PDA

View Full Version : Mandrel Problem/Question



BigBoy1
06-21-2009, 11:28 AM
I bought a set of mandrels and tried to use the set for the first time. I was going to use the mandrel to hold a gear blank while I cut the teeth. The hole in the blank was reamed to 0.500" and slide on the mandrel till it stopped, which was about 1/4" from end of the mandrel. The mandrel was placed in the dividing head and I proceeded with the first pass with the gear cutter. The cutter proceeded to push the gear blank right off the end of the "large" end of the mandrel.

I then tried holding the gear blank with an expanding arbor and same results, the gear cutter pushed the blank off the end of the arbor.

I put the gear blank on a 1/2" bolt and nut and then I was able to hold the blanks to cut the gear.

Now was I expecting too much holding ability from the mandrel and arbor? I would think the mandrel and arbor should have held the part. I measured my 1/2" mandrel and the "small end" was 0.499" and the "large end" was 0.501". I would except the large end to be at least 0.505". Is this an incorrect assuption on my part?

J Tiers
06-21-2009, 11:37 AM
The taper is pretty small. Your measured taper agrees with mine.

That said, I have in fact done what you say, quite successfully.

http://img.photobucket.com/albums/0803/jstanley/gear1s.jpg

You probably had a hole significantly bigger than you think it was..... it is easy to be fooled by " machining fuzz" that is easily wiped away by any pressure, leaving a hole that may have actually been 0.503 or so.

Carld
06-21-2009, 12:31 PM
The first rule for using a expandable mandrel or tapered solid mandrel is NEVER MACHINE TOWARDS THE SMALL TAPER END. If you machine towards the large end of the solid mandrel or the expandable mandrel and the work is PRESSED on firmly it should not move.

Evan
06-21-2009, 01:06 PM
Jerry is probably right. Unless you reamed the hole or had a very good and smooth finish by other means it is very easy to have what measures as correct really be only the minimum ID while the average ID is larger. The hole finish must be very good to work on a taper mandrel.

Carld
06-21-2009, 01:14 PM
I'll say it again, NEVER MACHINE TOWARD THE SMALL END OF THE TAPER. If it slid all the way toward the large end of the taper then the hole was to large. If you didn't press it on the mandrel it will come off. The hole does not have to be perfectly smooth.

Rules

1- select the right size mandrel for the job.

2- press the part on the mandrel.

3- Never machine toward the small end of the mandrel.

Well, I lied, the first rule is select the right size mandrel.

EDIT: with a gear cutter just think of the hammering you get as the cutter does it's job. Don't you think a reasonable person would expect to have the blank driven off the mandrel?

Evan
06-21-2009, 03:18 PM
According to the original post it came off the large end.

JCHannum
06-21-2009, 03:30 PM
A tapered mandrel will typically have a taper of 0.0005" per inch. Your 1/2" dimensions sound about right. They should be pressed in or driven with a deadblow hammer and as Carld says, all cutting should be toward the large end. Bore and mandrel should be clean and dry. The smaller the diameter of the mandrel and the thinner the workpiece, the less holding power it will have.

If the hole is oversized for the mandrel, it will merely burnish it to the largest diameter of the taper.

Solid tapered mandrels are generally used for grinding or very light turning operations. Gear cutting is pushing the holding power of a tapered mandrel, a stub arbor, threaded to positively hold the gear blank is the best insurance against slippage.

oldtiffie
06-22-2009, 08:09 AM
I think the OP discovered the answer for himself when the blank got "hammered/driven" along the tapered mandrel and then had it all work OK when he put the blank on an accurate parallel mandrel/arbor with a shoulder to rest against and a nut and washer to hold it in place while it was machined.

I'd say he was lucky he didn't drive the blank on really hard to the tapered mandrel else he'd have had quite a job separating them and keeping the mandrel straight.

I've only ever used a "very slow tapering" mandrel for very light lathe-work or primarily for work on a cylindrical or tool & cutter grinder - but I make sure it won't "slip" but without ever-doing it.

BigBoy1
06-22-2009, 04:36 PM
I'll say it again, NEVER MACHINE TOWARD THE SMALL END OF THE TAPER. If it slid all the way toward the large end of the taper then the hole was to large. If you didn't press it on the mandrel it will come off. The hole does not have to be perfectly smooth.

Rules

1- select the right size mandrel for the job.

2- press the part on the mandrel.

3- Never machine toward the small end of the mandrel.

Well, I lied, the first rule is select the right size mandrel.

EDIT: with a gear cutter just think of the hammering you get as the cutter does it's job. Don't you think a reasonable person would expect to have the blank driven off the mandrel?

First of all, I did have the CORRECT sized mandrel and the blank was slide from the SMALL end towards the LARGE end. The gear blank hole had been reamed to 0.500" so its size was correct. The mandrel was brand new, never used before so I would suspect the sizes are correct. Machining was done so that the operation would push the part towards the LARGER end. The blank was hand pushed onto the mandrel until it stopped. I assumed that the cutting operation would press it onto the mandrel further and "lock" it in place. This did not happen as it was pushed right off the LARGE end.

As to being a reasonable person, one would have thought the mandrel would have held the part as everything was done correctly.

As an additional test, I tried to use the mandrel to hold a piece to be turned in my lathe. The part just spun on the manndrel as soon as the tool touched the metal.

If the 1/2" mandrel only has a max. diameter of 0.501" at the large end, what are mandrels used for? It appears they can not be used for opearions that seem to be suited for them.

JCHannum
06-22-2009, 05:06 PM
I have Cleveland solid tapered mandrel, diameters are 0.499" & 0.502". Large end diameter will depend upon length. A more acute taper will serve to bias the bore, tapering it and making the workpiece possibly out of tolerance.

Slipping on by hand will not produce a tight enough fit for any operation of significant force. The mandrel should be pressed or driven on. If the bore is oversize, a larger mandrel is needed. Possibly your reamer cut on the large side, not leaving the bore enough oversize that the mandrel did not fot properly.

Mandrels are typically for grinding and very light turning, gear cutting, due to the vibration from the cutter is not the best application.

How thick is your gear blank?

BigBoy1
06-23-2009, 04:01 PM
I have Cleveland solid tapered mandrel, diameters are 0.499" & 0.502". Large end diameter will depend upon length. A more acute taper will serve to bias the bore, tapering it and making the workpiece possibly out of tolerance.

Slipping on by hand will not produce a tight enough fit for any operation of significant force. The mandrel should be pressed or driven on. If the bore is oversize, a larger mandrel is needed. Possibly your reamer cut on the large side, not leaving the bore enough oversize that the mandrel did not fot properly.

Mandrels are typically for grinding and very light turning, gear cutting, due to the vibration from the cutter is not the best application.

How thick is your gear blank?

My gear blank was 1" thick, 1/2" teeth and 1/2" hub.

Perhaps I was expect too much holding ability of the mandrel.

J Tiers
06-23-2009, 11:14 PM
if you have the hub hole sized right on, the mandrel will hold even for light turning of a fairly large OD. Like pulley truing.

Shafts and hubs are funny... the sizes are not always what they seem. I always forget if shafts are small, and hubs "on" or shafts "on" and hubs "over". I think the former, as shafts always end up loose, and tight mandrel tolerances would make no sense otehrwise.

Anyhow, I usually press mandrels in with an arbor press, and remove likewise. it takes some serious pushing, usually.

So, the system will definitely stand serious productive turning. No hogging, though.

oldtiffie
06-23-2009, 11:41 PM
The problem with (tapered) mandrels as opposed to (parallel) arbors is that the mandrel will usually only accept one part/job at a time and on a position on the mandrel that will only be seen when the job is pressed onto the mandrel. Mandrels are more demanding of the job bore as regards size and quality of finish (and of "round(ness)") than arbors are.

A multiple or "stick" of jobs will pretty well always require an arbor where the jobs on the arbor may be "clamped" by a nut and washer (for example) and positioned/located by a (for example) "key". There is rarely - if ever - any need to press a job onto or off/from an arbor. The arbor is much easier to make as its tolerances are "easier" as is the similar case with the bore of the job on an arbor.

A mandrel usually varies from a light clearance>push>light press fit/s with the job (much closer tolerances) whereas the mandrel may vary from a light push>light running>clearance fits - much "easier" tolerancing.

As said previously, mandrel "light" fits are for precision light work - such as light turning and cylindrical and tool & cutter grinding work.

Before I use or re-use a mandrel - particularly if it required considerable pressure to get the job on or off the mandrel - I would have that mandrel between centres and check it with a very good test/dial indicator for straight and roundness - followed up with a "roll" test on a surface plate and/or vee-blocks.

J Tiers
06-24-2009, 12:22 AM
The problem with (tapered) mandrels as opposed to (parallel) arbors is that the mandrel will usually only accept one part/job at a time and on a position on the mandrel that will only be seen when the job is pressed onto the mandrel. Mandrels are more demanding of the job bore as regards size and quality of finish (and of "round(ness)") than arbors are.


Mandrels hold parts, arbors hold tools............. ;)

GadgetBuilder
06-24-2009, 12:24 AM
I suspect your reamer is cutting over size. From what you wrote, your tapered mandrel sounds like a good one and the gear blank should have stopped near the middle of it rather than near the end. Your taper is likely a fairly precise gauge for hole size where the distance the part goes on to it is proportional to the hole size.

I ran into the reamer over size issue recently too. You can measure the reamer with a mic and a delicate touch. I found my 0.500 reamer measured 0.5008 and in my hands it cut 0.5017. So, I got another reamer and measured it: 0.5002 and it cut about 1 thou over that size when I used it. New reamers are apparently often a bit over size, some more than others. And they aren't the same size over their length, max is about 1/2" from the starting end on these two and they taper down after that. If you remove the reamer to clear chips and re-insert it while the work continues to rotate slowly (because any backward movement will dull the reamer) that can enlarge the hole by a half thou or more according to one source.

I gave up on reaming for my job and used a barrel lap which allowed creeping up on the desired size rather than the all-or-nothing reamer method. Not suggesting a lap for your gear blanks, just sharing what I learned in my adventure trying to get an accurately sized 1/2" hole :o

John

Carld
06-24-2009, 12:35 AM
Bill, I missed the big end part of your post but for gear cutting a mandrel would never work. I have tried to use them on interrupted cuts and it works them loose. I wouldn't even consider using one for cutting a gear. As another said they don't work well on heavy cuts either.

I would have done as you did, that is, make a mandrel with a snug fit and retain the part with a nut. I have had to to that several times and I always save the mandrel.

J Tiers
06-24-2009, 12:47 AM
Bill, I missed the big end part of your post but for gear cutting a mandrel would never work. I have tried to use them on interrupted cuts and it works them loose. I wouldn't even consider using one for cutting a gear. As another said they don't work well on heavy cuts either.

I would have done as you did, that is, make a mandrel with a snug fit and retain the part with a nut. I have had to to that several times and I always save the mandrel.

Please do see picture posted above....... look closely ;) t'ain't the only one I've done.....

Carld
06-24-2009, 12:55 AM
I guess your luckier than I am. Even when I pressed them on a solid mandrel or expandable mandrel interrupted cuts always caused me trouble. If it works for you then do it.

oldtiffie
06-24-2009, 06:24 AM
Originally Posted by oldtiffie
The problem with (tapered) mandrels as opposed to (parallel) arbors is that the mandrel will usually only accept one part/job at a time and on a position on the mandrel that will only be seen when the job is pressed onto the mandrel. Mandrels are more demanding of the job bore as regards size and quality of finish (and of "round(ness)") than arbors are.


Mandrels hold parts, arbors hold tools............. ;)

If and as it pleases you mi lor'.

It seems that the terms are inter-changeable as regards mandrels and arbors, but the opinions as regard the correct type to use are/remain correct. So, I for one have got to "walk back" and stand being corrected - which I do - gladly.

Machinery's Handbook 27 is a "busted flush" as regards use in providing a definition - and "Google" isn't much better.

Wikipedia does a much better job.

I can't see the point in getting into another pedantic "hair-splitting" and "bashing" exercise.

I have scanned a few pages from a book I have (yep "that" book published on OZ) and the links to them follow.

If the effort helps anyone here with terminology, application and uses of mandrels and arbors it will have been well worth it.

http://en.wikipedia.org/wiki/Mandrel

http://www.google.com.au/search?hl=en&q=mandrels&meta=&aq=6&oq=mandrel

http://www.google.com.au/search?hl=en&q=tapered+mandrel&revid=248466616&ei=NctBSsrTJomIkAXG4JjuCA&sa=X&oi=revisions_inline&resnum=0&ct=broad-revision&cd=4

http://www.google.com.au/search?hl=en&q=arbor&meta=

http://i200.photobucket.com/albums/aa294/oldtiffie/RMIT_book_details/Mandrelsandarbors1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/RMIT_book_details/Mandrelsandarbors2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/RMIT_book_details/Mandrelsandarbors3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/RMIT_book_details/Mandrelsandarbors4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/RMIT_book_details/Mandrelsandarbors5.jpg

chief
06-24-2009, 09:36 AM
Oldtiffie,
Don't let it bother you, it's just Tier's smug superiority. He has issues.

J Tiers
06-24-2009, 10:06 AM
Oldtiffie,
Don't let it bother you, it's just Tier's smug superiority. He has issues.

Certainly not one of your more intelligent answers, here or at PM.....

Somehow YOU got OFF my ignore list. I will fix that. Tiffie won't EVER get ONTO it, because he is an intelligent and reasonable person..

There certainly are differences between you two.....