screw length?

[sockgoblin]

Screw length (apologies this is a repeat of a post in the new project annoucements)


The sides of the cab will be 18mm ,  front and back panels 12mm

the beading /support strips will be 37mm x 37mm . I would like to drill from the inside out , trying to avoid having to fill and sand holes in the front and sides of the cab.

so my question is ,to ensure a strong structure how much screw needs to penetrate the MDF. Standard sizes are 40mm and 50mm , 50mm is too long and 40mm can be countersunk if a deeper penetration is needed. So my thoughts are that I go for 40mm screws countersunk by couple or 3 mm which would give 6mm into the MDF. If I glue as well would this be OK?

[Mysterioii]

No help at all, but just to show how my mind works, when I read the thread title "Screw length?" the first thing to pop into my head was "Yeah, and f*ck width, too..."

[Mysterioii]

Trying to be a bit more helpful, you're talking wood screws I presume?  So they taper to a point?  6mm doesn't sound like much penetration to me, especially if that includes the tapered point.  Not much to grip with.

[t3design]

Screws will not hold for long in MDF no matter how much thread engagement you have. Glue everything. Then the screws (if you use them at all) are just to keep things aligned while the glue dries.

My entire cab is glued together. There isn't a screw in the structure anywhere.

T3

[DLinkOZ]

Agreed with the glue.  I have MDF structures that I built 20 years ago, and are still rock solid.  Not a single screw in them, and I 100% believe that if you were to throw them out a window, the wood panels would break before the seems failed.  Screws are just a little added insurance, if you want, and put glue in the screw holes as well.

[Mysterioii]

I agree with the use of glue and wasn't trying to imply otherwise with my previous short post.  I haven't done much with MDF but I see a lot of disagreement on what works best.  Some screw right into it, others predrill holes.  It's my understanding that it can split pretty easily if you don't predrill, especially if you're going into the ends of the board, but I've seen people get by without predrilling.

If one was using them mostly for alignment then I would question as to whether a brad nailer might be better suited than either going through all the trouble to predrill holes or risk screws splitting out by not predrilling.  I've seen some people say that their brad nailers split the MDF too though.   

I've seen people use dowels or biscuits along with glue on MDF, but once again I've seen caution being given with regards to biscuits as they tend to swell when they sit in the glue...  this is by design, as it helps them grip tightly, but at the same time there is the risk of damaging the MDF.

To be honest all the warnings I've seen about joining MDF it makes me very apprehensive about actually starting a project with it.  After all, you can't JUST use glue (on a large project at least), unless you've got some really big clamps and a foolproof gameplan...   You'd have to use screws, brads, staples, dowels, biscuits or SOMETHING...  and I've seen cautions about every single one of those.   

[sockgoblin]

Thanks all . So screw screws for structural integrity but love them to keep in place for gluing. So are glues all created equal.

[Woodshop Flunky]

Thanks all . So screw screws for structural integrity but love them to keep in place for gluing. So are glues all created equal.

These days, most any wood glue is going to outlive you.  But I use Titebond.  I've also used Gorilla.  Both are top notch.

[kahlid74]

It's pretty much already been stated but I'll add that glue is the way to go.  For any builds I do I use glue and then I use screws to pull the pieces together and hold while the Glue dries.  You can certainly screw from the inside out (Yaksplat does it this way) but for length you'll probably have to test it.  You'll also need to be careful if you use a drill or a drill/driver as the drives can push screws into the wood sometimes and go further than you originally expected.  Just something to be cognizant of.

[DNA Dan]

I go a step futher and use biscuits in my joints. This helps line up long runs and prevents warping on large panels during assembly. I have also seen folks use a small nailing gun to tack items together while the glue dries. Nothing beats a clamp or screw for this though. Even on long panels with 4 clamps, you'll find that a screw every 4-6 inches pulls the pieces in tighter.

[sockgoblin]

thanks all .  I have used screws , clamps and glue. 

Im new to woodworking if I do this again I may try out the biscuit route looks clean

I definitely need more clamps.

[DNA Dan]

I definitely need more clamps.

And that's really the argument for using screws to hold the pieces together. Rather than invest $100 in some good long clamps, you can buy a box of good screws for $20.

[ChadTower]

Pipe clamps are your friend.  For sure.

[Hoopz]

Pipe clamps are your friend.  For sure.

+1

[sockgoblin]

cant afford friends like that

[ChadTower]

Pipe clamps are around $13 a set and you can get them cheaper in 8 packs.  The really cool thing is that you can get a couple of sets and just get yourself a few pipes of different lengths.  Now you have clamps of anywhere from a couple inches to 10' long!

[sockgoblin]

Im in the UK  are pipe clamps known as something else here. I can find F clamps at £60 a set cant find pipe clamps

[DNA Dan]

I would invest in pipe clamps over regular clamps any day. The problem is pipe is not that cheap anymore. By the time you buy the clamps and length of pipe, you're still up in the $100 price range.

[ChadTower]

$15 for the set of clamps.  $15 for a 3/4" x 10' threaded black steel pipe at Home Depot.  Shorter pipes cost less than that.

[DNA Dan]

I'm thinking for a enough to build a cab solely with glue. You're probably at about $20 a clamp for 2-3' in length. You would need at least two, one on each end, then one in the middle to control warping. So atleast three clamps like this. This is totally cheaper than buying a clamp outright and the length is adjustable. I did however come across this http://www.homedepot.com/h_d1/N-5yc1v/R-100194308/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=clamps&storeId=10051&superSkuId=202847868 which I am surprised is <$20 for a clamp that size already made. Screws are still cheaper however.

[LiquidFire]

Biscuits good if sized properly - but you probably aren't going to purchase a biscuit jointer either.

The glue-only idea does work, however a mechanical connection between boards is best. The contact area/saturation of a glue joint is minimal and can become weakened when stressed. The joint is many times stronger and less likely to get stressed if there are screws running through the joint.

In 3/4" MDF or particle/composite boards I would run 2" countersunk deck-type screws (I use 100% stainless fasteners since they will never rust for any reason) with a pilot hole sized slightly smaller, as deep as the screw. Use a corner clamp on eachside to align the joint during drilling. Dip the screw in glue, then glue on both sides of the joint and squeeze the assembly together. Wipe off any excess glue.

After assembly is dry, I would place 3/4" triangle stock (cheap) in every inside joint that your design can tolerate. Glue only OK, but use brads to keep in place till dry. Improves lateral strength by a lot.

Gorrilla brand (or polyfoam glue, everyone nearly makes it now) is by far the strongest when distributed properly, but water-based Elmer's (white or dark) is best for ease of application. Water cleanup means you can over-apply and damp-rag the joints clean.

One consideration in the use of MDF: It is much more susceptible to damp condition damage than plywoods, is heavy and is brittle. Not to ignore the widespread use of MDF for commercial arcade cabs, but that is due to cost and ease of working. MDF & particle board does not like humidity and will expand, warp or disintegrate when damp. Quality plywood (no voids), covered with plastic laminate is my choice. More expensive but negligible for one cabinet.


My opinions only.

[ChadTower]

Those are all excellent points.  He isn't building hardwood furniture, though.  He's building an MDF box.   

[DNA Dan]

MDF is such a nice material to work with, it's just so much heavier than anything else. It's like making a cab out of stone.

[LiquidFire]

There is nothing more uniform and flat than MDF, and it routs beatifully in all directions - not to mention the cost is easy. I have made templates of all of the popular control cutouts out of 1/2" MDF. Really could not use anything else.

My point about using better materials however is that laminated anything is stronger, and I have seen plenty of failing cabinets due to the structural joints not holding up through its usable life.

Your project depends on the foundation you build.

We probably won't be handing our projects down through generations, I get that.

That said, my next cabinet is going to be a 'cabaret' style that is light in materials to begin with. I think it is the only way it can survive in my scheme of things, and making sure it has a quality look and feel will give it a better chance of staying in the house.

Right now, I have departed to building an Air Hockey table (my second) - talk about weight...