perfect 45

[teresa wilson]

i am a framer and can not seem to achieve a perfect 45 on ay of
my cuts. can anyone help?

[Frederick Rowe]

I can only offer some general suggestions without more information. Picture frames, or any piece where mitered angles make a full circuit, are the least forgiving. The reason is, that any error from 45 degrees is cumulative and the final joint shows the compounded errors. In other words, a 1/2 degree error becomes 2 degrees at the 4th joint.

If you are using a power miter saw there are some ways to ways to fine tune a cut. First check you set up with a good square. Next, cut two pieces and check if they joint at 90 degrees. Many errors are user induced by poor technique. If you piece moves at all, your joint will reflect it. Try adhesive fine sandpaper to the fence of your miter saw if the wood is slipping.

Next, to fine tune a miter saw cut, you can use a thin shim, such as a 3"x5" index card. Placed between your wood and fence, it will create a change in cut by fractions of a degree which you could never match using the stop screw on the miter saw's pivot. The further from the cut you place the shim, the smaller the change. This is a good way to sneak up on a 45 degree angle otherwise eluding you, but can be difficult to repeat.

Another way is make your rough cut on the miter saw (powered or hand) then use a shooting board and plane to shave thin slices off to get to your 45 degree. Search this and other sites, there are many excellent guides to the construction and use of a shooting board. You must however have mastered the use of a bench plane and sharpening.

Lastly, there is a cutting device called a miter trimmer (see attached photo). With the trimmer you can trim fine slices from a piece, however, setting the angle still requires careful set up.

I hope this helps. http://www.leevalley.com/images/item/woodworking/saws/03h0101s5.jpg

[Chris Padilla]

How about a nice plane and a shooting board? It basically does what that trimmer that Frederick posted above does.

[David Romano]

By framer I assume you mean picture framing, not house framer. The term "perfect" needs some qualification. There is always some acceptable error.

As for angular accuracy, consider that the longer the side length of the frame, the more accurate the angle needs to be because the absolute error will accumulate more on longer pieces. Thus, on short pieces, a small error in angle will not produce much of a visble gap at the joint as would long pieces.

This is balanced against the greater ability of longer pieces to flex a bit to allow the joint to be forced together. Soft woods are more forgiving here.

Are your pieces straight? If not, the miters will never be consistent. I don't know how you are cutting them, but the tool's critical alignment is the angle of the blade relative to the edge or fence that the piece is registered against.

My suggestion is to not try to cut 45 deg angles on the same side of the blade, because this double the errors. If you have a tablesaw, get yourself a good 90 deg reference, like a well made framing square with smooth straight edges and use this to build a sled for the saw. You'll use it to make cuts on both sides of the blade. There are plans for this if you search, but you should be able to figure this out.

David

[David DeCristoforo]

Would you please post some more information? What are you using to make your cuts? What kind of stock are you cutting? Pre-finished frame stock? Wood? Composite material?Without these specifics, only general advice can be given which may be useful but may not address your particular situation.

[Eric DeSilva]

I haven't gotten around to framing yet, but the solution I've seen is a framing sled where you can set a pair of stops at a perfect 90 and lock 'em in place. Then, when cutting the frame pieces, alternate sides of the fence--even if you are off by a bit on one side, if your fence is truly 90, then the other side will be off the same amount to compensate. In other words, if you are off 1 deg, one side may be 44 deg, but the other will be 46, and you will still have a 90 degree corner...

[Steve Campbell]

Another thing to be sure of is that both top frame pieces are exactly the same length and the two side pieces are exactly the same length. I do this by using stop blocks when cutting the last miter. If they are not the same length you could be cutting perfect 45 degree miters but it still won't fit just right.
Hope this helps.

Steve

[Larry Conely]

As Frederick Rowe noted, a miter trimer is a fantastic way to get clean accurate miters. I have a Lion and it seems like the miters are one piece of wood once glued up.

I also cut miters on my table saw once in a while. It is well tuned and will give accurate cuts, but with a Woodworker II blade will not give as clean a cut as the shear cut from the Lion.

[Chris Padilla]

I haven't gotten around to framing yet, but the solution I've seen is a framing sled where you can set a pair of stops at a perfect 90 and lock 'em in place. Then, when cutting the frame pieces, alternate sides of the fence--even if you are off by a bit on one side, if your fence is truly 90, then the other side will be off the same amount to compensate. In other words, if you are off 1 deg, one side may be 44 deg, but the other will be 46, and you will still have a 90 degree corner...

While true, you'll have a 90 degree corner but the lengths of your sides will be just slightly off and it could cause problems....

[Chris Zenda]

Miter trimmers are fantastic!!!

[Todd Bin]

Miter saws pretty much suck for accuracy unless you are doing paint grade stuff. Then you could just cram some caulk in the corner. I second or third or whatever the vote for a miter trimmer. But this is kinda a single purpose tool. A nice hand plane and a shooting board and your off to the races. The shooting board is practically free and well it depends on how much you want to spend on a No. 5 or No. 9 if you want another specialty tool

[Eric DeSilva]

While true, you'll have a 90 degree corner but the lengths of your sides will be just slightly off and it could cause problems....

Hmm... I'm having trouble visualizing here. If you cut your horizontals on the right side of the jig and your verticals on the left side, and you use some kind of stop... Seems like you would end up with consistent lengths. But, I could be missing something here since I've never done it...

[Chris Padilla]

Eric,

Do the extreme: cut one at 30 degree and the other at 60 degree and think back to good old trigonometry. You'll see that the hypotenuse of the triangles are different lengths. :)

[Eric DeSilva]

Eric,

Do the extreme: cut one at 30 degree and the other at 60 degree and think back to good old trigonometry. You'll see that the hypotenuse of the triangles are different lengths. :)

Ah. But I guess I was assuming that you could get pretty darn close to 45 dead on with a fixed jig. I used 1 deg for a hypothetical, but if your jig is off by 1 deg, that seems pretty bad. If you can get within a 1/10th of a degree, the error is only 1/100th of an inch(*) for a frame w/2" wide sides. Within sandpaper range.

Since I was actually planning to build something like this, is that unrealistic?

(*) its been a *long* while since I did trig... Someone oughta check my math, but I think the difference in length should be |(width/sin(44.9))-(width/sin(45.1))| for a 0.1 degree error...

[Clint Schlosser]

Agreed on the nice hand plane. Its a much more vesitile tool and prolly costs about the same or less than a miter trimmer. I would advise to stick with a Lie Neilsen if you are not up to tuning up your plane even strait from the manufacturer.

[Roger Warford]

(*) its been a *long* while since I did trig... Someone oughta check my math, but I think the difference in length should be |(width/sin(44.9))-(width/sin(45.1))| for a 0.1 degree error...

Eric, IF (ALL CAPS! :)) I am not mistaken, what you are calculating is the difference in the length of the face of the miter. I would think what matters is the gap created by the error in the angle. Again IF my math is correct (it's been WAY too long for me too), the formula should be:

2 * (w* sin(a)) / sin(45-a)

where w is the width of the board and a is the angle of the error. I used the following diagram and a little trigonometry to arrive at that formula.

87635

In the diagram, G represents half the gap, hence the multiple of two.

So, IF my math is correct, then the gap produced by a 0.1 degree error on a 2" wide board would be about .00989". A 0.2 degree error would produce a gap greater than 1/64th of inch.

So, is my math right? And at what point does a gap become visible to the (average) naked eye?

Teresa and all, please forgive me if I'm dragging this too far off course. Believe it or not I actually like digging into this kind of problem! Being weird isn't bad, is it? :D

[Eric DeSilva]

Eric, IF (ALL CAPS! :)) I am not mistaken, what you are calculating is the difference in the length of the face of the miter.

I think the difference in the length of the face was what Chris was talking about. With a left-hand/right-hand miter jig that is a perfect 90, any amount you are off on the right hand side will be compensated for by the left hand side.

I tried to find a picture of what I was talking 'bout--try this (no affiliation or anything, just googled to find a picture of the type of jig I was talking about):

http://www.woodworkersguide.com/2008/02/26/the-perfect-picture-framer-jig/

Hopefully not offending and not trying to drag this off track...

[Michael Weber]

All the professional framing shops I have been in use a miter trimmer. If your going to do this to make money, its faster than any thing else and dead accurate.

[Roger Warford]

I think the difference in the length of the face was what Chris was talking about.

Ah, yes of course. I see now. Sorry - I wasn't thinking. The figure below illustrates what I think you and Chris are saying (greatly exagerated of course).

87639

So, the net net is that if you cut only one on side of a blade, TS or miter, then an error of 1/10th of one degree results in a gap greater than 1/64th of an inch. However, an error of 1/10th of a degree using a miter jig and cutting on both sides of the jig means an offset of less than 1/512th of an inch. Does that sound right?

I have a bad habit of making things harder than they should be. Oh well. It was fun trying to dust off the old algebra and trig skills anyway!

I'll be quiet now! :)