Guhring .25 25xd S&F

[Zoffen]

So yea i've been drilling lots of deep small holes and all was working fine until today when randomly the drill decided to explode about an inch in.

Material is aluminum and is held in a 5" makro grip 5 axis vise in a Mazak I-700 with 1000 psi coolant. Drilling with rotaries positioned @ A-90 C0.

 

Here is my process:

 

-Drill 144 spot

-Drill .25  x .25 deep with pilot drill

-Grab 25xD drill and enter hole at 300rpm and 20 IPM with thru tool coolant on

-Spin Drill up to 500sfm and drill at .006/rev

-If i have to break out or through a hole i will retract .030 in z and then drill through the intersection at 200sfm and .006/rev

-retract to top of hole -.25 and spin the tool down to 300 rpm and retract at 20 IPM

 

I have drill probably 100 or so holes with this process and it work awesome until today.

 

Today it went like this:

-Drill 144 spot

-Drill .25 x .25 deep pilot

-Grab drill and enter hole

-Spin up spindle and start drilling

-Tool makes i about 1" down then in .1 second chatters and explodes into multiple pieces leaving the tip of the drill still in the hole. The drill tip was not clogged up and was easily pulled out of the hole.

 

I'm thinking i have just been lucky @ 500sfm and .006/rev and need to tone the speeds and feeds down a bit.

 

Any insight into this issue would be greatly appreciated. What do you guys run S&F for this kind of situation?

 

[JMahon]

I'd start around 150-200sfm and go from there. Maybe have a 10xd drill in between too

[Eric@HorsepowerInc.]

What is the drill pt. angle of the pre drill? Same as your spot, must be equal to or greater than angle of next drill. Next culprit would be run out. We are doing lots of holes close to yours in dia. at 20-25D no problems, Guhring here as well but we don't have that psi for coolant, must be nice!

[The Cathedral]

Is that a solid carbide 3-flute? The only reason I can see that breaking like that is from walking or flexing. Are you sure the drill was sharp? Maybe one flute had a chip in it and forced the drill off center. Is the aluminum cast or wrought? If it's cast it could have hit a void. Runout on the holder?

 

Or straight up bad juju.

[crazy^millman]

I normally turn the high pressure on with the drill in the hole. Give a 2 second dwell and then drill. I have seen some drills give the sine curve harmonics going on if the drill has the high pressure turned on outside of the hole. That long of a drill is like a tuning fork. It will resonate at a frequency and keep it. Then you start drilling and the vibration as not not left the tool before you start drilling. Those high pressure coolant holes are not perfect through the drill. They are really good, but not perfect and putting a 1000 spit through the drill will make it sign. Want to test it and don't mind getting wet put your hand on the drill with the high pressure coolant on. You will feel the tool signing to you. Granted not much and the broken clock is right twice a day theory kicks in as to why you have been good so far. Read the instructions on the correct process and you will see you are not following the correct process.

[RaiderX]

ya what he said ^

also might want to consider dwell when spooling up spindle to drill?

[Zoffen]

Drills are all held in quality shrink fit holders.

 

All really good points to consider here. 

 

I talked to a Guhring rep this morning and he thought that the 500sfm for the 25xd was a little hot and the drill probably started bowing and then kaboom!

 

I'm gonna tone it down a bit and not break anymore expensive drills!

 

Thanks for all the replies and insight!

[DavidSV]

How many parts do you get per drill? If you drilled 100 holes with 1 drill, maybe you got lucky. If you get a set amount of holes per drill, it could be a drill problem. Even good companies have bad days.

 

I had a job where we reliably got 500 parts per endmill, and all of a sudden the mills started breaking at 20 - 40 pcs. We questioned our supplier and they replaced the remaining tools. Later they told us that the grind was in fact messed up on the mills we returned. 

[Zoffen]

I toned it down to 300sfm and .005rev and all is happy. Cycle time for these features dont matter as much as making these long drill last.

 

This is the original drill. It should last for along time in aluminum i would think but xxxx does happen....

[Tim Johnson]

My speeds for a 1/4" 30x Mitsubishi drill is 387sfm .0068 ipr. I pilot drill 3x deep.

[Zoffen]

Thanks for the parameters. Im thinking piloting deeper for the 25xD is a good idea too.

[crazy^millman]

Thanks for the parameters. Im thinking piloting deeper for the 25xD is a good idea too.

 

Yes the books I have seen always recommend at least 3X for the pilot hole. Again I think it is to help harmonics more than anything. I worked on Nuclear Turbines about 20 years ago. One place the Turbine Shaft was 140 tons. When the Turbine fired up to 1800 rpms it would go through harmonic sine curve motion of flew until it was up to speed. The engineers could not do the math and they asked me to work out the formula for them. Guess how mush that shaft would flew when getting up to RPMS? .03 was the amount of movement that 140 ton 36" x 120' long turbine shaft would flex. I had to make our packing that went between each stage .03 bigger than the OD to allow for it to not rub when fired up. Everything and I mean everything flexes at RPM. I have watched a 1/4 carbide endmill bend almost to a 30 degree angle and not break. Had I not personally watched it I would have told anyone telling me it could do it they were crazy. Part of the reason I don't like aluminum for fixtures for hard metals. The aluminum is like a tuning fork. It does not deaden the part. You get the right RPM and Feed and you amplify the harmonics of the tool back into the part. Think I am crazy go take a hammer and smack a piece of Aluminum and a piece of Steel see which one deadens the sound and which one reinstates the sound? We are fighting so many forces in a machine shop. Wear, Abrasion, Sound, and so many other factors people just don't think about when making a part. Every cut every part tells a story. Are you stopping to hear the whole story to going by the road sign at 100 mph and not hearing, seeing and understanding what the process is telling you?

 

Thanks for putting up this topic it has helped me teach some engineers some proper thoughts and process for machining parts.

[Zoffen]

Thanks for putting up this topic it has helped me teach some engineers some proper thoughts and process for machining parts.

 

As long as I learned something from the experience i guess it was worth it to break that drill. Might have saved alot more expensive and longer drills in the future!

[The Cathedral]

 The aluminum is like a tuning fork.

 

This man speaks the truth. I've snapped a 14" long, 1.250" diameter solid carbide endmill extension just trying to take .05" off a bore. It was so damn loud. By the time I could hit the e-stop button, it was already a goner.

 

It was a bad day.