Pen blank explosion while drilling! Bizzare

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Scottydont

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I had a first time experience yesterday. (Please note that I have turned over a couple hundred of pens.) I was drilling a Cocobolo pen blanks and when withdrawing the bit on my drill press for the third time, the flutes brought up a hot moist ball of sawdust. All I heard was a poof! from the blank. That little ball of sawdust exploded. I would equait it to about the loudness of a ladyfinger firecracker. Good thing I was wearing safety glasses because I heard the little sawdust fragments hit the walls of the shop. Also note that this is a new drill press (12" Shop Fox 1HP) and the RPM's are probably 1500-2000 range. I need to check that out because the only thing I can conclude is the speed may have been too high. I would hate to have to yell "incoming" everytime I am drilling blanks. :D

Has anyone else had a similar experience?
 
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Wow, never heard of that before Scott! Was the bit real hot when you took it out? Maybe the heat and the oils from the wood didn't mix well.
 
It happens. Especially with an oily wood like cocobolo. The heat builds up pressure inside the blank that can't escape due to build up of sawdust and oil that clog the drills cutting slots. When you pull it out, it blevy's (releases pressure). This can also be lessend, by many insertions and extractions of the drill bit (Which it sounds like you already do). Also, might be time for a new drill bit.

Cheers,

Fangar
 
Actually I had Ebony do that a couple of years ago!!!! I was just starting to turn pens and I assumed it was normal!!!
 
I concur with everythingh said, heat have built up and one common culprit is a dull bit mixed with high speed, oily hard wood and you got a perfect "explosive" recipe. [;)]

Periodic cleaning of the bit's flutes in between drilling will help a lot...also gives the bit time to cool down.
 
Originally posted by Fangar
<br />It happens. Especially with an oily wood like cocobolo. The heat builds up pressure inside the blank that can't escape due to build up of sawdust and oil that clog the drills cutting slots. When you pull it out, it blevy's (releases pressure). This can also be lessend, by many insertions and extractions of the drill bit (Which it sounds like you already do). Also, might be time for a new drill bit.

Cheers,

Fangar
Click to expand...

Fangar,

I've seen a B.L.E.V.E. when I was a USAF Crash Firefighter...

Boiling Liquid Expanding Vapor Explosion

The Propane Tank was on Fire, Tank Red Hot, the 1st responders put out the fire... The propane was still boiling and releasing huge volumes of vapors and that red hot tank ignited them... Shattered windows for miles. This is the stuff nightmares are made of...
 
I also had it happen to a cocobolo blank. I was drilling it for a Gentleman's pen - large bit, low speed but I guess that I didn't clear it often enough. Towards the bottom of the blank the whole thing exploded. It was loud enough for me to think that the drill press went.

Alan
 
I drill at a much slower speed, 540 rpm. That seems to be a good general purpose speed. I am very heat conscious when drilling. Coco and other oily woods can be problematic at high speeds. As for moisture, it seems to be ever present. I cut and drilled some osage orange that had been in storage for nearly ten years. Yet the center was still moist.
 
To those of you considering Tru-Stone, it's great material, but this condition happens there as well-extract bit often and don't let flutes get full. Also hot bit is best left to cool.
 
Jack,
Have you ever tried hitting the drill bit with a damp rag between cuts, to further help it cool? Or does this just ruin the metal (similar to "quenching" the metal, but it's at a lower temperature when quenched in this case).
 
I really appreciate this discussion and will always wear a face mask when drilling my blanks and in general when using my drill press. Many unseen hazards out there aren't there.
 
Originally posted by jwoodwright

Fangar,

I've seen a B.L.E.V.E. when I was a USAF Crash Firefighter...

Boiling Liquid Expanding Vapor Explosion

The Propane Tank was on Fire, Tank Red Hot, the 1st responders put out the fire... The propane was still boiling and releasing huge volumes of vapors and that red hot tank ignited them... Shattered windows for miles. This is the stuff nightmares are made of...
Click to expand...

I'll bet. I have never seen a BLEVE (Thanks for the correction), but I've been to numerous traffic collisions involving tanker trucks where it was of concern. I've had some training in the area, and you are right, heat pressure and ignition can ruin your day.

Good reminder that eye protection is a must. (I might where are a catcher's chest protector now too... [:D]

Cheers,

Fangar
 
A similar thing happened to me once. I was drilling a long blank for a pentel pencil and using steelewood. The hole lis a little ovet 5 inches long and after drilling about 2", I pulled out to clean the bit and re-entered the hole. After about another 1 or 1.5 inches I heard a sound about like a loud firecracker or a 22 rifle and looked dowm and the blank was gone. Later foune it in two halves of opposite sides of the shop. The steelewood split right down one of the glue joints.Safety glasses for me from then on.
Do a good turn daily!
Don
 
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