Why is front of frame fine, but side/rear isn't?

[RobynPlater]

I've got a problem that I've been trying to resolve for ages now, but nothing I try seems to work. I've gone through a lot of mouldings and I'm really at my wits end. When I join frames I find that the front looks fine, but (the rear of) the side profile is never as tight as I would like. A deep square frame illustrates the problem best. Does anybody have any tips as to what I can check? what I can do differently?

As I'm just starting up, it's important to me that my standards start off high and remain that way. I do not want to give a customer a job that isn't perfect.

[Roboframer]

I think you need to work out if it's a cutting problem or a joining problem and the best way to do that is with a flat batten, say 2x 0.5" - that will at least take the rebate supports out of the equation. Cut that and then just push the two legs together by hand and see how they meet up, if they meet up perfectly, either way up, then your cutting is OK. If they don't when pinned, then it's a problem with your joiner/ing.

Then pin them the other way up, if they're still gapping the same way then ......???

[prospero]

The classic issue that produces this symptom is insufficient top pressure on the pinner. What happens is that the two halves lift and separate slightly before the wedge bites into the wood. As it penetrates the wedge will pull the top of the joint tight, but there is no way it can do this at the bottom. The harder the wood, the more this will be apparent. Also worse on deeper-than-wide profiles.

[Graysalchemy]

I get this problem with twisted moulding which doesn't lie flat when cut and as a result is not a vertical cut.

[pichousepreston]

I use a lot of large square section mouldings & often have this problem too. Prospero, you are super helpful, as always! I'm opening a new workshop soon and looking forward to a new underpinner, which I'm hoping will make life easier.