Bogen CHB-20A Rebuild

[physics]

Hi Guys

I actually logged in here to post that fact regarding the support of the eyelet shank by the wall of the snug-fitting hole, but you beat me to it - hehe.

With a proper size hole, the eyelet is snug and does not fall out. This means the hole is the correct size and its roundness is very good.

With the eyelet pushed fully into the hole and then the card turned over so the factory roll is fully supported on the table of the arbor press, the eyelet is most likely going to form a proper roll when the staking toll is applied correctly. With the arbor press, there is no off-axis motion of the tool - alignment and light force in one motion provides the desired result.

Even without the arbor press, the correct hole tightness and roundness and a solid table surface to rest the factory roll against sets you up to make good crimps with the tool and a hammer.

The support of the eyelet shank wall is crucial to attained a proper crimp.

Thanks for the confirmation! Today I got several drill bits from McMaster-Carr: 2.6mm, 3mm, 3.048mm, and 3.1mm. 3mm was too small for me to get the eyelets in without using the arbor press to shove 'em in, 3.048mm was almost there but things got hung-up near the factory roll and required the press again, 3.1mm was just right. The eyelets fit snugly enough that if the factory roll has a little asymmetry so that one edge of it touches the board before the rest of the circumference, the eyelet won't go any deeper than that since the hole leaves no room to wiggle. 3.1mm is 0.122", one thousandth of an inch larger than the eyelet shank, and 3.048mm is 0.120", one-thousandth smaller. Seems I didn't give the drill press enough credit, it's apparently precise enough for one thousandth of an inch to matter. Nice.

Anyhow, with the 3.1mm bit I drilled a bunch of holes and did some test runs installing eyelets. With the cambion the results were tantalizingly close to perfect, there were still small defects but most of the time you needed to scrutinize the roll to see that part of its circumference was folded over on itself. If I squinted I don't think I'd notice it, but still not there yet. Using the cambion, I brought the tool all the way down to the eyelet and then tried to move it with my hand, and it appears there is still some wiggle possible at that point in the tool's travel. I assume that remnant wiggle source is the cause of the issue. I also tried using the Dake arbor press while just holding the keystone tool in place over the eyelet, with predictably poor results. The magnet chuck from earlier is in the mail, which should make it possible to securely mount the keystone 1715 on the arbor press without drilling into the ram. Hopefully that's the final key to the puzzle.

I also tried hand-swaging, but still ended up with parts of the eyelet walls folding in on themselves. Maybe that'll take some practice, but I was hoping that once the hole was properly snug it'd be a cinch to get a nice roll. We'll see how things go. I'll probably end up trying again several times while I wait for the magnet chuck.

The bulk of hobbyists do not have an arbor press and many do not have even a cheap drill press. Anything you can do to assure that the holes are round and tight is a good thing. You really do not want to see splits in the roll you make as that means the eyelet is going to loosen over time. Of course, almost immediately you will be inserting component leads and wires then soldering the connection, which ultimately keeps things in place.

I've gotten lucky so far with almost no splits, just the darn walls folding inwards. I assume the results of the folded-in walls is the same as the splits, but with the added aspect of trapping solder 'n flux in the fold and possibly resulting in blow-outs?

Thanks for your input and confirmation of my guess. I think I'm one step closer now.