edge banding with solid wood

[dnalley]

I need to radius a 1x8 board to a 40 inch arc (radius) and I know this can be accomplished with saw kerfs on the inside of the radius.  Years ago I used a formula found in a Sears radial arm saw instruction manual., (I think) ???.  This formula included radius, depth of kerfs, spacing of kerfs, and so forth to make a neatly radiused board (say something like the border of a poker table or such).  Do any of y'all know this formula by chance, and would you care to share it?  Need to make an indoor wheelchair ramp at our church.  I know this is clear as mud but from some of the craftsmanship I've seen on this board I feel someone can point me in the right direction.  Thanks so much.    ???   Dwight

[bedway]

I dont know the formula for cutting the kerfs to accomplish a certain radius but i have done it many times, with success. For that size i would make my cuts about 3/4 thru the material and spaced about 1" apart. Then try bending it and see what you have. If you dont have enough radius then you can deepen your cuts and/or make your kerf cuts every 1/2" Its a trial and error which has always got me the desired result. Hope this helps.

[dnalley]

Thanks bedway, that helps a lot, knowing you've done it sucessfully.  Guess I kinda figured it would be trial and error anyway.  You know what "they" say---if at first you don't succeed, read the instructions---trouble is the instructions went up in smoke many years ago, along with the tools

[bedway]

Im looking forward to hearing how you made out, keep us posted please.

[SwampDonkey]

Build a steam chest and cook the sucker, she'll bend.  ;D

As for Kerfing by saw, this is how I see it described.

Ok, you want a 40 inch arc, on the outside bend, and it's 1 x 8" material.  What is the angle subtended by the arc? You need the width of the arc as well as your known length to do this. Here is an online calculator to find the angle subtended by the arc.

Spacing of the cuts need to be equal for an even bend, and the degree of bending will be equal at all cuts. To determine the optimum spacing of kerfs required to make the bend,saw almost through the thickness leaving 1/8" wood. From this first cut, measure and mark the length of the bend section on the`edge of the work. Clamp the end of the board on a bench, then lift the free end of the board until the saw cut closes and bending stops. Wedge the board in this position. At the mark (far length of bend at 40" from first kerf), measure the gap between the underside of the board and the bench top. The distance from the bench up to the underside of the bent work piece (which will be the outside of the bend) gives the spacing of the saw cuts. But, you need to take this one step further or you'll be faced with a lot of trial and error. The angle between bench and work piece, made by bending the first kerf to the limit, will tell you how many degrees the piece will bend in the arc at each kerf.

To get an even bend:

#kerfs = Angle subtended by arc/angle bent per kerf.

For the spacing, length of arc/ (# kerfs+width of saw kerf). The pencil lines for the kerfs will be centre to centre or easier if you have a gauge or jig for the spacings

Try it first on some scrap before using the final work piece. I can tell you that any thicker than 1/8" left after the kerf cut will likely end up in failure unless it's green.

Glue up the kerfs when you have achieved the bend along with a 1/8" thick piece of veneer on the inside of the bend for strength. Otherwise it's not going to take much stress. Do you have a shop band saw with 8" throat?

See how it goes. Maybe someone else has another way. I can tell ya, my way is to steam bend the sucker.

[pasbuild]

Draw out your 40" radius take a scrap piece make your kerf cuts and see how it fits on your layout that should tell you weather to increase or decrease the cuts, I'm thinking two or three pest pieces will get ya there

[dnalley]

Hey Donk and Pasbuild, thanks to y'all for the suggestions on the bent radius.  Should have already tried this but was told that old so and so's brother-in-law's nephew does this for a living and he'll make it out of metal ( indoor ramp), for nothing!  Guess what.....no ramp yet, just promises.  Think i'll just go ahead and build the ramp and if it's not satisfactory I'll set it aside as a memorial to "working with a committee", of which I am a member.

Donk it's been a long time but your line of thinking sounds vaguely similar to the formula I was asking about.  I've read your post about four times and I finally think it's starting to sink into my feeble mind what you're trying to tell me.  Must admit--I am impressed!!! and thanks. In any event there's always the two or three boards trial and error that Pasbuild and others mentioned.  Thanks all.    Dwight

[Lud]

SD,  why didn't you offer to steam-bend  it for him! ;D ;D

Oh, yeah,  there's sort of an on site requirement to steaming it...I shouldn't have said anything.....forget I mentioned it....

[SwampDonkey]

Steam chests are portable.  8)