A simple mitre question (beginner)

[Markymark]

Hi all

New to this Woodworking hobby. Please can someone tell me where I am going wrong? I am trying to make a simple picture frame from some moulding stock. I use my SIP (cheapy) Mitre saw and cut 45 degree angles on the stock to the same length (square picture frame). When I come to assemble them it wont produce a square. I assume that if the 45 deg angle is not presise for every cut then I will multiply the error as there is 8 cuts.

Wow what seems to be an easy project has turned in to a begineers day in the workshop.

Is it my Mitre saw that is at error? Or the user?

If it is the Mitre saw then what use is it? What make and model of mitre saw should I buy as a beginner?

Ta

Markymark

 

[davy_owen_88]

Hi Mark, the problem is that many mitre saws don't have accurate measurements for angles. Reading 45 degrees from the mitre saw may not mean its at 45 degrees. You need to use a protractor or similar angle measuring device to check that the 45 degree mark is accurate. If you have no way to measure the angle then print out a perfect square using your computer and fold it into a triangle then you can use 2 of the 3 edges to check the 45 degree mark.

If it is accurate then you may not be holding the moulding tight to the fence or there may be saw dust or something else stopping it laying flat to the fence.

Hope this is of some use to you and good luck getting it all sorted.

 

[Shultzy]

A picture frame is one of the most difficult items to make for exactly the reason you have stated, each of the errors in the joint are magnified. The best way to make a good frame is to make three sides to the right lengths. Then cut the 4th side slightly over size and sand to fit. Use mitre or band clamps when glueing and you should end up with a good fit

 

[Steve Maskery]

Hi Mark
Mitres are notoriously difficult to get right, and it's a challenge, especially for a beginner.

First of all, you can get good results with a SIP. My friend Brian has one and it is fine BUT do consider putting a good blade on it. Freud blades are good quality and affordable. Make sure it is suitable for a SCMS and not just a table saw.

The fence must be adjusted properly. IIRC there are 4 bolts which fix the fence to the base. Spend some time setting it up accrately. As you suspect, errors are cummulative. 0.5deg per cut and you have a 4deg gap at the end. One way to balance it out is to make sure that for each joint you have a left-hand mitre and a right-hand mitre. That way, if one is a bit over, the other is under by just the same, and so you still end up with 90 degrees.

The other thing to remember, of course, is that opposite sides MUST be EXACTLY the same length. It's no use having accurate angles if one side is a millimetre longer than the other, it just won't go.

The best advice, however, is not to rely on the saw cut at all, but build a good shooting board and trim them by hand.

Best of luck

 

[woodbloke]

Very tricky to get absolutely right. The angles can also be sanded in on a disc sander with a fence at 135 deg to the disc tho' it does take a fair time to get the correct angle and test it so that its spot on. This method is useful if you have a deep picture frame where the timber is too big for a shooting board and as has been said each pair of sides must be exactly the same size - Rob

 

[Anonymous]

Mark

I have made 7 picture frames in the past month and all had very tight corners. This is not because I have expensive kit (SIP saw) or high skills, it is simply down to a shooting board and cheapo Stanley #6 plane.

I made a shooting board out of offcuts from the garage with 2 pieces of MDF for the base and a chunk of Cedar for the 'fence'

I screwed and glued the guide fence onto the MDF and took some test cuts whilst the glue was still wet. I tapped the fence with a hammer and repeated the test cuts until I got perfect 45 degree mitres and then left it for 24 hours to cure.

All boxes and frames made on this jjig have perfect 45 degree ends. Took about an hour to make.

As an aside, no matter how accurate your cut is, if the pairs of pieces (2 sides and top and bottom) are not exactly the same length, you won't get a good mitre :wink:

 

[Paul Chapman]

Hi Mark,

As others have said, in most cases a shooting board is the answer. There's a great tutorial here by Alf on how to make one https://www.ukworkshop.co.uk/forums/view ... 62&start=0

Paul :wink:

 

[Markymark]

Hi All

Sorry for the naive question but what is a shooting board?

Thanks for all the advicew so far. These forums ain't arf useful.

Regards

M

 

[George_N]

Hi All

Sorry for the naive question but what is a shooting board?

Thanks for all the advicew so far. These forums ain't arf useful.

Regards

M

Just follow the link in Paul's post...all will be revealed. :arrow:

 

[Alf]

Hi Mark, welcome to the forum. As you've discovered, no such thing as a "simple" mitre joint. To put it bluntly, they're a pipper. :evil:

A shooting board is just a fancy name for allowing a plane to take a controlled, precise shaving from a board in order to tweak a joint such as a mitre to fit. It can take off a mere thousandth of an inch, which even the fanciest mitre saw simply can't do. Trouble is it means getting familiar enough with a plane to use one, which may not be ideal for the beginner. But in the long term, it's a very, very effective device. The link Paul gives is to a thing to try and make it as simple to grasp as possible, but there are plenty of other varieties at my page o' links - The Shooting Gallery.

Cheers, Alf

 

[MikeW]

Hi Mark--welcome!

Along with the advice for a shooting board or a disc sander with which to fine-tune the angles, for something as "simple" as a mitered frame it is also imperitive that each of the respective pieces be of the exact same length, just as Steve mentions.

If just one of say four pieces is a tad long, it affects the fit of the others. So aside from making sure you cut accurately, make sure the the opposing pieces are the same length.

So for instance, if both side pieces are brought together so the inside edges are touching, they should start and stop exactly the same. So too if one flips the pieces so the long edges are touching. Each corner should align.

Also, one can cut accurate 45 degree angle, have the exact [or near exact] length of pieces, and if the cut does not go down through the stock squarely, it will affect the fit at the corners.

Yep. Simple mitered frames. One of the hardest "common" joints, really.

 

[Anonymous]

Hi All

Sorry for the naive question but what is a shooting board?

Thanks for all the advicew so far. These forums ain't arf useful.

Regards

M

This is my 90 degree shooting board (no photos of the 45 available at the mo)

 

[Paul Chapman]

Sorry for the naive question but what is a shooting board?

Mark,

David Charlesworth's DVD on shooting boards would be well worth getting. It's very well done and everything is explained so simply. It will make you wonder how you could possibly manage without a range of shooting boards - and also that a bench plane and a few bits of wood are often far more accurate and effective than lots of expensive machinery :wink:

Paul

 

[engineer one]

what nobody has said so far is that to ensure that eachpiece is the same
length, there is value in putting a stop block on the fence of your saw.

the idea is that you clamp a piece of wood at a specific length
on the fence, and then make sure that each length is pushed
up to the block before you cut.

the two most difficult joints, and plain mitres, and half laps,
not least because the seem so easy.. :twisted: :?

good luck

paul :wink:

 

[Markymark]

Thanks

It's all become clear now.

Thanks

Mark