O/T How do you inspect flatness?

[SLJ]

#1. Hand it to the inspector.

#2 Tell him to fire up the CMM and get off his A**

[HEAVY METAL]

WWW.TEC-EASE.COM --good source of info for gd&t . they even sell a good pocket guide .

 

merry christmas

heavy

[mig]

Clean granite plate and checking surface first.

Put part on granite plate by checking face down.

Use feeler gages to check gap . This is simplest way to check flatness I guess

[billystein]

I'm shocked that there is so much division on this topic. this reminds me of the guy who told me that the true position was 1/3 of the tolerance.

[mayday]

just remove the bra

need i say more

[Guest CNC Apps Guy 1]

GD&T has so much division period. Only about 10% of the Inspectors in my experience even come close to having a reasonable handle on it. They are clueless when it comes to measuring True Position. What is so difficult about going from a square tolerance zone (±) to a Round Tolerance Zone. God help you when you have a Maximum Material Condition callout. The reason they went from assume MMC to assume RFS is because too many inspectors had no clue how to calculate it.

 

I think the division in this instance comes from assuming paralellism is the same as flatness.

[Andy]

Take a piece of sheet metal.

Bend it in a slight arc.

Are the two sides parallel?

[pip]

Does that not depend on the quality of the paper?

[Guest]

quote:

---

Are the two sides parallel?

---

Yup, they are not however flat.

[Guest]

in my opinion gd&t is the best way to control the

specs that the designer has intended.

parallelism is refering to a datum plane or axis,

flatness is the tolerance zone defined by 2 parallel planes within which the surface must lie.

so if in this instance the datum plane is parallel to the flatness plane they are one and the same in that context.

[Guest]

quote:

---

in my opinion gd&t is the best way to control the specs that the designer has intended.

---

Once you understand it.

 

However I have seen and work with engineers who are clueless about it, as well as machinists/operators who do not have a clue, even AFTER taking the class.

 

I just went through a GD&T class, as a refresher, offered by WPI and several of the machinists literally had that "glazed" look in their eyes, they did not have a clue.

[gcode]

quote:

---

but I don't like 123 blocks or jo blocks for smaller parts

---

Old school surface plate inspectors use valve stems from old engines for this. They take 3 of them and grind them top and bottom to make a matched set. They are nice and tall so access to the bottom face is easy. They have a wide base for stability and a small contact area on top.

Perfect for establishing a 3 point plane

[gcode]

quote:

---

I just went through a GD&T class, as a refresher, offered by WPI and several of the machinists literally had that "glazed" look in their eyes, they did not have a clue.

---

Overheard on my shop floor just last week.....

"I became a machininst cause I don't like to read."

[Guest]

g code,that's funny.some people don't like that fancy book learnin' stuff do they.

[MLS]

I'm a fan of a certified surface table and feeler gages.

 

With allowable restraint it becomes difficult to NOT distort the part using 3 points with 5 pounds of weight on a certain area.

 

If it is a nice solid part, or a large surface area, then sure.

 

How many places have certified surface tables?

[Guest]

quote:

---

How many places have certified surface tables?

---

We just had ours done 2 weeks ago.

[Guest]

all of our surface plates are redone and checked each year.

[cheeves]

What? Nobody even mentioned optical flats.

[Jerosu]

quote:

---

Posted by James Meyette:

GD&T has so much division period. Only about 10% of the Inspectors in my experience even come close to having a reasonable handle on it. They are clueless when it comes to measuring True Position.

---

+1 to that. People get really stuck on "plus or minus" in two directions. What is even better when they combine block tolerances with GD&T and get some hybrid nonsensical method.

 

I really do wish that the "bonus tolerance" was given out on little tickets so I could save them all up and use them at once Applied to the block tolerance of course.

[Kevangel]

After reading all of this.."How many machining people does it take to screw in a lightbulb?"

[MLS]

LoL

Is that a 40 watt or 100 watt bulb?