Screws and pilot holes

[Pete W]

How big should a pilot hole be in hardwood?

I've looked at various sources online and most suggestions are in the region of using a bit a little more than half the diameter of the intended screw. Well, I've tried that and the going gets tough pretty quickly, so much so that I'm afraid of snapping off a screw in the hole (using steel screws).

I assume I can go a little bigger, but how big before it's too big and the screw loses its grip?

Any help appreciated!

 

[andrewm]

I don't know of any hard and fast rules but I normally try for a drill that is the same diameter as the shank (not the thread) of the screw that I am using.

Others may have different ideas though and it probably depends on the timber that you are screwing into. Softwoods are probably more tolerant to small holes.

Andrew

 

[Alf]

http://www.diydata.com/information/screwholes/screwholes.htm

I haven't actually checked to see if they've got it right mind you. Generally the same diameter as the shank, minus the thread, as Andrew says is a reasonable rule of thumb. Oh, and a little wax on the screw before driving it can make a world of difference too.

Cheers, Alf

 

[ydb1md]

I second the use of wax or some other suitable lubricant when you're working with hardwoods brass screws or both.

Whatever you do, don't use soap as it attracts water & corrosion, etc. I use beeswax because I have it at the ready but it seems a shame to waste on a screw.

I want to try out some of this Ackempucky stuff: http://www.mcfeelys.com/product.asp?productID=la-0900

 

[MikeW]

How big should a pilot hole be in hardwood?
I've looked at various sources online and most suggestions are in the region of using a bit a little more than half the diameter of the intended screw. Well, I've tried that and the going gets tough pretty quickly, so much so that I'm afraid of snapping off a screw in the hole (using steel screws).
I assume I can go a little bigger, but how big before it's too big and the screw loses its grip?
Any help appreciated!

Hi Pete,

A few things. When I use screws, I usually test my hole sizes in a piece of scrap and move up or down in 64ths or, most often, use letter or numerical sized bits. And as others mention, I always use a little wax.

I placed a drill sizing chart for general guidlines on my website if you want.

Drill Size Chart

The other "advice" isn't in response to your question, but hey, it's free :lol:.

Second is that when using screws I always use a steel screw of the same size to cut in the threads if the hardware is going to use brass screws, then replace with brass for the final assembly. Not directly on point as you are using steel screws, so just an fwiw.

Third and totally off point is that for hardware such as hinges, clasps, etc., I usually avoid the whole screw thing and use appropriate brass bolts and drill and tap the holes for them. A bolt has a much stronger hold than a screw, esp. in thin material.

 

[Anonymous]

same as andrewm here - if possible a little smaller than the shank

 

[Midnight]

I usually avoid the whole screw thing and use appropriate brass bolts and drill and tap the holes for them.

someone wanna tell me why I didn't think o that...?????

](*,)

there's months when this whole former blonde thing jus.........sux.....

thanks for the tip Mike.....

 

[MikeW]

I usually avoid the whole screw thing and use appropriate brass bolts and drill and tap the holes for them.

someone wanna tell me why I didn't think o that...?????
](*,)
there's months when this whole former blonde thing jus.........sux.....
thanks for the tip Mike.....

You're welcome...btw, this was something my grandfather use to do, as well as my dad.
It wasn't until few years or so ago that I started doing it. I had made a jewelry box that had a 1/2" thick top and needed something with a stronger hold than screws to attach the hinges.

Since then I use them in place of screws to attach most hardware that would otherwise use screws.

I purchase most of my taps and screws at a local hardware store, but Lee Valley has these taps and these flathead bolts.
Beware that your currency might switch...

 

[Midnight]

I've seen machine screws used in holes tapped into wood quite a bit; Pat Warner's a fan of them, but I've never seen anything below a 1/4" being used.. never would have thought that a #2 would work...

I presume these are UNC threads?? Wonder how it'd take to metric...

hmmmmmm... drill, tap and heli-coil..??

ideas blossoming at this time of night is never safe for me..

plenty food for thought though... thanks again Mike, just might have cracked a prob I've been mulling over...

 

[SlimShavings]

Mike W
Do you actually drill and tap the hardwood. SOunds like it would work to me in harder woods but how about stuff like cherry and poplar :-k

 

[MikeW]

...I presume these are UNC threads?? Wonder how it'd take to metric...

Hi Mike,

Smallest I've done is a #3, maybe a #2 sized small box hinge.

I've done metric, hence the chart has metric /drill/tap sizes on it. Works just fine. Of course, you would need to find the source of the flat head bolts else just get the taps and bolts listed by LV.

I had retrofit some existing metric stuff so I didn't need to find the bolts.

... thanks again Mike, just might have cracked a prob I've been mulling over...

Glad I could help...

 

[Chris Knight]

I can't find it now but Lee Valley had an article on the subject of using machine screws in wood based on some research they did. Rob Lee might be able to point to it.

Bottom line was that they were generally stronger than woodscrews IIRC

 

[MikeW]

Mike W
Do you actually drill and tap the hardwood. SOunds like it would work to me in harder woods but how about stuff like cherry and poplar :-k

Hi Slim,
Yep, drill and tap the wood directly. I've done cherry and it works fine. Never tried poplar. But as there are more threads per inch than a wood screw, I would imagine it would work fine, other than it would be important to control the tap feed really well.

With a screw, the softer the wood the smaller the pilot hole. Same with taping for a bolt. The chart shows drill sizes for 60% and 75% thread contact. The softer the wood, use the drill for 75% thread contact.

As I almost always use hard exotics, I typically use the 60% thread drill size, though sometimes I use somewhere between it and the 75% size. For really short bolts I use the 75% drill size no matter what. As always, I test in project scrap.

The first time I used bolts it was for a thin box lid. In scrap of the same thickness I attached a hinge using two unaltered screws just and pried it off to feel the amount of hold the screws had. Really, there was little hold. I then tried screws I ground the points off of and tried them. Easy failure again. I nearly could not make the bolts fail.

Make sure to get both the starting tap and a bottoming tap. In fact, I ground the bottoming tap a little to really go all the way to the bottom.

 

[Alf]

I can't find it now but Lee Valley had an article on the subject of using machine screws in wood based on some research they did.

Not exactly what you mean, I don't think, but fwiw.

<ramble mode on> Whilst looking for it I found a reference to the Museum of Garden History in their letters which was a surprise. I did a bit of voluntary cataloguing of exhibits for them some years ago, about this time of the year. Suddenly I was right back there again, listening to the chinking of tea cups and relishing the coolness of the old church in contrast to the heat and dust of the busy main road outside. S'tordinary thing. Sorry, totally irrelevant, but I thank the thread for casuing me to happen across the reference. </ramble mode>

Cheers, Alf

 

[Pete W]

Thanks for the help, everyone.

Candlewax made all the difference. Sorted now

 

[devonwoody]

I'm not running down the tip made by mikew but if I was using brass bolts
I would most probably want to countersink a brass plate (hinge dimensions) on the underside and tapped for the bolts.

I like belt and braces.