Kreg Jig in MDF....

[Corey Hallagan]

I have some sheets of 3/4 MDF laying around and I want to use it for the carcasses of my shop base cabinets. If I use the Kreg to assemble some of the cabs, do I use the coarse or fine screws? Any tips on using the jig to on MDF?

Thanks,
Corey

[Steve Evans]

Corey

Keep in mind that you're getting this advice from someone who's never used the jig on MDF, but if I was a betting man. I would bet that you'd use the coarse screws. You can also try a couple of each out and see if their is any difference.

Steve

[Jim Becker]

Honestly, Corey...not the best method for MDF. There is little or no holding power whether you use the coarse of fine screws, although if you do, the coarse ones are probably better. MDF assembles best with Confirmat screws that are specifically designed for MDF, particle board and other similar products. Because they are pre-drilled with a special step-drill and are larger in diameter, they have good holding power without blowing out and splitting the material.

[Dave Falkenstein]

Corey - Use coarse pocket hole screws in MDF. And I would use glue in addition to the screws. An even better method for MDF cabinets is to use confirmat screws, available from McFeely's, here:

http://www.mcfeelys.com/subcat.asp?subcat=20.1.1.1

Oops - I see Jim and I were answering at the same time - almost the same answer too. Smile.

[Dev Emch]

You want the good news or the bad news? Sorry about this.

MDF cannot not hold a screw for beans. There is one manufactuer of doors in Denver that actually holds a patent on a special inlay strip along the edge of the door to allow for the door hardware to be screwed in. Fancy That!

I would suggest that if your going to use the kreg jig on MDF, that you need to go back after the intial hole is drilled, rebore with a larger hole and glue in a dowel. Come back and redrill the pilot into this dowel and then it will work just fine.

Sounds like a lot of extra work. Its one reason I dont use the kreg jig. Clever idea. But I just prefer not to use it.

[Corey Hallagan]

Hmmmm..... didn't realize this. Well crud, I need the screws in a matter of days. Any chance that these Confirmat screws and drill bits are available at home centers like Home Depot or Menards? Thanks for the info guys.

Corey

[Jim Becker]

Dev, I agree with you regarding pocket screws in MDF or other compressed wood products, but they hold wonderfully in solid stock and plywood, especially when you use glue as you should. (The glue does most of the work) They are fast, strong and self-clamping and also allow for very easy precise alignment...the only thing I use for face frames and similar constructions anymore. But then again, you are also right...preferences count!

[Jim Becker]

Any chance that these Confirmat screws and drill bits are available at home centers like Home Depot or Menards?

Very unlikely. A sheet goods supplier may have them...check your yellow pages.

[Corey Hallagan]

I was planning on using a wood face from on this and use overlay face frame hinges to put on the doors. I will just clamp and glue/finish nail the face frames. Sounds like the Confirmat screws are the answer, problem is time! I have a week off to work on the cabinets.
Corey

[JayStPeter]

I've used both in MDF and prefer coarse. The fine sometimes don't grab.

After reading the other answers, I agree that they won't hold the MDF on their own. I guess I was assuming you were going to glue also. In which case they work great.

Jay

[Jim Becker]

The Confirmat screws are only to assemble the carcass. What you can do to speed things up is use some small square stock to act as glue and screw blocks along the joints on the inside of the MDF carcass...maybe 3/4" square. In this manner you can drill/countersink through the faces of the MDF so your screws/nails will have something to go into rather than the edge of the MDF. It's the edges you have to deal with. I have used this method to build speaker cabinets that you could drop off the back of a truck without problems. Again, you just need to avoid putting "incorrect" fasteners into the edges of the MDF.

Use the pocket screws to build your face frames and biscuits to provide alignment and additional glue surface for fastening the face frames to your MDF carcass.

[Corey Hallagan]

Jay, I would use glue definitely but did the coarse screws pull the two pieces of MDF fairly tight and have you been able to avoid the joints blowing out while putting in the screws?

Corey

[JayStPeter]

Jay, I would use glue definitely but did the coarse screws pull the two pieces of MDF fairly tight and have you been able to avoid the joints blowing out while putting in the screws?

Corey

Yes, and yes. Try on a few scraps to find the right torque setting for your driver. They will strip out if driven too tight. But, the right setting will pull the joint nice and tight. Use the lightest setting that pulls the joint. Using kreg screws I rarely have problems with the pocket hole side. More often, it strips right out and I need to put another hole next to the one that stripped. If you do try to use a regular wood screw there, it will drive itself right on through (same with some plywood).
Also, make sure you have your drill depth collar set properly. If it is too shallow, you leave too much material and it will cause the MDF to split a little. For MDF, I set it on the deep side of recommended so the drill tip is just peeking through.
Heck, since these are only shop cabinets, you can decide if you want to continue using them on MDF based on the results

Jay

[Corey Hallagan]

Thanks Jay, it seems like the Confirmant screws that Jim and others advise of are probably the best choice, but I can't get them here quick enough. I will try to use the Kreg screws first and your advise on testing is a good one. Thanks for all your help guys! Also Jay, when you strip a pocket hole out, are you saying you can usually run a regular wood screw in that hole and it will hold or are you saying it doesn't work to do that.
Thanks!
Corey

[Alan Tolchinsky]

Corey, I've found that biscuits hold great with MDF. Do you use biscuits? I'd rather use pocket screws myself ( they're so fast) but sometimes you have to go with what works better. Biscuits!