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Dovetailing MDF?

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flanajb

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I have to make an MDF carcass and wanted to avoid having to use screws to joint it. Given that I think that biscuits and glue alone will not provide a sufficiently strong joint I was contemplating joining it all together using a through dovetail?

A dovetail joint will provide plenty of surface area for the glue and will make a strong carcass?

Just interested to hear whether anyone has done this themselves and if so did it work out as planned?

Thanks
 

MickCheese

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I would probably be more inclined to use finger joints as they are easier to cut mechanically, unless you are intending using a dovetail jig.

I don't think chopping dovetails in MDF accurately and by hand is that easy and you will spend more time sharpening your tools then actually cutting the joints.

Mick
 

flanajb

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MickCheese":2re203dn said:
I would probably be more inclined to use finger joints as they are easier to cut mechanically, unless you are intending using a dovetail jig.

I don't think chopping dovetails in MDF accurately and by hand is that easy and you will spend more time sharpening your tools then actually cutting the joints.

Mick
I have a dovetail jig, which is why I was planning on doing a dovetail.

The only downside is that I suspect it will ruin the cutter
 

dickm

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Not convinced either a dovetail or comb joint will actually be any stronger than biscuits. The limitiing factor is surely the fracture strength of the MDF, and the interlocking isn't going to change that? But that's just an opinion, and the actual answer will depend on the exact nature of the stresses that will be involved.
 

9fingers

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I suggest you cut them a little on the loose side as during the time taken to apply glue, the mdf is likely to swell and banging 7 bells out of the joint to get it to fit will possibly weaken/destroy the joint.

Bob
 

flanajb

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dickm":37ecgrcw said:
Not convinced either a dovetail or comb joint will actually be any stronger than biscuits. The limitiing factor is surely the fracture strength of the MDF, and the interlocking isn't going to change that? But that's just an opinion, and the actual answer will depend on the exact nature of the stresses that will be involved.
Biscuits are not that great when you want to avoid the movement that you associate with cheap kitchen carcasses where the carcass can sway.

A dovetail joint will surely offer a much stronger joint in that scenario?
 

Hudson Carpentry

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Its even harder with a dovetail jig if its the bench top type. The cutter ends up ripping the ends into what look like layers. You will need some sacrificial material both sides of the MDF. Finger joints are less trouble in MDF.

IMO though its not worth going to the effort of dovetails in MDF. Save them for nicer real timbers.
 

Paul Chapman

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flanajb":vebe9g9x said:
Biscuits are not that great when you want to avoid the movement that you associate with cheap kitchen carcasses where the carcass can sway.
Aren't you putting a back on the carcasses?

Cheers :wink:

Paul
 

Charlie Woody

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In my last workshop I had built all my cabinets out of 18mm mdf biscuit jointed together. When we were moving I had to clear the workshop and the cost of storing the cabinets would have been greater than the material costs. So I spent almost a day with a sledgehammer trying to break the joints so I could take them to the dump. Most of the joints remained intact the mdf just broke where the sledge hit it!

I had 18mm backs and they very rigid as the biscuits were spaced every 100mm or so. Don't think dovetails or finger joints will work very well in mdf personally.
 

flanajb

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Ok. Given the feedback, I think biscuit jointing and ensuring the back is well fixed will suffice. I will also be putting a face frame onto the front of the carcass, so that will add extra strength
 

Wouldchuk

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I recently made kitchen cabinets with 18mm MRMDF for the sides and base. The 'tops' were under the worktop so I just made horizontal rails of around 100mm in width, also from the 18mm MDF.

I used three biscuits in each join, just one in the top rails, glued and clamped. If just left without a back, they do indeed sway and very quickly the MDF splits and the joint fails.

I routed a rebate into the sides/base/top and let the back in - glued and clamped only - the subsequent carcasses had face frames added, doors hung etc etc.

Once the back was in, they were solid as a rock - I had to man-handle these an awful lot as they were moved from the workshop, into the back of a car, carried down a footpath, over a kissing gate, and then into a small narrowboat...!
They needed repainting but they didnt fall apart! :lol:
 

mack9110000

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9fingers":1lgo4clo said:
I suggest you cut them a little on the loose side as during the time taken to apply glue, the mdf is likely to swell and banging 7 bells out of the joint to get it to fit will possibly weaken/destroy the joint.

Bob
If you "Google "Jim Chestnut" it will take you to his website
,which tells you how to set up a little "slop" on a biscuit jointer.
That is if you don't already know. :)
HTH, mack.
 

mailee

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Huds is right, they just splinter into layers. Also there is no strength in MDF when you try to assemble them. Biscuits is the way to go..........unless you have a DOMINO. :roll: :lol:
 
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