Allowing for wood movement

[Marci Anderson]

Hello folks. I have a basic question I was hoping to get some feedback on regarding elongating holes for screws allowing for the wood to move. I see people suggesting to do this, but I would love to hear the different methods on how to elongate those holes. What works? What doesn't? Any tips?

Thanks!
Marci

[Mike Cutler]

Marci

The easiest way I know of to elongate a hole is to mark the length of the oblong necessary to accommodate wood movement, drill the required diameter of the mechanical device that is going through the oblong at both ends of the line,and then use a rat tail file of the correct diameter to make a nice oblong. It takes a few minutes at most.

What is sometimes amazing is just how much wood will move across the grain. I made some 30" wide shelves out of Jatoba and they moved more than a 1/4" across the width, and that's a dense tropical.

I'm sure there are a lot of tips on this one. I'm interested to see other folks solutions for dealing with wood movement.

[guy knight]

i use my domino makes nice holes or if you want fancy holes whiteside makes a couple of bits one for flush head screws and one for pan head screws

[Fred Belknap]

One way I have used is to drill an oversize hole in the head side and use a washer. They have router bits for elongating screw holes.

[Fred Belknap]

I just noticed the little green dot that indicates who is online, nice touch.

[Jim Becker]

I don't get fancy with this...with corner blocks on the aprons (and any necessary intermediate fastening blocks...I just drill the hole and rock the drill back and forth to elongate the hole in the appropriate direction.

(Nice hat Fred... :D)

[Tony Bilello]

I make dado slots on the apron and stretchers and attach as shown in the sketch with shop made wood 'clips'. At the time I made this sketch for a different forum, I couldnt find the steel clips. Since then, I have found them at Rockler and I think I paid about $3.50 for a set of eight. I bought about about a dozen sets.


BTW: The rule of thumb is 1/8" movement for each foot of width across the grain. This is a fiarly close approximation. Along the grain the movement is nominal and I never compensate for it.

[Marci Anderson]

Thanks for the replies. I appreciate the practical advice.

In reference to Mike's suggestion to use rat tail files: I haven't spent too much time on searching for rat tail files, but I haven't easily stumbled across a place (physical or internet) that has alot of these. Where do these things come from? Are they hard to find or is it just me?? :)

[Jamie Buxton]

I find that Jim's method of rocking the drill back and forth elongates the hole at the top and the and bottom, but not in the middle. The bit kinda pivots in the middle. Lately, I've used a bit designed for a Rotozip. It looks like a standard twist drill, but is sharpened so that it cuts well on the side of the bit. I chuck it in a normal drill and just lean on it sideways. Every lumber yard sells bits for rotozips.

For me, the trouble with files is that the hole is maybe 3/16" diameter, and files that small have very fine "teeth", so that filing takes forever.

[Jim Becker]

Jamie, after I rock the drill and with the bit still spinning, I find I can easily add some elongation in the middle of the slot by just holding the drill vertical and manually moving it back and forth...the material in the middle is quite thin at that point and the slot really doesn't need to be very long unless it's a very wide table top. But your point about the "spiral cutting tool" is a good one and folks who own them could leverage the tool for this particular task very nicely! (I don't own one)

[David Keller NC]

Marci - Rat tail files, and chain-saw sharpening files (i.e. - round files) are available at any good hardware store. Not sure if the Home Despot and Lower's has driven out the traditional hardware store in your area, but those small stores are the place to go - I've rarely been in one where there wasn't an older gentleman or lady running the show that knew what everything in the store was, what it's used for, and whether it'll fit your need. The big box stores rarely have employees that can privide that kind of service.

I personally use Jim's technique when I'm building "modern" pieces (as opposed to colonial period repros - those I just allow the part that's cross-grain to crack, as so many of the antiques have done). One thought about rocking the bit - it's better to rock the end of the bit back and forth rather than the using it as a pivot to rock the drill back and forth - the former technique provides a conical hole that's narrowest where the screw head is seated, and the latter technique provides a conical hole that's largest where the screw head is seated.

In typical table-top attachments, you want the space to move on the top of the apron directly adjacent to the underside of the table top. When the top expands/contracts, the screw will pivot on its head, which allows expansion/contraction without the top coming loose from the apron.

[Jamie Buxton]

But your point about the "spiral cutting tool" is a good one and folks who own them could leverage the tool for this particular task very nicely! (I don't own one)

Jim, I didn't say I used a rotozip tool. I don't own one either. I just bought a rotozip bit ($5 for several), and run it in a standard drill. It cuts sideways much better than a twist drill does.

[Doug Shepard]

I think if you find yourself doing a lot of these over time that one of the LV bits is probably worthwhile.
http://www.leevalley.com/wood/page.aspx?c=2&p=52607&cat=1,46168,46171&ap=1

[Jim Becker]

Jim, I didn't say I used a rotozip tool. I don't own one either. I just bought a rotozip bit ($5 for several), and run it in a standard drill. It cuts sideways much better than a twist drill does.


Ah!!! Excellent! (I guess I read that too fast, eh?)