What drill for deep holes in wood?

[king nero]

I got extensive experience with drilling in steel, so I know the importance of correct sharpened drills, correct rpm, ...

I don't got much experience of drilling in wood though.

I need to drill about 40 through holes, diameter 5/8" and 3/4", thickness of the wood = 5".

Type of wood: nothing really good, don't know but it's certainly not oak or birch or walnut or similar. it's cheaper and lighter.


I got a milling machine, so it is able to take most types of drills.

What kind of drill would you recommend for this?

 

[MoonRise]

Re: Whhat drill for deep holes in wood?

A 'standard' drill bit for use in wood through holes is a brad point bit.

For a flat-bottom 'blind' hole in wood, a Forstner bit is often used.

A plain old twist drill bit can be used in wood, but they can wander a bunch in the non-uniform nature of wood.

https://en.wikipedia.org/wiki/Drill_bit

For 'cheap' and rough holes, a spade bit can be used (I generally don't like them though, too rough for my likes).

Make sure the bits are longer than 5 inches long.

Use a backer board when drilling through, to minimize chipping and splintering when the bit breaks through the far/bottom side of the workpiece.

 

[Thumper68]

Re: Whhat drill for deep holes in wood?

Auger bit

 

[jerrdanjohn]

Re: Whhat drill for deep holes in wood?

I work with steel, I just don't like wood, but I put a roof up the other day and had to drill threw some power poles and the best thing I found was a paddle bit. I was lucky enough to have an extender for the bit also because the boles were 10" diameter. Drill a little ways then with the bit still running pull it out to clear chips then go back in, learned that the hard way. I am sure someone that knows wood could give better advise.. Jonathan

 

[king nero]

Re: Whhat drill for deep holes in wood?

Thanks for both your suggestions.

Don't really care for the "cleanliness" of the hole, so that's not an important factor.

DO I need cooling of any type? I guess no, as it's wood, but I also know a spade drill can get hot as fu(k when working it hard, playing havoc with the cutting edge.

What would be the advantage of an auger bit over a brad point bit?

 

[rlitman]

Re: Whhat drill for deep holes in wood?

What would be the advantage of an auger bit over a brad point bit?

Most augers have a gimlet tip (the screw) that self feeds them through the wood. That's not going to work on a milling machine.

Augers also are great at cleaning the hole. and will not get bogged down easily in a 5" deep hole. But they cut a rough hole, and you can expect a lot of tearout at the end.

A regular twist drill bit has a lower twist rate than a ship auger, which means you will need to remove the bit from the hole more frequently to clean out chips.

A forscher bit will. Especially as the hole gets deeper than the diameter, you will need to continually remove the bit to clean out the shavings, but they make a very clean hole. They also get hot as spade bits. In the dimensions you gave, you'd have to stop to cool a forschner bit 1-2 time PER HOLE.

Being that you've got a mill, and are asking on the internet, the most complex and best solution would be to use a gun drill with air.

 

[tarbellb]

Re: Whhat drill for deep holes in wood?

Auger.

Make sure you select a self drilling (threaded tip) or non.

Fast, clean, strong.

 

[MoonRise]

Re: Whhat drill for deep holes in wood?

Thanks for both your suggestions.

Don't really care for the "cleanliness" of the hole, so that's not an important factor.

DO I need cooling of any type? I guess no, as it's wood, but I also know a spade drill can get hot as fu(k when working it hard, playing havoc with the cutting edge.

What would be the advantage of an auger bit over a brad point bit?

Auger bit (usually) self feeds. That little screw point on the tip of the auger bit pulls the bit in as it turns.

Auger bits can leave a rather rough hole.

For 'decent' general purpose holes in wood, I'd reach for a brad point bit almost every time. A 'regular' length brad point bit in 5/8" or 3/4" should just make it through your specified 5" thick workpiece. Or you can get the 'long' length bits, which in those diameters will usually be ~10-12" long.

http://wlfuller.com/html/long_length_brad.html

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/drlbrad.html

As to cooling, any bit can get hot when used. Let the bit do the work, back it out as needed to remove 'swarf' (wood, in this case) and make your holes. Done.

No 'coolant' generally needed. A 'spray' of compressed air might help blow the wood chips out of the way (might be good or bad, depending on where the chips end up blowing into ).

Don't use cutting oil when drilling in wood.

If you wanted flat-bottom (mostly) blind holes, or overlapping holes, or pretty smooth holes, a Forstner bit would be the one to generally use. As mentioned, you have to back-out a Forstner bit much more often to clear the chips as you drill. For a 5" deep hole (might also need a 'shaft extension' for those depths) with those diameter bits (5/8" or 3/4"), I'd say you'd probably have to back out the bit about 5 times or so per hole (roughly once every rim depth of the bit). But you said you don't want/need 'clean' holes, so I wouldn't reach for the Forstner bit here.

Brad point bit. IMHO.

 

[king nero]

Re: Whhat drill for deep holes in wood?

Thx. Will see what my local mom&pop metal store got in stock, as I need to buy this any way. They do stock a large selection of brad point bits.

Never used an auger bit before, I will probably get one as well just to play with for a bit...

Gun drills aren't cheap, and need pre-drilled start holes. The air cooling would probably do wonders though...

 

[rlitman]

Re: Whhat drill for deep holes in wood?

Gun drills aren't cheap, and need pre-drilled start holes. The air cooling would probably do wonders though...

LOL, yeah. They're way overkill for 5" holes of that diameter, and especially if you're only doing 40, but I had to mention them.

A brad point will be fine, but they're hard to resharpen. I'd probably just use a regular twist drill bit. Easy to resharpen, but you'll have to lift the bit every 3/4" or so to remove chips. This is something that's easy to do on a drill press, but not so easy on a mill.

The sacrificial board underneath is a MUST.

 

[csp]

Re: Whhat drill for deep holes in wood?

You're overthinking this.

Think of how many people drill holes in wood every day with any number of different types of drills and bit and manage to get the job done without giving it any thought.

 

[James-W]

Re: Whhat drill for deep holes in wood?

When I drill all the way thru a piece of wood I usually use a small drill bit to bore a hole all the way thru first. Once I have a pilot hole I drill half-way thru the wood with the larger bit, then I finish drilling the hole from the other side. By doing this I don't splinter the wood when it breaks thru on the opposite side.

 

[brianh]

Re: Whhat drill for deep holes in wood?

Spade or paddle bit however you want to call it, already said finish was not an issue cheap fast and done.

I got to wonder with some replies if actual experience or google ninja technology was used

 

[shawhite]

Re: Whhat drill for deep holes in wood?

Auger bit will be the quickest by far. We use them to drill utility poles all day. ive used spade bits at home for wood working projects while there hole is cleaner it takes considerably longer to drill a hole

 

[rlitman]

Re: Whhat drill for deep holes in wood?

Spade or paddle bit however you want to call it, already said finish was not an issue cheap fast and done.

I got to wonder with some replies if actual experience or google ninja technology was used

You have any experience with doing lots of deep holes with a paddle bit in a drill press? I think not. They're fine for horizontal holes, but won't clear out 5" deep vertical holes drilling down. They also heat badly after just one deep hole.

 

[theoldwizard1]

Re: Whhat drill for deep holes in wood?

For 'cheap' and rough holes, a spade bit can be used (I generally don't like them though, too rough for my likes).

I have always found that spade bits are slow and dull quickly

IMHO, you need a silver and deming bit. 5-6" is right at their limit. Worst case, use a extra long 1/4" to make a guide/pilot hole. Then you can drill from both sides. Like drilling steel, keep the speed down.

Every 1/2-1", pull the drill back to make sure the chips are clear.

About $30 at HF for a full set, but there are some tool stores around here that sell individual bits cheap.

 

[brianh]

Re: Whhat drill for deep holes in wood?

You have any experience with doing lots of deep holes with a paddle bit in a drill press? I think not. They're fine for horizontal holes, but won't clear out 5" deep vertical holes drilling down. They also heat badly after just one deep hole.

Yes I have, I run a wood shop if its getting hot its dull spade bits are easy to sharpen, use a peck drill technique for each inch of depth. If I was doing production day in and out it would not be my choice.

 

[theoldwizard1]

Re: Whhat drill for deep holes in wood?

Y... if its getting hot its dull spade bits are easy to sharpen, ...

That would be a LOT of time in front of the grinder for 40 holes, 5" deep !!

Silver and Demmings. Slow and steady so you don;t over heat the bit. Clear chips often.

 

[gahrajmahal]

Re: Whhat drill for deep holes in wood?

I found when building my deck and pressure treated wood the best bit was a regular metal cutting bit. The spade and auger bit both wandered. (I was trying to drill from both sides and meet in the middle). The small screw tip on the auger pulled it off center when finding different wood densities in the posts.

 

[FullRaceMerc]

Re: Whhat drill for deep holes in wood?

At the shop we'd use a spur bit for that job. About 6" long, so you'd have to chuck it carefully. We cut a lot of holes between sharpening. These don't have a self feeding pilot, which is nice for drill press type work. We use a similar self feeding bit in the field to drill thru framing over about an inch diameter, & auger bits for smaller field drilling, but those don't seem to be as controlled & accurate as the spur bit is in the drill press.

Looks like it's actually called a "multi spur bit" while searching for a pic.

 

[tarbellb]

Re: Whhat drill for deep holes in wood?

I would pour exactly 2.4 oz of pure ethanol, wait 3-4 minutes for it to properly penetrate, then light with a torch (LP ONLY!).

That should yield a perfect 0.625" hole at 5". Adjust your ethanol to 2.8575 oz for a 0.75" hole.

Has this question been beat enough?

 

[king nero]

Apparently, for what I thought was a simple question, there isn't a real consensus. Many ways to skin a cat, I suppose.

 

[brianh]

Re: Whhat drill for deep holes in wood?

That would be a LOT of time in front of the grinder for 40 holes, 5" deep !!

Silver and Demmings. Slow and steady so you don;t over heat the bit. Clear chips often.

Now I understand why your bits are burning up in wood, fast feed rate and lower rpms the bit is cooling as it cuts cold wood.

Too slow a feed rate and you have heat friction.

And yes this thread is beat to death.