We have a drawer that needs a new bottom, and possibly new sides and back as well. The drawer front was made from a single piece and the dovetails were cut into it.
How do you make pins when you don’t know what angle of bit was used to make the tails? The tails are 3/8″ deep, 3/8″ wide at the top and 5/8″ wide at the bottom, which seems to me is over 18 degrees! Yet, the bits for sale seem to hover around 7 degrees.
Am I calculating the angle the wrong way?
Janet
Replies
19 degrees, 17 minutes
Janet,
Based on your dimensions, basic trigonometry gives an angle of just over 19 degrees. MLCS has a bit #5400 that is 18 degrees, couldn't find anything steeper. There is no standard angle for dovetails, so anything is possible especially if the dovetails were hand cut. It is unlikely that you will find a bit with that exact angle.
You could hand cut the dovetails for an exact fit or you could mill them away and fit a new side panel with a simple lap joint reinforced with a line of wood pins for strength. You could also recut the sockets a bit larger with the 18 degree bit. All of this presumes you have a jig system that allows you to adjust the spacings of the pins to match the spacings on the drawer front.
How do you calculate the angle? I am not good with numbers. You know the old "measure twice; cut once"? I'm always better off not measuring at all--that is, using marks instead of numbers.
The back of the cutouts are round, not chiseled out, so the dovetails must have been router-cut. Even if I can't find a bit with the exact angle, we still have the piece with the pins. I suppose that could be used as a guide for making the pins by hand.
Janet
MATH ERROR!
Janet,
Being I made a really basic math error when I gave my original answer, I am probably not the best person to be answering this.
First of all the angle is 18 degrees not the 19 degrees I gave in my previous post. So the good news is that you can get a router bit for that angle.
The answer comes from using trigonometry, commonly called trig, which is a set of formulas that allow you to get the angles and dimensions of a triangle as long as you have some of the dimensions or angles already. In this case what was known was that one side of the tail was 3/8" tall and flared out 1/8" and you needed the angle that was formed.
One of the three basic formulas in trig is meant to solve exactly this type of problem. To start, using the formulas, you divide 1/8 by 3/8 which results in an answer of .3333. Now all you do is go to a set of trig tables in a handbook and find .3333 in a column for that formula and then read across that line to the left most column which tells you that .3333 means the angle is 18 degrees. I got the .3333 but then read down the wrong column and so read the wrong angle.
The exact angle for .3333 is actually a fraction of a degree more than 18 degrees but given that your measurements probably aren't all that precise the angle of the cut is more than likely a true 18 degrees.
John
Not sure where the mistake is but I come up with 18°26'6" or 18.435°. These are rounded to nearest full second and three place decimal. The 18° bit should work fine. I don't think anyone would notice a half degree difference in 3/8 depth as it's only about .003" .
Rich
Rich,
You are right, I was reading down the sine column instead of the tan column in my trig tables, a real amateur mistake. An angle formed by a 1/8" by 3/8" right angle would be .33333 which is, as you said, 18 degrees 26 minutes.
MLCS is good resource--free shipping! Okay, I realize that the shipping costs must be built into their pricing structure, but it's much better than getting a shock at checkout time.
>> You could hand cut the dovetails for an exact fit <<
Uh, no, I seriously doubt that! I'm a stranger to these here parts.
Janet
Don't look for uneccesary work
If the drawer is anything like the drawing you posted the dovetails were made on the simplest kind of router jig, but if you don't have the corresponding jig and bit just do it another way. Make an entirely new drawer. You could attach the old drawer face as a false front, but you could also plane off the 3/8" thickness that includes the dovetail joint, then laminate a new piece of 3/8" thickness in its place and start from scratch using the old facade.
Got the terms confused. Should have said "pins" when I said "tails," and vice versa.
Janet
terms
I often put my self in a tails-pin with talking about dovetails, too, Janet. ;-)
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