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Problems with Mitre Joints

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Forum topic by Zelbar posted 02-21-2009 10:46 PM 1950 views 0 times favorited 17 replies Add to Favorites Watch
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Zelbar

74 posts in 3001 days


02-21-2009 10:46 PM

Topic tags/keywords: mitres

I am having a small problem getting perfect mitre joints.

I am using a Delta contaractors tablesaw with an Incra 1000 Mitre Jig and a Woodworker II blade

I am getting a small gap at the out side corner. If I tighen it up in the jig for glueing I will get this gap at either one corner or two adjacent corners. The gap shows on both the top and bottom of stock.

We are talking a small gap here but there is a gap and I am anal about that sort of thing.

I have checked everything I can think of:

Blade is 90 degrees to table top
Mitre jig is 90 degress to table top
Mitre Jig is 45 degress to blade
I have measured my mitres after cut with digital angle finder and all mitres show right on 45 degrees
I am using a stop block and all pieces are same length.
The stock is square.

I can not see why they should not be perfect

Any other thoughts on what to check or what my problem my be.

Thanks
Earl

-- With more power you can make toothpicks faster


17 replies so far

View blackcherry's profile

blackcherry

3313 posts in 3283 days


#1 posted 02-21-2009 10:58 PM

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

View TomHintz's profile

TomHintz

207 posts in 2859 days


#2 posted 02-21-2009 11:05 PM

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

View douginaz's profile

douginaz

220 posts in 3463 days


#3 posted 02-22-2009 01:00 AM

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

View gbvinc's profile

gbvinc

629 posts in 3407 days


#4 posted 02-22-2009 01:10 AM

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

View CharlieM1958's profile

CharlieM1958

16241 posts in 3679 days


#5 posted 02-22-2009 01:22 AM

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"

View ChicoWoodnut's profile

ChicoWoodnut

904 posts in 3276 days


#6 posted 02-22-2009 01:29 AM

Now that’s funny Charlie

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

View John Ormsby's profile

John Ormsby

1283 posts in 3197 days


#7 posted 02-22-2009 03:32 AM

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

View GaryK's profile

GaryK

10262 posts in 3449 days


#8 posted 02-22-2009 03:55 AM

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 - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View TwistedRedneck's profile

TwistedRedneck

41 posts in 2952 days


#9 posted 02-22-2009 03:42 PM

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.

-- Nails are better wood fasteners than screws, if both are applied using a hammer.

View GFYS's profile

GFYS

711 posts in 2931 days


#10 posted 02-22-2009 04:34 PM

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.

View Gene Howe's profile

Gene Howe

8239 posts in 2889 days


#11 posted 02-22-2009 05:40 PM

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 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View gerrym526's profile

gerrym526

267 posts in 3269 days


#12 posted 02-23-2009 01:38 AM

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

View Eric's profile

Eric

875 posts in 3244 days


#13 posted 02-23-2009 06:55 AM

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 https://adventuresinwoodworking.wordpress.com/

View tooldad's profile

tooldad

660 posts in 3175 days


#14 posted 02-23-2009 07:17 AM

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.

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tooldad

660 posts in 3175 days


#15 posted 02-23-2009 07:19 AM

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.

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