Piston Fit Drawers

[groeneaj]

Hey,

I have a question in regards to piston fit drawers. I understand you measure from the opening and it should be zero tolerance (no movement side to side/up and down).

When the wood expands, won't it be very hard to open and close?

Or do you have no movenet side to side, but allow for movement up and down (cross grain - where the wood will move the most?)

Cheers,
Andy

[AlexS]

You have to allow for cross-grain movement of the drawer front. If the drawer fits into a frame, ie the grain at the sides of the drawer runs vertically, this means that at low humidity there will be a slight gap at the top or bottom. If the drawer front is cut from a larger board that surrounds it, as in the desk in this example (http://www.woodworkforums.com/f40/latest-projects-133474/), both will expand at the same rate, so you can have a close fit all round.
It's usual to make the drawer sides slightly smaller vertically than the front, so you don't have the problem of the sides jamming.

[spencer411]

rob cosman has a good dvd on piston drawers.. check it out.

[ian]

Andy
the way I was taught is
1) you measure the opening and cut a board that is an exact fit
2) the drawer back is fractionally narrower (1 -2mm) than the front
3) the drawer sides (cut from quater sawn wood) are an exact fit top to bottom and arranged so the grain runs from the front to the rear

when you assemble the drawer it is very slightly tapered from the front to the rear.
you plane the sides so that the drawer fits in the opening
you plane the top and bottom of the front with a slight front to rear taper rather than a 90° edge -- this is most easily done after cutting the DTs and before glue up
when finished, it's only the last mm or so of the fit that is tight to the opening


hope this makes sense

[Rattrap]

That actually sounds like a great method Ian. :2tsup::2tsup:
I like to get draws very close fitting but am always concerned with draws sticking as humidity changes. In the end i usually just allow 1-2mm all round but that layout sounds a lot better.

[Woodwould]

Andy
the way I was taught is
1) you measure the opening and cut a board that is an exact fit
2) the drawer back is fractionally narrower (1 -2mm) than the front
3) the drawer sides (cut from quater sawn wood) are an exact fit top to bottom and arranged so the grain runs from the front to the rear

when you assemble the drawer it is very slightly tapered from the front to the rear.
you plane the sides so that the drawer fits in the opening
you plane the top and bottom of the front with a slight front to rear taper rather than a 90° edge -- this is most easily done after cutting the DTs and before glue up
when finished, it's only the last mm or so of the fit that is tight to the opening


hope this makes sense
This is basically the method used since the early eighteenth-century: The drawer front is the only element that actually 'fits' the drawer opening; the remainder is almost a loose fit. This was to account for seasonal movement.

I normally make the drawer front and back the same width and after the drawer is constructed, I plane both sides from the back to achieve the necessary free fit.

The tops of the drawer fronts were tapered as Ian suggests* (even the side cockbeading was often slightly tapered for the same reason), but it's not necessary to taper the bottom edge because the drawer runners should be fractionally proud of the bottom edge to permit an unimpeded sliding fit.

Traditionally, the drawer sides were about 1/16" to 1/8" lower in height than the drawer front (see image below) to ensure they didn't foul the kickers or warped dustboard/carcase top above them. The drawer backs were fractionally lower again to prevent them catching or 'chattering' on the same obstacles.

*The exception being lipped drawers which overlapped the edges of the drawer openings allowing for even looser drawer fits without unsightly gaps (see image below).