Biscuits

[Munroast]

we have a whole load of these that are a little too fat to go into the slots. they are old and I suspect dampness has allowed them to swell a little?

Will nipping them up in a vice or squishing them a bit by whacking them with a hammer restore them ? I take it they will just re-swell when they are dampened with the PVA?

(i have experimented and it does seem to work just fine)

 

[Justin Passing]

I'd bet you're right. I had some do it. Get as many as you can into piles and into a strong vice and leave them squashed for a while, like overnight!

 

[Deleted member 174758]

we have a whole load of these that are a little too fat to go into the slots. they are old and I suspect dampness has allowed them to swell a little?

Yes. They need to be kept in doubled sealed bags with a small bag of silica gel.

The problem with biscuits is that they are manufactured specifically to fit into an accurately machined slot, then to swell a controlled amount in order to fill the slot in contact wih PVA glue (which is water based), but not over swell and damage the material. Sand swelled biscuits down and they just don't work reliably any more becausecthevdon't swell to the same degree any more. Squishing them in a vice won't work either, because they are made by compressing under quite a few tons of pressure (say 20 tonnes) whilst also being dried to a low moisture content (not sure what, but one source I read a while back stated around 8% +/- 1%).

TBH, being risk averse, and biscuits being so inexpensive, I personally would not be such a cheapskate - I'd just throw them away and buy some fresh ones. The last ones I bought (last week) I paid £16 for 500 of them on Amazon (100 was £9) - and that is far from the cheapest I've seen

 

[^woody^]

My recipe for biscuits is

Preheat the oven to 190°C (gas mark 5), and bake for 12-14 minutes

 

[Diver Fred]

Neighbour keeps his beech biscuits in a Crawford's 'biscuit' tin on a shelf over his workshop radiator.

 

[Old Salt]

My recipe for biscuits is

Preheat the oven to 190°C (gas mark 5), and bake for 12-14 minutes

Sorry to be pedantic ( it is my turn) that’s not a recipe, its cooking instructions

 

[^woody^]

Sorry to be pedantic ( it is my turn) that’s not a recipe, its cooking instructions

No problem. I cut out the ingredients as I note that the OP has already made the biscuit base. But if he wants to add choc-chips or frosting, I'll post grandma's full recipe.

 

[Justin Passing]

Squishing them in a vice won't work either,

That's your prediction then, not having tried it.
Suggest you do if the need arises, because I have done it. It's probably a question of degree, and maybe how strong you/your vice is.
If you leave them out they swell again quickly.
I've not done it much but had no problems in the joint/product.
I keep them in a Tupper box normally.

 

[Munroast]

Been playing with my digital calipers...

New dry Biscuit 3.95mm
width of cutting blade 3.94mm (cuts a slot 4.1mm)
dipping biscuit in and out of water it swells to 4.3mm

Old biscuits are mostly around 4.15mm thick , hence can't use them

A good crush in the vice takes them down to 4.08 ish
dip these in water and they quickly swell up to 4.25

Sand one down from 4.15 to about 4.0mm
dip it in water and it swells to about 4.15


Conclusion, give them a good nip in the vice and they will work just fine.

Interesting observation, and I used a number of biscuits in my experiment - the new biscuits always swelled to a greater thickness than the vice squashed old biscuits ! of course this may just be down to the batch of wood the biscuit was cut from.

 

[Deleted member 174758]

That's your prediction then, not having tried it.

No. I've been ysin biscuits since about 1980 (at first with an Elu DS140) and there are plusses and minuses to them so it's down to being trade and needing a guarantee that they will perform as required. I tend to use Dominos these days, many workshops do when a KD delivery is required and screws won't do (normally a visibility thing), but biscuits were used in the past and when people fannied around with them in the workshop it was always a case of will they/won't they work? Sometimes they didn't (i.e the joints were loose and tended to fail when the item was moved) which would lead to problems doing the install, the use of screws (which would need to be hidden) and a bit of bad language. Hence my risk averseness.

The other thing about biscuits is that they tend to telegraph through MDF, so when using them the material should be left a day or so after glueing before sanding for the minor swelling of the MDF caused by the glue to subside. If not you can end up with biscuit-shaped depressions along the joints. Only a few thou deep but nevertheless quite visible in obtuse light

BtW in the 80s and 90s I remember this subject being discussed almost ad naseum in FWW with the conclusions being similar to my own, i.e. that biscuis are cheap enough , etc