Practical Tolerancing for Manufacturing
Episode 4
August 13, 2020
Dan:
You can have a set of tolerances that only would get you in trouble at some extremes and most of the stuff you build would actually work. Depending on if one part was built to an extreme, either high or low, and the tolerance, then when things stack up, you can run into a problem.
Rob:
You were just listening to a clip from today’s Get Sparked podcast featuring Dan Gonzalez. I’m your host, Rob Hamm, along with Pete Kogel and Allan Stoltzfus, continuing our conversations on manufacturability with a topic this week on tolerancing. Pete, would you be able to give a brief history and where we are in the manufacturability series?
Pete:
So we started a series of podcasts on design for manufacturability and talked about materials with Marc Glasser. And now we’re really going to focus on tolerancing of components. Now, the scope of tolerancing in our world primarily drives into fabrication and machining. Today, as Rob mentioned, we’ve got Dan Gonzales. Dan’s our Engineering Manager here at R-V Industry. Dan’s been with the R-V for 30 years. He’s a professional engineer, has his bachelor’s in mechanical engineering from Pitt, unfortunately. So, uh… Really excited to talk to him and just get his view. From Alan and I’s perspective, I think we do a really good job internally with detailing and design. Some of those aspects play into how we are attached to a manufacturing plant and how that can, can really develop and engineer differently than maybe someone that’s looking to design a new component that might not have that direct feedback. Some of the things that we’re talking about today. So Dan, yeah, thanks for coming on and talking to us.
Dan:
Yeah, you bet. It’s kind of hard to believe. It’s actually been 30 years. That’s a little crazy, you know. It all started for me, I actually went to VoTech my senior year of high school and learned the drafting and then got a job here at R-V right out of high school. Then worked part-time during my college years, getting my engineering degree. All that time I was doing mechanical design and drafting. So that foundation is really critical for engineers to have any way at a company like ours, where we, you know, our deliverable is manufacturing drawings that have to tell the story of how that equipment is to be built.
Pete:
I share that philosophy heavily when I started here with a welding engineering degree, got the opportunity to be working on the floor for a few months, built those relationships. I know that’s how we are targeting to actually own board new engineers that are starting, you know, full mechanical engineering degrees are actually working in assembly areas and working directly with the guys that they’re going to be supporting with their drawings, their fabrication drawings, assembly drawing. I know this is near and dear to how you came through the organization and how you’re now trying to grow and build the next generation.
Dan:
Yeah. When you get to grind a bevel or a weld on a, on a plate, on a, a butt weld on a plate flat in stainless steel, you start to understand how long it takes to actually do some of these activities. They get a new appreciation for it. So getting our young engineers that experience on the floor is critical. And we actually have one right now that we just have In may. Who’s currently working in his first phase of onboard. He’ll be finishing that up here and to September, and then, uh, digging more into some core engineering concepts as it relates to our life science equipment, our line of autoclaves.
Pete:
Yeah, that’s awesome. For us and the people that, R-V employees, typically are not the type that if you want to go get tucked away in a cube in the corner and not get bothered, right. You want to be able to get out, get involved, and build those relationships to build the best product we can.
Dan:
Yeah, that’s right. That’s feedback from the floor is Critical.
Allen:
Absolutely. I mean, I think about it from my end being in the sales side of stuff, but coming out with a mechanical engineering degree a couple of years ago, it’s very valuable and builds a really good platform or base for it. You know, the feedback loop we have here by having engineering and also the manufacturing presence all under one roof really provide a real feedback loop that most engineers, the places they go, they, even if they’re not, you know, say fully tucked away, but you don’t have that open communication even for facilities that do have all of that. I think that’s something we really push and really helps to open that communication.
Dan:
Yeah. That’s great. That’s right. Allen.
Pete:
So what’s your view. If you’re going to explain tolerancing, do a, a five-year-old Dan, what’s the Albert Einstein phrase; If you can’t explain it to a five-year-old, you don’t know it well enough. If you were going to explain that to my son in a couple of years, what’s, what’s the best explanation of, of how that, uh, applies to everyday life?
Dan:
That’s getting really basic. I guess the truth is everything has a tolerance to it. So if you’re going take, uh, a piece of wood, get your five-year-old a piece of wood and have them cut it, have them cut your five pieces and see if they all right. Right. Exactly the same. You might give them a tolerance. Hey, every single one of these has to fall within plus or minus an eighth of an inch. Right. See if he can hit that.
Pete:
What’s the stuff that we work with on a daily basis that people don’t even recognize. The kind of extreme high-level tolerances that go into it.
Dan:
Yeah. As I said, everything, everything has a tolerance. So a good example of how tolerancing really works in practical application is you have manufacturers all over the country, making bolts and nuts, like a quarter 20 bolt made in California is gonna work with quarter 20 nuts made in Pennsylvania. Because they’re following a standard tolerance that’s been established and as long as they make the part within that tolerance, it’s going to work. That’s the idea of tolerancing is that you’re setting up a window to hit dimensionally so that you know, that the parts will work and they’re repeatable. You can make them again and again, and again, and as long as we hit the tolerance, it’s going to work.
Allen:
Going back to the basics of it, I was just reading today about some of the origins of geometric dimensioning and tolerancing. It seems like most people point back to Eli Whitney was awarded a contract to build rifles on a pretty large scale for the US government. Up until then, it was a lot of skilled craftsmen making them, making sure everything fit together on an individual basis. He quickly realized they’d never get an affordable price point if that was the approach they took. So he started giving this skilled craftsmen, he’s going to make 500 simple parts that then fit into another simple part on the rifle. But if you don’t have some kind of document dictating what those dimensions need to be, there is no guarantee they’re going to fit together.
Dan:
Yeah. That’s a great example. That’s neat
Pete:
For us building and designing custom industrial equipment. There isn’t necessarily, I guess a standard that we follow in general, but every part’s different, obviously hardware probably has a greater standard that it follows for all hardware, but how we approach a drawing and how we communicate that on a drawing is I guess, in a standard format.
Dan:
Communicating, the design intent on the drawing obviously is very critical. That manufacturing drawing is the deliverable out of engineering to the rest of the organization to get things made. That drawing tells the story of tolerancing a drawing that’s done well, you can quickly look at that drawing and know where the critical features are and are able to quickly see what features aren’t as important. As opposed to an example would be a drawing that we’ve dealt with recently, where every dimension on the drawing was a two-place decimal and a standard tolerance block down in the corner of the drawing set a two-place decimal meant everything had to be plus, or minus 20 thousandths. It was very obvious that applying practical manufacturing processes to making this part, you were not going to hit plus or minus 20 thousandths on a lot of those features. That became very cumbersome and trying to resolve that issue with our customers.
Pete:
To give a designer who isn’t necessarily working in the metals world. So we see things in kind of two buckets. You know, you have fractional tolerances, you have a nominal, let’s say it’s a five-inch dimension and that’s just listed as a or five and a quarter. And it’s listed fractionally on the drawing. We would typically apply what we refer to as fractional tolerances to that. And that would be fabricated manual tolerance. Say, it’s a drill pattern that you could layout by hand, say it’s a sheared part to size kind of the next stage in those would be, you know, either laser cut or machine parts where we’re looking at a two-place decimal like you mentioned 20 thousandths of an inch. It was that particular drawing tolerance on a two-place decimal. We use in machining, you’re obviously getting down to, you know, the 30 10, five, one thousands down to pretty tight tolerances. Laser cutting you can easily achieve 30 thousands, 15 thousands. So, just to give a general scale.
Allen:
The reality of it is when we’re looking at dimensions as a manufacturing shop where we’re actually building it. We’re not just looking at a dimension saying, Oh, that’s tight, that must be important, but we’re also tying it to our process within our facility to either cut it or machine it or weld it. That’s ultimately what dictates how it’s built. A certain tolerance you can only hit with a certain process.
Dan:
Yeah, that’s correct. And that’s where, that’s where as a designer, as an engineer, it is really critical to know how something will get built. So if you know the steps that are going to be taken to build a component, it becomes a lot clearer how you should dimension and tolerance that part as well.
Allen:
We keep saying, telling a story, but that is the story we’re telling the story of how it’s actually being built. And that’s what the tolerance is dictating.
Dan:
That’s right. Pete, you had asked earlier, you know, what standards we follow. When we have questions about how we should depict a tolerance on a drawing. When we have questions about that, we go back to ASM me, Y14.5 as our guide for how to communicate tolerances and dimensioning on drawings. The other tool we use in selecting tolerances is the machinery’s handbook. It’s a very practical application reference or a resource that really helps describe the kind of tolerances you might apply based on the function that that part has to perform. So the machineries handbook actually gives some descriptions like that, that are practical.
Pete:
So ASM me, Y14.5 essentially gives a standard format to show it? Is that what would that standard does? It doesn’t necessarily give you that this should be held within this tolerance. It gives you the format to give it. Then the machinery’s handbook would give you, if you want this type of fit, or if you have a bearing, or if you have this type of finish or something like that, that you’re looking for, this is the actual tolerance, or this is what the RMS or whatever should be shown on that.
Dan:
That’s right. The Y14.5 is the guideline for how to communicate tolerancing. The machinery’s handbook we use in the selection of a tolerance. An interesting piece of, Y14.5 that we used our standard block is they make a statement in there that the dimension of size also communicates the expected tolerance of form. So what that means is if you’re making a box and you have a dimension on there that from one side of the box to the other is 20 inches. And you’re saying you put a tolerance on that 20 inches of plus or minus a 16th. Okay. What, Y14.5 says, as a rule, is that it also has to be flat both sides have to be parallel. They have to be perpendicular to the base. All that stuff has to be in that plus or minus a16th window. So we use that as a guide. Even when we’re looking at a dimension says, plus, or minus a 16th, we’re also evaluating whether or not that’s good enough from a flat standpoint, from a perpendicular standpoint, from a parallel standpoint and so on.
Pete:
So that would be more of geometric dimensioning and tolerancing. I remember my first internship, it was a, like a training initiation of GD and T. I’m like what in the heck is GD and T. Especially going into a, kind of a manufacturing engineering role and coming back, coming from, welding engineering, GD, and T what is this stuff? Parallelism, flatness profile, circularity, concentricity, that gets you into the spatial recognition of a part and how that really is going to have fit form and function.
Dan:
So Y14.5 addresses all that?
Pete:
Got it. Okay. So on custom equipment, we’re talking what resources we use. We have, I’m assuming kind of a standard that we follow. Then after that standard, an engineer or designer needs to go to the next level and think about how this is actually interacting in an assembly. So I’m assuming over the years established our standard and then had to confirm that standard within a given assembly.
Dan:
Here at R-V we have our different market areas where we specialize in certain types of equipment. In each of those areas, we have design standards. We also have an engineering services group where we could be designing anything from a simple crosswalk to a fully automated machine that has many, many parts fabricated machined, and so on. We have design standards, but then when we’re designing something truly custom, the engineer and designer have to think about how all the components need to interact. This includes commercial components. So when we’re buying a commercial component and we’re integrating it into our equipment, the manufacturer of that commercial component has recommended tolerances. You need to know what those are, and we have to apply those into the design.
Pete:
One thing that I’ve run into, not even commercial components, but just raw material, like someone’s using a piece of pipe, say A106 grade B seamless pipe has pretty broad tolerances. We get pretty heavily into some product lines that we’re gaging the actual pipe for roundness. When you say the commercial components, I don’t know if you mean like actual buyout stuff, or actually even commodity type raw material like pipe and angle, like flatness on a piece of angle. That’s not going to be flat within 10 thousands across a 10-foot span of angle. That was an interesting thing for me when I’ve started to see tolerancing on actual raw material, and then we’re going down the line of, does this need to be machine, pre machine, final machine,
Dan:
That’s right, Pete. Whether we’re buying a bearing that has very, very tight tolerances, or we’re buying a 10 foot piece of 12 inch schedule 40 pipe, all of those things have tolerances that we have to understand what they are in the design phase so that we can make sure that our design is going to work with whatever pipe we buy that meets the pipe standard. If we know we’re out of bounds with that, then we have to put some special tolerancing on the drawing that has us performing some other processes to get it back in line.
Pete:
One thing that’s always interested me, and sometimes typically in what Allen and are working with and what we work within one-off custom equipment. In some of our market areas, I know over the years, and you’re probably a part of those decisions, using other processes to get to a tolerance. So the conventional thought is fab, raw material, machine something, but, investment castings are really cool. The tolerancing that you can get that we have in some product lines that we do. Maybe you could speak a little bit about some of those decisions that we’ve made over the years, but I’ve been at a couple of trade shows, looking at some example, investment cast parts, and obviously the tooling cost is high, but what you can get out of that tolerancing wise is really impressive.
Dan:
Yeah. We’ve, we’ve utilized that process. I’ll say, primarily in our power division where we have standard pivot, pins, sockets, lugs for adjusting links, things that we make, and sell by the hundreds. We’re able to put the bolt holes right in, that we want to hold to a tighter tolerance than what a burned hole would be on a, on a plasma cutter or something.
Pete:
What kind of talents can you hold? Can you hold 10 thousands?
Dan:
I think it’s in the 15 thousands range. Don’t hold me on that. We’ve used that process to replace calling out a drilled hole. But it’s certainly not as tight as a drilled hole. The other thing we’ve started to really pay attention to here recently, I’ll say in the last five years or so is 3D laser cutting using our SolidWorks tool. When we designed something in solid works and got all these holes that are being cut in a, say a six-inch square tube, we’re able to send our solid works model to 3D laser cutters and they can put all those holes in very quickly and very accurately.
Pete:
We’ve talked about that. Previously where Alan does quite a bit, especially when we’re looking at higher volume parts and you’ve got to balance the programming and handling time versus, if you’ve got one part that has a bunch of holes than it might not make sense, but your gut five, 10, 20, 50, that’s where it starts to make sense. They’re becoming a lot of smaller cut shops. Laser-cut shops are buying these machines, and we can’t necessarily justify, but we all of a sudden have this two, three, four supply chain sources for that process. So in the past two, three years, it seems like here locally to us, there’s at least two or three within 30 minutes of us. So it makes no sense for us to think about going out and spending a million and a half dollars on these big machines when you have that kind of supply chain around us.
Allen:
That’s what makes it so interesting. We might be held to one set of dimensions and tolerancing. That’s not changing, but there’s always evolving machinery and processes to do this. Whenever a job comes through, you can think about the vendor source you have maybe recent stuff you’ve seen at a trade show, developing technology, and it’s always changing. There’s always an evolving process to see what kind of availability and options there are. It definitely makes it really interesting. An example that I had a few years ago was someone had essentially a Hastelloy C276 cap and they had a perfect square in this cap. If you were going to make it just like they had it shown, you would have had to have like a plunge style EDM, like a plunge EDM to get that perfect square in that part without having any radius in the corner.
Pete:
The cost of that, and the tooling to that versus going back to them to say, Hey, do you really need this, or can we have relief cuts in the corner, or can we have a slight radius, makes a complete decision on the process? So we needed to hold that profile and that tolerance in the part.
Allen:
That’s the kind of feedback loop you could say. That’s so important when you are the ones doing the drawings and that’s more an internal discussion. If it’s a customer coming to us saying, Hey, this is what we want to be built. Whenever you can have that kind of communication feedback and going back and forth and being like, yeah, we can do that, but this is the process or being held to. Sometimes it does need to be exactly that. Other times through that discussion, you can adjust and come up with a way more affordable option. It just depends on each item.
Dan:
Yeah, there’s a recent example we had here in engineering where we were building some gas piping manifolds. We had three inch pipe going into five inch pipe and we had to build it to B31.1. We needed full penetration welds at those joints. We were able to model in the actual bevel. If you can think about how a three-inch pipe fits into a five-inch pipe, you know what that fish mouth looks like and having a full penetration weld joint all the way around that pipe. We were able to model that in solid works and then send it to a 3D laser cutter and have them cut those shapes for us and have it ready for fit-up and weld when they showed up worked out really well.
Pete:
Dan, when we have an application and we’re tasked with a very unique piece of custom equipment, it could be different material grades. You could have things that are maybe carbon, stainless, Inconel, or brass. You’re dividing this piece of machinery up to maybe multiple designers that you kind of have to come together as a group and come up with fits and tolerances. What’s, what’s your approach.
Dan:
That’s right. We often create design teams, but there’s always a technical lead. Someone who is going to oversee the whole design and make sure that all the moving parts are working. Which includes verifying all the different dimensions and having each designer prove to you as a technical lead that they designed it properly. You mentioned all the different materials. That’s the other thing that we’re, we’re looking at. An interesting thing is if you’re talking about tighter tolerances, when you’re down in the few thousand, maybe even plus or minus 5,000. As an example, if you have a 60 inch part and it happens to be made out of 304 stainless steel, something to think about is that materials coefficient of thermal expansion. As an example of that material and over 60 inches, a two-degree temperature change is going to either have that material expanding or shrinking by 1000. You can also look at what temperature change would it take to move at 5,000? Well, that’s nine degrees. So just around a 10-degree temperature change your part just moved 5,000.
Pete:
Not even from the design standpoint. From what we get into on inspection and a customer’s in reviewing something. How you’re inspecting these parts to tolerance, how you’re holding it. We see plenty of customer specifications, especially in the higher end work that tells us the temperature of the room or the facility that it needs to be inspected at. I’m sure we’ve had plenty of examples where we’ve had to really scratch your heads for a second and then come back together to say, are we looking at this? Right?
Dan:
Even back to what was the temperature when we machined it? Yup. Knowing what temperature we machined it at and knowing what temperature we’re going to check it at is a piece of that puzzle. We can’t be tripped up by thinking we missed a tolerance when, you know, it’s, it’s 90 degrees out today. You know, when we machined it in the middle of winter. That’s something we need to be cognizant of. It’s an interesting piece of tolerancing that I would say most people wouldn’t think about unless you’re involved practically with this stuff every day. There are times we get specs from customers that say, we have to do our inspection at ambient temperature, which is often 68 degrees Fahrenheit, and they give us a plus or minus five-degree window on that is what I’ve typically seen. We have to make sure we’re machining things within those temperatures, and if we can’t, we make an adjustment for it at that time. Then when we’re checking it, we have to make sure we meet the requirement.
Pete:
The interesting side of being an engineer in your role at a company that has manufacturing, that works in so many different industries. You’re seeing other customer’s requirements, maybe other customers, tolerancing schemes, as well as incorporating those best practices into what we do, all the way out to, you’ve got a laser inspection of a machine part that is 12 foot tall that has concentricity of two features that are six feet apart. I remember that we had a nuclear project that I wasn’t here for, but I think we were all pretty impressed with ourselves with some features that it was a 12, 14 feet apart of two plates that had concentricity, like essentially rod, I think they were like fuel rod, like holders that had to have hold a tolerance. So just really, really cool stuff. It makes you appreciate the everyday world. You close your car door, right, and you see like this little gap, you know, difference or something like that in the car door. You’re thinking, oh wow, this thing’s junk. That might be 30,000 or something like that. Right. People, you know, uh, no offense to a new engineer necessarily, but a new engineer might go and put some crazy tolerance requests on a little sheet metal part. Not necessarily understanding the full implications of the costs. So we’re trying to convert that into a process, as Alan said, I think it’s cool to give the the hardware and like the every day, just the appreciation of what we work with in automotive stuff that people see and hardware they might be using to wrench on something in your house.
Allen:
Because the point is it’s not that tight tolerances are bad. It definitely can make different processes, very challenging, but they’re absolutely critical. It comes down to choosing tight tolerances when it’s necessary and understanding the application of it and the ramifications. But then having the ability to not choose tight tolerances when it doesn’t need to be. It can easily sound like, Oh, we’ll just make everything lose tolerances. Cause it’s so hard to hold. That’s not obviously going to work for a lot of applications, but it’s just knowing the how and the when.
Dan:
We’ve used the laser inspection method a number of times and that’s a really interesting tool to watch, watch it being used and, and watch it work. We had a piece of equipment where we designed a shop fixture piece of equipment that needed to be assembled vertically. It had about a five-foot diameter flange on it that sat on the fixture we built at three points. The bottom of that flange had to be flat within just a few thousand. The lesson we learned was once the weight was on that flange resting on three points, just the deflection of the weight, put us out of tolerance. When that support wasn’t a reality for how that piece of equipment was going to be used. We didn’t see it until we took the weight off. We used the crane to take the weight off of that assembly. And that’s when we saw that it went back flat.
Pete:
So just that little elastic deformation at that point loading.
Dan:
Another thing as an engineer to keep in mind, as we support stuff in our shop and we’re going to use those fixtures to hold things in place while we verify things, what is the deflection of the equipment under its own weight?
Pete:
If you were an engineer starting out, you mentioned the, machinery handbook or someone that has a custom piece of equipment that they’re designing, obviously, we always tend to feel that we’re a really good resource for people, but outside of reaching out to a manufacturer, say you’re still too early of a stage. What other good resources can you think of that might be available for someone trying to understand? I know ASME also has some good education. Is there anything else that you’re aware of?
Dan:
That’s a good question, Pete. I was fortunate enough to have a drafting and design formal education in my background. Most mechanical engineering curriculums don’t teach our engineers, those things. They touch on it, but we find that our entry-level engineers, part of the onboarding plan and actually it’s the next step of the onboarding plan for a young engineer we’d talked about earlier, who’s currently working in the shop, is to spend four to six months with a designer. A senior designer. Who’s been doing this for many, many years, so they can learn the craft of drafting and design.
Pete:
So, you’re saying the art of drafting and design is a little lost on a conventional mechanical engineering curriculum.
Dan:
Yeah, that’s exactly right.
Allen:
I can certainly attest to that. We hit on it here and there, but you know, by far the focal points are your intensive math courses, your physics courses and that kind of stuff. There’s some may be designed for manufacturing stuff thrown in there, but it’s certainly not the priority.
Pete:
Most of these new age, you know, Alan and I’s generation of engineers out there designing and building equipment, the hope is that there is that senior guy that they’re working with that understands that practicality. Or a lot of times I think we find that the people that are hands-on themselves might not necessarily have a shop that is attached to their engineering firm but likes to turn wrenches right. You know, has a mechanical aptitude. Typically those types of guys understand that same hands-on application.
Dan:
If you come out of school as a mechanical engineer, there are three fields you can specialize in. You can specialize in fluid mechanics and thermodynamics or fluids and thermodynamics are one. You can specialize in HVAC. Or you can specialize in machine design. If your passion is machine design, you have a lot to learn as an entry-level engineer to really understand how to design a machine and actually hand off your deliverable to manufacturers, to have them make it. You might be able to size a bearing. You might be able to size a shaft, but my experience is, you know, coming through engineering school and what Alan just described and making the drawing, being able to check the designers, drawing that it’s going to be made properly is something that you have to learn on the job.
Allen:
Another point on that, not to sound discouraging to these mechanical engineers coming out of school. I think there could certainly be a greater focus on it, but how I’ve kind of had it described to me in multiple instances is; It’s a program designed around engineering, the mechanics of it, the design of it, but it’s broad and they’re giving you the tools and the problem-solving ability. So that when you do get out of school when you go to a company and you start working, you have that framework to start learning. This is a hour-long podcast and we’re touching on some ideas. You could have hundred-hour podcasts and you’re still just touching on concepts. It’s a lifetime of learning, but it’s building that framework.
Dan:
That’s right, Alan. What we’ve found with young engineers is that they’re really quick learners. We’ve found that in four months with a designer, they got the foundation that they need to be a really good machine design engineer. That’s worked really well, and almost every engineer that we bring in that’s entry-level that doesn’t have this experience, we get them that experience right away.
Pete:
Very cool. All right, Dan. Well, we appreciate the insight, appreciate the, anecdotes. I’m sure you have too many to list in about an hour’s worth of conversation and 30 years of experience. So, very good. Thanks for talking. Yeah, that was great. Thanks a lot.
Dan:
Appreciate the opportunity to, to share a little bit about machine design and how engineers and designers can Excel some resources they can go to. I would encourage any designer engineer, go talk to the people that are making the parts. That’s the best feedback you can get to improve your skills as a machine designer.
Pete:
Very good. All right. Great advice. All right. Thanks, Dan. All right. You bet. Thank you.
Speaker 1:
Thank you so much for your insight, Dan, and thank you, Pete and Alan, for walking us through that conversation on practical tolerancing for manufacturing. Get Sparked as a series of podcasts dedicated to bringing you insights into the world of manufacturing. Listen out for our other podcasts, focused around synchronizing innovation with manufacturability, and join us next time as we get sparked about innovations in manufacturing.
