hey,
right now i am building a block constructed rim out of some beautiful ~100 year old mahagony parquet which i came to in the course of a house renovation. Because of the dimensions of the boards i decided to go with a 12 segment rim in order to save as much material as possible.
So now i am wondering what are your preferences in terms of the amount of segments and why? Of course less segments mean less joints and therefore fewer potential vulnerabilities. The downside is you produce a lot of waste..
I am just wondering what are your thoughts on this?
I always go with 6 segments mainly because I’m conscious of keeping strength in the grain.
I use eight. I have three "The Dayton" banjos in the shop that used four segments/three layers--all are in good condition--made 1910-1920.
As long as you use three layers and they overlap, you should be fine.
The issues with making segmented rims is getting some sort of adhesion between the ends due to end grain as you assemble each layer. I coat the ends and let them dry for ten minutes, and then reapply glue before clamping. Also, the individual glued up layers need to be dead flat, and the tops of the layers should be roughed up for best glue adhesion when gluing the three layers together. Additionally, the angles must be cut exactly. If your miter is off by a half-a-degree, this error will be additive and you will end up with a gap between one of the segments when you strap them together. The more segments cut with slight errors, the greater the cumulative gap. One reason to use fewer segments.
Lots of other little issues with making segmented rims, learned thru experience--something you get right after you needed it.
I use 18 blocks per layer. I get less waste, and less grain runout which helps when turning. I use a 4 or 6 piece rim cap too, as well as 3 or 4 layers of blocks per rim.
The gap from angle error can easily be eliminated if you simply make two half-rings. Sand the ends flat before joining together into a full ring.. Problem solved.
I have used 8 segments so far. Have had a little trouble with tearout on the inside when turning, so planning to do a couple with 12 next, see if that helps.
Something else I've started doing is marking the top of the workpiece that I'm cutting into segments, and numbering them as I cut. When I assemble the rings I keep the tops of the segments up, and keep them in order. I find that the rings come out flatter and with less "spiraling". (I think that my mitre saws don't cut at 90 deg precisely, and that this way I am alternating this slight error when I assemble). Anyway, saves me a lot of lapping.
Like Bob, I treat the end grain before gluing, but I thin the glue for this. Not sure about "roughing up" - I've alays been taught that the flatter the surfaces the better the joint.
that's quite a lot of useful information and interesting thoughts already thank you for this.
I will definitely follow your advice to glue two half circles to avoid gaps. that's simple and effective.
The end grain connection is definitely a little bit of a problem. The surfaces must be completely flat, so i am going to grind them on a marble slap. Soaking with thinned glue is also a good idea for sure.
Another advantage of fewer segments: a bigger angle is cut an therefore you get a more stable and "less end-grain joint"..
I have a miter gauge on the wall next to my bandsaw that is dialed in for 18 segments, and I never change the angle on that one. That way I can glue a full circle with tight joints every time, regardless of the size, as long as there are 18 blocks. I only rely on the end grain joints to hold the rings together while I am flattening them. I used to do that on top of a 4x36 belt sander, and then in 2018 I got a drum sander that I can run the whole ring through, then flip it over and lower the head 1/64", and repeat till both sides are smooth and flat.
I would find it hard to clamp a half octagon, but a full ring of however many pieces can be easily clamped with a band clamp or a huge hose clamp. I roll a length of masking tape out on the table, sticky side up, put glue on one end of all the blocks for that ring, lay them out end to end and stick them to the tape, and then grab the two end blocks and bring them together quickly to make the ring. If I move slowly the blocks start to fall off the tape and there is no joy in Mudville, but speed makes it work.
To Lapsteel.
I am a fan of banjos a little deeper than average. how deep is the pot on the very nice pictured banjo, and where can one read more abot these banjos? Steen
quote:
Originally posted by steenTo Lapsteel.
I am a fan of banjos a little deeper than average. how deep is the pot on the very nice pictured banjo, and where can one read more abot these banjos? Steen
It's about 2.75 inches deep. It has 5 layers. A wooden tone ring is one of the layers. It is the nicest sounding banjo I have ever made. I have made a couple that are 3 inches deep. Dave Holt plays a lovely one that is very deep too.
I do the same gluing technique as Zachary's, except that I clamp it up as a full circle, but leave two opposite joints unglued the first time so I can cut the inside circle on the bandsaw. Then it's simple to clamp it up again for the last 2 joints. I suppose you could cut the inside curve on each segment instead. Oh, and I couldn't find a hose clamp long enough, so I joined two together. Works a treat.
I've used both manual and power mitre saws that have lockable 15, 22.5, and 30 degree settings, but not 20. These are pretty accurate, but the 90 Degree bevel doesn't have to be off more than a whisker to affect the flatness.
At first I cut both inside and outside circles before laminating, but found it's much easier to get the laminations evenly spaced with the external angles being intact.
Lapsteel, I also like your deep rim, especially the color variation in the blocks - is that a trick of the light or something in the finish?. Have considered making a rim with alternating contrasting blocks.
Good thread.
so i just glued the first half circle. It worked very good. After i joined the two half circles i will cut the outer and inner diameter with a router. To keep everything exactly in place i an going to use three toothpicks as small dowels.
I thought this was a great question. It seems that the number of segments is not a critical issue with smaller or larger numbers of segments having minor tradeoffs.
My reference to roughing up the surface between layers (using 80 sandpaper or similar), is that flatting each layer, particularly with a drum sander, could result in a rather polished surface and resulting reduced glue adhesion. Takes seconds to do.
If using a router and template to cut the inner and outer diameters, the extra expense of a template spiral or compression router bit is worthwhile to reduce tear out and get cleaner cuts. Also, probably a little safer.
quote:
Originally posted by Banner BlueI thought this was a great question. It seems that the number of segments is not a critical issue with smaller or larger numbers of segments having minor tradeoffs.
My reference to roughing up the surface between layers (using 80 sandpaper or similar), is that flatting each layer, particularly with a drum sander, could result in a rather polished surface and resulting reduced glue adhesion. Takes seconds to do.
If using a router and template to cut the inner and outer diameters, the extra expense of a template spiral or compression router bit is worthwhile to reduce tear out and get cleaner cuts. Also, probably a little safer.
I keep 80 grit on my drum sander, as even that is painfully slow and 120 tends to burn easily in my experience. I think, from the conversation on the woodworking forum I also visit, that that is not an uncommon situation, and that most folks that are using a drum sander to flatten things (which is really the job they do best) usually keeps 80 or 100 grit on it for flattening, though some opt to go to higher grits for finishing passes once the intended thickness has been reached.
Banner Blue
Zachary Hoyt
Ah, cutting the circles with a router and template- something I hadn't thought of. Been cutting them on the bandsaw, resulting in slight inconsistencies, which make it harder to align them perfectly. If anybody has more info on techniques of using a router for this, I'd be grateful. Have a plunge router, and access to a table.
I use locator pegs when gluing up the layers, but you have to get them lined up first.
The drum sander I have access to is in a community shed, and the powers there don't like work pieces with glue going in it. I do my flattening by hand on a lapping board with 80 grit - tedious, but it works
And yes, Rob, I get that you don't want face grain glue surfaces to be polished.
