Drilling dilemma

[qquake]

I have a hard time centering the drill bit when I drill blanks. I use a drill press vise with a prismatic jaw, and the vise is held down with tee slot nuts and studs. I've tried other methods, including a cross-slide vise, but this is what I've found works best for me. Normally, it's not an issue, as the blanks are big enough to overcome any drilling issues. But I'm thinking about trying one of PSI's Over/Under kits, which requires a 9/16" hole in the cap blank. That's a big hole! If I drill a 3/4" square acrylic blank, that only leaves 0.09375" wall thickness. I tried a practice run with a blank cutoff this morning, and you can see the results. The thinnest part of the blank is only 0.077". Now theoretically, that would leave me enough wall, because it only requires 0.045". But that's cutting it awfully close. The piece I drilled was short, and the longer the blank the more chance there is for the bit to wander. But the cap is only 1.8", which isn't very long. Now I realize, I could use a wood blank larger than 3/4", but I'd really like to have a solid black acrylic cap on it.

My question is, does anybody have any advice for drilling centered? I mark the center on the end of the blank, but that only really helps me if I'm using a brad point bit. I think my problem is, I can't tell exactly where the center of the tip of a standard drill bit is. All thoughts and suggestions are welcome.

https://www.pennstateind.com/store/PKCP6020.html

https://www.pennstateind.com/library/PKCP6000_ins.pdf

 

[Sappheiros]

When I first started turning, I had originally bought a drill press to drill the blanks, but I realized the cheap (but good) one I had bought only had a 2.5" dip, not quite enough for drilling the blank. I use it now just for squaring the blank, but I bought the drill chuck and pen vise chuck for the lathe. I feel like that has quite a bit more accuracy. If I had kept drilling with the press, I would not only have had to drill using my perception of the blank canter, but I would also have had to flip the blank over to finish the drilling. It does add more steps on the lathe, but I'm happy with the setup.

 

[JF36]

I would start out with a smaller bit first, anywhere from 1/4 to 3/8. The smaller bit will help you get the hole on center, and decrease the amount of material that needs to be taken out by the larger bit. This will prevent the larger bit from wandering as much.

 

[jttheclockman]

Get yourself some starter drill bits.

Use an awl to make starting mark and the use an appropriate size starter bit. Then switch over to normal bit.

 

[KenV]

Jim,

Then there is not much room for error, I start with an automatic center punch and then a center bit. The positioning of the center bit into the punch divot is much easier then trying to align the big bit.

Drilling with a smaller bit and drilling with successively larger bits can also help.

 

[KenV]

Get yourself some starter drill bits.

Use an awl to make starting mark and the use an appropriate size starter bit. Then switch over to normal bit.

Those are sold as center bits.

 

[jttheclockman]

Get yourself some starter drill bits.

Use an awl to make starting mark and the use an appropriate size starter bit. Then switch over to normal bit.

Those are sold as center bits.

Yes my bad

Home Depot, Lowes and even Harbor Freight have them

Proxxon 2 - 2.5 - 3.15 mm HSS Center Drill Set (3-Piece)-24630 - The Home Depot

 

[qquake]

Well, I tried a couple of things, but I don't know if they helped or not. First, I drilled through with a 7mm brad point bit, then drilled it out with the 9/16" bit. Since the end of the practice blank blew out, I can't tell how the exit hole was.

 

[qquake]

Next, I tried a center bit, then followed it with the 9/16. It doesn't look to me like it was any better. I do know one thing, I need to make sure my drill press table is square to the bit.

 

[jttheclockman]

Jim

I am not a fan of brad point bits for what we do in any case. Yes you need to check your accuracy of the bit to the table but also to the device you have holding the blank. Just because the table may be square does not mean the blank is sitting square in the jig or the jig is square itself. I am assuming your blank is needed for a kit that requires exactness and there is no leeway.

If you have the ability to drill on your lathe you may want to visit that drilling method. It does make a difference.

 

[Monty]

Just wondering, have you tried drilling on your lathe?

 

[qquake]

No, I've never drilled on my lathe. I don't have the jaws for my chuck, nor do I have the stand alone drilling chuck. Since I may never have to do this again, I can't see spending the money. I really don't have any desire to start drilling on the lathe. I'm happy with my drill press setup.

 

[qquake]

I wonder if a Forstner bit would work.

Buy 9/16" Forstner Bit at Woodcraft.com

 

[KenV]

I wonder if a Forstner bit would work.

Buy 9/16" Forstner Bit at Woodcraft.com

Not any better, and probably with more heat from friction. Foresters are famous for heat. Heat is not good with acrylic.

 

[jttheclockman]

I wonder if a Forstner bit would work.

Buy 9/16" Forstner Bit at Woodcraft.com

You would not be happy and they will dull very quickly. They will get hot also as was mentioned.

 

[ANMH265mvd]

I realize that the thread is a bit dated, but I wanted to mention a tool that should work for the problem at hand. Adjustable spring tensioned tap guide. They are 1/2" in diameter, so may not fit all chucks. Once the work piece is aligned, switch out the tap guide for the needed drill bit and tighten the chuck from all sides.

 

[Joey-Nieves]

I use my Lathe, a centering bit Pen Jaws and crossed fingers!

 

[farmer]

drilling

4 jaw chuck and a drill bit in the tail stock.

I always turn everything round. and then drill it, I have a 1 3/8 spindle bore or larger on all but one of my lathes.

Then slid blank on the mandrel and recut the out side of the blank so the hole is always perfectly centered.