Problems with Mitre Joints

Recently on the blog section Spaid enter a blog on this same subject the response was first rate, check it out….Blkcherry

I have a story at the link on the things I do to get better miters. I know this should be easier than it is but as it turns out, lots of stuf in woodworking is tougher than it seems like it should be…..

See the story

-- Tom Hintz, www.newwoodworker.com

Hey all, the last time I encountered anything like this the miter gauge was loose in the miter slot. It does not take a lot of slop to get the “rocking” motion you are talking about. The longer the miter the more pronounced it becomes.
Hope this helps.
Doug in AZ.

-- If you need craft books - please visit our small business at http://www.wittywife.com

You say the stock is square…but is it flat?

Sounds like you might have a tiny bit of bow in the stock.

Getting perfect miters is like marrying the perfect woman. It happens… but not very often.

-- Charlie M. "Woodworking - patience = firewood"

Now that’s funny Charlie

-- Scott - Chico California http://chicowoodnut.home.comcast.net

It could be that the blade is too thin. I use thick, industrial blades for cross cutting or mitering. They will not flex. Thin blades have a tendency to flex at the start of the miter thus leaving a small gap that will give the miter a curve look.

-- Oldworld, Fair Oaks, Ca

I usually make rough cuts to get it close. Like a blades width, and then take a clean up cut for the final dimension. That way the blade thinkness won’t be a factor.

If you do a lot of miters you might want invest in a miter trimmer like this on I reviewed:

http://lumberjocks.com/reviews/14

They work great!

-- Gary, East TX -- The longest journey begins with a single step.

Check your blade teeth. If you have a bent tooth or excessive gum buildup on a single tooth, it will throw off your cut. Using a miter sled will increase your accuracy but that will depend on how accurate you make it. To create a miter sled that can be 1/100 accurate, you should build one that is adjustable and can be fine tuned. Also if you make your own miter slot jigs, try adding a flat headed screw to allow you to remove any slop. Another sure fire way to get an accurate miter cut is to make a rough cut then fine tune it on your sander. The more test pieces you use the better the final results will be.

Gaps suck in any joint and using a combination of different tools and techniques will get you closer to a professional and more accurate finished product. Never rely on one tool to get you to your final goal.

-- "Love is like standing on wet cement, the longer you stay the harder it is to leave...and you can never go without leaving your prints behind..."

I didn’t see what kind of wood you are using. It sounds like you need to try a different blade. I’m not familiar with the incra 1000 mitre thing though they look handy…and spendy. I use a shop built sled when I have alot of mitres to make.

-- Dan, Sterling Alaska, http://sullcon.homestead.com/ Before you criticise some one, walk a mile in their shoes...then you will be a mile away and you have their shoes!

All suggestions posted are great ones. Here is another one to add to your arsenal.
Go here:
http://miterset.home.comcast.net/~miterset/index.html
Might not solve all your problems but, at least you’ll be absolutely sure of accurate settings for the miter gauge.

I’ve always had better luck (and as Charlie indicated, it does involve luck) with a table saw.
I’ve had great luck in marriage. Third time’s a charm!

-- Gene

Think Douginaz might be on to the cause of the problem. It might not be any play in the miter guage slot of the table, but rather that the slot is not parallel to the blade. Common problem with contractor saws (no offense), they can have the table ever so slightly out of parallel to the blade.
An easy test is to put a small brad in the end of a piece of wood you just crosscut. Then pick one tooth at the front of the blade and mark it with a crayon. Hold the piece with the brad against the miter gauge and move it and the gauge forward until the brad touches the side of the marked tooth . Then with your free hand rotate the blade backward until the marked tooth is at the backside of the table insert (you’re holding the piece of wood with the miter guage at the original point). Now move the miter guage and piece of wood forward to the marked tooth (now at the back of the table). If the brad doesn’t make contact with the same tooth in the same place (ie. it doesn’t touch the marked tooth, or touches on the other side of the tooth), then the problem is your miter slots are not parallel to the blade.
There should be bolts on the underside of the saw table that you can loosen so you can gently tap the edges of the table with a dead blow mallet until the miter slots are parallel to the blade.
I had this problem on my original Delta contractors saw, and was fortunate to have the Delta technician come out to re-adjust it while the saw was still under warranty.

-- Gerry

I say don’t sweat the initial cuts – just do as close to 45 degrees as you can and then clean it up with a shooting board.

-- Eric at http://adventuresinwoodworking.com

Did anyone think of the length of the pieces? I preach to my students that in most cases in woodworking exactness is more important than accurate measurements. Most of the time it is both, but there are critical dimensions that need to be exactly the same regardless of the size. For example in a mitered box, the two opposite sides need to be EXACTLY the same to get a perfect miter, along with the blade being set correctly at 45 deg, well duh.

Think about it, who cares if your bookshelf is 35 7/8 or 36” as long as everything is square, flat and parallel. The key to making it that is a good setup and using a stop block to insure exactly the same length on each shelf. People that design the top shelf to overhang are asking for a little headache because now they can’t cut the top with at the same time as the shelves. Hope this makes sense. PM me if it doesn’t. Tooldad.

I did overlook you stated that the pieces were cut using a stop block. However if sawdust gets trapped, it can affect the length not enough to notice with the eye, but enough to screw you up on miters. Good luck in finding the solution.

Well I got it solved. I reajusted the back of the mitre gauge, there was some slight movement in the slot at the back end that I tightened up. After doing that I recalibrated the mitre gauge. After the tightening my digital angle finder showed 45.1 degrees. After some test cuts I ended up moving it to 44.9 degrees on my digital angle finder and everything is coming out as close to perfect as I can ask for. Have cut about 10 sets since then and they all look good.

Thanks to everyone for the suggestions as it got me looking at other things.

Earl

-- With more power you can make toothpicks faster

Did you check to see if the blade is parallel to the fence. That blade runout could account for the small gap