The Shop > Wood & Stuff
Banjo Build
Lew_Merrick_PE:
Simon -- I start off with two blocks laid up as 8 inches X 16 inches X 4 inches. I create mortises in between the outer area (16 inch OD X 11 inch ID) and at the center of the (7 inch OD) inner core that I will use to screw together (and release) the "halves" of the mold. I then bore a (usually ø1-1/2 inch) hole on the "inside tangent" of my 11 inch ID right on the (8 inch) "center mate." I bore a (usually ø1/4 inch) hole at the center of my block set to use as a "pivot" when cutting on the bandsaw.
I cut the (16 inch) OD, take the pieces apart to insert the bandsaw blade into the (ø1-1/2 inch) clearance hole, reassemble the pieces, and cut my (11 inch) ID. I can now unscrew the batten/inserts in the OD ring and remove it from the bandsaw.
It is now trivial to cut the 7 inch OD on the inner core. I then drill a (ø1-1/2 inch) hole approximately 1 inch inside of the (7 inch) ID. This is to access the filler stem of the inner tube. I then bore (approximately centered on the 4 inch thickness) a (roughly) ø7/16 hole into that (ø1-1/2 inch) access hole for the filler stem itself.
Add a couple of "side plates" to cover the "gap" between the inner OD and the outer ID and you have a chamber that will support an inflated inner tube. Lay-up the pieces as indicated in my previous missive.
When you are done, you can clamp the lay-up such that it extends a bit beyond the edge of the OD ring and hold that against a rip-fence of your table saw to get a nice, clean trim.
Does that clarify things?
S. Heslop:
Got it all back together, which took a while since everything was going wrong. Forgot if I mentioned it but the faceplate got knocked when the thing exploded, so I had to remake that part since the hole was warped and it'd become fairly loose. Had to turn that flat by hand since I could only drill an undersized hole, and the shaft was crooked when I hammered it in (kind of wish I recorded it all but it seemed boring at the time).
Got all ready to cut though and the drill seized up.
The top hat part is stuck pretty solid. Too late to make alot of noise doing a postmortem, but I wonder if it managed to friction weld itself on. I'd actually made that top hat part myself since the original once (which appeared to be made from steel, but maybe it was a zinc alloy) was incredibly worn. I'll try find a new cheap drill to replace it at the boot sale on Sunday. Hopefully one with better speed control.
Anyways I had a go at cutting a bit turning the thing by hand, to see how the tool works. Cuts lovely and smooth going into the wood but was leaving some ragged stuff when going into endgrain. Perhaps it'll work better spinning at a higher speed.
vtsteam:
Simon there's a silver colored heavy duty oilite sleeve bearing material that could be mistaken for steel. Maybe that was the material your first bearing was made from.
S. Heslop:
--- Quote from: vtsteam on May 08, 2015, 07:43:44 PM ---Simon there's a silver colored heavy duty oilite sleeve bearing material that could be mistaken for steel. Maybe that was the material your first bearing was made from.
--- End quote ---
Yeah that seems likely. The shaft wasn't too worn if I remember right but the bearing was insanely so.
At the boot sale I managed to find a cheap drill that had the exact same problem with an extremely worn plain front bearing.
Lots of chips. The new tool geometry needed a slight change to flatten the tip of it so it'd not leave the cut strands still attached to the wood. I'll have to remember to get a close up photo of that. The new drill worked fairly well, the speed control built in is much more adjustable than the first and didn't require any fussing, but since the drill is running in reverse the chuck tended to unscrew itself since there's no second left hand screw to lock the chuck on. Some locktite more or less sorted that out though.
Got the inside turned true-ish and sanded. I made a wooden set of inside calipers to try gauge the diameters, and according to those measurements the inside should be fairly parallel. It'll of course be easier to measure the outside diameter (via the circumference) to get that closer to parallel, then I can see how well those calipers worked for the inside.
Got it partly set up for cutting the outside tomorrow. Too late now to continue making noise.
I'm also trying a new thing with also attaching the same photos for longevity. My usual image host went down for a bit a few days ago and it worried me that it might be gone for good.
S. Heslop:
More problems. It's easy to blame all this on bad luck but it's probably more just carelessness.
I was getting a particularly rough finish on the outer diameter, and this probably should've tipped me off that something wasn't right. But after a few passes the tool dug in and stalled the drill, which was enough to cause something to start smoking inside of it. It wouldn't work at all after this.
So I opened it up to have a look inside, and it turns out that it was just the brushes overheating. They must've swollen or melted the plastic housings since they no longer fit, and the wires had detached from them. I had to shave down some oversized brushes with a file to get them to fit. It's working fine now but i'm gonna give it some time to cool down fully.
It also gives me a chance to think about tool geometry again. My guess is that the large relief for the inside diameter meant that not much of the tool was getting supported against the workpiece. I'll probably grind the other end of the tool similar to the first but give it no end relief.
I am a little concerned that I might've overdone the cut though. What I really need for this is a pair of long calipers. I made a sort of giant scissor caliper from wood but it's all too flexible to feel at all accurate. I might make some sort of caliper extender for the digital calipers. Hopefully I haven't already overdone the cut though.
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