Help Please help a newbie struggling with corners!

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Riddling

Grumbler in Training
Joined
Oct 24, 2021
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New Zealand
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Framer
I started working at a framing shop a few months ago, but still struggle tremendously to get perfect joints in my frames. Even when dry fitting the frame, there always seems to be a gap in the inside corner, and consequently I tend to have to wrestle with the pieces to get them to come together ok whilst underpinning. At the same time though, if I manage to get the inside corners joined nicely, a gap along the back edge of the corner also appears?? My process is: glue one face of each corner, underpin two 'L' pieces (first pinning the inside corner, then the outside), then connect these together, is this alright? As well as this annoying corner gapping, I often find that one piece always seems to sit slightly higher than the other side, so quite a bit of wiggling is necessary to make the faces of these joints flush. I also notice that in the underpinner, when bring the inside corners together, it requires one side of the moulding to be moved away slightly from the 'fence' that I thought it's supposed to sit flush against if the mitre is accurate?

Usually I can get away with passable frames if the moulding is quite narrow, but my issues are amplified the wider the moulding is, so that it requires two of us two try get the corners together (one using brute strength to hold the pieces together, one to fire the v-nails in). I hate constantly feeling dissatisfied with the frames I produce, but I don't know how to fix this! The owner of the shop doesn't seem to notice any issues in the frames he makes, so I feel it must be something I'm doing wrong?

I hope this makes sense, I don't know a lot of the technical stuff/framing jargon but I'm desperate for help!
 
Hi Riddling, and welcome to the G!

From you comment about the width being a factor in the degree of imperfection, I would guess that the cuts are not true 45s. They may total 90 degrees total, but be more like 46+44. This would certainly be more noticable the wider the frame profile gets. Get a machinist's square to check the alignment of your saw/chopper.

The gapping could be due to many factors, including the brand of v-nailer, the proximity of the v-nail to the inside or outside of the frame, the quality of the cut (in particular the sharpness and quality of the blades), and the density of the wood. Post a couple photos of a corner showing the gaps (from the face) and the v-nail placement (from the back.
 
It sounds like you're not gluing up the frames first. I always put the frames in a vice and glue them and let them sit for a while before I use the underpinner. That way you're not wrestling with the corners that aren't set when you use the underpinner. Are you cutting the frames yourself? If so, it sounds like your miter saw isn't cutting an accurate angle. Our shop is pretty small so we don't have space to stock much, so I'm lucky that most of the frames we sell are ordered chopped to size, the distributor's saws are pretty much always spot on.
 
For sure you are not getting a true 45 degree cut. That is typical for a table top type of saw that has been around for awhile, bearings do wear out causing from movement in the blade and of course with wider moulding it will be seen more. I would suggest changing saws or getting a trueing sander - also a square is just about mandatory. Unlike Echobelly, I very seldom put my frame in a vise before underpinning. I use a Morso chopper on the majority of my frames but for the few I do not I have a Frame Square Saw. Both gives me perfect 45 degree cuts so that my corners are tight without the vise.
 
Welcome to the G, Riddling

If the owner does not have any problems cutting/joining the frame, couldn't you ask him to show what you are doing wrong? Or is the owner just satisfied with less than perfect corners?

There is either something wrong with the miters, which can be due to the saw/chopper but could also be due to operator of course.

As for the fence on the underpinner and having the corner be flush:

Are you joining the first two corners without a problem and then struggling with joining the two L's?

My fence on my underpinner is 'loose', so the two pieces of moulding never sit truly flush against the fence. It gives me a bit room to play.
You can adjust the fence.

Also, trying to get the corners together like that with two people: you will put too much stress on the frame corners and compromising the glue bond. It will, I believe, be a very weak joined corner.

I do not glue, let it dry and then underpin. I glue and underpin right away, so the glue can dry while the underpins hold it together.

Then for the height difference between the legs (if I understand correctly), which might be due to glue build up on the underpinner. I assume the legs are cut from the same piece of moulding so it would be very rare to have that difference in one stick.

I would take a closer look at the underpinner, and how you are handling it versus how your boss is handling it. Whatever you do, don't try to force something together that requires 2 people to do so.

Keep asking questions, we are here to help as much as we can.
 
If you are not using stops on your saw or chopper, any slight difference in length of the moulding will result in poor joints. Cutting to a pencil mark or equivalent will usually end up in different lengths.
 
My first thought is that, certainly, your mitres are out of true so the first question is what sort of machine are you using to cut them?

I would suggest that the minimum requirement for a professional framer is either a framing guillotine or a double mitre saw. If you are trying to get by with a single bladed saw with a pivoting blade you are on a hiding to nothing as these tools are suitable only for a "handyman". As soon as the turning and locking mechanism wears a little your cuts will be off. There are eight mitres in a frame so any error is multiplied by 8.
 
If your saw is true and sharp then you're probably not holding the stock right and/or pressing the saw too forcefully. Those wood fibers are fighting to go the way they want to, not necessarily the way you want. Let the saw do the work and just put steady even pressure on the cutting. Saw blades and wood fiber both will deflect due to rushing the cutting.
 
Thank you all for the advice! I should have clarified that we use a Cassese chopper, not a saw, and also a Cassese pneumatic underpinner, and I do cut the frames myself. @wpfay I'd like to check the alignment of the chopper, as I had wondered whether perhaps it is off slightly, but have no idea how to actually do that? The owner bought it second hand from a retiring framer and didn't even seem to know the fences could be adjusted :oops:

I've told him about my struggles with the corners and he's gone over the cutting/joining process with me a few times, but he's very laid back and seems happy enough with my work, I just know that to others my joints would look pretty shoddy.

@Ylva Generally the first two joints come together ok, sometimes I still struggle a bit particularly where one side won't sit level with the other. It feels like I have to sort of roll one back or forward a bit to get the top face smooth and level? I've started using a folder paper shim sometimes to help with this. I'm always very careful to scrape off any dried glue, so I don't think that's the problem here. The underpinner does sit in front of a work table the owner built which acts as a support whilst joining the frame and I've noticed that one side of the table is slightly higher than the other, but the owner dismissed this as a potential contributor to my issues. Wider mouldings are the worst though, I can usually get each L together fine, but when I try to bring the L's together the gap on the inside is huge!

We do use stops when cutting the moulding, so there shouldn't be any slight variations in length causing this gapping.

Today I had a go adjusting the fences on the chopper the tiniest amount, don't think I did it 'properly', just held a long metal ruler against the extended supporting arm of the chopper and tried to get the fences reasonably flush against it? Wouldn't know how to check the exact angles though.. Wish I was more mathematically/mechanically minded! I made a test frame and the gapping on the inside did seem better but now I feel like the gap along the back of the corner is more exaggerated? Will experiment a bit more tomorrow and hopefully sort this once and for all!
 
Check the bed of the chopper and the bed and back fence of the underpinner. Could there be some debris, glue residue, etc. keeping the moulding from sitting flat and flush to the surfaces?
It sounds to me like either that or, as Wally suggested, your angles are not being cut accurately due to misalignment of the fence(s).
:coffeedrinker2: Rick
 
CHolt said:
If your saw is true and sharp then you're probably not holding the stock right and/or pressing the saw too forcefully. Those wood fibers are fighting to go the way they want to, not necessarily the way you want. Let the saw do the work and just put steady even pressure on the cutting. Saw blades and wood fiber both will deflect due to rushing the cutting.
Click to expand...
Same for the chopper, possibly even moreso (pun intended). Make the last slice just right. Those notches (detents) that lock the head through the stages of the miter cutting are not law of the land, consider them as advice that isn't always good advice.
 
Riddling said:
Thank you all for the advice! I should have clarified that we use a Cassese chopper, not a saw, and also a Cassese pneumatic underpinner, and I do cut the frames myself. @wpfay I'd like to check the alignment of the chopper, as I had wondered whether perhaps it is off slightly, but have no idea how to actually do that? The owner bought it second hand from a retiring framer and didn't even seem to know the fences could be adjusted :oops:

I've told him about my struggles with the corners and he's gone over the cutting/joining process with me a few times, but he's very laid back and seems happy enough with my work, I just know that to others my joints would look pretty shoddy.

@Ylva Generally the first two joints come together ok, sometimes I still struggle a bit particularly where one side won't sit level with the other. It feels like I have to sort of roll one back or forward a bit to get the top face smooth and level? I've started using a folder paper shim sometimes to help with this. I'm always very careful to scrape off any dried glue, so I don't think that's the problem here. The underpinner does sit in front of a work table the owner built which acts as a support whilst joining the frame and I've noticed that one side of the table is slightly higher than the other, but the owner dismissed this as a potential contributor to my issues. Wider mouldings are the worst though, I can usually get each L together fine, but when I try to bring the L's together the gap on the inside is huge!

We do use stops when cutting the moulding, so there shouldn't be any slight variations in length causing this gapping.

Today I had a go adjusting the fences on the chopper the tiniest amount, don't think I did it 'properly', just held a long metal ruler against the extended supporting arm of the chopper and tried to get the fences reasonably flush against it? Wouldn't know how to check the exact angles though.. Wish I was more mathematically/mechanically minded! I made a test frame and the gapping on the inside did seem better but now I feel like the gap along the back of the corner is more exaggerated? Will experiment a bit more tomorrow and hopefully sort this once and for all!
Click to expand...
Get yourself one of these.

Amazon product ASIN B07XLGNKWV
 
Hi and Welcome Riddling. :cool:

I've heard this so many times from chopper users. It's the "Left Fence Tweak issue".

Thing is, you can set your blades with a gauge until the cows come home and it won't fix the issue.
Wood is weird stuff and although you set the angle perfectly you won't necessarily get a perfect 45Âş cut face.
The tolerances are sooooooooooooo critical and any tiny variation will be multiplied x4 and and manifest themselves
on the final corner. As blades dull they go slightly 'off-track'. You need to set the angle empirically by chopping 4
scrap pieces of equal length and dry-fitting them. If there is a gap on the inside then slacken the left fence and move it
slightly toward you. I'm talking a spiders eyebrow here... Chop the pieces again and see if the gap has either gone or has reduced.
Keep repeating until you've got no gaps. If you start to get a gap on the outside, then you have tweaked too far. It sounds a lot
of hassle but once you have it right it will stay right. * Wider pieces will point up the error better due to the divergence. You don't have
to use moulding - 4 flat pieces of PSE timber will do.
I like the last two faces to be just slightly apart (1/8"?) when you come to pin them. That's why I always pin the outer wedge position all round first.
This acts as a fulcrum and has the effect of cinching the inside of the corners nicely tight. It's a fine point, but theoretically you should get a better
glue bond. Doing it inside first gives the opposite effect.

Have a good old think about that. :rolleyes: 🤣
 
Jeff Rodier said:
Back fence is the adjustment to your chopper. Take a 4' metal ruler and loosen the adjustable back fences. Hold the metal ruler against the outfeed table against the back of the guide on the extension. Now swing the left and right adjustable fences against the metal ruler and tighten them in place. The 45 degree angles are stationary so that is all that is needed. If you don't have a four foot metal ruler they sell them at Lowes for less than $10.
Click to expand...

( This was posted July 9, 2012 )

David Waldmann said:
This may well work if you're cutting soft woods, but we have never found it successful in cutting hard woods. Our fences are never in a straight line, and in fact we have to check (and often adjust) them per set of blades that are on them. Again, a hard wood is less forgiving in making a tight join, as the wood will not squish up the way a soft wood will. We adjust each side separately, and our customers tell us that no one supplies chops that fit together as well as ours.

From our website, here's the method we use:


  • Get a piece of flat stock (such as strainer). Something 1½" to 3" wide and ÂĽ" to ½" thick works great. Cut the right end of it (with the left blade).
  • Cut a piece 3 to 6" long (the best length will vary based on the width of material and how big your square is).
  • Now take that piece, flip it over and re-cut the second end, but with the left blade. Now you will have a piece where both ends were cut with the same knife and angle. This will double any error, making it easier to see and correct.
  • Hold the two 45° angles against the inside surfaces of an accurate square. A machinist's scale is preferable. Observe if there is a gap at the inside or outside:
    • If there is a gap at the point the angle is too obtuse. With a chopper, you will need to loosen the fence and push it away from you. For a saw, check your manual for applicable adjustments.
    • If the gap is on the inside the angle is too acute and you will need to pull the chopper fence towards you.
    • Re-cut both ends, re-check and repeat until you can't see light anywhere
  • Start over at point 1. for the other side.
 
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The most common cause of gappy mitres from a guillotine is worn or dull blades. The machines themselves are rugged and simple tools which rarely play up because there simply isn't much which can go wrong with them.

When the blade gets blunt it pushes the moulding back instead of slicing cleanly through it, even on the right hand side where the end is supported by the stop. If you are holding the moulding against the fence you can actually feel this through your fingers.

Often, if you (carefully) feel the cutting edges in the middle of the blades they will feel sharp enough but test the edge near the point. This is the part which does the most work and also pares off that last, critical finishing cut. If that is anything less than razor sharp send it off for sharpening and put on a fresh set.

Finally, many modern mouldings are run on all sorts of crappy wood, often covered with thick compo to compensate for the poor finish. A guillotine simply cannot cut this stuff or any hard mouldings and will give you gappy corners even with sharp blades.
 
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