I need a little help

[MarkHix]

I was trying my first acrylic blank tonight (Woodcraft) to use on my first attempt at a Wallstreet. Both times the blank blew out at the bottom while drilling, about the last .50-.75 inch. It was a brand new bit. Slow drill speed. I took alot of care to be sure that the holes were centered. I tried to go slow. Maybe not slow enough?

 

[jedgerton]

Not sure why the would be blowing out but one way to address this is to leave the blank a little long, stop before the bit punches through and then saw it to length (plus a little for squaring). I drill these often with inexpensive harbor freight bits without blowout.

John

 

[bgray]

Are you using a drill press?

I know that this can be an issue of debate here, but I only drill on the lathe.

When you get to the final exit of a drilled hole, the waste has a tendency to grap the flutes.

If you are drilling wood, don't forget that you are drilling endgrain...this tends to grab the flutes. If you are drilling acrylic, you are drilling a harder material than wood...it will grab the flutes even though there is no "grain".

This will pull the quill of a drill press down, resulting in tearout.

With a lathe, the tailstock will not allow the quill to be pulled into the material...no tearout.

I have not drilled a pen blank with a drill press in years, and I've I can probably count my tearouts on one hand since.

This of course is only my opinion...there's plenty of guys here that drill every pen blank with a drill press with no problem.

-------

edit

I know that you can just drill ALMOST until you break through, and then cut off the waste. I don't like doing this.

If you have a blank with beautiful grain that you want to continue from cap to barrel, then this cut interrupts this continuity.

My 2 cents...

 

[DaveM]

bgray43050 said
"I know that you can just drill ALMOST until you break through, and then cut off the waste. I don't like doing this.

If you have a blank with beautiful grain that you want to continue from cap to barrel, then this cut interrupts this continuity.

My 2 cents...drill on the lathe."



I agree with both of your points, but there is also another method

I do my drilling, both on the lathe, and on a drill press. I agree, the I hate to break up the grain, or pattern on an acrylic blank. If I want to prevent blowout with the grabbier acrylics, I cut the blank to length, leaving room at both ends of the blank for an overshoot. Then I drill both halves starting at the center, and stop just short of the end of the blank. This way, I save my pattern, and I get to preserve the end of the blank. Just another way of accomplishing the same thing.

For my tougher acrylics, I find myself using the drill press, because I can go back and forth easier, and eject the chips better. My lathe has a very short quill travel, and I have to move the tailstock back and forth to clear the hole as I am drilling it. If I had a different tailstock, I would probably use the lathe method more often.

Dave

(Edited because I posted before I finished writing message...)

 

[gerryr]

If you are using a DP, how are you holding the blank? What speed is the DP? Are the bits sharp? Have you got a piece of wood under the acrylic where the bit will exit? The only time I drill plastic on the lathe is when it's already round and that isn't often. I don't remember the last time I had a blowout drill plastic. I run the DP at about 800 rpm, use a PHD vise, have a solid chunk of wood underneath the blank and use freshly sharpened split point bits.

 

[bgray]

I just thought of something that I forgot to mention...

When drilling acrylics, I always have a spray bottle on hand.

I keep the blank wet when drilling.

Make sure to wipe up the water off of your cast iron...

And Gerry brings up a good point. Drill acrylics at a very slow speed with sharp bits.

 

[JayDevin]

you can also place your blanks in the freezer for about 30 min before drilling. I also drill on the lathe and personally fee that the blank spinning vs the bit has a cooling effect. I find it as easy to clear your chips as they come out almost in 2 long streams.

 

[ashaw]

Jay
Putting your blanks in the freezer it not a good thing. If you leave them in there to long and start drill they will crack before you get about 1/4" into the blank.

Mark

They best way of overcoming a blow out is to add additional 1/8" to your blank.

Go slow remove the drill bit often. I put my finger under the blank and when I feel the point of the drill bit I know I have going far enough. While the end of the material is still soft I punch end out will a blank mill.

 

[Fred]

I always drill on the drill press if I have more than 5 or so to do. Otherwise I drill on the lathe. If I have a blow out no problem as I ALWAYS leave at least 1/8" oversize to account for that possibility. I have honestly never had a blow out on the end that was not taken off by squaring the blank with the mill.

For those that think they are 'interrupting the grain', what do you use to avoid the kerf when you cut the blank in half? My suggestion for that would be to drill past center prior to cutting the blank to length and then carefully use the bandsaw and mill the ends square carefully as well. Then finish drilling the second piece. The bandsaw is the thinnest kerf I could expect to see in my shop.

Cooling the blanks as suggested by JayDevin makes sense if splitting from excessive heat is found to be a problem. VERY Frequent cleaning out of the drilled hole would also be advantageous. However I would never re-wet a wood blank to try and keep it cool, and since I don't turn acrylics I can't comment on that aspect of using water. I might also recommend the pre-drilling of the blanks with a bit somewhat smaller if one just can't get it drilled otherwise. I.E., drill a 7mm hole then re-drill with a 10mm!

I do believe if one is experiencing heat built-up, then many things need to be addressed ... such as drilling to deep without cleaning out the cuttings very frequently, drilling with a dull bit, drilling too fast, drilling without the use of a vise (the slightest off-center the blank moves - disaster is just a micro-second away), drilling through the bottoms without a sacrificial piece of wood up tight underneath the bottom, all these are just a few that can and will cause blow-outs. There are many others as others will probably add. []

 

[gerryr]

First of all, plastic gets brittle when it gets cold. The colder it gets the more brittle it gets. What does it tend to do when it's brittle? Crack. Do not chill acrylics before drilling or turning, you are only asking for trouble. When you drill plastics, if you start to get little crumbly bits coming out, the bit is dull and overheating. You need to withdraw the bit, let it cool off completely and sharpen it. If you continue to drill, the hole can easily get too large, and the blank can crack because you're basically trying to push a piece of steel through it, instead of letting a sharp piece of steel cut through it. After having made a few hundred acrylic pens, I am convinced that most of these kinds of problems are caused by dull bits. I never drill more than 2-3 pens worth of plastic without re-sharpening. And I probably drill plastic faster than most people dare, but I know exactly what it feels like when it's cutting correctly and when it isn't.

 

[jeffj13]

Originally posted by bgray43050

I know that you can just drill ALMOST until you break through, and then cut off the waste. I don't like doing this.

If you have a blank with beautiful grain that you want to continue from cap to barrel, then this cut interrupts this continuity.

My 2 cents...

I'm not that skilled a penmaker and typically wrong more than I am right, but this doesn't make sense to me.

Given that most pens have an upper and lower barrel, don't you have to make this cut anyway for the two barrels?

The interuption would be magnified if you cut the barrels, drilled almost through and cut again, but couldn't you drill just the upper barrel from the full blank, then cross cut it to length?

jeff

 

[Rmartin]

I know that you can just drill ALMOST until you break through, and then cut off the waste. I don't like doing this.

If you have a blank with beautiful grain that you want to continue from cap to barrel, then this cut interrupts this continuity

This doesn't make sense to me.

Mark one side of the blank , cut in half, drill each from the center cut. The ends are cut and barrel trimmed. How do the ends have anything to do with continuity?

My suggestion is not to drill so slow, or so fast. You have to find the happy medium. The shorter the time the drill is drilling, the less the heat, but don't drill so fast as to melt the blank. If the drill bit gets too hot, walk away. Give it time to cool down before continuing.

 

[MarkHix]

Wow! Lots of good advice. I have one lower speed on the press so I will move it down. Cold blanks is never a problem in Texas. After reading your posts, it sounds like it happened because I was trying to take too much at once in the lower portion of the blank and need to clear it out more often to keep if from grabbing in the flutes. I am not set up for drilling on my lathe (yet)but I can see the advantages.
I should change my quote to "I always learn things the hard way" LOL

 

[MesquiteMan]

I am going to be the lone man out. Personally I drill everything fast. I drill at 1,800 or so (don't remember the exact speed). I drill everything at that speed and have yet to have ANYTHING blow out. I clear the bit frequently and drill all the way through. I use a PHD vice as well and do not use any lube.

Personally I think that faster promotes better chip extraction and keeps the flutes from getting clogged up. Anyway, I am sure someone will say I am crazy and that it does not work that way but it works great for me.

 

[LanceD]

Personally I think that faster promotes better chip extraction and keeps the flutes from getting clogged up. Anyway, I am sure someone will say I am crazy and that it does not work that way but it works great for me.

I drill every blank on my Jet VS lathe set on the middle pulley with the variable speed set at almost wide open. I have had problems trying to drill at a slow speed and since I started drilling at a faster speed I have all but eliminated blow outs.

 

[MarkHix]

I'm game for anything that will help. I'll try it both ways: fast and slow.
Once agein..thanks for all the help.

 

[Fred]

Learn to watch for different slivers of acrylic as they are coming from the hole. A really fine ribbon is want you want to see. If the stuff exiting the hole appears to be gunked together you are melting the material and will cause yourself problems.

Keeping the bit cleaned out quite often is the answer. Like MesquiteMan said he retracts the bit often... that is one reason he can get away with turning using faster speeds.