Foamcore doesn't hold a bend great, but if you backup the bend with a gusset cut to the proper angle, and glue it in, then yes - you can get rigid bends.
And I used a 3D printer all the damn time when I was designing offroad parts.
Foamcore doesn't hold a bend great, but if you backup the bend with a gusset cut to the proper angle, and glue it in, then yes - you can get rigid bends.
And I used a 3D printer all the damn time when I was designing offroad parts.
airwerks wrote: Inventor is over $10k for a single seat now, I'm thinking that's not likely going to happen. I just bought a copy of Alibre pro (pro = minimum for sheet metal capability) for just under $1k.
Alibre is a decent deal for an inexpensive sheet metal CAD program. It's what I use at work for 3D work.
You know the bend radius, just simulate it. Card board sounds like exactly what you need, or luan if it needs to be sturdier.
It's not just the bend radius, cardboard doesn't take into account K factors. If you are fine with grinding parts to fit or ending up with gaps to fill on your first one it would probably work. I'm assuming thick mild steel so it wouldn't be the end of the world for the first one you make......
(Note: I'm a SolidWorks person and am not familiar w/ the capabilities of SolidEdge)
In SolidWorks you can model a part as sheetmetal. The initial extrude is a "base flange" and subsequent features are flanges. You specify the bend radius, K factor, and other parameters of each bend.
You can flatten the part after you're done, save that as a .dxf and your friendly dude who has a CNC plasma table can burn your parts. They'll fit ~IF~ you can bend accurately enough.
Make a conventional 3-view of the un-flattened part and you have all the info to make the mock up out of 1/4" plywood and 5 minute epoxy.
At least that's what I do if corrugated cardboard isn't burly enough.
Thanks all for the ideas. I think it's going to be a combination of 3d printer, ply and epoxy.
Solid Edge has a similar sheet metal application, I do very much enjoy it. I have to get back on SolidWorks soon. 
Any shop with a modern press brake can bend a full 10' sheet of 1/4" A36 without problems. It's not unreasonable to ask a shop to bend 1/4" steel.
Keep in mind any material you use for mockup WILL bend differently than steel. Unless you're trimming it to fit after it's cut and formed, it will be a non-trivial amount. Look into bend deductions for more information. There's no formulas to accurately (within 0.010" or so) determine bend deduction because so much of it is dependent on the style of tool, style of bending, etc. The majority of the time the bend deductions shops use is determined empirically.
Your best bet would to be to give the shop a dimensioned print of the formed part, that way it's on them to get the bend deduction correct and give you the part you want. That's usually preferred by the shop rather than hoping the customer did the flat layout correct.
Source: currently employed at a shop that bends lots of steel, and I spend lots of time in the sheet metal side of SolidWorks. Let me know if there's anything else I can do to help.
airwerks wrote:Kenny_McCormic wrote: 3D Solid Modeler, Inventor, Solidworks, etc.Inventor is over $10k for a single seat now, I'm thinking that's not likely going to happen. I just bought a copy of Alibre pro (pro = minimum for sheet metal capability) for just under $1k. Or you could go to your local job shop, and pay them their hourly rate to have an engineer draw it up for you. We do that all day long where I work- they have 2 guys doing nothing but walk-in projects for small companies and guys with hobbies. You will come out ahead doing this compared to having the shop draw all of it up for you twice (once for flats, then once again as sheetmetal models).
Get a .edu email, DL for free.
You could call Unevolved and have G&H Diversified, Houston TX, prototype it in steel. The rates might be friendlier than you think.
The loads on any offroad part will be nontrivial. Make sure you've done some good stress analysis. If the safety factor's big (5+), hand calculations are adequate.
I would be happy to model it in flats and a sheetmetal part if you send me the sketches. Its going to be in Solidworks.
And yes, if you want it to be super accurate, ask the shop bending it what K factor they are going to use. Every brake is set up a bit different. For super accurate parts like a U-Flange with a pin going through that needs to be a tap fit or a press fit, we either line bore it after its bent or use weld-in bushings in oversized holes after its bent.
aacthree at gmail and you know the rest.
4cylndrfury wrote: I cant recall the material name right now, but there is a lightweight plastic board (not corrugated) that is used for real estate signs and the like. Probably 3/16" thick. It melts at (high) heat gun temps, so bending it to form will not be a chore. It also can be drilled/tapped/shaped like metal...sorta.
I think the material you're referring to is foam core PVC, one of the main trade names is Sintra. We used a ton of it in the sign biz for cnc routed indoor signage. It's great stuff, but not really cheap. There are off brands, though, and a good sign shop might dell you drops from other projects cut-rate. It's usually available in 3mm, 6mm, 12mm, and on up to almost an inch in varying colors. It heat forms well, bends in a brake with some care, routes like a dream, glues with PVC cement, and can be pretty damn structural if done right. Never tried to laser it, but waterjets like buttah. I still have scraps around my shop I use for switch panels, instrument bezels, etc.
Corrugated plastic (coroplast, politician signs) isn't going to hold a shape like you want for fabrication, even with heat bending. You can't weld or glue it effectively bcause it's polystyrene and nothing sticks to it. It does bond okay with double sided tape. I've built plenty of crap from it, but it's just that. Crap. Cardboard is just as useful and easier to work with for this kind of thing, IMHO.
Spent five hours reading about bolted joint design today. It's a humbling realization that you learned more useful stuff about engineering design in five hours than you have in two years of MEE classes.
I'm using a safety factor of 3 and doing basic stress analysis in SolidEdge.
I wish we did more real design in school. It's not hard, but when you have to start from nothing, I'm sure I'll make oversights in the beginning.
I'm aiming to keep all stress below yield stress for the material in SolidEdge... where can I read up on that type of design decisions? I don't want to be "that guy" who designs based on the colored scale, but none of my classes have even bothered to discuss the issue...
Do you own a copy of:
Engineer to Win by Carroll Smith?
I've been making stuff for most of my 54 years and have been a mechanical designer/prototype machinist/fabricator professionally for about 15 years.
I have an art degree.
At my last gig at a huge solar energy company I worked with a battalion of guys with BME and MME degrees and to a one they were largely lost when it came to designing good, manufacturable parts. They could all calculate me under the table effortlessly, but if you someone needed to design something that was strong, cheap and manufacturable and would actually fit in the field, first time, it invariably ended up on my desk.
I had loaner copies of all the Carroll Smith books and I tried to get people to read 'em, but it was perceived as below their station, generally. Sad because they're fantastically useful books.
Make it easy on yourself and incorporate as few features as possible that are dependent on holding tight bend tolerances. As stated above, for U-shaped brackets in which something is located by a pin in shear, make the hole after the fact.
I actually do have a copy, it was gifted to me a while back. I LOVE his fasteners book. I admit that I haven't given Engineer to Win a good enough look yet. I'm going to go find it now.
I do not hold your art degree against you. A friend graduated from MEE recently and is working with [deleted for anonymity] on one of their race teams. He couldn't tell me if preload subtracted allowable tension force from proof load of a fastener. I didn't know the answer because it was my first attempt at any real bolted joint design.
Then I found this page, and all was right again in the world: http://www.boltscience.com/pages/basics3.htm
chaparral wrote: You could call Unevolved and have G&H Diversified, Houston TX, prototype it in steel. The rates might be friendlier than you think.
Don't do that, I've already tendered my resignation.
But yeah, OP, looks like you've got plenty of help.
unevolved wrote: Your best bet would to be to give the shop a dimensioned print of the formed part, that way it's on them to get the bend deduction correct and give you the part you want. That's usually preferred by the shop rather than hoping the customer did the flat layout correct.
Yep. I give the shop a flat layout view, but it is undimensioned, and ius only given as a reference. The dimensions are for the finished part. I don't care how they get there.
ultraclyde wrote:4cylndrfury wrote: I cant recall the material name right now, but there is a lightweight plastic board (not corrugated) that is used for real estate signs and the like. Probably 3/16" thick. It melts at (high) heat gun temps, so bending it to form will not be a chore. It also can be drilled/tapped/shaped like metal...sorta.I think the material you're referring to is foam core PVC, one of the main trade names is Sintra. We used a ton of it in the sign biz for cnc routed indoor signage. It's great stuff, but not really cheap. There are off brands, though, and a good sign shop might dell you drops from other projects cut-rate. It's usually available in 3mm, 6mm, 12mm, and on up to almost an inch in varying colors. It heat forms well, bends in a brake with some care, routes like a dream, glues with PVC cement, and can be pretty damn structural if done right. Never tried to laser it, but waterjets like buttah. I still have scraps around my shop I use for switch panels, instrument bezels, etc.
some googling and yes, thats the stuff. When we bought our last house, the realtor never came to get their sign. So, after a year, it began to be recycled into all kinds of stuff...I found out that with a heat gun, you could bend a pretty tight angle into it when I needed to make a cover for a fan with a curve and then a sharp bend.
Wish I woulda known about the PVC glue bit though, duct tape is still holding that fan shroud together lol
DILYSI Dave wrote:unevolved wrote: Your best bet would to be to give the shop a dimensioned print of the formed part, that way it's on them to get the bend deduction correct and give you the part you want. That's usually preferred by the shop rather than hoping the customer did the flat layout correct.Yep. I give the shop a flat layout view, but it is undimensioned, and ius only given as a reference. The dimensions are for the finished part. I don't care how they get there.
So, I have a question about this.
I give them a dimensioned drawing of the formed part... but I also hand them a *.dxf of the flattened part. Should I expect them to adjust the DXF for bending radius or .... what?
I'm also having them cut the bolt holes on the plasma table, I've been looking around for hole finishing methods and it sounds like a tapered reamer is the way to go for finishing a lot of different sized holes fast.
I haven't asked them if the table does layout marking as well, if it did, do you think it would be cheaper to ask them to just drill all the holes?
If you're only dealing with 1/4" steel, why not go to a laser shop? Then you won't have to finish the holes at all. A good laser can get a real nice surface finish on 1/4" A36, more than adequate for bolt holes.
I wouldn't give a DXF'd flat layout at all, honestly. Don't take this the wrong way, but there's a good chance you did the bend calculations wrong. I'd give them a reference view of what it should look like flattened, but that's it.
No offense taken, at all. But the thing is, the bolt patterns are VERY weird, so I could either give them something with 30-40 dimensions or give them a DXF file that was designed from the wrong bend radius or k value. Which would you prefer as a fab guy?
Also, I would much prefer to use a laser shop, but I haven't been able to locate one. That's one problem with being in the middle of nowhere, you're kind of at the mercy of your surroundings.
I wouldnt bolt through a plasma'd hole for anything requiring precision. Unless the operator of the burn table is pretty good and he doesnt have the feeds cranked up to 11 to go smoke a bowl ASAP, you are going to end up with some pretty ugly holes. We do at least 1/16" on the diameter oversize for plasma'd holes.
Agree with the laser comment, it makes parts good enough to use right out of the gate. Good surface finish and minimal saw kerf.
As far as DXFs are concerned, all our fab shops that don't use Solidworks require them for flat panel parts. The best part with a DXF is that you don't have to redraw everything on a flat pattern, you can just export it from the model. Just one less chance of error. As long as your bend radius is reasonable, and your K factor is close, you should be golden. As stated before, holes going through both sides of a clevis that have to be very precise should be bored after bending or bushings or a tube should be welded through the clevis after bending. You need to call this out on your drawing. Holes need to be concentric to X (a few thousandths) and parallel to X (a few thousandths).
If you're not sure what sort of tolerances to specify, please ask us here. You could really shoot yourself in the foot if you ask for +/-0.005" on hole position after forming. Your price will skyrocket, because the only way to hit that will be with a mill operation post-bend.
If you want some critique on your drawings before you send them out, I'd be happy to help. I've seen lots of poor drawings come in from very well-respected oil companies, it's not a common skill to make good shop drawings.
I will take you up on that. Will be doing a lot more design here in the next week or so. Thanks.
Ive always used cardboard and a hot glue gun. That way I could check weld clearance and ability to physically get the weld gun in to tight places... If the glue gun fir the mig should.
sanyarcosean wrote: Ive always used cardboard
this. for 3/16 or 1/4 I use cardboard. For sheet metal I use posterboard
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