Concentric holes and drilling straight

Re: Concentric holes and drilling straight

Don Stephan

Given that the early wood and late wood growth rings of some woods are not the same density, and small bits can flex, I don't know how one can avoid the problem. One can advance the bit is very small increments, but even then it will want to move to softer wood. Is it possible to carefully mark the location on both sides of the wood?

Re: Concentric holes and drilling straight

John in NM

Try either a tapered Fuller bit, or if that is too large, try re-grinding a twist drill to a pointier profile, like less than 75 degrees between the two edges. A Fuller has two very small normal (like 135 degree) cutting edges on the very tip, I've heard of duplex grinding a regular twist with the bulk of the edges at 75 and just a small portion at the tip at 135.

In the past when I've had to do this kind of thing, I've set up a jig that could register for both counter bores on the same place on the block of wood, rather than depend on a pilot hole. A 1/16 drill bit can wander impressively in 1-2" of wood!

High speed, slow feed, pecking drill action

Re: Concentric holes and drilling straight

Lee Schierer - McKean, PA

Drill your counter bore on one side with your forstner bit. Then put in a 1/8" brad point bit. Drill the 1/8" hole slowly, raising it back out of the wood frequently to allow the chips to escape. Stop the hole just as the tip of the brad point starts to exit the back side. Flip your piece of wood. Put your forstner bit back in the drill press and use the tiny hole to line up the point on the forstner bit. Hold the wood in place and drill your other counter bore.

Your holes should align pretty closely if not exact.

You could also bore the hole all the way through with the forstner bit, then plug the hole with a dowel and drill your shaft hole through the dowel.

Lee

Re: Concentric holes and drilling straight

Bruce, a MN Galoot

Get over to harbor fright and get a set of cheap center drills, short little drills with relatively large shanks. Use that and your DP to start the hole, then go in with a larger regular bit.

Re: Concentric holes and drilling straight

John K Jordan

CJ,

I always start holes in wood with either a center drill (made for metal lathe work) or a spotting drill bit (made for NC/CNC work). These are both short, very stiff bits that won't deflect and follow the grain. Both of these come in a variety of sizes; the center drills usually come in a set like this and are cheap: https://www.amazon.com/gp/product/B004MOJVKU Typically these are used to make only a shallow starting hole then drilled with the correct size.

You said a "small" drill bit but didn't say the size. I usually use a center or spotting bit to start a hole for a larger bit.

That said, for minimum deflection a "screw machine bit" or "stub length bit" might be your best bet for drilling the hole. These are much shorter than the standard "jobbers" length bits and are much stiffer. They are not as easy to find locally - I bought them from a machinist's supplier but I see a variety of sets on Amazon, for example: https://www.amazon.com/TTC-PRODUCTION-Screw-Machine-Length/dp/B002ZOEFSW

I drill a tiny bit then back off, repeat, sort of stabbing at the hole rather than drilling in a continuous feed motion.

I have no experience with drilling a small guide hole then following it with a Forstner bit.

JKJ

Re: Concentric holes and drilling straight

John K Jordan

"I always start holes in wood with either a center drill..."

A clarification: I meant to say "when I need precise holes in wood I always start them with either a center drill..."

I find this is especially helpful for drilling into end grain such as into the end of a spindle blank on the wood lathe, but the special bits are good for side grain as well to help keep the bit from being deflected by the grain for a bad start. Quite useful for metal work too!

JKJ

Use a brad point drill

Bill Tindall, E.Tn.

They can be bought in sizes down to 5/64. When used on a drill press with slow feed rate they will drill straight. LV Valley makes especially good ones.

Re: Concentric holes and drilling straight

Barry Irby

I am going to look into some of the bits mentioned above, I think there are some good ideas there, but I had a couple of other thoughts.

If you know where you want the hole, why not drill the counterbore first and then drill through with the bit for the shank?

Can you make a jig or pattern on the DP to make it possible to flip the piece back and forth?

How many do you have to do? Would switching drill bits back and forth be too much of a pain? I recently had to drill about forty holes into but not through some poplar and the forstner bit slipped back into the chuck slightly and I had to redrill some of them. It was easy to get the bit back into the hole without damaging the hole to deepen them.

On some that had to go all the way through I put a backer piece on the DP and the hole were clean on the exit side. To be sure you could clamp the backer piece on tightly.

Re: Concentric holes and drilling straight

Brian Holcombe

I did this recently using a boremax bit, using their recommended speed which seemed fast to me but was right on.

They recommended 1600 rpm with a 20mm bit.

Re: Concentric holes and drilling straight

BrianMonumentCO

Depending upon what type of fastener you are planning on using, I would stay closer to the final shaft dimension to avoid wandering bits.

The centering bit used in metal working does a great job in not wandering but the actual starting part of that bit is relative short. Read that as near the diameter of the shank in length.

For a normal wood screw using the fuller bit set like John from NM mentioned is a good way to avoid wandering bits as the whole bit is larger and a single straight bit and has the countersink built in.

If you are using a machine type threaded item then go with a drill size much closer to the thread diameter.

Small bits wander because they are not rigid enough.... Shorty bits could help but again small bits wander.

Stay away from small bits.

Go big or go home.

Update

CJ in MPLS

With a bit of faffing about I was able to get the job done.

I used a forstner bit as a center drill to correct the offset at the reverse side of the workpiece. But first I had to determine where the forstner bit should be centered. To do this I first marked a line across the surface of my tail vise. If the vise opens and closes in a linear fashion, as I believe it does, then two halves of the line should indicate either end of a line drawn straight through and perpendicular to the workpiece, the antipodal endpoints of the bore I was supposed to have drilled in the first place.

I placed a drill bit into the end of the bore on the reverse side of the workpiece, which was then positioned between the jaws of the tail vise with the bore on the front side of the workpiece on the line. I then rotated the workpiece until the drill bit laid flat on the workbench. When the drill bit is flat, the line on tail vise should line up with where the bore should have been positioned. As it turns out it was close, but not perfect. But in the end, everything worked out as you can see for yourself.

Re: Update

Barry Irby

Nice job, looks great. Next time and there will be a next time....

Do yourself a favor and try a different approach. Leave your block of wood rectangular and cut the kerf for the saw blade. Mark it carefully and reposition it accurately on the top of the blank. Then use a enter punch to mark the holes. Drill a shallow 1/16" hole in each position. Clamp a waste block to your table on the DP, drill a shallow 1/16" hole and insert a short pin that will insert into the holes on the handle block. Then drill from the other side with the forstner bit. Turn the handle blank over and use the shallow pin holes to position the blank.

Or you could figure a way to register off the perimeter of the rectangular blank.

Once the holes are established, cut out the handle.

A question. Should this piece of wood be quarter sawn or flat sawn? I'm chasing that around in my head. I need to go look at some old saws.

Re: Update

Barry Irby

Another approach might be to cut the slot for the blade in the rectangular blank and then clamp the blade to the DP with one of the holes perfectly centered and then slide the handle blank into position and drill it. Get one hole lined up the register the blank on the blade and then repeat.

Re: Update

CJ in MPLS

Barry - You have identified the problem. Once I lose the reference edges, I have to rely on the drill bit to drive straight through. Having started down that path, one needs good technique or luck and preferably both.

While the experience can be a mixed blessing, errors like this make it possible for me to grow as a woodworker. I now have some added knowledge of drilling and new approaches to handling a saw.

CJ

Yep

Barry Irby

Its and "order of work" problem. Do the interesting and exciting part first or the technical part. Might be better to drill the holes first and then saw out the handle. If you were doing a bunch of them you could set up a jig to drill the holes first and then a jig using the holes as an index to shape the handle.

Re: Update

John in NM

Yep, always good to keep your reference faces as long as possible.

Any chance those counterbores are 3/8"? If so, next time just use the step drill for a Kreg pocket hole setup and bore out the smaller part to the proper size after doing the two counter bores.

and even better...

Tony-Memphis

Now that you have posted this, I have learned something and may be able to avoid an "issue." Thanks!

My problem (well, one of the many) is that I get so little shop time, I am usually rushing. So, when I need to drill a hole, my mind is focused on drilling instead of thinking it through. After a few dozen mistakes or issues caused by poor execution, I may manage to learn a lesson to avoid next time. I hope so anyway.

Tony