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45 degree mitre

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Forum topic by siouxdawgs0409 posted 09-14-2010 10:21 PM 1496 views 0 times favorited 12 replies Add to Favorites Watch
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siouxdawgs0409

107 posts in 1748 days


09-14-2010 10:21 PM

Ok so this may be a simple question but for some reason it has got the best of me.

Now I did some test cuts and since they were shorter I am guessing that is why the mitres seemed dead on with the test cuts.

Now I go “live” and it seems that I am a little larger than 90 degrees when I place four together, talking about 1/16th in gap at fourth corner when three are together and looking lined up. Now common sense tells me to lessen the angle and shave a little off to fix this. The thing that has got me so stumped is that it seems that I should shave a little off the inside, or the heel of the mitre to fix this problem, but if I go to the saw and lessen the angle because I am greater that 45 degrees, it will take more off the toe or outside corner, which would in my eyes only worsen the problem. I suppose it has something to do with inverse angles and such but I just thought I would throw this out and see what responses I get.

So what is the best way to fix this problem? It is on a picture frame so I dont have to be exact on the lengths, I can shave a little here to fix this, picture frame will just be a tad smaller than planned.


12 replies so far

View sras's profile

sras

3838 posts in 1783 days


#1 posted 09-14-2010 11:23 PM

It is pretty easy to get things flipped over when working on mitres. I am not sure how to help out given only your verbal diescription.
A possible alternative might be to carefully run a handsaw down the last gap and create two parallel surfaces rather than trying to create 8 perfect 45 degree angles…

-- Steve - Impatience is Expensive

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1769 days


#2 posted 09-15-2010 12:05 AM

it could have been a little fraction of dust between the last piece and the fence
you have to check those things every time both on the fence and the piece before cutting

take care
Dennis

View rance's profile

rance

4132 posts in 1814 days


#3 posted 09-15-2010 12:22 AM

sras, that can still cause a problem. When you remove the saw from the kerf, bringing those two sides together will tend to open up another corner.

descout, opposing sides MUST be EXACTLY the same length. Stop blocks are used to achieve this. This is all AFTER you get your miter gauge set to EXACTLY 45. Test, and adjust that FIRST.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View Gene Howe's profile

Gene Howe

5642 posts in 2082 days


#4 posted 09-15-2010 01:31 AM

I use stop blocks on BOTH sides of the blade. One at a time, though.
I cut one miter, then cut the mate on the other side. Do that for each joint.
Use the previous piece to set the stop block.

-- 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 TopamaxSurvivor's profile

TopamaxSurvivor

14746 posts in 2330 days


#5 posted 09-15-2010 04:23 AM

You can achieve prefection with a sander to fine tune.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View siouxdawgs0409's profile

siouxdawgs0409

107 posts in 1748 days


#6 posted 09-15-2010 05:54 AM

rance,
I have stop blocks (with 45 degree angle) and have opposite sides exactly the same. The problem is getting the 45 degree angle. Is there any way of getting this set up easier. I can get smaller pieces no problem, it is when I put up my 34 inch long pieces that I notice the gap. Measure on the smaller pieces and I see no gap at all, but then throw up the long one and wahla, there that pesky gap is. lol i guess if I could find some long pieces of scrap I could measure out easier. Or at the rate I am going I will just keep readjusting and my piece will eventually be short enough that I wont notice the tiny fraction I am off.

View rance's profile

rance

4132 posts in 1814 days


#7 posted 09-15-2010 06:29 AM

descout, IMO you should use 90 degree stop blocks, not 45’s. I expect that is the cause of your longer and not shorter pieces being off. Check a pair you’ve already cut to see if they are STILL the same lengths.

Whether you are using a miter saw or a table saw, keep the pieces vertical, not laying flat. If using a table saw , set your miter gauge to 45 rather than trying to tilt the blade to 45. If you are using a miter saw, set the 45 using the knob out front, not the one that tilts the blade left and right. I would use the term ‘lateral’ but that could be interpreted either way.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View siouxdawgs0409's profile

siouxdawgs0409

107 posts in 1748 days


#8 posted 09-15-2010 02:43 PM

I will take a look at the bow, but I did check earlier and there was nothing I saw then, but maybe the weather or something got the best of them.

I am using a table saw, blade set at 90, with an accurate mitre gauge set to 45. When doing this I must keep the pieces flat. If I were to stand them on edge, (vertical) I would need to bevel the blade to 45 and have the mitre 90.

Little more on my process… I have the Mitre on the right side of the blade, angled back at a 45. (The piece was better supported on the table this way vs angling fwd) I run one edge through the pieces of same length, then set up a stop block to length and flip the pieces end for end which puts other end at blade and the piece is upsidedown, but same face against mitre. I then run it through again and cut my second mitres. Repeat with other length boards.

View JimF's profile

JimF

141 posts in 1947 days


#9 posted 09-15-2010 04:29 PM

This is where a shooting board and handplane come into play. It’s a lot easier to take the small amount off of the miter with a plane than with a miter saw.

-- Insert clever tag line here

View siouxdawgs0409's profile

siouxdawgs0409

107 posts in 1748 days


#10 posted 09-16-2010 01:55 AM

Thanks guys,

I did get the mitres to an acceptable degree of accuracy. I ended up using a stop block, so the points would only touch so that the boards would be EXACTLY the same length. I think this was the biggest thing, my boards were slightly off when using a mitred stop block. I also cut them on top of each other together. All this and I ended sanding a tiny fraction off the heel and it seemed to work. I have about a 1/32 gap in two of the corners, but the frame will be black so I highly doubt it will be noticed.

View TominTexas's profile

TominTexas

42 posts in 1490 days


#11 posted 09-16-2010 08:03 PM

I use a shop made miter sled on my table saw for cutting picture frame miters. If you google tablesaw miter sled you will get a number of links for contructing one. The basic principle is having two 45 degree fences on the sled – one on each side of the blade. The two fences allow you to cut perfectly fitting miters because the sum of the two intersecting fences equals 90 degrees. It doesn’t matter that one or the other is off a half degree or so because together they make 90 degrees. You’ll get perfectly fitting joints everytime. You can use stop blocks on the fences to insure that your pieces are cut to the same length as well.

Tom

-- East Side of Big D

View agallant's profile

agallant

429 posts in 1540 days


#12 posted 04-05-2011 07:40 PM

Tomin Texas is right the miter sled is the best way to do it. Just make sure that you don’t cut from the same side on the sled, you have to use one peace on one fence and the other on the other fence that was if you are 90 but the cut relation to the blade is a bit off where you may end up with one 44 and 46 angle you still get a 90 corner.

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