Rules on pre-drilling sizes for screws

[Thomas G. Marshall]

I'm never quite sure what the best practices are for pre-drilling holes for screws.

What I have been doing is holding the drill bit in front of the screw at eye level and trying to sight it to see if I can still see the shaft of the screw behind it. If I can just /barely/ see it, then I know that the screw's shaft will be a smidgeon larger than the hole it's teething into, and that's what I'm aiming for usually.

Note, I'm not talking about the case where I need a hole large enough in a board for the threads to spin freely to pull the board down to something underneath. I'm talking about the underneath business, but perhaps there are rules for the board here too.

Fundamentals:

1. Does pre-drilling generally create a stronger hold, because presumably there is less wood pushed to the side of the screw? Or does the stress of the wood split to the side add to the hold against the threads?

1. Should a pre-bore be large enough to only grab the threads? Or is this only necessary for the harder of the hard woods?

Thanks!

[Andy]

Sounds about like my technique - except sometimes I measure the screw's shank with a dial caliper, and grab the next smallest drill bit from the size I measured. I'm definitely not suggesting this level of precision is necessary - just for me, my caliper and decimal- fraction conversion chart are easier to reach than my drill bits, and this way I can grab the right drill bit the first time. Sometime if I get smart I'll measure shanks on all the screw sizes I use commonly, and write them on the screw bins, so I won't have to measure for most of them.

I don't know about this, but it sounds like the beginnings of a very interesting experiment! I'm guessing it would depend a lot on wood type, screw type (especially thread depth?), and probably grain orientation. I'm looking forward to seeing more educated replies and/ or good references for this information.

Sorry I can't actually help more, but I think you're on the right track. At least you're not alone! Good luck, Andy

[Charlie M. 1958]

Easier yet...Somewhere on the internet (sorry I didn't save the link but a little googling should get you there) I found some pdf files with all sorts of interesting shop reference charts. One of these tells you exactly what size drill bit to use for each different wood screw size. It even breaks it down to different size bits depending on whether you are using hardwood or softwood.

I printed out the charts with the info I use frequently, laminated them, and keep them in easy reach of my workbench.

[J T]

Wed, Oct 31, 2007, 1:34pm (EDT+4) [e-mail] (Thomas=A0G.=A0Marshall) doth posteth: I'm never quite sure what the best practices are for pre-drilling holes for screws.

Rules? We're supppsed to have rules now? My rule is to not use screws unless it's o something I plan to take apart again. On the few occassions I do use screws, and pre-drill a hole, I just make sure the bit is no larger than the body of the scew.

JOAT It's not hard, if you get your mind right.

- Granny Weatherwax

[papadoo1]

You should be able to find a chart here =

[Lew Hodgett]

Use a dial caliper (About $20) and measure screw.

Use 75% of thread dia for pilot holes.

Use thread dia +.015 for clearance holes.

Have fun.

Lew

[Kerry Montgomery]

Rules? We're supppsed to have rules now? My rule is to not use screws unless it's o something I plan to take apart again. On the few occassions I do use screws, and pre-drill a hole, I just make sure the bit is no larger than the body of the scew.

So just use a 1/16" bit for all pre-drilling? Kerry

[Pat Barber]

Let's go to the source:

One of the older and largest producers of drill bits.

Thomas G. Marshall wrote:

[LRod]

Top posted for your convenience.

(In other words, you can look at the earlier text by scrolling down if you *want* to, but you're not forced to wade through dozens of lines of unedited material to get to the meat of THIS post:)

**************************************************************

There is an article at WoodCentral which has the correct sizes of drill bits for screwhead, shank, and root diameters of common sizes. There's also drilling and tapping information for metal work.

[J T]

Wed, Oct 31, 2007, 11:47am (EDT-3) [e-mail] (Kerry=A0Montgomery) doth query? So just use a 1/16" bit for all pre-drilling?

Are you asking? Or what? Using just one size bit might make sense for you, but not for me. I might use screws with a body smaller, or larger, than 1/16". How about pre-drilling holes for nails? Any thoughts on that? Or furniture glides? I usually pre-drill for those, for sure.

JOAT It's not hard, if you get your mind right.

- Granny Weatherwax

[Limey Lurker]

I forget where I saw it, but some research was done that proved that pre-drilling for wire nails (round-shanked nails) made the nails grip more securely, (probably because the wood contacts the nail over 360 degrees of the nail's circumference, and not just on 2 sides where the grain divides around the nail).

[Nova]

See:

[Thomas G. Marshall]

LRod said something like:

Top posting is convenient as you point out for email, because in email there are two contributors, and less need for interleaved posting.

Please see further down (for a visual demonstration.)

But if in a usenet environment, you have many interleaved posting opportunities. Pretend I was someone who wanted to repond to both your post and this part of my post. In such a case, top posting is the formula for a mess.

Please scroll further down....

Someone replying now to this point as well would want to interleave here.

Interleaved posts by their nature follow top-down. An interleaved comment follows immediately the paragraph or line it refers to. But your top post is bottom up. But a response to a *part* of your top post (interleaved) would be top down. If there were several cycles of interleaved posts and top posts a complicated conversation would be nearly impossible to follow.

And you have no idea as to how complicated a conversation an existing thread might turn into.

[David Todtman]

All this is interesting. I too, occasionally, use callipers to help in pilot drill bit choice. However, I usually just eyeball it: hold a bit against the screw seeking the bit that looks like it is the same size as the shank of the screw. I don't build wood stuff for NASA.

[Puckdropper]

"Thomas G. Marshall" wrote in news:kn7Wi.6420$pT.2027@trndny07:

*snipped and trimmed for content and length*

My newsreader makes reading messages that are either top, middle, or bottom posted easy. I have it set to display the original message (denoted with the standard character > by 98% of posts) in a smaller size font than the new message.

It will also automatically scroll down to the new text when I ask it to.

Because of these settings, I just don't see what the problem with where someone put his original message is. As long as things are kept neat and trimmed, reading messages is really quite easy.

Fyi, I'm using Xnews.

Puckdropper

[Upscale]

I usually do that too unless I'm afraid of something splitting or I want to be more exact and then I fit the screw to one of the holes in my drill index. I can tell what kind of grab the screw will have depending on how far up the shaft the threads grab in the index.

[Thomas G. Marshall]

Puckdropper said something like:

*snipped and trimmed for content and length*

My newsreaders delimit different reply indentation levels with differing colors. Does *not* solve the problem of the mess that you're inviting when you top post.

As an example I just did what you did. *Of course* you can hack out all but one sentence and claim you have trimmed it down neatly and made something easy to read. But then you have also misrepresented the entirety of what was said.

This is made much worse by the fact that there are some newsreaders out there that group messages into threads by subject line and not id's. When you change subjects, you have to go out of your way to make sure that the entirety of what was said is represented, because people with such newsreaders will not easily understand what the original point was because it is embodied in a different thread.

There are many well written explanations out there for why top posting is bad. A quick google gave me too many to start listing them here.

For the record, years and years ago I used to top-post in usenet myself. I felt that it was a cleaner representation of information: place the information right at the top, like in email. I was dead wrong.

[Thomas G. Marshall]

Limey Lurker said something like:

...[rip]...

That much makes intuitive sense, but it's not 100% clear to me that the force from the memory of the wood (the degree to which it is trying to slam back in place) isn't a stronger force to hold the nail in place.

[Mike Marlow]

Some might consider it better to snip unwanted text rather than leave that unedited material in place. Obviously, others don't, but the dozens of lines of unedited material has never been a good argument for top posting. In fact, leaving all that irrelevant text in place has never been a good practice for a lot of reasons. But... I don't really care that much myself about top or bottom posting and I'm getting out now before this turns into another extended thread debating the two styles.

[Thomas G. Marshall]

Mike Marlow said something like:

Good idea. I was convinced once that top posting was superior, but it wasn't long before I figured out why.

But of all the usenet skills, getting out before the flame happens is one of the better ones. :)