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Valued Mentor
jeanchile
Posts: 724
Registered: ‎11-10-2009
Message 1 of 15 (612 Views)

Ladder Cage Bar Challenge!

612 Views, 14 Replies
05-09-2013 11:31 AM

Hello all,

 

I was wondering if you all could help me with a part I am trying to model? I have a ladder that needs a small cage and that has the cage bars extended down to the nearest guardrail per OSHA/MSHA requirements. This ladder is not our design, we are matching an existing design, or I would simplify a lot of things about this. The part I need modeled is shown in this picture:

CageExtensionBars-1.png

 

I have created a part that should show you what is needed. The lines in the sketches show the profiles of the part at the various locations.

CageExtensionBars-2.png

 

The particulars:

1.) This needs to be plasma cut from a flat steel plate, then bent to the angles needed.

2.) No twisting of the steel is allowed, only bending.

3.) The profile doesn't neet to have a uniform width (2") in between the upper and lower portions but something close would be preferable.

4.) I originally tried creating surfaces and thickening to get a shape but some of the bends need to be thickened inside and some of them outside and I couldn't get the results I needed.

 

Anyone care to take a crack at helping me with this?

Inventor Professional 2013 (SP-2.3), Product Design Suite Ultimate
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LT.Rusty
Posts: 744
Registered: ‎10-23-2012
Message 2 of 15 (579 Views)

Re: Ladder Cage Bar Challenge!

05-09-2013 01:28 PM in reply to: jeanchile
Why wouldn't you just use 3 pieces of flat bar for each section of the cage? One vertical coming off the rail, one angled between the rail and the lower ring, and one between the lower and upper rings? Seems that would be a lot easier, although perhaps not as pretty ...

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Valued Mentor
graemev
Posts: 294
Registered: ‎11-03-2011
Message 3 of 15 (568 Views)

Re: Ladder Cage Bar Challenge!

05-09-2013 02:35 PM in reply to: jeanchile

I'll give it a go, but is there some reason why sketch 7 isn't aligned with sketch 2?  It would be quite a bit easier a job - both modelling and manufacturing - if it was.

Valued Mentor
jeanchile
Posts: 724
Registered: ‎11-10-2009
Message 4 of 15 (519 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 05:03 AM in reply to: LT.Rusty
I am not opposed to doing that but the shop usually prefers to bend this from one piece of plate or bar. There is no welding on this project in the field because the equipment is in service. They said they prefer to bend it in the shop because of it warping while welding, then they have to grind it smooth and make it look pretty so nothing catches on it, and they have difficulty holding all the complex angles.

That being said, I would still have to get them all the details for the individual pieces. If you can get me an example of how you would do it from three pieces I would certainly consider telling them they'll have to do it that way. The first preference would be one piece of material though.
Inventor Professional 2013 (SP-2.3), Product Design Suite Ultimate
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Valued Mentor
jeanchile
Posts: 724
Registered: ‎11-10-2009
Message 5 of 15 (515 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 05:09 AM in reply to: graemev
I agree it would be easier, and I am not opposed to seeing your example with the bars aligned in those sketches. We are trying to match existing ladders already installed on the platform (not our design) and we were given a drawing that shows them not aligned at the bottom parts (10" from outside edge to the middle bar, each side). I'm not sure if this is an MSHA, OSHA, or CAL-OSHA requirement but I can't see it in my documentation. This is also one of the areas I am willing to change if it means I can get the shop what they need. I would certainly appreciate your attempt or input on getting this modeled with them aligned as I don't think anyone at the site would ever even notice they were slightly further apart than the others.

Thanks everyone for the help!
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LT.Rusty
Posts: 744
Registered: ‎10-23-2012
Message 6 of 15 (495 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 07:10 AM in reply to: jeanchile

If there's no field welding, then how are they planning to install the new cage parts?

 

Honestly, for something like this, I'd probably just grab three pieces of flat bar and field run everything.  Wouldn't be any less functional.  Weld it all to the outside of the existing cage, then there's no issues with cleaning up catchy spots.

 

OSHA doesn't care if it's pretty, they care if it meets their requirements. 


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Valued Mentor
jeanchile
Posts: 724
Registered: ‎11-10-2009
Message 7 of 15 (490 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 07:19 AM in reply to: LT.Rusty
My apologies for being unclear Rusty. The entire ladder shown in the first picture is being fabricated at the steel shop and then delivered to the field to bolt into other steel framing we are providing. All of the field connections on this project are going to be field bolted (they can drill but they can't strike an arc).

Also, you are correct that OSHA doesn't care if it's pretty but they do mandate that the inside surfaces of the bars and guards are to be smooth and free of burrs. That plus the client is going to want it to look decent.
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Valued Mentor
graemev
Posts: 294
Registered: ‎11-03-2011
Message 8 of 15 (472 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 09:31 AM in reply to: jeanchile

Here's the critical part.  You can attach the upper and lower straight segments to your shop's preferences.  This is done as a solids bend, so there may be slight variance from actual results, but it should be close enough for a field fit.

Contributor
jaybear
Posts: 22
Registered: ‎04-22-2011
Message 9 of 15 (446 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 10:44 AM in reply to: graemev

See if this works for you

Distinguished Mentor
swhite
Posts: 531
Registered: ‎11-08-2012
Message 10 of 15 (442 Views)

Re: Ladder Cage Bar Challenge!

05-13-2013 10:53 AM in reply to: jeanchile

Take the line as you now have, add another sketch at the top or bottom may be best in this case, and sweep the profile similar to the attached. We do this all the time for our caged ladders. When you are done convert to a sheet metal part, set the sheet metal thickness and it will create your flat pattern for the shop.

 

Since your line is touchiing the frame, simply attach the rectangular shape to that line so it sweeps away from the frame, not into it. this can be done by projecting the end point of the line into the new skrtch for the metal shape. When setting your top sketch start your workplanes, click on the endpoint of the line, then the line itself, setting the WP perpindicular to the line. Start sketch on that WP.

 

And I seriously doubt the original has no twist, being that it is not aligned at all points towrds the center, but was probably added in the field to make it fit both ladder and handrail. At the most you will get a gap on one side and a small intrusion into the cage rail, unavoidable without twisting the part after it leaves the cagerails.

Steven White
Lee C. Moore, Inc.
www.lcm-wci.com
Inventor 2011
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