12-08-2011 06:41 PM
Hi everyone, I'm new to turning and have turned a few pens using Penn State Industries material with pretty good results I think. But now I've split the last 3 acrylic blanks and am pretty dismayed at that with Christmas coming and the gifts in the trash now. The blanks split just as the brad point pierces the end and the flutes tear the blank apart. I'm drilling on the slowest speed (620?) and going slow and clearing the chips...anything I else I should do? Should I be using a regular bit and not a brad point? Any other tips I should know?
FYI: the splits were when drilling a 3/8 hole in a 3/4 in. blank and 8mm holes in 5/8 blank acrylic and acrylester blanks.
Thanks for your help and advice.
12-08-2011 07:08 PM
At least two ways around this problem.
First, put a piece of scrap wood under the blank and push the blank down tight and tighten the vise. Pretty much have to have a vise for this to work.
Second, cut the blank long by at least the point on the drill. Say 3/8ths of an inch longer. Now mark the drill bit somehow so the full diameter of the drill goes the length of the tube plus a tad more. For instance; the tube is 2 and 1/4 inches long then make the blank 2 5/8 inches long or more. Now measure up on the drill bit 2 5/16 or 2 3/8 inches, this is the full diameter only not including the point, and put some tape around the bit so the bottom edge of the tape stops you as it enters the blank. You've now drilled a hole a little deeper than the tube. Take the blank and carefully measure a 1/16th longer than the tube and cut the end with no hole off. Should leave you a blank with a hole just longer than the tube. Glue the tube in and after it dries sand the excess from the ends so the tube is flush with the end of the blank and turn and finish.
12-08-2011 07:13 PM
Back to the vise. If you do this then it still helps to have that tape marker on the bit. As you get close to drilling through the end feed really slow. My Drill press has a little play up and down in the quill and every now and then as the bit starts breaking through it will "suck" itself on down and the blank will blow up...not often but it happens. A piece of hardwood scrap seems to work better than pine for me.
Hope this helps and hasn't confused the issue for you.
12-08-2011 08:53 PM - edited 12-08-2011 08:55 PM
Welcome to the forum! Glad to have you, this is a great place to come learn, grow and share your projects. Let us know if you need assistance navigating the site! I may be repeating Randy here but I wanted to be sure it was spliting as the bit exits the blank and not entering? I do what Randy does, cut the blank longer than the tube insert, drill the hole stopping short of the bottom then cut off the end of the blank to expose the hole, make sure you don't cut the blank too short though! Another way....If you have a self centering vise to drill your blanks and can lock it it place. drill from one end of the blank, flip it, and drill from the other end, to meet the hole in the middle. Then cut it in half to expose the holes. Take the time to clear the debris often, it can compact in the hole and the pressure and crack the blank although I think it's rare on acrylic.
12-09-2011 04:48 AM
Randy and Eric have you on track with their response. Cut your blanks longer than needed and drill your hole only as long as the tube plus 1/16th. Cut off the extra to expose the hole after drilling.
I drill on the lathe and occasionally use Pam cooking spray to lubricate the bit. Clean the blank inside well with DNA or acetone if you use lube.
Make sure your blank has good support on all sides also. Most pen drilling vises only support 2 sides of the blank. If you hit a hard spot or drill to fast the blank has a chance to split from the 2 unsupported sides. As I said, I drill on the lathe using a pin chuck. The pin jaws support all 4 sides allowing less chance of a split. Most times however, I round the blank between centers to just over 3/4" or 5/8" and use a collet chuck. This will true up the blank, spins it concentric, and supports it on all sides.
Take Randy and Eric's advice, drill a perfect blank, and show us some pens!
12-09-2011 06:51 AM
Randy, Eric, and Greg,
Thanks for your tips. I think I'll start cutting them longer than needed and cutting them off.
Greg, I like your avatar or icon, I spent 20 years in the Navy as a Hospital Corpsman. I enjoyed those years, had some memorable times and experiences.
12-09-2011 07:06 AM
I too spent 20 years floating around the Atlantic. MM for me. If I had looked closely at you user name I might have gotten the corpsman surface warfare part. Thank you for your service to our country.
There are a lot of good pen turners on the Wood forums. There are a lot of good anything turners on here also. Keep in mind we all do things a little bit different. Take all you can get and then do it your way. For enough information on pen making to make you head explode try the IAP. I had no idea how much I didn't know until I found that site. The library and photo gallery will inspire you to try many different things. There even some squids over there.
Good luck on your turnings. And we love pictures.
12-09-2011 09:53 PM
The cause could be one of several things. I was not sure if the blanks were breaking when the bit entered the acrylic or exited it. The drill bit is probably dull and you are probably compensating by applying a lot of pressure with the drill press. Acrylic will dull drill bits fairly rapidly. I also recommend using special drills for pen turning made by Colt. They are absolutely amazing.
Like others have said, the blanks should be cut slightly long and then trimmed with an end mill designed for pen turning.
12-10-2011 02:24 PM
I tend to agree with Bill about your drill bit not being sharp enough. I can't remember that I have ever broken a blank while drilling into or out the bottom. This includes corn cobs, wood and acrylics. I know that the Colt bits are very, very good, but I just use the regular brad point bits. There are bits made especially for acrylic. Go to google and type in " drill bits for acrylics ". Cost a bit more, but ??