Blank Drilling Problems

[JoeOCNJ]

Hi gang,
I've been noticing lately when I drill blanks on my lathe using the PSI "C" series chuck with the dedicated drilling jaws for it, along with the tailstock drill chuck; the hole that is drilled does not remain the same size. It's tapered and off by as much as 1mm (checked with a caliper). It's always the side that the drill bit makes contact with first, and I'm not sure how deep the size variation goes but I'd guess at least 1/4 - 1/2 inch through the blank. This is the first time I have had any issues with drilling this way since I got the equipment to do it like this.

BTW.. this only occurs with acrylic blanks, wood ones seem to be just fine.

Any thoughts??? I'm stumped (other than my bits magically grew as time went on :wink

Thanks in advance

 

[BKelley]

Joe,

It could be a number of things causing this. My first guess would be heat distorsion.
What type drill are you using? Try Colt brand drill using manufactors suggested feed and speed for the particular type material you are drilling.

Ben

 

[JD Combs Sr]

Are you using a pilot drill first to start the hole? Regular bits will want to "walk" a little on entry especially on hard items like acrylic. If the drill starts slightly off-center it will tend to wallow out the starting end as it gets deeper into the blank and the starting end of the blank gets closer to the drill chuck(less flex in the bit). A pilot drill helps ensure that the bit starts out centered.

 

[GoatRider]

Start with something like this:

Amazon.com: Anytime Tools 5 Lathe Mill CENTER DRILL COUNTERSINK Bit Tooling SET: Home Improvement

using the size that's a bit bigger than the chisel point on your drill bit.

 

[Jim Burr]

I've noticed that if I don't clear every 1/4"...especially on plastic and the like, I'll get a warp on the top. Drilling at 150 RPM on Jet 1642, 7mm stuff. Maybe check your drill bit for round? I had some HF bits that wobbled more than a Saturday night drunk on Sunday morning.

 

[eldee]

How long are your bits? The longer, the more pronounced the runout will be. By the time you exit the blank, the hole will typically be normal size. This may be the same as the wallowing referred to above. I have some long Colt bits that tend to do that.

 

[Carl Fisher]

A center drill bit should definitely help. Also what type of bit are you using (twist, brad, split etc...)

 

[Curly]

I see two possibilities. The first being the bit skating a touch to the side as it starts, especially if the end isn't square. The second is that the tailstock and headstock are not aligned. If you have a pair of dead centers or one dead and one live, check the points are inline, both side to side and up and down. If out you will never get a good hole until the lathe is adjusted.

Sent from my iPhone using Forum Runner because I can't reach my desktop!

 

[leehljp]

IS your blank square or have you rounded it to fit perfectly into a chuck? IF it is not tight or square in the chuck, it can do that. It will be magnified by head stock/tail stock not aligned, as Curly wrote.

Another thought - is the tail stock locked tight when you advance the drill bit? Any looseness will cause your problem also.

 

[JoeOCNJ]

Thanks for all the replies, my work schedule as interfered with my turning and internet surfing.... I use different types of bits, I'd say about 99% came from PSI with various starter kits, or just one's I've ordered to go with new kits I'm making. I don't drill a pilot hole, but I guess I could give that a shot. I do think I am letting too much heat build up, so I will definitely try clearing more frequently, and on my lathe, which is a Turncraft Commander VS. My slowest setting im still turning just over 1k rpm. Not sure if thats the slowest speed or maybe I have something set up wrong. I do know the tail stock is locked down as tight as I can get it before I drill, and I usually dont leave much material stick out past the jaws on the chuck (guess i think it will help me stay centered without much sticking out past the jaws). Great ideas and as always, thanks for the help I will definable try out some of these ideas.