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Help me make decent miters please.

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Forum topic by spaids posted 2115 days ago 3231 views 8 times favorited 31 replies Add to Favorites Watch
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spaids

699 posts in 2327 days


2115 days ago

Topic tags/keywords: question joining

I am trying to make a frame and the mitered corners are really killing me. I tried using my miter gauge and it was not adequate. I made a miter sled which worked much better but I still have a small gap on the inside corner of one of the joints. I guess a tiny bit off on the angle will multiply times 4.

I’m I just a slacker and everyone else is capable of awesome precision? Is there a trick I’m missing? My miter sled could be (obviously is) off a tiny bit but I don’t know how to get it any closer than it is. The gap on the miter on the inside corner opens up to only a 64th maybe so my sled is off by only a 256th? Am I really supposed to be able to make a miter sled that tight? And then am I supposed to be able to use it that tight?

I glued up the frame last night. probably shouldn’t have. It dawns on me today that I should have sanded that one corner to get the final fit.


All advice is welcome.

Thanks

-- Wipe the blood stains from your blade before coming in.--


31 replies so far

View lew's profile

lew

10003 posts in 2389 days


#1 posted 2115 days ago

One way to eliminate some of the gap is to make your miter sled so that it can cut both “right and left” miters. That way if one angle is off, the opposite angle will compensate. If you need a picture of this type of sled, let me know and I can send you a photo.

Lew

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View Robb's profile

Robb

660 posts in 2567 days


#2 posted 2115 days ago

I agree with Lew. That’s the best advice I’ve seen for low-tech great miters. I made a sled like he’s talking about, and it’s easier to get nice miters now.

-- Robb

View TheCaver's profile

TheCaver

288 posts in 2473 days


#3 posted 2115 days ago

I don’t think this is always possible, so I’d look to see why you are not getting accurate cuts. I’d check for slop in your miter gauge, or perhaps replacing it if your cuts are not repeatable. Once you have a repeatable error, you can correct it.

JC

-- Somewhere, something incredible is waiting to be known. -Carl Sagan

View BigBob's profile

BigBob

64 posts in 2123 days


#4 posted 2115 days ago

I think what you need is a shooting board. You can find many examples of this easy to make jig. There are two kinds of shooting boards. One is used to cut a perfect 90 degrees and the other is for a 45 degree cut. You use a block plane on its side and by shaving a little of the miter you can sneak up on a perfect fit. One of the frustrating things about miters is if the board is now too short after you corrected the miter.
Here is the fix, you can make the short board longer, that’s right longer.
Use your plane and take a few swipes off of the inside edge of the board. It will move the board closer to the mitered corner and actually make the gap come together. After glue up, just resqaure slightly and you have a perfect fit.
The other tip, and the one I use to dial in my miter gauge is to go buy yourself a large plastic drafting square from an office supply house for about $3 bucks. Raise the blade of your table saw to max height. Place the long side of the sqaure along the blade, making sure that you are not resting on a tooth but on the blade itself.
Now set your miter gauge to the 45 degree side of the drafting sqaure.
You now have a perfect miter. If you attach a long fence board to the miter gauge with a stop on it, you will cut exact lenght miters and a perfect fit, every time. If it’s off, use the above techniques to fix it.
I hope that helps you.

View Don Newton's profile

Don Newton

712 posts in 2252 days


#5 posted 2115 days ago

There is a hand tool method that works well for truing up miters. Clamp the pieces together, take a dovetail or gents saw and “kerf in” the mitre by sawing the joint. This method removes wood from both sides of the joint and is amazingly accurate.

-- Don, Pittsburgh

View 8iowa's profile

8iowa

1489 posts in 2395 days


#6 posted 2115 days ago

Frankly, not all table saws & miter gauges on the market are capable of the kind of precision to produce consistantly perfect mitered frames. The selection of a high quality crosscut blade is also desirable.

That being said, not only do the angles have to be very precise, but the opposite sides of the frame have to be exactly the same length. I made a miter gauge extension out of baltic birch and with a stop block clamped in place can cut to exact lengths. I invested in a stainless steel dial protractor that is accurate to 1/12 of a degree. (Highland Woodworking product # 168072, www.highlandwoodworking.com)

Last year I made a sled to cut bowl segments. There are four fences: four, six, eight, and ten sided angles. The angles are precise down to a “knat’s hair”.

Photobucket

-- "Heaven is North of the Bridge"

View jsheaney's profile

jsheaney

141 posts in 2622 days


#7 posted 2115 days ago

I pretty much always clean up my miters with a handplace and a shooting board. I don’t even bother with a 45 degree fence anymore. I just use the standard fence and hold the workpiece at the 45 +/- the fraction I need. In your example, I would hold the workpiece such that the sole of the plane isn’t quite touching the inside of the miter. After a couple of passes I would check the actual fit. Assuming that was correct, I would then make some more passes at the same orientation until the plane touches the inside edge and the gap disappears. In that sense, relative to the inside of the frame, you haven’t change the length of the workpiece. With a well tuned handplace (I use either a block plane or a jackplane), this is a really quick and accurate technique.

-- Disappointment is an empty box full of expectation.

View spaids's profile

spaids

699 posts in 2327 days


#8 posted 2115 days ago

Thanks for all the help. It seems that at least some of you seem to think I should be trying this with the miter gauge. My sled is set up to both sides. So I basically have a ”/\” with a kerf running through the center. I notice that the sled doesn’t pass through the miter slots with even force. like it gets tight in the middle.

OH!!! wait a minute. So you guys that use sleds are saying that it doesn’t mater if I’m off a little bit because they should still match up. Hmmm I guess I would still have to have my fences on the sled at a perfect 90 degrees to each other.

I wonder if my angles were good but maybe one side was a hair short? Could that cause it to open up a fuzz on the inside corner?

-- Wipe the blood stains from your blade before coming in.--

View BigBob's profile

BigBob

64 posts in 2123 days


#9 posted 2115 days ago

If you are using a sled, instead of the miter gauge try this. Get a drafting square. I cannot tell you how much I use it. They are very accurate and cheap.
First, check to be sure that your sled is cutting 90 degrees to the sawblade. Once again, rasie the blade, put the square against the back fence of the sled and run it up the blade the blade ( POWER OFF!!!!!)
Is it square? does it lay flat against the saw blade and flat against the rear fence?
If not, adjust the rear fence until it is.
Once you are sure that the sled is tracking square to the blade, put the drafting square against the blade, NOW install your triangle shaped piece right up to the 45 degrees on the drafting square and fasten it to the sled.
Also, check to be sure that your blade is sharp. If it’s dull, it will slighlty flex under load ,and cause the cut to be off by a hair.

View spaids's profile

spaids

699 posts in 2327 days


#10 posted 2115 days ago

BLADE FLEX?! Crap! That’s a brand new thing for me to worry about.

-- Wipe the blood stains from your blade before coming in.--

View Thos. Angle's profile

Thos. Angle

4435 posts in 2596 days


#11 posted 2115 days ago

One thing to check is your saw. some saws just don’t produce the accuracy needed for true miters. If the saw is junk and the blade is dull it just won’t work. I do miters on the chop saw and a miter box works well. I think Blake wound up with a guillotine miter trimer which is the way to go on moldings and small picture frame stock. cheapest fix is the shooting board and a SHARP miter plane. Maybe some filler as well.

-- Thos. Angle, Jordan Valley, Oregon

View juniorjock's profile

juniorjock

1930 posts in 2399 days


#12 posted 2115 days ago

Lots of good info in this thread. It can be very discouraging trying to get a perfect joint. The blade has to be at a 45 to the miter gauge… and of course, the blade has to be 90 degrees to the table too. I found that’s where some of my problems were coming from. Good luck.
-JJ

View niki's profile

niki

426 posts in 2713 days


#13 posted 2115 days ago

Hi Spaids

For a mitered picture frame to come-out square and tight joints, 4 conditions must be fulfilled…

1. The 2 opposite frame member must be at the same length

2. All the frame members should be at the same width

3. The sum of the two corner miters must be exactly 90°

4. The sum of the two corner miters – vertically – should be 180° (I mean that the blade must be exactly 90° to the table).

Those 4 conditions are very easy to achieve in a perfect world or when you are drawing it with CAD…but, when we have to make actual cuts….well, yes, its’ not a “perfect world” :-)

For the reasons above, I prefer to cut the miters on a sled.
Cutting at the method of “Left” and “Right” will compensate for any very small deviations from 45° and for the blade not exactly at 90° to the table.

You will notice, that I’m first, cutting the members to “Final Dimensions” but because of my method (I put the stop at the front of the board and not 10 feet behind…), the blade removes half kerf thickness at every cut and, because we are cutting every member from both sides, the member will be shortened by one kerf width…

In simple words: If you want the frame to be 20” x 20”, cut your members to “Final dimension” of 20-1/8”....the 1/8” will be removed during the cutting of the miters and you’ll get 20” as you planned.

I went through my posts here but many pics are missing (from the time that I lost the Photobucket account) so I’m sending you to other forum…just across the pond….

First, how to make the sled…most of the pics are not for your TS but the on the last pictures, you’ll see how I’m setting the fence to be square to the blade (or more correctly – to the miter slot)
http://www.ukworkshop.co.uk/forums/viewtopic.php?t=18879&highlight=

Another post that you can see how I made the sled and set the fence.
http://www.ukworkshop.co.uk/forums/viewtopic.php?t=23367&highlight=

On this post, you’ll see my method of cutting the miters
http://www.ukworkshop.co.uk/forums/viewtopic.php?t=10072&highlight=

On this post an actual cutting of a frame
http://www.ukworkshop.co.uk/forums/viewtopic.php?t=22924&highlight=

And here another mitered frame for glass coffee table
http://www.ukworkshop.co.uk/forums/viewtopic.php?t=15648&highlight=

I would like to note that I didn’t need or make any “fine tune” – - from the table saw, directly to the gluing table (well, passing through the router table to make the “biscuits” and rabbet for the glass)...

Regards
niki

View PetVet's profile

PetVet

329 posts in 2121 days


#14 posted 2115 days ago

Depending on the type (shape) of the frame members, cutting the top and bottom at the same time, as well as the sides at the same time keeps them the same length. You can tape them together to make the miter cuts. This assumes that there is a flat side to the frame pieces.

-- Rich in Richmond -- Experience is something you don't get until just after you need it.

View matter's profile

matter

210 posts in 2403 days


#15 posted 2114 days ago

A well tuned mitre saw does a pretty good job…

On the table saw I usually use the aforementioned drafting square to set my fence or sled. The only time my mitres go sloppy is if I let some crap build up between the fence and the sled. To combat this, I cut a relief kerf on the very bottom of the fence so that there is somewhere for any errant fibres to go.

If all else fails- plastic wood

-- The only easy wood project is a fire

showing 1 through 15 of 31 replies

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