Mill choreography

I've long been of the opinion that a machinist should have the right to had a drawing back to the designer and say, "there's the mill; go make it..."

A little cleverness in the design can save a world of time (and cost) in the making...

Jerry

[snippage]

I'm probably not the only guy that gets part way through something and change how I process things as I figure out a better way to do the job. Maybe some day I'll consistently get it right from the start.

Wes

I'm a firm believer that engineers should spend some time as apprentices making the things they aspire to design.

Wes

Ayup! I try not to cut metal until we are on version 3 or better in Solidworks. Even then, I make note of all the improvements for the next version of a machine subsystem but we don't change design in the middle of the build anymore, that version gets built and run knowing another complete version might be justified. I have to be careful not to let the good be the enemy of the perfect.

This machining I did was for version 3 of a mechanism that has been in use for four years. I haven't thought of a single improvement yet and it will go on a production machine next week. If it works, it will be the last version...probably.

On Oct 12, 11:11 pm, "Tom Gardner" wrote:

This is sort of related and I'm dying to share it with the group, so I think I'll put it here. I just got back from a trip to the good old Boston area and made it a specific goal of my trip to visit the Starrett factory in Athol, MA when I was there. I went and devoted about 3 hours to the place. In particular, I had called ahead and found out that if you ask them, they will send down an apprentice to give you a tour of the factory. I went on the tour and was amazed by what I saw. Basically, the Starrett approach to manufacturing is to use older specialized machines and toolroom-built tooling and fixtures specific to each type of component, rather than more expensive, newer, multipurpose machines. There inventory rarely undergoes major changes and so these make sense. This is not to say they don't use CNC, for example, I saw a half dozen high capacity CNC milling centers (Japanese, as it turns out, don't remember the exact company) turning out parts dozens of times faster than manual equivalents. However, they still use over a dozen automatic multi-spindle screw machines to turn out all sorts of parts. Not CNC, changing the part requires manipulating cams and gears inside the machine, they still have an edge over a CNC turning center. In particular, they have 6 spindles rather than just one. I saw machines with more than a 2" bar capacity, dating back to the mid 1900's. I found this system of specialization and custom tooling to be very much suited for the kind of production they make. ww88

I did 18 mill operations in less than 2 hours including set-up time. This by changing the way I do my drawings and visualizing all the operations with the thoughts of reducing set-ups, minimizing tool changes, laying out the tools and parts and figuring the correct order of events. With my old BP and methods I guess this would have taken close to two days! And, every operation was within two thousandths. Think/cut!

So, after all that outrageous productivity, I took a little nap at my desk!

That was somewhat the case at one time in some places. It's still a good idea. New engineers weren't exactly apprentices because they didn't need to achieve the skill level that an apprentice must to become a journeyman. They were there to gain an appreciation of what is done and how things work on the shop floor, in the drafting room, in the test & eval lab, etc -- and the only way to gain that is by doing it, working side-by-side with people who do it for a living. Newly-degreed young engineers did not design anything until they had about 2 years of such OJT and experience to complete their education.

30 years ago, as a new engineer fresh out of school, I had coffee with the shop foreman and mentioned to him I'd like to know more about he made things. He set me up with a couple second shift fellas. I learned a ton AND got a bunch of government projects done. Plus, making good friends in the shop made all those rush jobs get done on time.

Any young engineer should do the same thing today.

Karl

Having worked from prints for what seems my entire life, it wasn't uncommon for me to redraw (on scratch paper) and re-dimension parts so they were meaningful in the way they'd be made. No changes were introduced, just dimensions provided in a way that was useful. By working to nominal dimensions at all times, you are able to use any portion of a machined piece as the datum point. That's important when you start changing reference points.

Harold

There are many different ways to make a drawing with different ways to how to place the dimensions. For manufacturing For functional checks (in the pre-CAD times) For structural analysis For quality checks

Nick

I know that some companies punish stupid or hard to assemble constructions an engineer did by sending him to the assembly line and letting him do the work for at least one day.

Nick

"Tom Gardner" wrote in news:jIWPi.2936$ snipped-for-privacy@nlpi069.nbdc.sbc.com:

Tom, Here is a post I wrote a few years ago over in a.m.c., that addresses what you are talking about.

Long URL:

Tiny URL:

And repairing them also....

Paul

A smart company (try and find one of those) would do it as S.O.P., regardless of design "good" or design "bad" - the opportunity to see what went right and what wrong, and what thing the designer thought would help that's irrelevant, and what thing the designer thought would be easy that's hard - all these are important.

Thats where the Methods Engineer comes in. He/she bridges the gap between the designer and the machinist.

I give my Engineering Machine Design students a short stint on the lathe and the mill. Sure calms down the exotic nature of the designs!!!

And when they cay that the project MUST have someth> I did 18 mill operations in less than 2 hours including set-up time. This

Harold,

My early engineering education happened just before CAD took over completely. It existed, but our colleges had not yet ripped out all of their drafting machines. As a result of that, I learned graphical methods from books that probably had their first several printings in Sanskrit. My descriptive geometry class started with a grinning instructor saying "... all but one of these guys are dead" - referring to the author. He of course was not taking joy in their demise, but emphasizing how long the book had been in print.

Ok, so the book was ancient. However, we were clearly being taught how to pass the buck on responsibility for mistakes. Over-dimensioning introduces opportunities to get something wrong, so it is strongly discouraged (IMHO) to let the other guy/company be the one who absorbs the cost of any mistakes.

Understood. I ran into this just yesterday, having taken ten thou too much off of something. The good news is that I picked a good dimension for the mistake, but it lead me to have to start thinking about what could/should and must not move as a result. Basically the parts are rectangles with holes near the corners and a window (weight reduction) inboard of the holes. The hole spacing has to match another part, so I left it alone, and slid the window back ten thou in the affected direction.

One could argue that I should simply eye-ball the window, but the next parts won't be so forgiving, and I (clearly) need the practice holding tolerances. So, I try to build what I design down to a thou or two, and use common sense in what I scrap. Of course, I made the mistake on a stack of five plates, and after all other block dimensions were correct - too much time and metal to toss over a matter of pride.

As for how I blew it, I had noted I was about 0.050" from final size, so the plan was to take 0.020 twice and then measure again. I was flycutting a stack, which is not the best way to hold tolerances on my mill-drill, but if I stay on top of it, it works. Perhaps my real mistake was to be emailing and making phone calls between cuts, but somewhere either something slipped or I made a cut I forgot about (I'm starting to think that is what happened). At one point, I was expecting to have to take off ten, but measured 20+ to go. I measured, looked for burrs and chips, re-measured a couple of times. Shortly after that I measured again and found it undersized.

Bill

ABSOLUTELY!!! Let the engineer listen to the gripes from the assembly workers in the break room

Heh, heh, true story: Years back, I worked > >

I taught a short class to a bunch of design engineers and techs. One major point was to dimension the parts in the way they were going to be inspected. Picture a 3 hole group where two of the holes were dimensioned from one end of a 6' long tube with a sweep bend in the end, the other hole from the other end. Since there were more dimensions involved, it was a lot of math to get to the desired hole spacing. Why not just dimension the parts as a group? It was easier to snap the lines on the CAD system.

Some snot in the back mentioned that under geometric tolerancing, the tolerances were not cumulative. My response: that's true but you better have better inspection folk and way more training because they are going to reject the parts.