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Making your own finger-jointed stock?

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Forum topic by William Shelley posted 08-02-2017 08:28 PM 381 views 0 times favorited 4 replies Add to Favorites Watch
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William Shelley

477 posts in 1302 days


08-02-2017 08:28 PM

Recently, I milled out some simple picture frame stock for framing my girlfriend’s artwork. I started with 8/4 poplar and painted the finished / milled profile with my HVLP gun. The frames turned out okay, and poplar is pretty forgiving, but I notice that commercially-available painted frames are made with edge-laminated finger-jointed clear pine, typically. Same goes for other paint-grade items like door jambs, trim/moulding, and such.

Clearly it’s cost effective for companies to use scraps to build up this stock, and it does work well because, like plywood, the built-up stock is very stable and generally free of defects. I ran into the issue of my dried and aged 8/4 stock warping significantly after ripping and milling.

The question I have is whether it makes sense to make my own finger-jointed built-up stock for these applications? If I could spend $50 to $150 on a good router bit or other tool to do this, and end up re-using a lot of offcuts or other ‘bad’ lumber, it might be worth it.

Thoughts? Suggestions on a finger-joint cutter?

-- Woodworking from an engineer's perspective


4 replies so far

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Rich

1969 posts in 422 days


#1 posted 08-02-2017 09:33 PM

I bought an Amana bit years ago and it sat in my chest doing nothing. A couple of years ago I was building a shed and used it to glue up some trim pieces from cutoffs. Basically, it saved me from having to go buy an $8 piece of trim…lol

However, if you’re going to be doing a lot of frames, it’ll pay for itself eventually. Once it’s set up properly, it does a great job of getting scraps ready to glue up.

-- No matter how much you push the envelope, it'll still be stationery.

View Madmark2's profile

Madmark2

370 posts in 421 days


#2 posted 08-03-2017 03:20 AM

It’s called ‘paint grade’ for a reason. The pieces are only viable if you can get all the labor out, otherwise milling & gluing drives the cost thru the roof. Unless you’re dealing with mill output the automation is cost prohibitive.

M

View JBrow's profile

JBrow

1269 posts in 753 days


#3 posted 08-03-2017 01:57 PM

William Shelley,

Another method for end jointing cut offs would be a finger joint at the table saw with a dado blade. Once the jig is setup, every finger and socket should perfect fit together. This method would be slower than with a finger jointing router bit, but since time is available, the dado blade/table saw method would save some money. A scraf joint could also be used and could be potentially the fastest and easiest method. Here are some images of various styles of scraf joints, but a long simple bevel would be the easiest.

https://www.google.com/search?q=scarf+joint&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwi1v9fxmLvVAhVHziYKHdZ9CLEQsAQIQw&biw=1366&bih=622

But it seems to me there are other problems with end jointed boards. The first is gluing the joints so that no glue seam telegraphs through the paint. If the joint is a tight-fitting joint and lots of glue is used, I would think that the cracks in the joint would fill in with the glue, solving this problem.

The second problem, especially with the finger joint, is ensuring the longer board is straight once the glue has set. Since the finger joint would require clamping pressure along the length of the glue-up to bring the joint together, the pieces would need to be clamped to a flat surface that would not flex. The scraf joint could probably be glued with only downward clamping pressure on a flat ridgid surface.

The third problem is that the cutoffs may not all be same thickness. Even if they are all of the same thickness, some post-glue-up milling would probably be needed. The end result would be a single longer board that is not as thick as the individual boards.

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William Shelley

477 posts in 1302 days


#4 posted 08-03-2017 09:29 PM

Thanks all. I realize it’s a bunch of extra labor and that the return might not be great. In my case, I’m willing to trade time to avoid buying more lumber, and unless I’m totally mistaken, built-up stock is more dimensionally stable than solid pieces of the same species. The application for this is pretty much just picture frames, so not load bearing, not subject to wear and tear, and not subject to exterior or undesirable environmental conditions.

I know that the glue-up needs to be done well because uneven clamping pressure can give you a curved or ‘v’ shaped board, so I’ve got some ideas to solve that. The other issue to overcome is that, either the finger-joint end needs to be perfectly 90 degrees to the reference edge, or else the sum of the end-angles of the two boards needs to add-up to exactly 180 degrees.

I enjoy designing and building machines and jigs as much or maybe more than I enjoy actually producing end-user items. My idea here is to use a dedicated router with a finger-joint bit installed that will travel along one axis perpendicular to a fence that extends left and right (and is dead straight), and allow me to cut the ends of the boards to be joined at exactly the same/opposite angles. Board A would be placed on the left, and it’s right-end would be cut, and board B would be placed on the right, and it’s left-end would be cut. As long as the fence that they both register against is perfectly straight, then it won’t matter if the angle of the router’s travel axis vs the fence is not 90 degrees.

For clamping, I’d probably make a flat L-shaped reference surface and use some of my spare pneumatic cylinders mounted at a 45 to 60 degree angle, with a swiveling rubber pad on the end. The cylinders would push down, and away, and force the boards together, but also push the face against the reference surfaces, so the result should be a pretty damn straight board after glue-up.

One thing I’m not sure on is what type of glue to use that will reduce telegraphing of the glue line through the paint.

I know that Urea-Formaldehyde glue would probably do this but it has to be mixed up and is toxic to work with, so something in a bottle would be preferable.

-- Woodworking from an engineer's perspective

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