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Tamper84
07-25-2012, 11:28 AM
I was watching a video from tubal cain on you tube. He was making a pulley, and turning it between centers on an arbor. He drilled and reamed the hole and pressed it on the arbor. All I understand. My question is, wouldn't pressing that on the arbor "stretch" the bore a little? Or am I over thinking things. I'm sure I will learn more about it next month. Couriousty has me :D

Thanks,
Chris

lakeside53
07-25-2012, 01:05 PM
It may "stretch" a little but unless it's way over-done, it won't "yield". i.e., it goes back to where it was. Every time you snap in a morse taper center into a tailstock, same thing happens.

Errol Groff
07-25-2012, 01:27 PM
I realize that I may be picking nits here but parts are generally turned on a mandrel, not an arbor. Mandrels have a slight taper (.003 or so per foot) so that they can be pressed tightly into the part. Arbors on the other hand are straight (no taper) and are more commonly used for holding cutters, think the arbor on a horizontal mill.

However mandrels are pressed into a part using an arbor press. Go figure

tdmidget
07-25-2012, 02:40 PM
Errol is correct. As an apprentice this was emphasized with such importance that it was a pass/fail question on a test. 49 correct answers and that one wrong? You flunk.
Arbors hold tools. Mandrels hold work.

Jaakko Fagerlund
07-25-2012, 03:06 PM
So you guys are saying that if I turn a straight section to hold a part, it is wrong as it is a tool holder? *confused*

You make what you need to hold work or a cutting tool, doesn't matter what's it called, was it an arbor, a mandrel or a jig.

Tamper84
07-25-2012, 03:07 PM
Ok a mandrel :D lol. I didn't know that, now I do. And thanks for the explanation.

Chris

tdmidget
07-25-2012, 04:43 PM
If it holds the workpiece, it is a mandrel. Arbors hold tools, such as the arbor on a bench grinder or the piece that a drill chuck is mounted on.

We had several such questions. Another was the difference between a bolt and a screw.

Carld
07-25-2012, 05:00 PM
An arbor has a straight shank and a shoulder for the work to rest against with no taper and a nut to hold the work while it is machined or if an arbor for a cutter to hold the cutter without slipping.

A mandrel has a slight taper so it wedges into the bore of the work so it can be turned between centers.

That's about as simple an explanation as it gets.

Errol Groff
07-25-2012, 05:14 PM
Since the subject of test questions has been mentioned I thought that some of you might like to see the final exam I used to give to my sophomores. I had these students for about half of their freshman year and all of their sophomore year for a total of 130 days in shop. Figure about one hour of theory time per day and this is what I expected them to know at the end.

I gave the test as open book, open notebook and Machinery's Handbook. Each year I would see grades ranging from a low of 17 one year to 100 occassionally. Some kids are just dumb and should be left behind!

http://neme-s.org/Final%202005.doc Questions

http://neme-s.org/FINALANS.doc Answers



I realize that some questions might be answered differently given the wide range of experience on this board but my answers are based on the text we used at the time.

goose
07-25-2012, 05:45 PM
I realize that some questions might be answered differently given the wide range of experience on this board but my answers are based on the text we used at the time.

Number two I answered "digital and vernier",.......it was downhill after that. I don't think I even got 17 right.

RussZHC
07-25-2012, 06:20 PM
A mandrel has a slight taper so it wedges into the bore of the work so it can be turned between centers.

I'd like to add "expanding mandrel" to the list, got what I hope will be one sitting in the lathe half done right now. Have not found a good enough deal on quality between centers mandrel yet, a non-import set would be even nicer.

Tyro 001
07-25-2012, 06:47 PM
I have a set of expanding arbors and a set of expanding mandrels. I bought both from Enco. The mandrels are used between centers; the arbors are held in the lathe chuck.

GT1
07-25-2012, 11:40 PM
Since the subject of test questions has been mentioned I thought that some of you might like to see the final exam I used to give to my sophomores. I had these students for about half of their freshman year and all of their sophomore year for a total of 130 days in shop. Figure about one hour of theory time per day and this is what I expected them to know at the end.

I gave the test as open book, open notebook and Machinery's Handbook. Each year I would see grades ranging from a low of 17 one year to 100 occassionally. Some kids are just dumb and should be left behind!

http://neme-s.org/Final%202005.doc Questions

http://neme-s.org/FINALANS.doc Answers



I realize that some questions might be answered differently given the wide range of experience on this board but my answers are based on the text we used at the time.



Question 64. If an alligator's eyes are six inches apart what is the approximate length of the beast?

And I thought they only taught that in Florida.

Paul Alciatore
07-25-2012, 11:56 PM
I am glad to see the proper terminology explained. I hope I can remember.

tdmidget
07-26-2012, 01:58 AM
An arbor has a straight shank and a shoulder for the work to rest against with no taper and a nut to hold the work while it is machined or if an arbor for a cutter to hold the cutter without slipping.

A mandrel has a slight taper so it wedges into the bore of the work so it can be turned between centers.

That's about as simple an explanation as it gets.
About as dumb as it gets. Carl, does an arbor for a Jacobs chuck meet your requirements above? Do expanding mandrels have a taper? What would you have scored in Eroll's class?

Jaakko Fagerlund
07-26-2012, 04:51 AM
So if I'm making a new chuck and I have the unfinished (work)piece mounted on its arbor ready for internal grinding, it is actually a mandrel I'm using as it is holding work, but once the grinding is finished it is suddenly an arbor as it now holds a tool and not a workpiece?

To put it more simply: it is a tool.

Tamper84
07-26-2012, 09:47 AM
Sorry fellas, I didn't mean to start a fight or anything else on here.

Chris

Carld
07-26-2012, 09:59 AM
tdmidget, I meant to type straight shaft and typed shank, sorry 'bout that. Is it your normal way to deal with people, to say someone is dumb and then expect them to be courteous to you or show you respect? Why didn't you just ask me if I made a mistake with that word.

loose nut
07-26-2012, 10:06 AM
Sorry fellas, I didn't mean to start a fight or anything else on here.

Chris

Don't worry about it. With this group it's hard not to start a fight. You have probably made a few peoples day.

Now get back in there and come out swinging.

tdmidget
07-26-2012, 12:50 PM
tdmidget, I meant to type straight shaft and typed shank, sorry 'bout that. Is it your normal way to deal with people, to say someone is dumb and then expect them to be courteous to you or show you respect? Why didn't you just ask me if I made a mistake with that word.Shaft/ shank regardless. My beef is that Errol, a professional and teacher of this subject, gives the correct information. Then you contradict him. Now we know his credentials. What enables you to say he is wrong?

michigan doug
07-27-2012, 11:58 AM
Just ignore Mr. Midget. He wastes no opportunity to insult anybody he possible can. I would think it would get boring and tedious after a while, but he never seems to tire of it.

Finest regards,

doug

Jaakko Fagerlund
07-27-2012, 01:50 PM
Shaft/ shank regardless. My beef is that Errol, a professional and teacher of this subject, gives the correct information. Then you contradict him. Now we know his credentials. What enables you to say he is wrong?
Wow, one person says something so it must be the ultimate truth - he is a teacher after all! What makes his words the truth?