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:
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.
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?
Rusty
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.
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.
Rusty
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.
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.
Thank you all for your suggestions and help with this. I was able to play around with this some more this morning and the shop has preferred a method similar to jaybear's second example.
I checked the ones already installed in the field and none of them are twisted and they are laid out exactly like my sketches (the bottom verticals don't line up with the hoop bars). They are all bent plate material with no twist but the width is not uniform. It tapers from 2" to something slightly narrower. I'm not sure how they determined the angle of the plane they used for the "critical" in-between section and that's the part I'd like to figure out.
Thank you to all for helping me get something that works for the shop (especially jaybear). I hope to play around with this some more to figure out how they did this before, if nothing more than to further my IV knowledge a bit.
That a twist or bend is required can be easily determined. Rotate your center strut with the circular array command to align with the position of your strut to your line at the top. You will find that the straight strut will not even come close to aligning where they show it to be. This requires either multiple bends to create a no twist situation or a twist itself. There is no other possibility besides a large gap between the top strut and rail where they bolted it together, or bending the strut to create a twist. Granted, if the radius is large enough, the gap created might be forced closed with enough pressure applied to the bolts, which is going to form its own twist if tightened down enough. I expect this was not done and that a gap still exists where the two meet at the top rail, or the twist applied from tightening the bolts is not redily apparent by eye, being that steel tends to flex back when pressure is released. Not that you need model such a twist, when they tighten the bolts it will do it all by itself.
@Anonymous wrote:...This requires either multiple bends to create a no twist situation....
This is what has been done. They used a plate profile that was similar to what jaybear provided in his second example but theirs was not a uniform 2" width. It couldn't be because it was aligned as shown in the sketches in my first post. The middle part of this bar is sloped, skewed, and canted to achieve the travel in the three planes.
When I have more time I'm going to play with this to see how you would model something like that but it will only be for my education as they are already burning the solution I provided the shop (which doesn't match the field conditions).
Can be done with loft in inventor, but it will not provide you with a form acceptable to the shop to make a pattern from, Sadly one cannot get flat patterns from a twisted shape. But as i said am sure when they tighten the bolts it will cause its own twisting. In the loft option there are two different types. One of those options will allow the shape to follow the line using it as the not only the guide, but the falcrum point the shape revolves about as it changes direction. This would require a starting steel shape and an ending steel shape, lofted ogether, with the line as the rail. Starting and end shapes exactly the same except for their orientation with regard to the line. The loft will then curve and twist as necessary to follow the line and reorient itself from the beginning shape to the end shape. It may also be necesary to put one ot more other shapes along the path to fine tune it, where obvious direction changes ocurr perhaps with additional guide rails as well. Something one cannot tell until one just does it 🙂
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