Drilling dilemma

[qquake2k]

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

 

[Bigblackdog]

i would drill it on the lathe, and if possible use a colt drill bit, although I dont have one that big, and for a one off hole it would be expensive (if they even make one). I would also start it with a centre drill bit, or the point of a skew.

I am not sure whether other people use a dab of water or oil on the drill bit to help cool it- I do on ebonite, but am less regimented with doing so on acrylic.

 

[Grump]

You have already done the hard bit, mark X in the middle at the end of blank.
Line the vice up and test the alignment by switching on and touching the drill to test.
If it's not right move the bloody vice until it is init?
Only other thing to do do is put a square against the drill and blank to ensure it drills straight through the blank and not through the X and out the side.

What does it matter about being center of blank? As long as there is enuf meat on it it will find it's own center on the lathe, assuming the lathe kisses.

 

[davidj44]

I do all my drilling on the lathe - a Nova G3 chuck with extended jaws - and always start with a centre drill in both acrylic and wood.

 

[chas_41_uk]

As already mentioned. Plus if you start with a smaller drill bit you'll be able to see where the tip is easier

 

[Penpal]

I share your agony and intend to never use kits that require only a modicom of timber around the brass for obvious reasons. Drilling lesson mark 1 is to ensure the drill is at right angles to the vice in all directions it took me hours to set up my wonky drill press. The skills needed on these kits have to be developed first when drilling. You will receive advice on drill speed, types of drills etc before you jump into precision the term for accurate drilling and lathe set up accuracy. Everything depends on you. I humbly suggest you lash out and fit another prismatic jaw on the other side of your vice the use of only one is fraught with slip. When I can I will show you my simple set up and I commend also the use of that cross slide vice for increased versatility using two of those prismatic jaws. Using the cross slide features demands setting up each slide movement using the screws provided to take up any slop there they are called gibbs. What I suggest comes before the drilling process and using your best kit and top blank. Incidentally there are many and various prismatic jaws as you will discover.

All the best

Peter.

 

[wm460]

Just a quick conversion

0.09375 inches is 2.38 millimeters.

0.077 inches is 1.9558 millimeters.

0.045 inches is 1.143 millimeters.

 

[GeordieB]

I would second Chas,s comment to start with a smaller drill and is the hole parallel if it is every thing is running inline and your just not hitting 100% centre

 

[bellringer]

Just drill the hole you have loads of room I can even see why this need a post on here

 

[Pierre]

Personally having marked the centre I use a small nail and tap a dimple in the centre and the drill naturally follows it at the start although I do mainly use a brad point set in mm from axminster which has all the half sizes as well, try here for your area. Brad Point Wood Drill Bit Set, 29 Pc If after using these you still need to enlarge the hole then the drill that you have shown should follow a predrilled hole with no problems.

PG

 

[qquake2k]

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.

 

[qquake2k]

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.

 

[Penpal]

True prismatic jaws two necessary from grizzly

True Prismatic Jaws must be used in pairs the pic shows the two ways the jaws work that day I did two hundred Slimline pen blanks by two non stop with the drill running.


Peter.

 

[Woody]

Hi I have made quite a few of these pens and always use 25mm African Blackwood for the cap end and if its a plastic look your after then it will polish up to look like plastic but if you really want to use plastic then I would suggest you cut your blank to long and dont exit with the drill and cut the excess off after also when you mount your blank in the vice use a small engineer's square to make sure it is upright then just touch the blank lightly with the drill running to see if you are central and make any adjustments if needed and withdrawing often to clear the swarf and you should be OK good luck look forward to seeing your pen

 

[monophoto]

In looking at the pictures, the first thing I noticed is that the hole started out off center. That's a consequence of starting with the large bit.

My approach to this would involve two things. First, I would start the hole using a center bit. Center bits are intended primarily for metal work, but they are really useful when doing precision work in wood. Basically, they are very short tapered bits - a thick body to resist flexing, with a very short small diameter extension, and with a tapered section between the body and the tip that can also be used as a countersink. When I'm doing precision drilling, I use only the narrow tip to start the hole.

You can accomplish the same effect by using a small bit, but the problem is that small bits can flex. You can minimize flex by mounting the bit in the drill chuck so that only a short portion of the bit extends from the nose of the check. If you can't find a center bit, an alternative is to grind 3/4" off of the end of a standard bit so that it can be mounted in a chuck with only a very short length of flute exposed.

After starting the hole with a center bit, the next step is to chase that hole with a larger bit. A large 118 deg spiral bit can still wander around a small starter hole, so using a brad-point bit is preferable; the brad will lock in the small starter hole to keep the bit centered. Alternatively, you can drill the hole in several steps, increasing the diameter slightly with each drilling.

Finally, while I appreciate my drill press, I find that this kind of precision drilling is more easily done on the lathe. I routinely make 'throwaway' pens by redressing cheap Bic biros in a wooden sleeve. That requires that i drill a 9/16" hole 5" deep in blanks that can be as small as 3/8" in cross section. That would be impossible on a drill press, but I've done it on my lathe.

 

[qquake2k]

I wonder if a Forstner bit would work.

Buy 9/16" Forstner Bit at Woodcraft.com

 

[Penpal]

Good luck. Conquer one method at a time.

Peter.

 

[AllenN]

One final point assuming you use a centre bit, just check that the quill on the drill is running true and not actually shifting as you put the load on it.

 

[bellringer]

I am going to say it again just drill the blank job done if you really worried than point a little spot in the center an drill job done

 

[Vic Perrin]

I had all sorts of issues when drilling with the drill press. I listened to the comments made on here and changed over to drilling on the lathe and have never looked back.