LumberJocks Woodworking Forum banner

Drilling a 4" diameter hole.

2K views 27 replies 15 participants last post by  JohnMcClure 
#1 · (Edited by Moderator)
Needing to drill a 4" diameter hole through 5" thick wood. These need to be perpendicular to the surface and fairly accurate. Was thinking a 4" diameter forstner bit

Any recommendations for tooling and etc? Thank youi!!
 
#2 ·
That is a big hole to drill. Are you using a drill press or hand drill? With a drill press you could use a hole hole saw in stages, at each stage drill a few smaller holes with in and break the meat out if the hole with the grain. Then back to a 4" hole saw.
I would a small long drill to create a pilot Al the way through first.
 
#4 · (Edited by Moderator)
If your drill press can reach 5" and has enough muscle to do it with a forstner bit, sure.

If not - and I've never tried this - but here's one thought:

1. Use a hole saw to make a template for a plunge router. You could use a scrap piece of plywood, for example.

("Hole saw" is the actual term - if you look it up you'll see what I'm talking about.)

2. Clamp the template to your 5" piece in a way that you can put it in the exact same spot on the other side of the board when you turn it over (see step 4).

Alternative: I think the hole saw will cut out a circle with a center hole (it's been years since I used one, so I forget). Put that circle back in and use the center hole to drill through the board so you have a center hole on the other side to align the template when you turn it over.

3. Cut as deep into your 5" piece as you can with the hole saw, and route out the wood inside the cut using the template.

4. Keep doing that until you get as far as you can before the router runs out of room, then turn it over.

Hopefully you can get reach 2-1/2" deep. If not, you'll probably have to use some kind of hand saw to remove the remaining piece.
 
#6 ·
I would probably drill a pilot hole the same size as the pilot bit of the hole saw and then drill half way in from both sides. If you get a deep enough hole saw, you might not have to do any chiseling and you won't get any tear out as you break through.

For a cleaner hole and to minimize burning, drill several relief holes just inside the wall. This gives the sawdust a place to go, making the process easier.
 
#7 ·
+1 forstner bit is best

Going to be a very expensive hole, considering a high quality long reach Bormax has retail price over $1000!
Carbide Processors has it for only $369?

Cheaper tooling would be Chinese made Carbide bits. Shopfox and other sell the Roman Carbide brand.

Only way to safely and accurately drill a hole that large is in the drill press.
If you don't really care about accuracy; still need a 2 handed Milwaukee Hole-Hawg Drill and must be young enough to enjoy physical punishment of using one.

A much slower and time consuming method is as MadMark and Lazyman suggest with hole saw. Drill a pilot all the way thru, drill some swarf relief holes on plug side, use hole saw to cut ~1.5" deep, chisel out plug, and repeat twice on each side.

What ever method is used, be sure to keep the cutting edges cool. It is easy to overheat cutting edge on deep hole, especially in hardwoods or wet pitch filled softwoods. Clear chips often. Use compressed air to clear chips can also help cool edges too.

Best Luck!
 
#8 ·
4" forstner is going to need big drill press. Mine runs out of gas at 2-1/2", you'll need a monster to turn a forstner that size.

4" hole saw bit can be hand drilled with a corded VSR drill, plumbers do it all the time, although not normally thru anything thicker than 2X stock.
 
#9 · (Edited by Moderator)
It did not say if it is in hardwood or soft. I have drilled a few 4" plus holes in softwood. A Forstner Bit will be interesting to force through without a screw point. A wood auger will be nearly impossible to control the drill motor. If you are using a drill press, you will not need a pilot hole for hole saws. I would hole saw a series of smaller holes and work up to 4 inches. You can chisel out the scrap as you go. Keep the hole saw cool.

If I were using a handheld Hole Hog or another drill motor, I would drill the pilot hole for the hole saws. Start all of the hole saws working up to 4" about 3/4" deep. Remove the pilot drill and progress keeping the hole saw cooled and chiseling out the waste.

Good luck. I can't imagine doing it in hardwood.
 
#10 ·
Just to be different….
Mark out the hole on the wood, saw the wood into two halves on the bandsaw, including going around the hole.
Stick the two halves back together again.
I've used this system several times.
 
#17 ·
This is a fun thread.
Opticsguy,
Can you share some details? What are the requirements for this hole? Concentricity, precision. Surface finish. What Material. Can you access both sides of the material? What tools do you have? How fast? Just once, or production? Many ways to skin a cat but you're getting an ungodly amount of advice for a very vague question.
 
#19 ·
If we are suggesting all the possible ways to remove saw dust from hole, don't forget explosives.

Might be able to use commercial HMX shape charges oil drillers use for rock drilling? The accuracy and consistency has improved dramatically in last 10 years thanks to better computer simulation tools. :-(0)

Now that would be fun!
 
#20 ·
Needing to drill a 4" diameter hole through 5" thick wood. These need to be perpendicular to the surface and fairly accurate. Was thinking a 4" diameter forstner bit

Any recommendations for tooling and etc? Thank youi!!

- opticsguy
I would take it to one of my buddies who owns a tool and die place. They have for real drill/boring machines that make really quick work out of wood, and can get you end results in the 0.001 range. Cost is a biatch though. :)
 
#21 ·
I do have a few 2-1/2" reach piloted router bits.

Drill most of the waste out with smaller bits leaving minimum waste inside the 4" circle
With a 4" diameter template (hard board) aligned and installed, a top (shaft mounted) guide bearing on a 1/2" shaft, 3/4" or 7/8" long router bit, clean and perfect the top 2-1/2". A similar bit with a tip mounted bearing can be used with a router on the opposite side, allowing the bearing to guide along the freshly cut hole half.

Square and clean 5" hole with a dimensional accuracy equal to that of the template.
 
#22 ·
What you need is a "self feed bit" and a Hole Hawg. The bit needs to be sharp and you need to eat your Wheaties before attempting it. I used one for years in my trade and it only got me once. I was kneeling down, going through plywood with a 4 1/2" bit, I found an unseen nail, the bit jumped, grabbed my new blue jeans and almost left me naked. If you have never used a Hole Hawg, approach it with sufficient respect. (a quick prayer may not be overkill either. ;)
 
#23 ·
That is a thick piece to bore through accurately
I was thinking along the lines of sunnybob, but I would cut the piece in half, flatten surface of the two pieces so they will glue together seamless. Then layout the 4" hole so it will be right to size( no loss for the saw cut as if you laid it out before cutting) .Separate the haves and bandsaw the hole in each half and glue it back together. If it needs tweaking to fit an exact 4" piece, a spindle sander would take care of that.

Cheers, Jim
 
#24 ·
OP here.
The project is an experiment and a crazy idea. Four, 6 inch diameter logs turned on a lathe with only the one end turned to 4" diameter. Think in terms of a 4" dowel. The rest of the wood would be kept natural with the bark peeled off. I am using alder for the legs. Table top is laminated doug-fir, 5" thick. I plan to make a "V" cut into the end of the "dowel" and insert into the table and then pound in a wedge after gluing. my plan is to turn the legs to-fit after the holes are drilled. My question was in regards to recommended drilling techniques.

Thank you everyone.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top