What's the problem?

[Ste]

Hello, the amount of use my framing equipment gets varies a lot. As an artist and photographer I tend to frame in batches when necessary. Though I have mostly been making thin frames, maybe half to three quarters of an inch wide I have occasionally make deeper frames for paintings using mouldings approximately one and a quarter by two inches in size. I have a mitre trimmer as I don’t have the space for a bigger machine. I bought this a few years ago from Axminster and it still seems mechanically fine. My underpinner, a Charnwood M4 is quite new and also works well.
The problem I am having is something I have noticed happening more so when I have used the wider deeper mouldings but is still apparent with the narrower ones. This is that slight gaps are noticeable at the back of the joint. With the deeper mouldings this is more of an annoyance as it is more noticeable to the point where I have felt it necessary to fill the gaps. These spaces can tend to double up for the last joint.
When I first got the underpinner I wondered if the gaps were due to the wedges being designed to force the visible front joint together which caused the slight opening at the back. This didn’t really make sense to me so I decided to check out the angle on the mitre trimmer. I did this by using a set square by pressing against the blade whilst bringing the frame guide up to it firmly and then tightening the fixing nut.
Having done all this and still having the problem I am now puzzled and hoping someone might be able to cast some light on the most likely cause.
I do try to hold the moulding firmly whilst trimming the edges after rough cutting the mitre by saw. The only other thing I can think of is that the blade needs sharpening though it does seem as sharp as when I bought it. Thanks.

Steve.

[prospero]

Sounds like the angles on the trimmer are a bit off. Is there a way of fine adjustment? Never used one..... But before you start tweaking anything, I would get the blades sharpened. They may seem sharp to the touch, but not not quite sharp enough to cut a clean angle without deflecting slightly. Wood is funny stuff. Setting the angles with a protractor is not accurate enough. You need to tweak one angle to compensate for any errors and keep trying it on four pieces of wide scrap wood until the angles are right. The ideal situation is for the two faces of the last joint to be just a tiny bit apart when you come to join them. Then, if you place the v-nails around the outside first (or nearer to the outside than inside in the case of a single nail position), pushing the faces together imparts a small amount of force on the inside of the joints due to the nail acting as a fulcrum. So you get a nice tight joint and a good glue bond.

Also, consider that whatever small error in the angle on each corner will accumulate in the last one. And the wider the moulding, the more the gap will become apparent due to the divergence.


Hope that's some help. Even with a Morso it's usual to tweak one angle at some time or other. But remember that we are talking very small amounts - gnats eyebrows. As any adjustment is multplied x4 on a whole frame.

[Ste]

Hi Prospero, Yes that all makes sense. I am not keen to look at the expense of having the blades sharpened professionally so I will experiment with adjustments on spare moulding first to see if any significant changes occur. What kind of place would sharpen these blades, is it a matter of sending them to the manufacturer. Is it possible to sharpen them yourself or would you advise against it?
Steve.

[prospero]

Not sure on the specs when it comes to sharpening the blades. Morso blades are very critical when it comes to angles and they should also be hollow-ground.

You could try contacting the manufacturer for any sharpening info. Shouldn't be too expensive. In fact, the carriage will probably cost more.
If you want good cuts it's not something you should skimp on. There will probably be a local sharpening service and they might know what they are doing. Snag is, if they do them badly it's harder to re-grind them back to spec.

[misterdiy]

To me it sounds like the classic case of the underpinner pins too near the outside edge. Also I find that this is magnified on the very thin mouldings so the pins should not be any further than centre. It would be best to try this before Prosperos method as it is simpler and easily ruled out... or not.

Oh, and Axminster have a shop at Warrington so not too far to go