screwing into a glued join gap - Woodworking Talk - Woodworkers Forum
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post #1 of 11 Old 01-06-2016, 11:25 PM Thread Starter
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screwing into a glued join gap

Hi, please can anybody tell me how safe or bad is doing what you see in the picture below? I got this circumstance in a project, and I don't know how recommendable is screwing like this. I know that I can use 2 screws and screw into each board. but for aesthetics, I don't want to do that and need to use only 1 screw. I have planed pre drill and then screw, will be the glued join compromised with this action? I can also move a little the screw, in order to take it away from the gap, but I need centered, just for aesthetics.

Wood thick is 0.75", and screw is about 1.5"

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post #2 of 11 Old 01-07-2016, 02:40 AM
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With a well prepared glue joint, you shouldn't have any problems. I do that all the time, and I've yet to have problems. Just make sure to pre-drill, otherwise you'll split the joint

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post #3 of 11 Old 01-07-2016, 09:31 AM
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Hopefully you don't have a gap, but a line where the glue is, just drill a pilot hole for the screw.

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post #4 of 11 Old 03-11-2016, 06:32 PM Thread Starter
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Hey guys, today had some problems screwing some #8 screws into this MDF configuration. They are splitting and ruining my mdf piece very easily. Excluding the threads, the screw is 3.0mm, and 3" long, then I drilled a hole using a 3.00mm bit, 3" depth, but it ended like this (second picture below, that mdf piece was a test). did this happen because of the mdf sandwich? I notice mdf to be very delicate, I split it even when drilling the hole, so next time I was more careful with the drill bit, but still the mdf was ruined once I screwed the screw. So then whats going here? I tried using a bigger bit, 4mm, but I am loosing screw tightening. In the picture below, the screw looks very forced, I did that once I noticed a light splitting, and it ended like that. Now I am not confident about using screws, but dowels and glue, even machine screws and glue, making a hole of same diameter including threads, I did this before and of course impossible to split the piece. What do you think about this?

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post #5 of 11 Old 03-11-2016, 07:28 PM
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Could your pilot hole be too small?
What kind of screw is that?
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post #6 of 11 Old 03-11-2016, 08:09 PM
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I dont recall ever screwing MDF. I always used glue and an air nailer with "T" head nails.
You will also have better luck with just joinery and glue with MDF. Also note that all MDF is not alike, just like all metals are not alike.
The stuff from Home Depot is about the crappiest you will ever find.
If properly laid out, the dado joints, when assembling, would be self aligning.
There are several ways to make identical pieces and mirror images with dados
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post #7 of 11 Old 03-11-2016, 08:51 PM Thread Starter
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Originally Posted by GROOVY View Post
Could your pilot hole be too small?
What kind of screw is that?
The screws are #8 - 3" phosphate power interior wood screws. Their diameter is 3.0mm ignoring threads. But that does not matter, with my little experience in present and past, and after reading internet, have concluded that it's not convenient screwing mdf into the edges, only on its surface (picture below).

In the past I had the same problem, I thought it was because of the 1/4 screws I was using, which were to big, I pre drilled also, but the same thing happened, so I ended drilling with 1/4 bit, and put glue in the hole and on screw, and inserted it as if it was a dowel, I liked this idea, but found more convenient machine screws because their threads are less aggressive and play better with the glue we add. There I used titebond III, don't know how convenient is using regular glue, because we need to consider that are using glue as a filler (very little gap between wood and the screw), titebond did a great job, has good viscosity and strong as hell, even harder than the whole wood.

I will never screw a MDF on its edge, only loosen dowels or box joints and a good wood glue. I was so frustrated to see the thing being splitted.

I see a person recommend this technique (picture above), surely it works, but I still feel like we finish with a fragile structure that will eventually rip, just because the screw is not part of the structure, that's why I recommend gluing the screw or using dowels. When I use a screw as a dowel or a segment of threaded rod, I prepare the rod segment by brushing it with a metal brush, that way the glue will hold with more force, now having three holding factors, the threads of the rod, that they are clean and treated with the brush and a good wood glue.
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post #8 of 11 Old 03-19-2016, 09:14 PM
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We don't use MDF for anything anymore, too many issues.

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post #9 of 11 Old 03-20-2016, 06:28 AM
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Yes, plywood would be a better choice, After all, always drilling into end grain on one layer with plywood.
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post #10 of 11 Old 03-20-2016, 06:37 AM
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You could embed a dowel in the bottom piece of MDF for the screw to bite into.
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post #11 of 11 Old 03-30-2016, 05:41 PM
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Screwing into the face of mdf is OK otherwise biscuit joints and glue. Mdf 's only redeeming feature is it paints well apart from that it's a pain in the ass, mind u I recently made some lovely display cabinets out of oak veneered mdf at a fraction the price of solid oak and once I'd veneered the edges you can't tell its veneer. Mdf knackers your tools and its carsonagenic, why the hell do we use it? oh yeah it's cheap.
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