I need to pilot counter bore some existing 3/8" holes out to 3/4" OD in some MDF to get the nuts below the surface. Some sort of flat counterbore that fit on a 3/8" drill bit would be ideal. Any suggestions on where I could find one reasonable? Thanks
Need a Pilot Counterbore for MDF
- Thread starter i4ni
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DGersic
Well-known member
Forstner bit? That’s what I’d reach for first.
larry4406
Well-known member
Not sure if this helps, but I have screwed a sacrificial board to the back side of the board with holes that need to be enlarged. I then take the hole saw with pilot bit that matches the existing too small hole and drill a pilot in the sacrificial board on center. Then switch to the hole saw that's needed using the centered pilot hole. Patch and paint the screw holes from sacrificial board.
Shiftless
Well-known member
Unless the OP is using a drill press, I don’t think a 3/4 “ Forstner bit would self center in a 3/8 “ hole. I have seen guys clamp a sacrificial piece of thin plywood over the work, drill a small pilot hole to each the center of the original hole and then drill through that with a Forster bit to achieve the desired result.
edit: I see Larry4406 beat me to this idea while I was still typing. Clamp or screw it down…depends on the situation.
Firebrick43
Well-known member
Larry has the right idea. I have never seen any wood working piloted counterbores of any size, and even though metal machining counterbores would work well if sharp, the sizes available are pretty standardized, and a 3/8 pilot is 1/2 diameter on the counterbore
larry4406
Well-known member
I had to drill a 1.5" hole thru high dollar marble to mount a steam shower controller. Hole had to be in a precise location. Hole saw had no pilot as shown below.
I put blue tape on the marble and carefully marked the needed centerline with large cross-hairs both vertically and horizontally.
I then took a 2x4 and thru drilled it with a 1.5" hole saw and marked the hole centers on the face and sides of the 2x4 prior to drilling. I then put two-sided tape on the 2x4 and pressed it tight to the marble aligning my marks; this centered the bored hole on the centerline of the hole to be cut. The 2x4 then served as the pilot for the pilot-less hole saw.
Used a putty knife to pry off the 2x4. For the record, the Gorilla Glue 2-sided tape is damn strong!
I put blue tape on the marble and carefully marked the needed centerline with large cross-hairs both vertically and horizontally.
I then took a 2x4 and thru drilled it with a 1.5" hole saw and marked the hole centers on the face and sides of the 2x4 prior to drilling. I then put two-sided tape on the 2x4 and pressed it tight to the marble aligning my marks; this centered the bored hole on the centerline of the hole to be cut. The 2x4 then served as the pilot for the pilot-less hole saw.
Used a putty knife to pry off the 2x4. For the record, the Gorilla Glue 2-sided tape is damn strong!
It's an 18' work bench top so there wont be any drill press action going on lol. A forstner bit was my first thought but that won't work unless I build some sort of drill jig i can clamp on and i imagine a wood jig is going to wear with every hole unless i use hardwood. Keep thinking guys theres got to be something out there
I did basically the same thing you did on a granite tiled garden tubI had to drill a 1.5" hole thru high dollar marble to mount a steam shower controller. Hole had to be in a precise location. Hole saw had no pilot as shown below.
I put blue tape on the marble and carefully marked the needed centerline with large cross-hairs both vertically and horizontally.
I then took a 2x4 and thru drilled it with a 1.5" hole saw and marked the hole centers on the face and sides of the 2x4 prior to drilling. I then put two-sided tape on the 2x4 and pressed it tight to the marble aligning my marks; this centered the bored hole on the centerline of the hole to be cut. The 2x4 then served as the pilot for the pilot-less hole saw.
Used a putty knife to pry off the 2x4. For the record, the Gorilla Glue 2-sided tape is damn strong!
That might do the trick
I found a wood working set but it only went up to 5/8
Firebrick43
Well-known member
have a link?, there are times I didn't want to use my nice Chicago latrobes.
Garcky
Well-known member
Forstner bit. Drill the 3/4 hole to depth and then drill the pilot hole. If you have to drill the counter bore after the pilot hole is there, it gets more complicated to center the counterbore.
The 3/8s holes are existing
Garcky
Well-known member
Or, if you really need to do the countebore with the 3/8" hole already drilled, this tool will work:
www.snappytools.com
34824 – 3/8″ x 3/4″ 3-Flute Flat Bottom Counterbore with TiN coated twist drill
Use SD-3 Counterbores to drill a pilot hole and counterbore a flat bottomed hole in one step. Perfect for lag screws, lag bolts, washer head screws, T-nuts & more. Drive Shank: 1/4″ Hex P…
www.snappytools.com
Garcky
Well-known member
See my reply above this.
no but it was Penn tool company i remember that that. i think they had two styles (sets}of adjustable counterbores around a$100
By-Jove i think you may have found it
Firebrick43
Well-known member
Something like this?
https://www.penntoolco.com/precise-...erchangeable-pilot-counterbore-set-2007-0023/
https://www.penntoolco.com/precise-...erchangeable-pilot-counterbore-set-2007-0023/
Garcky
Well-known member
I used to use that tool when I was building frames with 4x4 materials. I did half lap joints and tenons for the construction. I'd do the initial bore and counterbore on the outside component and then a 1/4" pilot bore on the inside component, for 3/8" lag screws. Two lag screws on a diagonal for each joint. It made for very solid joints that were perfectly square. I did all of the material removal on components using an adjustable dado blade on my radial arm saw. Since the joints were half-lap, one set-up on the saw was the only thing I needed, along with markings on the workpieces. I could turn out dozens of joints per hour with that setup. I did the assembly with a 1/2" drive speed handle and socket. Very fast and efficient.
My son said I was wrong they're not for wood sorry
yea but i think theyre for metal according to my son
Firebrick43
Well-known member
They would work however, certainly not super expensive and the ability to change pilots would be nice. I would be leary of using them in anything metal other than aluminum. But what garcky posted is probably exactly what you need.
PelicanPines
ALLIANCE MEMBER
I have a lot of Snappy products. Great customer service too. Now I have to look to see if I have that size in my Snappy Drawer.Or, if you really need to do the countebore with the 3/8" hole already drilled, this tool will work:
34824 – 3/8″ x 3/4″ 3-Flute Flat Bottom Counterbore with TiN coated twist drill
Use SD-3 Counterbores to drill a pilot hole and counterbore a flat bottomed hole in one step. Perfect for lag screws, lag bolts, washer head screws, T-nuts & more. Drive Shank: 1/4″ Hex P…
10-4. I'm gonna get one ordered
Garcky
Well-known member
It's a very handy one if you work with 3/8" lag screws on any material. I had to go hunting for it online, since it has been decades since I bought mine. It's usually pretty easy to find 3/8 washers with a 3/4" O.D. Kind of an expensive drill bit, but...
they would be handy 4 sure. if they made a set that went up to an inch i'd be on board
rayra
Well-known member
Forstner bits are the answer. Especially for a clean cut in MDF. Spade bits are likely to tear it up.
DGersic
Well-known member
The forstner won’t wear out a scrap wood guide. Even if it does, just make another one.
a 3/4 hole saw with a made up centre arbor with a 3/8 diameter would work
Walkers
Well-known member
Just use Tee nuts
HUSTLESTUFF
Well-known member
In this video,
he hammers a piece of dowel the size of the hole onto a forstner bit and re-drills a larger hole. You could do something similar but don't go all the way thru. HF has inexpensive bits $9.99 https://www.harborfreight.com/power...-bit-set-with-38-in-shanks-7-piece-62361.html