 07-03-2019 08:26 PM

Quote:

Originally Posted by SteveNelson46 (Post 81559)
Not me! I've never broken a bit. And if you believe that you'll believe there'll be a Richard Simmons Jr.

Now that is just plain hilarious! Thanks for a good laugh.

Ger21 07-04-2019 11:23 AM

1200ipm @1500rpm will snap a 1/2" bit after about 1" of cutting. [embar]

BradyWatson 07-04-2019 02:42 PM

Quote:

Originally Posted by Ger21 (Post 81570)
1200ipm @1500rpm will snap a 1/2" bit after about 1" of cutting. [embar]

Would have gotten away with it if it wasn't for those pesky zeroes....

DVE2000 07-04-2019 05:05 PM

Quote:

Originally Posted by BradyWatson (Post 81573)
Would have gotten away with it if it wasn't for those pesky zeroes....

Yeah, after I broke a bit with a missing zero, I updated my Vectric Tool Renumber Gadget to display the minimum RPM and the corresponding bit of all the toolpaths...

The real JP 07-05-2019 09:39 PM

I've done that twice now with the forgetting a zero thing... One day I will learn.

guitarwes 07-06-2019 02:44 PM

My teacher always called me a zero. Now I know they're important. Thanks guys!


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