Brass rod through untempered glass....cracking? 1

[j0shm]

Hello engineers,

I have a fixture designed with 1/4" glass (untempered) and two brass rods going through it, 1/8" diameter. There will be a force downward on the rods, probably max 10lbf total. I'm trying to see if I need to put a bushing in there or rubber, or if I can get away with just the rods going through the hole in the glass. I've never really worked with glass, so this might be a silly question. Any insight greatly appreciated.

Thanks,

Josh

 

[IRstuff]

> you show two diameter changes on the rod, where are these in relationship to the glass?
> how is the hole made and what is its finish?

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[j0shm]

Sorry, the transparency makes it a little confusing. The diameter change is on the back face of the glass. On the other side(front side) the two rods actually thread into one piece, which gets the downward force.

The hole will most likely be water jet cut. But possibly drilled. No finishing operations though.

Thanks,

Josh

 

[IRstuff]

I'm not personally familiar with water-jet cutting; does it leave sharp edges or chips?

Unless the glass has no surface imperfections loaded by the rods, there would be some likelihood that you might crack the glass.

Is the loading a instantaneous, singular, event, or is it repetitive? How much slop is there between the rod and the hole?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[j0shm]

Waterjet leaves a sharp edge.

The object is a hook of sorts. So people will hang some weight on it..leave it there... take it off... repeat.

I guess it would be safe to add a layer of rubber or plastic around the rods? Although I'm having a hard time finding an off the shelf bushing with sizing that would work. Do you think a layer of 0.006" rubber is enough to stop potential cracking?

Thanks IRstuff!

 

[IRstuff]

Seems to me that would depend on the compressibility of the rubber, but the rubber needs to give quite a bit to minimize the stress on the glass, so I'd guess that 6 mils is a bit thin; it's about the thickness of 2 sheets of paper, isn't it?

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I can do absolutely anything. I'm an expert!

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[j0shm]

Yeah, about 2 sheets. So I guess I'll look for something around 20 mil or so to wrap around it. Am I correct that I would want a lower durometer rubber? Something around 40 or so?

 

[EdStainless]

You might find some low Duro urethane for the cushions.
Glass is very unforgiving when it comes to edge loading, alignment, and impact.

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P.E. Metallurgy, Plymouth Tube

 

[Compositepro]

You do want to use plastic washers and bushing. Nylon or polyethylene would be appropriate. You do not want to use a soft rubber. The purpose of the plastic is to deform where the loads too high so the load can be spread over a larger area, but you do not want the washers or bushing to move as the loads vary. A small burr or other imperfection will crack the glass if you tighten metal directly to glass.

 

[MikeHalloran]

Amen to plastic bushings.
Probably best to bond them in, since the waterjetted surface will be perfectly abraded for bonding. ... and for providing microscopic stress raisers.

You could probably get away with suspending _one_ brass object from a fire-polished hole, but not two.



Mike Halloran
Pembroke Pines, FL, USA

 

[1gibson]

People hanging stuff and 10lb load does not mix. Whatever they hang on it, someone is eventually going to yank it down/off instead of gently removing it.

If that's 1/4" glass, then those are 1/8" rods, they will be flexible. What happens when they bend inside the hole using the front edge as a fulcrum, and pry upwards towards the middle/back?

How about acrylic instead of glass?

 

[3DDave]

I wonder is a suitable plastic-laminated safety glass might be available. Or if you could be happy cutting the glass and having it tempered (some distortion). If people are hanging things, there's a chance it will get broken and it would be good to not injure them, even if they do something to deserve it.

Search for bolted glass on Google and you should see some images of other approaches.

I would go with edge clips on tempered glass to avoid the need to drill and to make the acquisition easier.

 

[j0shm]

Thanks for the help guys. I had a hunch that this wasn't a great idea....and know I know so. I'll have to think up something else.

 

[MikeHalloran]

Take a look at 3M Command brand adhesive hooks and related products.


Mike Halloran
Pembroke Pines, FL, USA

 

[mcgyvr]

Why glass?
What about polycarbonate/acrylic?

 

[j0shm]

I have a special glass I wanted to use.

Also, the load probably wouldn't be 10lbs, I just set that as an upper limit. It's just for coats, bags, etc. But I guess glass still isn't the best option.

 

[IRstuff]

Never, ever, underestimate the cleverness of fools. If it's intended to be used as a hanger, then people will hang all sorts of stuff on it, and you won't be there to tell them that you didn't design for that. I would guess that there will be a 90-lb kid thinking that it'll be great to hang from your hook.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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