How does one judge "quality" of a finished machine? (Mechanical)

[Gerald D]

Thought to put this topic on the table to see if we can describe "quality" in the mechanical sense. (Electrical here)

- Deburring, rounding over rough edges. Wearing a blindfold, you must not be scared that you might cut your hand on any part of a machine. You should be able to put your hands in anywhere and it should feel smooth and "polished". A big reason for this is to reduce corrosion - paint does not stick to a sharp edge.

- No signs of corrosion. No surfaces that look if they will corrode. Good corrosion protection. Good paint.

- No small holes or "cracks" in welds - paint won't go in there. It is a corrosion point.

- No grinding marks, especially around welds. That is a lazy way to get a nice looking weld.

- Screw heads un-damaged by wrenches or screw-drivers

- Washers under screw heads or nuts.

- Look as if painted before screws installed. ie. painted under washers. An unpainted washer gives proof of this. (Use zinc coated fasteners (unpainted and un-damaged)

- Turn washers the right way around - sharp edges away from the fingers. (if applicable)

- Use correct length screws. At least one thread showing beyond nut. No more than about 3 threads showing.

- Avoid cutting screws to length (buy the correct length). If you have to cut, then deburr and paint where the zinc is damaged.

Any more?

[firebrick43]

Hello, I agree with all of them but one and wish to add a few more.

"- Look as if painted before screws installed. ie. painted under washers. An unpainted washer gives proof of this. (Use zinc coated fasteners (unpainted and un-damaged)"

This has little to do with quality, and in fact can be detrimental to quality. I work for caterpillar and they have done more testing in torque techniques and methods than just about anyone in the world. A fastener in theory should never have anything applied underneath it, unless specifically specified such as oil or antiseeze on special applications like fine thread bolts or stainless steel bolts. A fastener maintains torque by stretching the bolt in its elastic range. Paint underneath will migrated because it is softer than the bolt, washer, and underlying metal. This will release the tension and therefore causing the joint to become loose. Also paint applied to the fastener after assembly keeps water and out out preventing corrosion. Now these might not be serious factors on a machine in its intended environment but it surely is not in my opinion a factor of quality. It is merely aesthetically pleasing.

Also you forgot that mechanical quality in the since of this machine means that the structure is geometrically accurate(square and plumb).

Also that all mechanisms move freely without binding or deviating from their designed course.

As well as the machine is robust, reliable, and durable meeting the customers/endusers needs.

[Gerald D]

Thanks Jay, points taken.

Bolted joints are very complex things and there are many factors involved there. In critically loaded joints, I agree that paint in the joint is not good.

[Marc Shlaes]

Gerald,

One silly little question. You have made this point twice. I can't say that I fully understand it. Are you referring to lock washers (split washers)?

*** Turn washers the right way around - sharp edges away from the fingers. (if applicable)

[J.R. Hatcher]

Marc flat washers are stamped out so one side is rounded the other side is sharp.

[Greg J]

Can you expand on this. I ground allot of welds. Mainly because of ascetics. I'm not a professional welder (nor want to be), but I did pay attention to penetration, squareness, warping, etc. I am confident that the mechanical integrity is solid.

Before I start painting, what should be done to the welds that were ground. Aside from grinding out the weld and laying another bead.

Originally Posted by Gerald D

- No grinding marks, especially around welds. That is a lazy way to get a nice looking weld.

[Marc Shlaes]

OK, now I will have to go grab a handful of washers. Having used 10,000 washers in my life, (just a guess - I really didn't count them ), I have never particularly noticed "sharpnesss" but it does make sense. Interesting.

[J.R. Hatcher]

Marc most are zinc plated after stamping making those edges a little less sharp.

Greg ...................... paint it.

[Gerald D]

Originally Posted by Greg J

. . what should be done to the welds that were ground. .

My point was that those welds shouldn't have been ground in the first place. My welding guys are forbidden to run a grinder over a weld - it hides poor welding, makes noise and dust.