Metric Imperialism

[PerranOak]

I like to cut grooves for panels (e.g. drawer bottoms) with a router.

I like to buy ply for these grooves.

All my bits are sized imperial.

All ply is sized metric.

The world hates me.

 

[Shultzy]

The secret is to use a bit thinner than the panel, cut the groove in two passes, and creep up on the width to provide a nice sliding fit.

 

[PerranOak]

The secret is to use a bit thinner than the panel, cut the groove in two passes, and creep up on the width to provide a nice sliding fit.

Sneaky!

Funny though, init!?

 

[Niki]

Make yourself a jig like this one...it doesn't care if you are "Imperial" or "Metric"...
http://www.woodmagazine.com/woodworking ... -dado-jig/

And here, you have more detailed instructions...
http://www.woodsmithshop.com/download/2 ... adojig.pdf

Regards
niki

 

[Paul Chapman]

All ply is sized metric.

In my experience, the sizes are not always exact and can vary from board to board.

Cheers :wink:

Paul

 

[brianhabby]

Why not just buy a metric bit to match the size of panel you are using? I know it's an expense but makes the job so much easier.

regards

Brian

 

[Oryxdesign]

Even with a metric bit I often end up taking two passes to get a good fit

 

[Tony Spear]

Even with a metric bit I often end up taking two passes to get a good fit

Well you would wouldn't you? You can't fit a 6mm. panel in a 6mm. groove.

Personally for drawer bottoms I find that 3mm. goes nicely in 1/8" (3.2mm) grooves although sometimes that needs opening up a touch. 6mm. goes perfectly in 1/4" (6.4mm.).

 

[MikeG.]

All ply is sized metric??


:shock:

I have already made one cock-up in the last 24 hours, so do feel free to tell me I don't what I'm talking about, but I think that all ply is Imperial.

The sizes may be given in rounded-off metric equivalents, but they are actually Imperial. Certainly the sheet sizes are 1220 x 2440 rather than 1200x2400...........unless something has changed in the last 6 months. The standard thicknesses of 6mm, 12.5mm 19mm (sometimes called 18mm, which is a bit of a clue!) and 25mm are quite clearly Imperial measurements given a metric equivalent.

Or could it be that this all depends on the source of the ply?

Maybe North American ply, which is what I use, is Imperial in diguise, but Far Eastern stuff (for those following other threads.........using this stuff can be argued to be worse than using Wenge in a number of ways), may be truly metric? I simply don't know.

Mike

 

[Grinding One]

Sheet to sheet here is a toss up,the stuff is made offshore(5 miles out) and shipped back in....big box type.Other stuff you just scratch your head and say they must of had a bad day...no two sheets exactly the same but close.Still they sell a ply bit over here,it is still a toss up tho....

 

[AndyT]

In my experience you must always measure the ply and measure the groove that the cutter makes. There is so much variation between what different places sell as being the same nominal size!

Andy

 

[PerranOak]

Tricky, isn't it!

So, maybe I'm not doing things quite right?

My tendency is for a bottom that is very tight in the groove? Not good?

 

[Digit]

The traditional route PO has the base recessed into the front and sides. The rear panel then stopped at the top of the groove so that the base then passed beneath the rear panel, here it was glued and pinned but was a sliding fit, unglued, in the side and front grooves.
This allows the the front and side panels to expand and contract without splitting.

Roy.

 

[PerranOak]

What about a box bottom though? They are fully enclosed.

 

[Digit]

And can split PO. I was looking at a number of writing slopes before I started on mine for the competition and small cracks were visible on a number of panels, but size can play a major part in this PO. Timber shrinkage is proportional to its size, all other things being equal a panel of a size twice that of another will shrink twice as much and drawers, of course, tend to be much larger than boxes.
With a ply based drawer the ply grain on the visible faces should follow the shortest dimension, which is normally front to rear of course.
This is to stop sagging under load.

Roy.

 

[Niki]

Hi ParranOak

They have this problem also "Across the pond"...

http://www.sawmillcreek.org/showthread.php?t=114838

niki

 

[PerranOak]

Indeed!

Well, I tried the two-pass idea and, as I thought,, I cocked it! How? Not sure, I think it was to do with the width of the pencil line and all that - my fault entirely, of course.

So, now I have a groove that is 12mm wide and a plywood "shelf" that is 11.5mm wide (It was supposed to be 12mm - no excuse though as I did check this before cutting the groove! )

So, is there are sneaky, tricky, clever old woodworkers way of making this shelf sit tight in the groove - it's "structural" so I'd rather it was tight.

 

[DaveL]

So, is there are sneaky, tricky, clever old woodworkers way of making this shelf sit tight in the groove - it's "structural" so I'd rather it was tight.

Do you have any veneer? Glue a piece(s) in the side of the slot to get back to the required size.

 

[Digit]

First of all take up art so that you have a use for the pencil! You have just had a lesson as to why woodies use a knife. Glue a piece in and start again I would think is one option.
Next time make the groove too narrow then plane the lower face of the base to a slim taper till it fits, much easier than getting the groove to fit the base.

Roy.

 

[MikeG.]

Roy,

that isn't a great option with a ply base.....which is what this thread is about. It is obviously the correct technique with a solid base.

Not all woodies use knives, and no woody, I venture, would be knife-only to the exclusion of pencil in all circumstances.

Mike