Calling all screwing experts

[HeathRobinson]

Wood screws are not a subject I have given much thought to in the past ... What? :shock: You didn't think I meant that kind of screwing did you!?

I want to use some screws in the construction of my bench so that I can break it down in the future when moving. The bench is predominantly ply but overall is a mix of ply, MDF and solid wood. I'll describe the scenarios and perhaps those who have the experience can enlighten me as to the proper screw and technique for each scenario. This is the bench I am building.

1. Reinforcing the mortise and tenons in the legs. Legs and stretchers are all laminations of different lengths of ply. Srews will go through the face of ply on the leg and pass through the face of the ply on the tenon. Yes, before the comments from the peanut gallery begin, it is a plywood mortise and tenon :lol: Seemed a simple way to make a sturdy base for a beginner. At this point these reinforcements might not be necessary, I suppose I could even replace the screws with dowels. The mortise and tenons will be glued too.

2. I'm using a plywood panel as a side stretcher. Screwing a the face of the plywood panels into the exposed edge grain of the ply laminations of the legs. Effectively ply face to ply edge. I'm worried that this join will not be secure enough because I'll be screwing side on into the ply laminations and because it might split the ply.

3. I'm going to put solid wood battons along the inside of the aprons that I'll later use to secure the worktop and these battons will be screwed into the ply apron, so through solid wood into a plywood face.

4. The worktop itself is a layer of ply and a layer of MDF. I'd like to be able to keep the two unglued so that I can flip them over at some point. This means using screws to hold them together. So this is a plywood face to MDF face (as if that matters in MDF).

5. Back to the batons for attaching the worktop. I then want to screw the top to the battons installed in the base and this will be a screw going through the solid wood batton up into the face of the ply part of the worktop and possibly through that into the MDF.

6. A solid wood edging around the worktop. All screws will go through the face of a piece of solid wood but will be securing that to either the MDF layer of the worktop or the edge of the ply layer.

I plan to countersink all of these screws and would also like to know if there is any science to creating counter sinks? Or are they all pretty much the same and I can get away with any counter sink bit?

Thanks

PS. Woodbloke, the plan is to pop a solid bit of worktop on top of this worktop as suggested by you when I first came around for assistance with my woodworking woes I still have the plan you drew. Only the base is different in this design.

 

[woodbloke]

Wood screws are not a subject I have given much thought to in the past ... What? :shock: You didn't think I meant that kind of screwing did you!?

I want to use some screws in the construction of my bench so that I can break it down in the future when moving. The bench is predominantly ply but overall is a mix of ply, MDF and solid wood. I'll describe the scenarios and perhaps those who have the experience can enlighten me as to the proper screw and technique for each scenario. This is the bench I am building.

1. Reinforcing the mortise and tenons in the legs. Legs and stretchers are all laminations of different lengths of ply. Srews will go through the face of ply on the leg and pass through the face of the ply on the tenon. Yes, before the comments from the peanut gallery begin, it is a plywood mortise and tenon :lol: Seemed a simple way to make a sturdy base for a beginner. At this point these reinforcements might not be necessary, I suppose I could even replace the screws with dowels. The mortise and tenons will be glued too.

2. I'm using a plywood panel as a side stretcher. Screwing a the face of the plywood panels into the exposed edge grain of the ply laminations of the legs. Effectively ply face to ply edge. I'm worried that this join will not be secure enough because I'll be screwing side on into the ply laminations and because it might split the ply.

3. I'm going to put solid wood battons along the inside of the aprons that I'll later use to secure the worktop and these battons will be screwed into the ply apron, so through solid wood into a plywood face.

4. The worktop itself is a layer of ply and a layer of MDF. I'd like to be able to keep the two unglued so that I can flip them over at some point. This means using screws to hold them together. So this is a plywood face to MDF face (as if that matters in MDF).

5. Back to the batons for attaching the worktop. I then want to screw the top to the battons installed in the base and this will be a screw going through the solid wood batton up into the face of the ply part of the worktop and possibly through that into the MDF.

6. A solid wood edging around the worktop. All screws will go through the face of a piece of solid wood but will be securing that to either the MDF layer of the worktop or the edge of the ply layer.

I plan to countersink all of these screws and would also like to know if there is any science to creating counter sinks? Or are they all pretty much the same and I can get away with any counter sink bit?

Thanks

PS. Woodbloke, the plan is to pop a solid bit of worktop on top of this worktop as suggested by you when I first came around for assistance with my woodworking woes I still have the plan you drew. Only the base is different in this design.

Simon - as I understand it:
1. I'd use dowels here if it's to be a permanent end of the bench...couple to each tenon ought to do.
2. Not sound. Where you want the screw to go into the edge of the ply, insert a 25mm bit of dowling about the same distance in from the edge. The screw then bites into the dowel and will give you a much better joint.
3. No problem there
4. I'd glue and screw both together to get a really solid top which is one of the main requirements of a bench. You could use a piece of hardboard if needed as a sacrificial top...just pin this in place and punch the nail heads under, but if you're careful in how you work, you won't need it. If you decide not to have a hardboard top, make sure that the surface is well waxed so any glue is easily removed..you could also wax the hardboard top.
5. No problem there...just make sure that the screw won't break through the upper surface...you knew that though
6. You could get away with just gluing the edging on here...is it likely to be removed or damaged?
No problem with making a countersink...use a high speed steel rose bit if you can find one. When driving the screws in, make sure that they're lubed with a bit of candlewax or Vaseline, makes life a lot easier :wink: - Rob

 

[HeathRobinson]

Thanks for that Rob. A question regarding the glueing and screwing of the laminated top then ... what kind of screw to use? The ply is 18mm, MDF is the same but I've read of different screws being recommended for each type of man-made-panel. Coarse thread, thin shank for ply. Same again for MDF but with a shallow angle on the thread to guard against bulging. Confirmat screws were mentioned as ideal for this purpose but their ability in ply was not.

I've also read that joining panels face to face with screws like this can lead to bridging between the panels. Luckily the context I read that in also covered techniques to guard against bridging but one to be mindful of for me.

I suppose that with glue this may not be such a problem. I'd then use the removable hardboard top for protection like you suggest.

Thanks again for the input. Very helpful as always Should be getting the pieces of bench that were too large for the car delivered today and then it's on to cutting which I'm happy enough doing. The use of screws has got me a bit concerned though as my knowledge is seriously lacking.

Simon

 

[woodbloke]

Simon - there are some very fancy screws out there if you want to spend some dosh...Spax screws are good but very pricy :shock: I believe. I just use the el-cheapo ones from Axminster or similar, as long as the heads fit a No2 Pozidrive bit. It's also useful to drill a pilot hole ('specially for going into mdf) roughly the same size as the core dia of the screw you're using...easy enough to guesstimate the size by eye - Rob

 

[Chems]

I came in here to help but I think I may be the wrong kind of screwing expert. . . . . . . .

 

[Benchwayze]

HR,

I laminated two 8' x 2' sheets of WPBP ply, to make a benchtop for my Coronet Major.

I glued the sheets together and put screws in from the underneath, to act as 'cramps' whilst the glue dried.

I placed a dozen along each long edge and a staggered row down the middle; and if I recall, 6 across the short ends. I used plain old 1.25" x no 10s.

As I said, I removed them afterwards, and squared up the edges on the jointer. The bench is still in service. Nary a problem. Although a Coronet Major bearing down on a benchtop does tend to keep the layers together I suppose!

Were I to use screws to make 'K/D' joints in large timbers I might think about coach-screws of an appropriate size.

HTH

John

 

[Racers]

Hi, HeathRobinson

Is it going to be glued together? it it is then the screws are only used as clamps until the glue has set, so any screws should do. The side panels are going to be the weakest joint if you could make a rebate in the legs and glue it in would be best, may be you could use two strips of ply for the inside face of the leg and leave a gap for the side ply, like the leg tenon arrangement.


Pete