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jdogherman 01-16-2021 03:12 PM

JVC Dynamic Drum gear remold/repair?
Has anyone tried remolding new gears for the Dynamic Drum that crack or become damaged over time?

I saw this video on remolding gears with and it seemed promising.

The poster seems to use silicone and smoothcast 325 (urathane resin) creating 2 impressions to rebuild broken teeth.

One issue I see is that the failure of the gears appear to be a split all the way to the axle. Maybe impressions could be made from a working gear then multiple sets could be cast and shared. Removal and re-insertion of the metal axle might be an issue but I would think it would be possible.


latreche34 01-16-2021 06:57 PM

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Molding such tiny gears will be a challenge, I designed in SolidWorks based on the old part dimensions some gears and after trial and error tweaking the 3D printer resin settings I was able to achieve an almost identical gear in terms of flexibility as those are designed to be flexible for noise control for a dcc deck.

The gear in orange is the old part and it's about 12mm in diameter and the printing resolution of the new gear is 25 μm (0.025 mm).

jdogherman 01-17-2021 11:13 AM

@latreche34 That gear profile may be harder that most with the outside profile set at a non axially parallel angle and unique inner mating mechanism.

Does anyone know the specs on the dynamic drum gears? It looks from some of the pictures here that the black split gear is a 57 tooth but without knowing the gear module or the size of the gear I am unable to attempt to locate a replacement candidate. I dont have my VCR as it is shipping but I was hoping to work up some solutions.

latreche34 01-17-2021 12:28 PM

I do have some gears but they are split, The best way of doing those gears is using a soft metal, It is not easy to mount the plastic gear on the center metallic shaft, The whole two part gear has to be machined or cast in one piece with soft metal such as brass or aluminum, but then you run into the fast wear of the center shaft problem.

I gave up on this idea of repairing the gears for two reasons, One the DD drum feature is not needed for capturing tapes (playback), Second even if the gears are replaced there is no alignment procedure available. So the only solution is to just disable the system so that's why I did that write up over at videohelp and it worked fine on my deck. I have a second deck that will eventually fail one day and I will do the same thing to it.

jdogherman 01-17-2021 12:57 PM

First let me say, thanks for the write up.

As far as the question for the alignment of the head, is the issue because there are 2 sides in movement with gear mechanisms that side A would become unsynced with side B? Because, from the pics is appears that the motor driving this setup is not a motor with a position sensor attached. If that is the case then wouldn't it be possible to thread both sides to a zero (lowest) position and then mesh the gearsets?

Regarding the metal axle insertion into the gear, given a method for locating the center of the gear, (maybe a 3 jaw chuck) or some marking fluid and compass) a center hold could be drilled that would allow the metal axle to be reinserted. Moving to metal gears seems like a sure fire way to cause wear to the other gearsets.

latreche34 01-17-2021 01:47 PM

Correct, there is no positioning sensor, I would think the same way that the whole mechanism should be put in neutral and then power up but there is no guarantee that it will return to the same position after moving away from it, Counting the pulses by an optical sensor does not look too accurate to me if you don't have a well calibrated system to begin with. So I would assume that there is a special procedure to re-calibrate the mechanism wile it is in different angles using special test tapes and tools.

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