Blew out two blanks!

[gmreeves]

I blew out my first two blanks this afternoon at lunch time. Both blew out while exiting the blank. One was an acrylic from woodcraft and the other was a nice piece of cocobolo crotch. The only other blank that the drill bit was used on was a piece of Buckeye burl. These were the larger ends of a Jr. Gent, I beleive a 12.5mm bit and what appears to be a standard jobber bit. The bit came from CSUSA as part of the Jr. Gent. acsessories pack. The Buckeye Burl blank drilled through easily but it was stabilized so that may have had something to do with it.

I'm not sure what happened with the Cocobolo blank other than it was just big enough for the Jr. Gent pen and that may have caused the problem. It drilled fine until exiting the blank and then blew out and cracked up part of the grain. I am guessing the use of a backer block could have prevened this.

As far as the acrylic blank, this was my first attempt at an acrylic. I slowed my drill press down to 620 rpm's, proceded with light pressure, cleared the chips every 1/4" or so, and didn't have any issues until exiting the blank. I'm assuming all I need to do is like everyone mentions here about cutting the blank long, drilling part way through, and then cutting the excess off. Is there anything I might be missing before I attempt to drill the next blank. Again, I don't think over heating was the cause, just the drill bit catching as it broke through the other side.

 

[ed4copies]

Yes, the drill bit catching will do that.

IF you can hold it down, so it doesn't "climb" the rotating bit, it helps. Stopping short and cutting off the end is a much more "failsafe" answer!!

 

[Rfturner]

you can Use a backing board under the blanks and make sure that the drill bit is straight as well as in the Chuck correctly. I have had countless blanks blown apart at various stages some in drilling and some on the lathe. sometimes it just happens. You will get better as time goes on. It is a good idea to use slightly longer blanks and drill past but not through then cut off. if you have any questions you can PM me

 

[ToddMR]

I personally size up the end of the tubes with the end of the material first. If it looks REALLY close to barely being big enough, I select a different sized material. That's me personally though. If the bit is going to be close, you better be drilling straight, and also I am always paranoid of it blowing out on the lathe if the walls are too thin. Like I said that is my take on it. Sounds like you were saying that the cocobolo was barley big enough for what you were planning to work on. I am lucky and haven't had a blow out on the press yet. Thanks to my fellow turning buddy who made me a drill vise with wooden V blocks. What kind of setup on your press do you have for securing the blanks?

 

[PenMan1]

For what is is worth...... Any time that I drill a "just barely big enough" blank, I leave 1/2 inch extra and do not drill completely through the blank. Then after I glue in the tube (full of plumbers putty to avoid glue inside), I carefully "nibble" away the extra 1/2 inch at the band saw or coping saw. THEN, I sand to the tube, NEVER A PEN MILL.

I bet, if you took a poll here that most blanks are cracked, chipped, etc when the bit exits the blank. The thinner the material, the greater the chances of ruining the blank.

If you happen to br drilling bakelite or casein, Pam cooking spray will help keep them from cracking. It is really maddening to be 1/16th inch away from the drill exiting a $40 bakelite rod and hear that little "snap" sound.

 

[gmreeves]

If I snapped a $40 blank, you would be able hear me scream from however many hundreds of miles away I live. The fact that I blew up two ~$5 blanks was enough to make me hold it in. Serenity now! Serenity now.

Thanks for the vote of confidence. I'll be cutting long and drilling part way from here on out in these circumstances. I should have researched before drilling the acrylic as I see there are many discussions on the board about this. All I was told from the store was drill slow. Oh well, live and learn. Back to Woodcraft.

 

[Russianwolf]

one other solution is to drill smaller sizes first, then end with your needed size. Much less likely to blow out since you are taking much smaller bites.

 

[ed4copies]

Mike
You ARE correct, BUT when the flutes catch early in the "hole expansion", if the blank climbs the flutes, it will shatter when you stop it from rotating.

So, if it starts climbing, let go of the blank and let it spin while you turn off the drill press.

(I, of course, have never DONE this, it would be dumb--but I am TOLD this happens!!)

 

[randyrls]

I bet, if you took a poll here that most blanks are cracked, chipped, etc when the bit exits the blank. The thinner the material, the greater the chances of ruining the blank.

I ALWAYS cut my blanks long and drill short, then cut off the end. This gets my perfect blanks with no chip outs either on the inside or outside.

Tip: When drilling the blank, mark the tube length on the side of the drill bit with a sharpy marker. When the mark disappears into the blank, the hole is deep enough. Now trim to length. Make sure you trim the un-drilled end. DAMHIKT! :biggrin:

 

[MesquiteMan]

I still firmly believe that faster is better. I drill everything at 2,000 rpm and have never had a blank blow out. I do not cut long and stop short either. My belief is that you are making much smaller "cuts" and less chance for the bit to "grab".

 

[gmreeves]

Mike
You ARE correct, BUT when the flutes catch early in the "hole expansion", if the blank climbs the flutes, it will shatter when you stop it from rotating.

So, if it starts climbing, let go of the blank and let it spin while you turn off the drill press.

(I, of course, have never DONE this, it would be dumb--but I am TOLD this happens!!)

I have a pen vise that I use when drilling but I don't clamp it down. When the bit grabbed hold, I let go out of instict/fear and the vise spun until it hit the back of the drill press. I'm not sure when it broke but I'm pretty sure it was before the vise hit the back of the press. I've got a couple more acrylic blanks to play with. I hope it goes better tonight.

 

[Russianwolf]

Mike
You ARE correct, BUT when the flutes catch early in the "hole expansion", if the blank climbs the flutes, it will shatter when you stop it from rotating.

So, if it starts climbing, let go of the blank and let it spin while you turn off the drill press.

(I, of course, have never DONE this, it would be dumb--but I am TOLD this happens!!)

Sounds like another good reason for drilling on the lathe. The blank can't climb the bit when it's in a chuck.

 

[ToddMR]

I never get the blank climbing the bit when using the vise with V blocks. I cringe when I blow a blank when turning lol.

 

[Robert Taylor]

fwiw woodcraft has replaced blownout blanks free of charge for me under their satisfaction guarentee.

 

[PenMan1]

I bet, if you took a poll here that most blanks are cracked, chipped, etc when the bit exits the blank. The thinner the material, the greater the chances of ruining the blank.

I ALWAYS cut my blanks long and drill short, then cut off the end. This gets my perfect blanks with no chip outs either on the inside or outside.

Tip: When drilling the blank, mark the tube length on the side of the drill bit with a sharpy marker. When the mark disappears into the blank, the hole is deep enough. Now trim to length. Make sure you trim the un-drilled end. DAMHIKT! :biggrin:

Sure, you could do this IF you wanted to do it the EASY WAY:biggrin::biggrin::biggrin:
That is the reason some of us ride the short bus, we always insist on doing everything the hard way.
Great timesaving tip, Randy.

 

[diamundgem]

LOL!! My shop is about 50 yards from the house back door. My wife sticks her head out and hollers at me " you just blew a blank didn't you". She hears my Navy slang when I blow a blank

 

[PenMan1]

LOL!! My shop is about 50 yards from the house back door. My wife sticks her head out and hollers at me " you just blew a blank didn't you". She hears my Navy slang when I blow a blank

Marine slang is the same as Navy slang except they insert "squid" somewhere in the middle of the every tirade! To hear those guys cuss, you'd think Navy is responsible for EVERY bad thing that has ever happened:biggrin::biggrin::biggrin:

 

[diamundgem]

My vocabulary gets bigger when I,m nearly down to the last cut when it blows

 

[Russianwolf]

Marine slang is the same as Navy slang except they insert "squid" somewhere in the middle of the every tirade! To hear those guys cuss, you'd think Navy is responsible for EVERY bad thing that has ever happened:biggrin::biggrin::biggrin:

Well, we are responsible for the Marines after all.... :biggrin::tongue::biggrin::tongue::biggrin::tongue::biggrin::tongue::biggrin::tongue:

 

[Lenny]

I still firmly believe that faster is better. I drill everything at 2,000 rpm and have never had a blank blow out. I do not cut long and stop short either. My belief is that you are making much smaller "cuts" and less chance for the bit to "grab".

I agree! Partly because I don't think I can go wrong agreeing with Curtis ! :biggrin: But mostly because that's what I have always drilled at (and yes, it's really because I'm too lazy to change speeds on the DP)

I do, however, often drill part way and trim back .... And ALWAYS with a fresh back up piece underneath. I covered my tabe with 1/4 ply creating a space for a replaceable insert about 2" wide with 45 degree edges like this
/............\ that will slide into place. Trim or slide in or out to always have a fresh back up.

 

[jttheclockman]

I have a pen vise that I use when drilling but I don't clamp it down. When the bit grabbed hold, I let go out of instict/fear and the vise spun until it hit the back of the drill press. I'm not sure when it broke but I'm pretty sure it was before the vise hit the back of the press. I've got a couple more acrylic blanks to play with. I hope it goes better tonight.

Reread your statement and you will see what you did wrong from the getgo. When people talk about drilling on a drill press there are factors involved that I never see mentioned and they should be.

After reading this you will start to see why drilling on a lathe is so much better and more accurate and probably cheaper.

If using a pen vice and I have one and use it occasionally but I have noticed these are not very secure. They have a tendency to wobble and wobble is not good when drilling anything on a drill press. You need to secure the pen vice to the table, you need to secure the blank in the vice with a BACKER piece underneath the blank and the blank MUST be sitting on the backer piece flush. Most people don't even realize that their drill press may have some runout in the quill which can cause a couple things, an enlarged hole, and also can allow for a catch of the flutes on the material being drilled thus causing a crack or breakout especially if the material is thin walled.

I suggest try learning to drill on the lathe. You will be glad you did.

 

[jocat54]

Another good reason to drill on the lathe-I drill using a collet chuck, and if I think there is a danger in blowing out a blank (segments, ect), I drill part of the way through and then turn the blank around in the collet chuck and finish drilling.

 

[johnspensandmore]

I glue a quarter inch piece of scrap to the bottom of every blank I drill and I have never had one blow out. If you match the "blob" of glue to the diameter of the drill bit, the bit will separate the blank from the sacrificial piece as it exits the blank! If not, you can do it easily with a chisel.

Just my not worth two cents!

http://www.johnspensandmore.com

 

[gmreeves]

I cut long, drilled short, and sawed the excess on three acrylic blanks last night. I also speed up the drill speed to about 2000 rpm and didn't have any issues. I think that is the ticket for now but I will probably eventually drill on the lathe. Thanks for all of your help.

 

[snyiper]

I find drilling acrylics short works best for me while spraying with water. This cools the bit and blank. I drill at the slowest speed for less heat and build up and pull the bit out very often to clear.

 

[Bree]

Try putting some tape around the bottom part of the blank. That helps add a little strength. I also put a piece of scrap wood under the acrylic blank. I seldom get blowouts anymore.
:biggrin::biggrin::biggrin:

 

[penfancy]

I haven't had too many blowouts in the short time that I've been turning. But I have recently tried one of those Colt 5 star bits (33/64). Smoothest entry and exit I've seen thus far. (out of maybe 50 pens) Good odds. I sprung for that one over at Rockler 'cause The Handyman COA gets a $10 coupon in the mail from time to time. Brought the price back down to the split point.