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Flat Layout vs Formed Part Drawings

06/19/2012 9:21 AM

I'd like to get some idea on what the consensus is regarding what kinds of drawings sheet metal shops around the world are requesting from their customers. Flat layout patterns? Or formed parts? Or both?

A few months ago I started at a new company that design engineers and builds custom machines in the textile industry, world wide. I'm learning the way they do things here. This company is very small (20 people). The turnover here (in the Engineering Dept. and in Management) has been nearly non-existent. The same people that worked here in 1980, are still here. They've kind of been in a time bubble all this time. They have one machine shop vendor that makes our parts. And one sheet metal vendor that burns and forms our sheet metal parts.

Within the last 6 months they've realized that soon there will be a mass retirement and no one will be left that knows the company, so they've had a rash of hiring of "new blood". I'm the most senior engineer they hired as well as some young kids to be drafters and jr. designers.

My problem is this. The sheet metal shop we use, insists that we provide them with both fully dimensioned formed part drawings (2D ACAD 2000), and also flat layouts that they can directly transfer to their laser. This was unusual in my experience. The worst part about it is that they don't follow standard k-factor formulas on the drawings they want from us. They work it the way that novice drafters would position bend lines if they knew nothing about compression or stretching. They rejected my drawings that were drawn properly after the parts came out very wrong. But ALL their parts come out slightly wrong. All the designers here draw incorrectly (they don't know differently), and now are teaching the new kids (the company's future) the wrong way.

I suggested that we only provide folded part drawings, and that way the onus is on the sheet metal shop to give us accurate finished parts to print. And we wouldn't have to spend time figuring the flat patterns (since we're not doing it right anyway). But before I suggest we start considering other vendors, ones who require only formed part drawings... I'd like to know how you all feel about this vendor requiring layouts and formed part drawing (which don't actually match). What has been your experience with sheet metal shops?

My company is a very back woods small town company. In the end, we produce a great product. But very far from efficiently. Much tweeking is done on the shop floor during assembly and testing. More than usual. I believe this sheet metal issue is one of the many reasons.

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#1

Re: Flat Layout vs Formed Part Drawings

06/19/2012 9:42 AM

Is it time to consider insourcing these parts rather than outsourcing?

I know this doesn't directly respond to your questions, but there may be other issues to consider. If you let these people (the tin shop) know you are considering this, they may even join you here in the 21st century voluntarily, and the relationship can continue.

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#2
In reply to #1

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:06 AM

I need to tread lightly and tactfully, whatever I end up doing. I was hired to bring my diverse experience (I've been a traveling contract engineer all my career) to the company, which as I said, has been in a time bubble for 30+ years. So you know how that goes. Support from the owner (who doesn't even have an office within 50 miles), but a whole lot of "That's the way we've always done it" from everyone else. It's particularly bad at this place, since they've had no turn-over at all.

So at the moment, I don't have a whole lot of influence regarding procedural changes. I have some, if I play my cards right. But that means proof and facts and reports and information, which I have to present in the proper way and at the proper time.

And yes, I do believe the sheet metal shop is holding us over a barrel. I really think they should be doing their own layouts and not have us doing their job for them. But my peers have never worked with other shops.

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#3

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:06 AM

people have been there since 1980......been in a time bubble.........well I hope your on CAD now.

Doorman is correct for the most part.

What is now, company's have been putting together select vendors and suppliers. The reason for this, is that an understanding will be developed,

an example:

God forbid that if you sent out a drawing that will be fabbed, even though it is manufactureable, but,.... it is different from you norm. A norm that a select vendor would realize because they have done business with you before, will call for verification that this is what you want, saving you time and money.

There is value on customer/vendor relationships and understanding that will make your life easier.

As far as types of working drawings, the requirement is minimal for the most part.

A 3D CAD drawing, no flat layout, the reason for that is you put the responsibility on your supplier. Any competent supplier would rather have this.

And with a solid relationship, this can even be a faxed hand sketch, which happens on emergency 'fire-drills' to solve unexpected issues.

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#5
In reply to #3

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:18 AM

I've been dealing with customer/vendor relationships for 25 years, phoenix. I was a machinist in the beginning myself, so I connect particularly well. But I feel that this shop is taking advantage of my company because... they can. And have been since the beginning, since they hold exclusivity on our business.

As far as my norm... I have no norm. As I said, I've been a contractor always. My business is adaptation and flexibility. But it needs to be correct.

And as I said, I was hired to bring techniques and knowledge from the outside world, into this place.

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#4

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:12 AM

I agree that you should only provide the formed sheet metal part. Let the shop that is doing the bending do the flat pattern.

A reason for the k factor being wrong may be that the dies used aren't the correct dies. I have worked for a company that created special K factors and then had to change them once they got the correct dies. After they got the correct dies the tonnage used to form the parts decreased. The sheetmetal shop you're using may have a similar problem.

This company was a small (under 50) family owned company.

Another problelm you're facing is the lack of good designers willing to work in an old 2-D cad program. There will be fewer assemlby issues by going to a 3D cad program such as SolidWorks or Inventor.

Good luck.

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#6
In reply to #4

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:23 AM

Yes, they only use 2D drawings here. And AutoCAD 2000, at that!! Personally I didn't mind reverting to 2D. It's rather nostalgic. But they are not going 3D any time soon. So as I said, we have to draw our own patterns. And nobody quite has it right.

And yes, I don't mind their special k-factors (k-factor = 0.00). I can adjust. It's just that I don't believe we should be doing them at all.

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#8
In reply to #6

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:27 AM

Out of Box Experience

There is nothing wrong with sending out a 3 view 2D drawing.

This is going to sound augmentative, but why bring in a consultant with experience to bring the shop up to date, and then go with business as usual.

See what resources they have, and get a plan together to implement it effectively and efficiently.

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#9
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Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:41 AM

I don't have any problems with 2D 3-view drawings. I'm working with what I have, and that's fine.

My issue is the requirement by the sheet metal shop, for us to provide flat pattern layouts.

I've got a lot of work to do here to bring this company up to date. Will likely take a couple years at least, to make a dent. As far as business as usual, my only benefactor is the owner, who is not present, and to a lesser extent the general manager. But he's not over the top about it. It's a family atmosphere here, which is one of the reasons I took the job. So making huge waves isn't my plan. And since I've finally retired from contracting, have moved to a state that I enjoy, and have accepted this job on a permanent basis, I've got every reason to do this carefully. The brashness of a consultant or contractor can no longer apply.

So I'm tackling one issue at a time, as tactfully and effectively as I can. My current target.... the fact that we're drawing layouts for our vendor.

As far as a plan... that's what I'm doing. Hence... my current CR4 question. I'm gathering information and opinions in order to form my plan. You are one of my resources.

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#11
In reply to #9

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:04 AM

I see,

Yes, upgrading or modernizing is difficult in a somewhat engrain system with maybe limited resources.

I wish you well.

p911

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#12
In reply to #9

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:12 AM

OBE, you said "My issue is the requirement by the sheet metal shop, for us to provide flat pattern layouts."

The "We've been doing it this way for years." mentality at your new employer has been identified, and for the moment it is insurmountable but tolerable for you. Is there some belief that you can undo that mentality at the tinbender?

I'm with you on the tread lightly theme. Smaller places usually have a more relaxed sort of atmosphere, where personal relationships with vendors and customers can take years to develop but some new blood whippersnapper can wreck those carefully tended relationships in a New York minute.

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#14
In reply to #12

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:19 AM

No, not trying to change the way the vendor works. That's how they do it. I'm trying to gather info to eventually use as justification that it might be a good idea to start considering different sheet metal shops and start building other relationships. But I've got to have a strong case.

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#7
In reply to #4

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:23 AM

That is correct about the k factor which is often overlooked. Each shop is different.

And considering that the original company is brick and mortar, one should have some type of standards and understanding.

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#10

Re: Flat Layout vs Formed Part Drawings

06/19/2012 10:53 AM

My original question is really what I need answered most right now, depite the very interesting tangents and valuable, related opinions thus far.

I'd like to get some idea on what the consensus is regarding what kinds of drawings sheet metal shops around the world are requesting from their customers. Flat layout patterns? Formed parts? Or both?

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#13
In reply to #10

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:15 AM

I've only worked at one shop that also had a general sheet metal shop. We wanted drawings of finished parts (or a sample). We did our own stretchouts.

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#15

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:26 AM

If you keep doing what you always did, you'll keep getting what you always got.

That said, if this shop is the only game in town, you may have to accommodate them or look at a new pricing from your vendor.

These drawing take time to do, it's just a question of who does them and the difference in hourly rates of the drafter.

I'd also contact some new suppliers and find out what they would expect in the way of a drawing package from you, the prospective customer. You should be able to e-mail the part files and receive a finished part from the new vendor.

Good luck.

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#16

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:51 AM

The main issue here seems to be keeping the methodology within the business as people leave it and new ones arrive. Is the ISO9000-series way of doing things a complete unknown there? If so, then the concepts need to be embraced pretty quickly, otherwise the last person to leave will be turning out the lights.

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#17
In reply to #16

Re: Flat Layout vs Formed Part Drawings

06/19/2012 12:49 PM

Correct. ISO 9000 methods are completely unknown here.

But the fact is, that business is doing very well. That is solely due to the success and strength of the proprietary designs that we're producing. The product is really very good. But profits could be so much better if so many of their archaic ways of doing things were brought up to date. There are huge deficiencies in every step of the process. Yet even with that enormous handicap, we are still making money.

I took on this challenge because of the huge number of things that could be improved. And frankly, it wouldn't be a bad thing for my career if I was the driving force behind these improvements. Many of these things require nothing more than embracing industry and international standards, and employing basic technology that's been developed since the late 70's. The GM and second in command don't even have computers in their offices! They don't use them. Most of the people here resent change. Except for the 5 new people, everyone else is 60+ years old. One of my concerns is that the youngest people are learning these out-dated inefficient habits. But if I approach this correctly, the potential here is absolutely enormous.

Let me add, that the people working here are highly skilled, very intelligent, and know the product extremely well. They are just dug into the old ways, with no influence from the outside world. Most of them believe things are just fine; not knowing that other ways exist.

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#19
In reply to #17

Re: Flat Layout vs Formed Part Drawings

06/19/2012 5:40 PM

My comment is from an other country so that it is in the line you want.

I see 2 possible ways:

- use an extension of CAD which is thought for metal sheet design and which automatically makes the "flat" automatically taking care of the different factors at bending.

- send the piece design to an other possible supplier who does NOT ask for the flat part drawing and compare results (quality and price).

The 1st suggestion being less aggressive since you do not compare sources but use recorded know-how (in the soft).

Till now I usually supplied the drawing of the piece in final situation, good for assembly, how they managed to get it was their problem. Of course I took into consideration the expected process and in complex situations had a discussion with the supplier for explanations in both directions, me about what I expected and from him how he could make it or what changes should be done to make the manufacturing as easy as possible without loss of performance.

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#18

Re: Flat Layout vs Formed Part Drawings

06/19/2012 2:52 PM

I worked at a stamping plant with our own tool room to build the dies. Customers would supply finished part drawings and we developed the die and made the finished part to the drawing.

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#20

Re: Flat Layout vs Formed Part Drawings

06/19/2012 11:53 PM

Out of Box Experience-

Seems like only one of the first 18 answers actually comes close to addressing your original question about "what kinds of drawings sheet metal shops around the world are requesting from their customers".

My experience (here is Panama) is that it varies from shop to shop- there is no consensus. When I put a package together for bidding purposes, each shop I solicit has different requirements. Some prefer going with illustrations of finished parts (most often, 3-view 2D, because the dimensional information can be easily read directly). Others want flat patterns. It is not a question of the quality of the work coming out of the shops, generally, but, rather, a question of the depth of the shop's in-house engineering resources. Shops that want flat patterns generally work cheaper (lower overhead, obviously), but the cost difference is a wash, since there is an in-house cost of doing the flat patterns for them. If a shop wants flat patterns, I ALWAYS ask what their bend allowance is...Which means, I might wind up doing two or three different flat pattern drawings for a single project.

Not a consensus, but basically, an expression of what I run in to here in Panama...

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#21

Re: Flat Layout vs Formed Part Drawings

06/20/2012 4:42 AM

No. 1 advise:

Provide your supplier with sufficient information to manufacture your part. Move to town, get the paper but invest in a Solid Modeling Engineering/CAD package. I would recommend SolidWorks, makes sheet metal so easy.

No. 2:

You might want to second source your suppliers...sounds like your supplier is a little demanding and your company is relying on one source. Apparently competitive quotes are not a thought...Fat and Happy Sheet Metal Supplier. LOL you really have to be kidding.

No. 3:

Give the supplier a fully dimensiond drawing and a flat pattern (dxf file) if your CAD software can accomidate (bend factors are quite common if the material is correctly specified). The rest is up to your supplier. If it's manufacturable and they can't make it to your drawing then it is time to look for another supplier.

But seriously, get a second supplier, at least you can source it out and compare pricing. Sounds like your current supplier is raping you blind...unless he is related to the family?

Good Luck,

Frank

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#22

Re: Flat Layout vs Formed Part Drawings

06/20/2012 5:20 AM

We model in 3D & the software will automatically provide a 2D flat pattern. We often send a DXF file of the 2D pattern to the sheet metal sub-contractor who will use it directly to make the parts. You must however have agreed on k factors & notching beforehand so that you are both working to the same parameters.

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#23

Re: Flat Layout vs Formed Part Drawings

06/20/2012 7:57 AM

I worked at a sheet metal job shop for 6 years. We never asked the customer for flat patterns to use for programming. We requested finished drawings. It is up to the shop to determine what the flat dimensions are. They should be responsible for that. I would say most shops use 3D cad for sheet metal. It is so much more efficient. The shop you are dealing with probably doesn't have an engineering department.

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#24

Re: Flat Layout vs Formed Part Drawings

06/20/2012 12:37 PM

Drawings should describe the finished part that could be used for acceptance/reject. Therefore, I only provide the folded up drawing to outside vendors. If we are folding up a prototype, I add a second sheet with a flat pattern. The second sheet is removed before production release. My better sheet metal providers do not want the flat pattern. They tell me that they know that the K factor varies slightly depending upon the machine and dies and material that that they use. They use a CAD program to generate a flat pattern then they make a part. They measure the sample part and then modify the flat pattern to compensate for deviations.

Recommendation: Since you are stuck in a time bubble of 2D, I would push to eliminate the flat pattern. It has to be very time consuming to make and it is prone to error.

Leverage: If they insist on keeping the flat pattern, you might be able to get a 3D CAD seat and demonstrate that the labor saved making the flat pattern and reduced rejected material will more than justify the cost of the software.

Compromise: If your company insists on using the same sheet metal shop and the sheet metal shop insists on have a flat pattern, I would label the flat pattern "REFERENCE INFORMATION ONLY" and place the K factor next to the flat pattern. I would also add a general note explaining that the detail of the folded up finished part contains the controlling information and that the flat pattern is just reference information.

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#25
In reply to #24

Re: Flat Layout vs Formed Part Drawings

06/20/2012 12:59 PM

Yes, you and I think exactly alike. In fact, I did just that. I labeled the flat pattern FOR REFERENCE ONLY. They made the part to the flat pattern anyway, since they used the actual drawing as their Burn Pattern. Then called me and complained that it didn't match the folded dimensions and insinuated I'd done something wrong. They then told me to remove the REFERENCE words from the flat pattern. WTF? Who's the customer here? It's just an unusual situation. No one else here understands anything about k-factors.

Your other suggestions are good suggestions. And yes it's true, very reluctant to get even an updated version of Autocad, newer than 2000... much less a 3D modeling program. That's not going to happen.

At this point, I need to build up my reputation within the company so that my opinions on this particular subject will carry enough weight. I plan on using many of the quotes in this thread as additional information for them to show I'm not the only one that believes we could do better by looking at other sheet metal vendors.

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#26

Re: Flat Layout vs Formed Part Drawings

06/21/2012 9:40 AM

I use both. Sometimes the finished dimension is the Critical dimension, and sometimes the flat pattern dimension is the critical dimension.

Our company owns a laser plant in Calgary, and we have multiple places to get stuff bent, including a cnc unit here at our shop.

I use the same drawings for everyone... as well as providing a dxf to the laser plant. so I have all views on the drawing. While I do have some training and experience myself with sheet metal, and consider that very important to my function as drafter, the software is also excellent at giving all bend types and k-factors as options. I need to know the material thickness for the machine that is bending it, and which dimensions are Critical.

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#27
In reply to #26

Re: Flat Layout vs Formed Part Drawings

06/21/2012 9:44 AM

Sometimes the finished dimension is the Critical dimension

never thought of it that way,

I always thought the finish diminsion is always the critical one, but maybe not if a dimension was needed for a process prior to being finished after layout.

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#28
In reply to #27

Re: Flat Layout vs Formed Part Drawings

06/22/2012 9:12 AM

it is better to dimensions holes, cutouts, etc on the flat pattern (essential if cuts are being made. ie laser or water jet) also angled lines etc are best dimensioned on the flat..

Sometimes we have the bend lines (and text with bend direction and degree) scribed by the laser right on to the piece to be bent....so that definitely has to go on the flat pattern.

It is also useful for the overall material dimensions to be put on the flat pattern, to help determine the amount of material needed, and to help a bit with nesting. (I think...?)

Cheers,

Chris

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#29
In reply to #28

Re: Flat Layout vs Formed Part Drawings

06/22/2012 9:47 AM

Thanx Chris. Sure, I don't dispute the need for dimensions on a flat pattern. My issue is with who actually produces the flat pattern drawing. The customer? Or the sheet metal shop, that's supposed to be experts in flat patterns and bending? Should the shop insist on receiving both a dimensioned formed part drawing, AND a dimensioned flat pattern?... and then, prohibit the use of "FOR REFERENCE ONLY" on the flat pattern bend line locations?

But actually, I wasn't trying to justify it one way or the other in this thread. I'm just trying to find out what most shops do, so I can get some statistics to use in a report. I need to back up my opinion that we should look at other vendors because of this.

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#32
In reply to #29

Re: Flat Layout vs Formed Part Drawings

07/09/2012 12:27 AM

In true life the customer is always right...and you are the customer. Each part has there own characteristics (bend radii's, material thickness and how the sheeet metal shop is manufacturing the part). In your case the 2D drawning should be enough for the supplier to produce your part, but they may charge you a engineering fee to produce the drawings, dxf files or the documentation in order to manufacture yhese parts (in which they should be accumulating history). As long as the part is manufacturable and your 2D finshed part drawing is precise you should be ok...let the sheet metal shop do the rest, this is their job. If you recieve in the finsihed part that does not meet your specifications then reject the parts. For the most part you should have at least two suppliers, which makes your parts cost competitive. A 3D CAD package is also an important tool, SolidWorks is realatively reasonable and it has an excellent sheet metal package which is included in the per seat cost. K factore's can be changed withing the design cycle. If your supplier wants to be your supplier than they should be able to supply you with the correct K facter for the material used. Any problems please give me a call and I will personally help you out.

Franklin E. Bulley
Product Development Specialist
(Laminated Bus Bars)
Triton Manufacturing
5700 Triton Way
Monee, IL 60449
Office Phone: 708-587-4019
Cell Phone: 708-941-5336

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#30

Re: Flat Layout vs Formed Part Drawings

06/24/2012 7:55 PM

There are a few ways to look at this. We typically make a distinction between an engineering drawing and a process sheet. An engineering drawing by nature specifies the requirements for the finished condition of the part or assembly. This is as far as the engineers and designers go. A process sheet defines how the part is made. This is up to the shop or manufacturer. Defining a flat pattern is theoretically a "process" and not an engineering specification so...it should be the manufacturer's or shop's responsibility and not the designers.

Having said this, most shop's we deal with don't want to spend any time making decisions, figuring things out, or...working out a flat pattern (costs $$ to figure things out!). They expect us to provide them with the pattern so it saves them time and reduces the chances or error. Most of them know we work in 3D and providing a flat pattern is easy so they expect it.

My $.02

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#31
In reply to #30

Re: Flat Layout vs Formed Part Drawings

06/24/2012 8:40 PM

Thank you TerraMan, that's exactly the type of input I'm looking for.

The only caveat I have to what you said, is that if we actually used a 3D program her, it would be a non-issue. Because it was always simple enough to print out a flat pattern from a solid model. But we are using 2D AutoCAD, and the flat pattern must be individually figured out; with no direct connection to the engineering drawing, as you know. None of our designers really understand the entire bend allowance thing. They've been told to use zero k-factor, by the sheetmetal shop. Well k-factor has never been mentioned at all, so the theory of it isn't even knowledge here. That's a whole different story and beyond my control. But that's besides the point.

Anyway, under these circumstances it would be far more efficient on many levels, and make much more sense to just supply formed engineering drawings. That's my feeling, anyway.

I plan on using a printout of this thread as part of my presentation and supporting opinion. So far, it seems the vast majority here agree, for the most part, with my feelings on the subject.

The situation is workable as is... but I believe it would be a huge improvement to our system to do as most other shops do.

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#33
In reply to #31

Re: Flat Layout vs Formed Part Drawings

07/25/2012 10:34 AM

If I were you, I would be tempted to identify two or three competitive shops and ask them for an "expression of interest." I wouldn't ask for bids because you truthfully are not in a position to place an order and you also don't want to give the impression that you are shopping their bid to the local guy.

I would include a 3-view 2D drawing of the finished product (or reasonable facimile) and ask them if they could produce the product from the information provided in the quantities required.

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#36
In reply to #33

Re: Flat Layout vs Formed Part Drawings

07/25/2012 11:37 AM

I'll probably end up doing something like that.

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#38
In reply to #33

Re: Flat Layout vs Formed Part Drawings

07/25/2012 12:26 PM

you also don't want to give the impression that you are shopping their bid to the local guy.

As having been a fab shop owner, if you get a reputation for doing that, you will only have your single supplier.

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#34
In reply to #31

Re: Flat Layout vs Formed Part Drawings

07/25/2012 10:45 AM

None of our designers really understand the entire bend allowance thing.

You must have confused drafters as designers. But even as drafters, they must have a knowledge of discriptive geometry as well as developments.

And depending on the material type, tolerance I have found that the K-Factor is a non-issue on thinner material (1/4" and lower) with a lower tolerance.

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#35
In reply to #34

Re: Flat Layout vs Formed Part Drawings

07/25/2012 11:37 AM

No, I didn't confuse drafters with designers. We have some of both. Our designers have been here 15+ years, but very cut off from the outside world in practice and in thinking. None of our designers really understand the bend allowance concept. Mostly because that one sheet metal shop has told them to design with a zero K-factor. Therefore, our designers haven't even heard of a k-factor. Their mind-set is that all of the metal thickness stretches, and the inside face remains at zero (essentially, that the bend line is the inside face). That's how they picture it in their mind. And because of this, they are teaching our few fairly new and impressionable drafters the wrong information; all of which concerns me.

And I'm going to disagree with you on the relevance of K-factors on mat'l thinner than 1/4". For panels to match, and holes to line up and covers to fit... an error of half a material thickness could really screw up a sheet metal assembly, especially when it's assigned a low tolerance. You start adding up worst case tolerance stack-ups, and then add half-material thickness errors... that does not bode well.

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#37
In reply to #35

Re: Flat Layout vs Formed Part Drawings

07/25/2012 12:23 PM

And I'm going to disagree....

Thats fine, I have to add, with there were exceptions such as reverse bends, I used inside dimensions, (and Loose Tolerances).

Because like you stated, stack errors occur.........

I did not know until I had interacted with the shop floor early in my career, only then did I realize you throw your books out when it comes to K-Factors, and use imperical data from the shop your in.

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