Employment test

[hansdeberlin]

I just had an employment test with a MAGNA company in Toronto. These were some of the questions and I am not 100% about my answers. Anybody could confirm the answers.

Please give feed rate for the following at 100 RPM

M16*2

¾-10nc tap

 

The Micrometer spindle has……. Threads per inch

8

25

40

100

 

The direction in which the chip leaves the work is influenced by:

A radius on the tool

Rake angle

Side relief

End relief

 

Carbon in material:

Decreases ductility

Increases toughness

Improves machinability

 

The tensile strength of a material indicates:

Maximum stretching

Maximum load before breaking

Resistance to penetration

Resistance to shock

 

The cutter load or force is created by the:

Diameter of the cutter

Feed per tooth

Method of milling

Depth of cut

 

Length of thread in a tapped hole should be:

As long as bore

The same diameter as the bore

1 ½ times diameter

2 ½ times diameter

 

To test a grinding wheel for cracks before installing:

Hold to light and look for cracks

Test with a ring gauge

Put it on a surface plate and use an indicator

Hold by bore and tap with a non metallic object

 

If the safety factor on an overhead crane is 3-1 and the crane is rated at 20 tons what is the heaviest load that can be lifted safely?

[Jack Mitchell]

2= .03937*2 therefore .07874 pitch

100rpm works out to .0787 feed or 7.784” per min.

1/10 is .100 pitch therefore 100 rpm works out to 10.0” per min.

 

The Micrometer spindle has……. Threads per inch

Inch micrometer 25tpi

 

The direction in which the chip leaves the work is influenced by:

Rake angle

 

Carbon in material:

Decreases ductility - really odd way to state the question though. Increases hardness seems much more intelligent; but hey, who's the genius that wrote this dribble?

 

The tensile strength of a material indicates:

Maximum stretching or Maximum load before breaking – bad term used here, I see it as the maximum load before permanent damage or failure to return to its previous natural state. The first answer seems to be the most accurate.

 

The cutter load or force is created by the:

Method of milling

 

Length of thread in a tapped hole should be:

As long as bore

The same diameter as the bore

1 ½ times diameter

2 ½ times diameter

All BS – maybe the first answer is sufficient though. The real length of thread is stated on the print and handily given by the machinist.

 

To test a grinding wheel for cracks before installing:

The ring gage answer is surely brilliant

We call it ring testing when you hold by bore and tap with a non metallic object.

 

If the safety factor on an overhead crane is 3-1 and the crane is rated at 20 tons what is the heaviest load that can be lifted safely?

20 Tons looks about right to me.

 

So, do I get the job?

 

I would have loved to see Rodney Dangerfield answer these questions on a live broadcast.

 

 

Regards, Jack

 

[ 10-18-2004, 07:28 PM: Message edited by: Jack Mitchell ]

[Brendan P]

quote:

---

All BS – maybe the first answer is sufficient though. The real length of thread is stated on the print and handily given by the machinist.

---

Jack..

Thanks for making me fall off my chair laughing !!!

You just made my night.

[Thad]

There are 40 TPI on a mic spindle.

 

There should be 1.5 times the dia of thread depth.

 

Thad

[Mct010]

1000+ Thad

[Jack Mitchell]

Thad - always trying to make me look bad

 

1 rev = .025" on an inch micrometer.

4 revs = .1"

therefore 40 revs = 1 inch exactly

Therefore Thad = the hero and Jack = the putz

But at least I got most of them right

 

Besides - how many of the American members would have actually attacked the metric feed question? Maybe that's why I only got 79% on my Certificate of Qualification.

 

 

Regards, Jack

[Thad]

quote:

---

So, do I get the job?

---

I'd hire you, Jack. I just wouldn't let you thread any holes.

 

Edit: BTW Jack, you mentioned about a year ago (?) that you would start an in depth discussion on CRC. You're claim (correct me if I'm wrong) was something along the lines of CRC not being accurate/you didn't like it/it should be used as a last resort. I'm not trying to put words in your mouth, I just don't remember your exact issues with it. CRC seems like a questionable option to me sometimes too. I'd like to hear your comments when you get the chance.

 

Thad

[Jack Mitchell]

quote:

---

was something along the lines of CRC not being accurate/you didn't like it/it should be used as a last resort.

---

CRC? refresh my memory please. I don't understand the term. I can present an argument though. - ****! now I'm starting to sound like a politician.

 

 

Regards, Jack (the beaten pulp) Mitchell

[Thad]

Cutter Radius Compensation.

 

Thad

[Thad]

Jack, I just did a search but couldn't find it. But I *did* find this. OMG, 2 years later and it still hurts to read it! I think gstephens and Andrew McRae still don't like me. I still think I'm right.

 

Thad

[Jack Mitchell]

Bingo - I got you there.

Yes this is one of the most complex and misunderstood features available on machine tool controls. Basically, it's your best friend or worst nightmare given your understanding of the basics and how to apply them.

 

I have many good/bad habits to teach and with the end result in mind ( a learned student that can comprehend what it is, how to use it, and the do's and don'ts when applying it).

 

My background includes many different controls and will work if the student takes the time to go through the lessons and exercises. The effort is large as are the drawings that I have prepared through the years; I should really publish these in a PDF format.

 

This is monumetal since I need to plan a learning application and then suffer the argument back from those that approach it differently - but notice this - nobody else is doing so why not I?

 

Liken this to vectors - most likely 90% of programmers don't understand them and prefer to allow a cam program to generate them or the radius value that so many controls of today recogize. There is much to learn in this field as well.

 

But alas I am a little too busy right now to go for it, when I do I will put it on Jayson's site prior to publishing on the forum; Busy like in an S55 AMG that I'm going to pick up tomorrow at 4:00PM.

 

Regards, Jack

[hansdeberlin]

Thank You All for the answers. This company is 70 km from my house. Jack you can have this job anytime, since I do not want to commute on the 401.

Better Jack I would rather take your job in Paris ontario. I used to go there for about 15 years for a Canada day picnic. Nice tobacco country. Is there any industry around there?

Regards, John

[Thad]

So, John, how'd you do?

 

Thad

[Philcott]

Thad,

 

quote:

---

There should be 1.5 times the dia of thread depth.

---

Where does this come from? I don't remember ever hearing that 1 1/2 times the diameter is an industry standard? Not saying it is wrong, just that I have just never heard it.

 

Phil

[chris m]

Phil, my Engineering guys and I have arguments about this all of the time. It is definitely a design thumbrule that spans the globe but I always say 'find me a hex nut that has 1-1/2 diameter of thread in it'...

 

10,000,000,000,000,000,000,000,000 fasteners can't be wrong

 

C

[gcode]

quote:

---

The cutter load or force is created by the:

Diameter of the cutter

Feed per tooth

Method of milling

Depth of cut

 

---

I think feed/tooth is the correct answer to this one.

[Guest CNC Apps Guy 1]

Thad,

 

With all due respect, you just need to approach that bullnose radius issue a little differently and you can get the desired results. I played around with a part like this and by looking at it differently it is possible with no voodoo magic.

 

JM2C

[TQG]

maximum holding strength of a thread is reached when 1 1/2 times the diameter = thread depth. anything more than that is a waste.

[CAM-mando]

quote:

---

'find me a hex nut that has 1-1/2 diameter of thread in it'

---

Nuts are usually 2/3 D. Assuming similar materials, the screw will always strip before the hole. Using 1.5 D thread depth virtually guarentees that with most material combinations (screw/hole) the bolt will fail in tension rather than by stripping the threads. The calculations are a little tedious, so designers tend to use the rule of thumb.

 

Often 1.5D is over kill however and should certainly be further analyzed in production situations.

[Thad]

quote:

---

I don't remember ever hearing that 1 1/2 times the diameter is an industry standard?

---

Phil,

 

I always heard that 1.5 will give you max holding power. Any more than that doesn't make it any stronger. That's my story and I'm sticking to it.

 

Edit: Yeah...what TQG said.

 

Thad

[Thad]

quote:

---

With all due respect, you just need to approach that bullnose radius issue a little differently and you can get the desired results.

---

James, I'm sure I could get it to work. With MC's ability to crunch complex toolpaths, I just thought calculating this would be easy in comparison. I understand that it doens't, but I think it should. That's my non-software writing opinion.

 

Thad

[Thad]

quote:

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Often 1.5D is over kill however and should certainly be further analyzed in production situations.

---

I've gotta disagree with you on is one, Cam. Do you think that 3/4 inch of thread for a 1/2 inch screw is overkill? I sure don't. Now I've never climbed up to the ceiling, screwed a 1/2 inch screw in the rafters and swung on it to see if it would hold my fat azz up, so I don't know what the strength would really equate to. I will tell you that when I peak inside, or climb into a press with a die above my head, I'm sure glad we put 1.5 times D as MIMINUM thread depth.

 

Thad

[Philcott]

quote:

---

maximum holding strength of a thread is reached when 1 1/2 times the diameter = thread depth. anything more than that is a waste.

---

I get the strength/theory part but would any of you just assume the 1 1/2 rule if a thread depth was not given on a drawing? What if the part was drilled through and the thickness was 2 times the dia. Wouldn't you wonder if the thread was meant to go all the way? I consider it the job of the engineer to tell me the depth of the thread and will always ask for clarification and not just assume 1 1/2 dia. It is an interesting piece of info that is now part of my knowledge base. Thanks.

 

Phil

[Reece L Gibson]

Please give feed rate for the following at 100 RPM

M16*2

¾-10nc tap

 

Feed per minute, or feed per Rev?

[Philcott]

Thad,

 

quote:

---

when I peak inside, or climb into a press with a die above my head, I'm sure glad we put 1.5 times D as MIMINUM thread depth. [smile]

---

No Arguments with me on that buddy. I would be looking for 2.5 times the D in there.

 

Phil