First timer with dominos

[Martyj27]

After procrastinating for a while I finally pulled the trigger on. Df500 for an upcoming home library project.

some questions if anyone can help:

1) for 18mm plywood butt joints eg carcass assembly, are you using 30mm dominos with 15+15mm depths (i.e. leaving just 3mm left in the vertical sheet panel) or something different?
2) glue... Are you just glueing the length where the two pieces of wood meet or glueing in the dominos themselves?
3) for multiple shelf alignment, was thinking to make the left hand vertical dominos to be tight and right hand to be wider but for those that make bookcases etc, what did you find worked best?
4) further to the bookcase example, are you just using dominos for alignment eg 2 on each end and then supplementing with screws, purely relying on glue or adding more than 2 dominos to each shelf end? (Will be 350mm deep shelves, max span 700mm)

Thanks in advance

 

[ChuckM]

1) For 3/4" (19mm, close to 18mm) plywood, I prefer to use 6mm x 40mm dominoes; 15mm deep on the face grain, 25mm on the end grain (make sure you reset the cutting depth, or mill all the 15mm deep mortises first!)

2) Glue (after dry-fitting) -- on everything: the mating edges, mortises and tenons

3) Width setting -- Tight for the first two mating mortises (i.e. one tight mortise on the first board, one tight on the mating board) for alignment purposes. In practice, I mill all tight mortises on one board, one tight and the rest middle on the second/mating board. This way, you won't have to struggle with two "loose" (un-upright) tenons that sometimes can happen during glue-up.

4) For strength -- Dominoes all the way, no screws (at least for me). I use screws only for hinges, knobs, etc., not for joinery.

 

[Martyj27]

Thank you ChuckS great responses!

Makes a lot of sense re the width setting approach you take, have spent the morning watching quite a few videos and seems to be the approach many are happy with or a variation (i.e. the furthest apart are tight mortises and the ones in between are loose etc)

For 350mm shelf depth, I was thinking 3 dominos on each end is appropriate, does that sound about right? There doesnt seem to be a hard and fast rule but thinking given it will be for a bookcase, better to have the additional strength of the middle domino.

I will be adding hardwood lip to each shelf (20mm thick with around 40mm in vertical height) that I will domino and glue to the front of the shelf.

I see some people domino the shelf to the BACK panel and some don't. I'm only using 12mm plywood backs so my thought (and sagulator calcs) were that I wouldn't attach to the back to each individual shelf but happy to hear advice to the contrary if required

Thanks again!

 

[ChuckM]

Hi Marty,

My Tight-Middle width suggestion is general advice, mostly for ease of assembly. For max. strength, always go with the tight to tight configuration. In fact, if the no. of tenons involved is small, the tight-to-tight setup won't present much assembly problem. So in your case, I'd use 3 (4 max) dominoes all in tight setting, making sure you dry fit everything before opening the glue bottle. If one or two dominoes are stubborn to fit, you can shave their edges a tad (use a block plane or chisel or sanding).

You can find the spacing guidelines in the user manual.

[attachimg=1]

I use a back panel in a carcase work to resist racking, not for increasing the shelf strength, so I've never built a bookcase or shelf with the shelves fixed to the back. 12mm (1/2"?) plywood sounds quite a thick piece for a back panel. The back panels I use are usually 6mm or less. (I think IKEA bookcases are meant for the back panels to be nailed to the shelf pieces.)

 

[Martyj27]

Thanks again Chuck.

Will go with the 3 dominoes in a tight setting. I saw a youtube where a guy did exactly as you said and kept a separate box of shaved dominoes just for dry-fit ease so will set about getting that sorted. Have managed to learn a few alignment tricks over the past 24 hours so fairly happy and keen to give it a go. As luck would have it I've been locked out the workshop for the past fortnight as got an injury almost the day the DF500 arrived so itching to get back in.

Re back panel, my 12mm is definitely on the thicker end but after making quite a lot of built-in wardrobes I really like it, not just to resist racking but also to help square help the carcass at assembly. Additionally, and in this particularly case, I have some sockets going into the back panel and the dry-lining back boxes normally specify 7-15mm board.

Think given I'm using full sheet height 2.4m for the bookcase, I'll simply nail/screw from the back just into the middle shelf just to keep it nice and pinned tight to the back of the shelves as opposed to providing shelf strength. With the front hardwood lips and short spans, should be fine from a sag perspective and worst case if it starts to present itself, at a later date I can just add some strips underneath the shelves and glue to the back panel.

 

[ChuckM]

Have fun with your first Domino project!

 

[Huey52]

Excellent advice [member=57948]ChuckS[/member] !!  I tend to standardize on 5x30 simply so I don't have to readjust the depth and rather use more tenons if necessary. But I do use 6x40 for bit thicker/wider stock, again if I can maintain respective piece depth setting. I'm not really lazy but sometimes elder-forgetful so for me depth consistency helps. 

 

[ChuckM]

Yes, Huey, if the 5mm dominoes give enough for a project and they are used, they'd eliminate the risk of blowouts. For 3/4" hardwood stock, I also use 8mm tenons instead of 6mm ones for added strength where needed.

 

[C8H10N4O2]

Just a reminder to remember to only adjust the domino cutting width setting knob (tight/loose settings) with the machine is running (but not actively cutting).

 

[Lincoln]

Re. the back panel - definitely screw it to the shelves. For a 700mm shelf, three per shelf would be sufficient. If you don't, you'll get an unsightly gap.

 

[ear3]

[member=81765]Martyj27[/member] If you still want to use 5mm dominoes, would be preferable to do 12mm depth on the board where you are plunging on the face (giving you 6mm left of material, as opposed to 3mm) and 20mm depth on the board where you are plunging into the edge.  Or, if you are going with 6mm dominoes, 12 and 28 respectively.  3mm is not that much of a buffer, and particularly on the tight mortises, the hydraulic action of the glue can cause a blowout on plywood.  You will still be okay if you do 15x15, or 15x25, but just take care not to slather too much glue on the tenons in the tight mortise.

For that depth of shelf, I would do 4 tenons rather than 3 btw.

What's your clamping strategy for this?  First time I did one of these I got gaps in the middle of some shelves because I was just using bar clamps on either end.  Results greatly improved on subsequent iterations when I added cauls to apply pressure across the entire width, including in the center.

After procrastinating for a while I finally pulled the trigger on. Df500 for an upcoming home library project.

some questions if anyone can help:

1) for 18mm plywood butt joints eg carcass assembly, are you using 30mm dominos with 15+15mm depths (i.e. leaving just 3mm left in the vertical sheet panel) or something different?
2) glue... Are you just glueing the length where the two pieces of wood meet or glueing in the dominos themselves?
3) for multiple shelf alignment, was thinking to make the left hand vertical dominos to be tight and right hand to be wider but for those that make bookcases etc, what did you find worked best?
4) further to the bookcase example, are you just using dominos for alignment eg 2 on each end and then supplementing with screws, purely relying on glue or adding more than 2 dominos to each shelf end? (Will be 350mm deep shelves, max span 700mm)

Thanks in advance

 

[ear3]

[member=81765]Martyj27[/member]

One more note on the glue up.  Over the years I have found it worth the extra effort and time to protect up front against the glue mess in these sorts of builds.  At the time of dry fitting, I lay down blue tape on either side of the joint.  After 2-3 hours, remove the tape and virtually all the squeeze out comes with it, leaving only minimal clean up duties with a chisel, scraper and/or utility knife.  This is especially true with plywood, where it's easy to burn the veneer if you have to do clean up sanding of the glue (or even residual moisture) along the joints.

[attachimg=1]

[attachimg=2]

 

[Martyj27]

[member=81765]Martyj27[/member] If you still want to use 5mm dominoes, would be preferable to do 12mm depth on the board where you are plunging on the face (giving you 6mm left of material, as opposed to 3mm) and 20mm depth on the board where you are plunging into the edge.  Or, if you are going with 6mm dominoes, 12 and 28 respectively.  3mm is not that much of a buffer, and particularly on the tight mortises, the hydraulic action of the glue can cause a blowout on plywood.  You will still be okay if you do 15x15, or 15x25, but just take care not to slather too much glue on the tenons in the tight mortise.

For that depth of shelf, I would do 4 tenons rather than 3 btw.

What's your clamping strategy for this?  First time I did one of these I got gaps in the middle of some shelves because I was just using bar clamps on either end.  Results greatly improved on subsequent iterations when I added cauls to apply pressure across the entire width, including in the center.

Bloody glad you commented as truth be told I had no clamping strategy! This is my step up in woodworking as prior to this I've used pocket holes that effectively worked as my glue clamps but hadn't given it the required thought so looks like cawls & decorators tape are a very good technique.

Think I'll do some experimenting re domino depth, it's basically a U-shape library i.e. only 2 visible ends and even those will have MDF sheets covering the plywood vertical ends so a small bit of tear through is not the end of the world but my primary focus is strength following by reducing mistakes i.e. need to consider if switching from 20 to 12 and back could create a scenario where I end up with 2x12s or 2x20s by accident. Now I know in theory it shouldn't but with around 40 shelves I personally won't rule out my incompetence  [tongue]

 

[Martyj27]

Re. the back panel - definitely screw it to the shelves. For a 700mm shelf, three per shelf would be sufficient. If you don't, you'll get an unsightly gap.

Hi Lincoln, would you screw every shelf? Gaps between each is c300mm. My only hesistance is potential for error, ie i can overlay all the screw location measurements and draw corresponding lines on the back but then "blind" screwing into 18cm (3/4") stock leaves me little room for error (eg not going in perfectly straight and breaching the shelf)

 

[Lincoln]

Re. the back panel - definitely screw it to the shelves. For a 700mm shelf, three per shelf would be sufficient. If you don't, you'll get an unsightly gap.

Hi Lincoln, would you screw every shelf? Gaps between each is c300mm. My only hesistance is potential for error, ie i can overlay all the screw location measurements and draw corresponding lines on the back but then "blind" screwing into 18cm (3/4") stock leaves me little room for error (eg not going in perfectly straight and breaching the shelf)

Yes, every shelf. If you mark the centreline and pre-drill a clearance hole you will be fine. If centred, the screw has to be out a long way to break through a 19mm thick shelf. Screw only needs to go into the shelf by approx 35mm.

 

[Crazyraceguy]

Re. the back panel - definitely screw it to the shelves. For a 700mm shelf, three per shelf would be sufficient. If you don't, you'll get an unsightly gap.

Hi Lincoln, would you screw every shelf? Gaps between each is c300mm. My only hesistance is potential for error, ie i can overlay all the screw location measurements and draw corresponding lines on the back but then "blind" screwing into 18cm (3/4") stock leaves me little room for error (eg not going in perfectly straight and breaching the shelf)

Yes, every shelf. If you mark the centreline and pre-drill a clearance hole you will be fine. If centred, the screw has to be out a long way to break through a 19mm thick shelf. Screw only needs to go into the shelf by approx 35mm.

Agreed 100% This goes a long way to stiffening the shelves. Even a single screw in the middle can stop the sagging. This effectively shortens the single span into 2 separate short ones. It's not as good as if it was attached at the front too, like with a face frame, but it does help.
Screwed from the back means that the sag point then becomes, back to front. Shallower shelves also being stiffer and have the side benefit that you are likely to get less of a load on them in the first place.

As far as worrying about hitting the center of the shelf, with the screw, it's easiest done as part of a dry-fit. While assembled, you mark the location of the shelf, from the inside, onto the back. Then drill between those marks, also from the inside, after taking it back apart. Upon reassembly, the holes are predrilled, simple.

 

[Martyj27]

Consider me sold, will screw in from the back. Have c40mm hardwood lips on the front of the shelves but like the idea of extra support at the back.

Which brings me onto another consideration...

None of the shelf carcass sides will be visible (the ones on the end will have MDF covers to add to thickness but also to take paint better).

If I am marking out for screws at the back, is there any reason why I shouldn't screw from the external part of the sides into the shelves?

Will still keep the dominos for strength and alignment but thinking just 3 screws on each shelf side basically acts as a wonderful clamp for the glue-up?

 

[ChuckM]

What is the key purpose of driving those screws into the butt joint? To reinforce the joint?

A domino butt joint would be strong enough for a bookcase /shelf, if properly done. The joint could fail from racking (even with screws added), but the back panel should take care of that. As I said in my earlier post, I've never used screws in conjunction with a loose-tenon joint in any of my furniture builds.

The screws, if spaced properly from the tenons and pre-drilled, shouldn't weaken the butt joint. You could choose to do so, but it'd be an unnecessary step and extra work. If you meant them to be a clamping device, that's a different story.

If you're in the long haul with woodworking as a hobby, perhaps this is a good opportunity to start collecting your clamps of all sorts. I'm a big fan of the Dubuque clamps:https://www.leevalley.com/en-ca/shop/tools/hand-tools/clamps/bar/70618-dubuque-aluminum-bar-clamps (Buy once, cry once. [big grin])

Of course, you can build up your collection of clamps based on your budget and timeline for the hobby. None of us start our hobby with 200 clamps. [eek]

 

[smorgasbord]

None of the shelf carcass sides will be visible (the ones on the end will have MDF covers to add to thickness but also to take paint better).
If I am marking out for screws at the back, is there any reason why I shouldn't screw from the external part of the sides into the shelves?
Will still keep the dominos for strength and alignment but thinking just 3 screws on each shelf side basically acts as a wonderful clamp for the glue-up?

Sure, as long as you don't screw into where the dominos are, screws through pre-drilled holes could be a fine clamp. The pre-drilling is important, as otherwise screws could not only blow out, but actually force the pieces apart. Ideally, the screws would have solid shanks going through the first piece so that the screw portion in the second piece is what pulls the first piece to it.

 

[Martyj27]

What is the key purpose of driving those screws into the butt joint? To reinforce the joint?

A domino butt joint would be strong enough for a bookcase /shelf, if properly done. The joint could fail from racking (even with screws added), but the back panel should take care of that. As I said in my earlier post, I've never used screws in conjunction with a loose-tenon joint in any of my furniture builds.

The screws, if spaced properly from the tenons and pre-drilled, shouldn't weaken the butt joint. You could choose to do so, but it'd be an unnecessary step and extra work. If you meant them to be a clamping device, that's a different story.

If you're in the long haul with woodworking as a hobby, perhaps this is a good opportunity to start collecting your clamps of all sorts. I'm a big fan of the Dubuque clamps:https://www.leevalley.com/en-ca/shop/tools/hand-tools/clamps/bar/70618-dubuque-aluminum-bar-clamps (Buy once, cry once. [big grin])

Of course, you can build up your collection of clamps based on your budget and timeline for the hobby. None of us start our hobby with 200 clamps. [eek]

Was purely as a clamping exercise. I'm slowly building my (Bessy) clamp collection, got about 30 so far but only 8 of those wide enough for a bookcase and given each unit would have around 7 shelves it wouldn't be possibly to clamp front/back of each shelf for the whole unit at once so was toying with using the screws (avoiding the domino) to act as a clamp effectively 

None of the shelf carcass sides will be visible (the ones on the end will have MDF covers to add to thickness but also to take paint better).
If I am marking out for screws at the back, is there any reason why I shouldn't screw from the external part of the sides into the shelves?
Will still keep the dominos for strength and alignment but thinking just 3 screws on each shelf side basically acts as a wonderful clamp for the glue-up?

Sure, as long as you don't screw into where the dominos are, screws through pre-drilled holes could be a fine clamp. The pre-drilling is important, as otherwise screws could not only blow out, but actually force the pieces apart. Ideally, the screws would have solid shanks going through the first piece so that the screw portion in the second piece is what pulls the first piece to it.

Okay thats very clue, pilot holes and I think I've already got a jar of c50mm screws with solid shanks near the head that would suit this perfectly