pocket holes to glue or not to glue?

[andy photenas]

So I want to say thank you to all that answered my post about how you guys clamp pocket holes i got caught up and didnt get back to the post in time to be able to add too what ppl said.
I am not sold that its less work to pocket screw all of those joints compared to mortise and tenon. its really close on time and way less work to clamp 3 clamps then it is to screw 20-30 screws for a faceframe. Added to the fact you have to just hope the joint looks good because its on the side you cant see.

I see a lot of people talking about how glue helps with the pocket holes but u can just snap off that joint with no problem (without the screws)as its end grain to side grain.
That being said is it worth using glue in this joint at all? For me glue has been the hardest part of making a good clamp system because you need to have a flat plate of some kind to get the faces to line up this plate gets covered in glue after every joint . I would love to know what all of you people think thanks I really learn so much from all of you out there thanks again.

[Jim Becker]

Glue is required beyond test fitting with pocket screws for maximal strength. The glue does the work. The screw only helps a little...

[Cary Falk]

It may not be any faster to screw 20-30 screws then to make mortise and tenons for you. It would for me especially with a complicated glue up with 6 mortise an tenon. The beauty of the pocket hole is you don't have to wait an hour or so for the glue to dry. I also don't have a large table to do glue-ups I like the glue for extra insurance. Is it really necessary, probably not. If you remove the screws after the glue has dried it is surprisingly strong and usually takes wood with it. I also dye the glue to match the finish so I don't have to use any wood filer. Probably over kill but makes me feel better. I worked in a cabinet shop as a kid and they used half lap joints. I used a lot of filler and did a lot of belt sanding. I am just a hobbyist now. Speed demon I am not

[glenn bradley]

Lots of opinions on this. Your application will dictate your strength requirements. A pocket-holed face frame, pocket holed to the carcass is pretty well supported for its function. Higher end kitchen and bath will dictate higher end woodcraft.

For glued butt joints . . .

Butt Joint Comparison.jpg

Properly clamps the show faces should always be flush or close enough that just a touch will take care of them. If things are ending up skewed I would check:
- Are the parts milled true?
- Is the surface or clamp pad being clamped to large and flat enough to bring the joint into plane?
- Is there adequate clamp pressure to avoid parts shifting?

[Martin Wasner]

Glue, unless you want to take it apart again, like a loose stile or a temporary brace for an appliance opening end panel.

[Martin Wasner]

I take it you don't have a widebelt to send assembled frames through? We try to keep things as flush as possible, but we take .026" off of each face with the widebelt so things have to be pretty fouled up before it won't be perfect.

[Mike Cutler]

Glenn
Those are interesting graphs.
Thank you for posting them.

[julian abram]

I use pocket screws on most cabinet face frames and always use Titebond II in each joint, makes me feel better.

[Art Mann]

Sorry to disagree but edge grain to end grain glue offers essentially zero strength and you can verify that with a simple break test. I have used several boxes of a thousand pocket screws since I started using them and strength has never been an issue. I have never used glue and never plan to. You have to use them in applications where they are appropriate. They are not a substitute for M&T. However, they are strong enough for probably 75% of all applications where you would use M&T. My objection to them is not structural. My objection is that they are unsightly and should not be used where they can be seen. I suggest you do some destructive testing before you imply that pocket screw joints are not strong by themselves.

Glue is required beyond test fitting with pocket screws for maximal strength. The glue does the work. The screw only helps a little...

[Lee Schierer]

Sorry to disagree but edge grain to end grain glue offers essentially zero strength and you can verify that with a simple test. I have used several boxes of a thousand pocket screws since I started using them and strength has never been an issue. I have never used glue and never plan to.

I agree that the pocket screws add considerable strength to the joint. You can make and end grain to edge grain joint much stronger by applying two coats of glue to the end gran and a single coat to the edge grain before clamping. End grain tends to suck the glue right out of the joint. Once I started doing this with miter joints, (end grain to end grain) I was amazed at how much stronger the joints were.

[Lee Schierer]

Glenn, can you cite the source for those graphs?

[peter gagliardi]

Once you have a mortiser and tenoner, and they are set properly, pocket screws really aren't that much faster, but in either case, glue is needed for permanent fixing.

[Art Mann]

Actually, I sold my hollow chisel mortiser when I got my precision dowel jig and have never looked back. I have done a lot of M&T and found that either dowels or pocket screws are much faster. I have found that most of the time, M&T is 4 or 5 times stronger than necessary whereas dowels are only 3 times stronger than needed and pocket screws 2 times what is needed (guesstimates). The joint I find too weak is the typical glue only cope and stick joint. I have repaired several cabinet doors for people by using dowels to reinforce failed glue joints. Many years ago, this same discussion came up and I convinced myself by recreating an experiment described by Matthias Wandel in a Youtube video. He describes a simple way to obtain accurate breaking strength measurements.

Edit: I found the experiment here https://www.youtube.com/watch?v=apsH8eBfjVA

I forgot about the ridiculous wooden gear driven screw drive. I used a hydraulic jack to apply the force instead. One of Wandel's pocket joints broke prematurely because of his poor craftsmanship.

[Art Mann]

By the way, I have also seen legitimate experiments that show that dowels outperform Dominos in many situations.

[Ken Grant]

Sorry to disagree but edge grain to end grain glue offers essentially zero strength and you can verify that with a simple break test.

If this is true, then there is something wrong with your glue. I have tried to take glued/pocket-holed face frames apart (that I built incorrectly) in hopes of being able to reuse some of the pieces, and the joint will almost never break cleanly. It is certainly not as strong as a long grain glue joint, but in my experience the end grain will usually have some of the long grain attached to it.

I would not send a cabinet out the door without gluing the pocket hole joints.