Black rubber monitor feet / rollers

Started by pl212, November 07, 2011, 02:33:02 am

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Rob Blessin Black Hole

As most of the 4000 feet have melted long ago , so the easiest approach may be to use the inner spindle of the 4000 and the exterior of the 4000A .  Are you thinking about creating a mold or 3d printable replacement.
Rob Blessin President computerpowwow ebay  sales@blackholeinc.com http://www.blackholeinc.com
303-741-9998 Serving the NeXT Community  since 2/9/93

paolo.bertolo

As there are no master samples, it's necessary to create one, I'm working on the CAD. I already made a CAD model for the 4000A, I'm now waiting to get a N4000 display for measuring the main dimensions of the plastic spindle.
Idea is then to 3D print a master sample for checking fit and form. Once validated, next step will be making a mould for liquid rubber casting, either out of silicone rubber or directly out of solid blocks of aluminum or plastic (CNC).
As for the material, after some preliminary search, I've found some options with polyurethane rubbers for casting. Picking the right final hardness will be difficult, but I assume shore A 60 to 80 should be fine (more or less like a tire tread).
Long and complex project, but I want to give it a try.

paolo.bertolo

Some updates on this investigation. Today I finally received the N4000 display I was waiting for. Nice unit, crisp and bright CRT. The paint of the steel base is bubbling here and there but it's overall OK. The rubber rollers are gone, sticky and soft like bitumen. I managed to remove one and to disassemble and clean the spindle.
First finding: the rubber roller of the N4000A serie is not compatible, i.e. you cannot fit N4000A feet on N4000 spindle, not even the inner diameter is the same. Probably, you all knew that already.
Outer dimensions seem to be compatible, though.
So, I have no clue if N4000A rubber rollers are still available in some quantity, but for sure it would be much easier and way cheaper to 3D print / CNC a "hybrid" spindle (compatible with N4000 base and N4000A rubber) rather than casting new rubber...

paolo.bertolo

April 23, 2019, 07:30:25 am #18 Last Edit: May 12, 2019, 05:01:56 pm by paolo.bertolo
Hi Guys,

latest updates on this project.

After some additional trials, I've finally nailed the recipe (mix of different compounds), the final hardness is now definitely OK.

Additionally, I've put in the process a small vacuum chamber for "degassing" the mix before pouring it in the mould, this helps with the elimination of most of small air bubbles that may remain entrapped during the mixing process.

The final aspect of the roller with the graining coming from the mould is totally consistent, so one could even keep it "as is" right off the mould.
However, some sanding with a very fine grit paper and the aspect gets much closer to the matte finish of the original rollers.

It's a matter of tastes, but to my opinion - as we're speaking about a "replica" - it looks nice in both finishing levels.

Anyhow, from my angle this project is now over, I got what I was looking for, it kept me busy for a while, I learnt something new, I'm not planning to further develop it. Besides, it costed me already serious money and any improvement would require additional expenditure.

Now, I have raw chemicals (which have limited shelf life) for not so many more parts (my guess is between 10 to 15 pieces, including scrap rate, say 6-8 sets max), I will make pieces until chemicals and disposables will last.

Unfortunately, at this moment I can't commit to make more, as it's a very time consuming (and expensive) process (I can only work on this over weekends, and each set keeps me busy for hours...).

I attach some pics, as in the transition to the new forums (cool!) something went lost.
You cannot see attachments on this board.

paolo.bertolo

Final result, I'm OK with it!

krazycat

Very good Paolo, a perfect result imho  8)

barcher174