Author Topic: Mill Creep  (Read 14257 times)

Offline Mosey

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Mill Creep
« on: January 04, 2015, 03:16:22 PM »
Needed to mill a large slot, 1" x 5/8" deep x 3" long in aluminum bar, so I put a 1/2" roughing mill in a collet in my mill, and carefully set the depth to allow a little cleanup.
I had oiled the spindle this week and noticed a seepage out of the spindle nose which indicated that the oil had reached the spindle nose.
As I was milling along the piece I noticed under the huge pile of chips that the depth of the slot had grown! It was now well into my finished workpiece.
Apparently the roughing mill has so much bite that it walked out of the collet, especially one that was freshly oiled. The collet is a well-used one, so it probably doesn't hold as well as it should. I will check its inside dimension for wear and wipe it dry.

I have never had this problem with regular end mills. Also, I prefer ER collets to W-20's becasue I think they hold better, but they are not readily available in my spindle size.
So Dave, here is another place to use those metric change gears...to make an ER x W-20 collet holder
Mosey   :'( :'(

Online b.lindsey

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Re: Mill Creep
« Reply #1 on: January 04, 2015, 03:20:01 PM »
Mosey, did you notice the problem before the end mil depth spoiled the workpiece?  I suspect the oil is what allowed it to creep in conjunction with the helical milling forces pulling down on the end mill. I hope you may have caught it in time.

Bill

Offline Jo

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Re: Mill Creep
« Reply #2 on: January 04, 2015, 03:36:07 PM »
Why were you using an end mill to cut a slot  :headscratch:

End mills are designed to cut on the side not the face. If you try cutting a slot with them you get pressure on the two side and the front teeth, pushing the cutter backward and causing an over width slot. I would suspect the backward push is what also encouraged the cutter out of the collet  :-\. Did you damage the collet as well  :(

W20 collets are very good and like all collets they should be used dry  :) Schaublin do both ER and the W series collets, they decided that that W series were better for use in their mills so I will  :NotWorthy: to their greater knowledge on this matter.

Jo
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Offline Mosey

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Re: Mill Creep
« Reply #3 on: January 04, 2015, 03:46:12 PM »
Mosey, did you notice the problem before the end mil depth spoiled the workpiece?  I suspect the oil is what allowed it to creep in conjunction with the helical milling forces pulling down on the end mill. I hope you may have caught it in time.

Bill
Bill, The problem became visible just as the mill spoiled the work, hidden by the large pile of swarf. I will clean and dry everything and make a test cut before proceeding. It is possible to cut most of the one-sided recess ( I should not have described as a slot) away on the table saw, so I may see about that to eliminate the large milling event.
In my experience ER collets hold better than W type, but are not as accurate in centering of short pieces. They are much better at releasing the mill or other piece. I think they each have their advantages in certain circumstances, not a universal one type better than the other situation.
Mosey

Offline cheepo45

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Re: Mill Creep
« Reply #4 on: January 04, 2015, 04:00:38 PM »
This is a well known issue in production machine shops where the depth of cut and the feed are much more aggressive than in home shops.
I prefer to use end mill holders with set screws to avoid this. This is also the cause of the tapering gouges found on many used milling machine tables!
I hope your part can be saved or you have more material. The rest of us can learn a lesson from this. Thanks for posting.
            cheepo45

Offline gbritnell

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Re: Mill Creep
« Reply #5 on: January 04, 2015, 04:10:55 PM »
Jo,
I'm a little confused about you statement. If not using an end mill to cut a slot what would one then use? I use end mills to cut slots all the time but having learned the things that could possibly go wrong while doing so I make adjustments, stay well away from side and bottom surfaces when roughing, make sure that the chips are continually cleared from the slot, (air) and make sure the cutter is fully held by as much of the shank as possible. Roughing end mills are generally quite forgiving while taking heavy cuts as they break up the chips into smaller bits so as to lessen the load on the cutter.
gbritnell
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Offline Jo

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Re: Mill Creep
« Reply #6 on: January 04, 2015, 04:47:01 PM »
Jo,
I'm a little confused about you statement. If not using an end mill to cut a slot what would one then use?gbritnell

You use a slot drill to cut a slot ;)

Jo
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Offline DavidF

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Re: Mill Creep
« Reply #7 on: January 04, 2015, 05:07:58 PM »
I dont know if my technique would be considered proper, but I use a center cutting endmill to plunge cut the majority first. The chips priral up and out of the hole just like drilling and get the hole opened up so there is somewher for the chips to go once you start milling out the sides.

Offline Jasonb

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Re: Mill Creep
« Reply #8 on: January 04, 2015, 05:10:39 PM »
Jo as Moseys slot was 1" wide and he was using a 1/2" cutter the problem of an over width slot does not come into it. I suspect he did one cut down the middle and would then use the SIDE of his cutter to take the slot to width.

It is also possible to buy roughing end mills that are suitable for slotting and even ones that are suitable for cutting keyways to the same tollerance as slot drills ;)

What worries me more Mosey is were you trying to take a full 5/8" depth cut in one pass with the 1/2" ripper or did you go down in steps and it moved on teh last one. A full 5/8" depth in one go would be a bit much in my book.

J
« Last Edit: January 04, 2015, 05:30:15 PM by Jasonb »

Offline Jo

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Re: Mill Creep
« Reply #9 on: January 04, 2015, 05:40:34 PM »
We seem to have gone over slot drills and end mills a number of times  :facepalm:. This is how Tubal Cain explains it in the Model Engineers handbook, P77: 

"End mills are designed for profiling, and are at their best in the situation shown in the sketch below. The maximum width of cut is one quarter of the diameter of the cutter, and the depth of cut is up to one diameter deep. This depth should not be less than about 0.006"; the width of cut should not be greater that that which engages two teeth at once. A better result will be obtained, with probably longer cutter life, if several cuts D/4 wide are made rather than fewer cuts the full width of the tool.

If an endmill is used as a facing cutter, with a very light depth of cut, then the corner may break down and rubbing will result. It is preferable to stone a 45 degree bevel or chamfer on the sharp corner, ensuring that clearance or relief is maintained, and to emply a depth of cut not less that 0.006" even in finishing; more is better. The bevel need not exceed 1/32" even on a larger cutter.

End mills are not suitable for cutting slots equal to the cutter diameter. For this duty a slot drill should be used; this has the advantage that, unlike the endmill, it may be fed axially down into the work so that slots with blind ends may be cut. "


Jo
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Offline Jasonb

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Re: Mill Creep
« Reply #10 on: January 04, 2015, 05:51:26 PM »


End mills are not suitable for cutting slots equal to the cutter diameter. For this duty a slot drill should be used; this has the advantage that, unlike the endmill, it may be fed axially down into the work so that slots with blind ends may be cut. "[/i]

Jo

Like I said Mosey was not cutting a slot equal to teh cutter dia, he used one half the size of his slot so after a basic pass where the width is not critical would have used the side of teh cutter to profile the slot to the required width.

Also the old slotdrill/endmill differences have become somewhat irrelevant with modern cutter technology, you can have centre cutting endmills and as I said above endmills and roughers that will cut a keyway to P9 tollerance the same as a slot drill would.

J

Offline Mosey

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Re: Mill Creep
« Reply #11 on: January 04, 2015, 06:03:58 PM »
"What worries me more Mosey is were you trying to take a full 5/8" depth cut in one pass with the 1/2" ripper or did you go down in steps and it moved on teh last one. A full 5/8" depth in one go would be a bit much in my book.
J"
[/quote]
Jason,
Yes, of course, that would be foolish.
I chose to take a 1/2" depth cut, with passes about 1/8" wide. I considered taking shallower depth cuts and wider passes also. My feed was quite slow to allow the cutter to cut freely, as chips are quite abundant with such a large cut as this. Is a wider shallow cut better? Honestly, my table moves much more conveniently in the X axis than Y, hence the choice of deeper narrower feed yielding less passes. Naturally I intended to leave sufficient meat to finish with a couple of cleanup passes of .005", final pass of .001".
Keep in mind this is an open-sided cut.
Perhaps, an high-helix 2 flute end-cutting mill for aluminum with a dash of Tapmagic (shaken, not stirred) would be best? I don't know what a Slot Drill is.
At no time did I attempt to cut a blind slot the full width of the mill, so I think that is a red herring. This thread is about mills being pulled out of their holders.
I am learning here and thank you all for your great inputs.
Mosey

Mosey  :headscratch:

Offline Jasonb

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Re: Mill Creep
« Reply #12 on: January 04, 2015, 06:14:54 PM »
1/2" deep x 1/8" width should be OK.

Not quite sure how you were able to take 1/8" cut though? did you feed in 1/8" then move 1/2" across, then another 1/8" if so this does put more cutter edge in contact with the work, maybe a picture would help?

A slot drill is a term more often used in the UK for a two flute centre cutting milling cutter

Offline crankshafter

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Re: Mill Creep
« Reply #13 on: January 04, 2015, 06:43:45 PM »
Hi Mosey.
is it possible you can put up a picture of the W20-ER collet-holder that you have. My be you have a drawing too :naughty:
CS
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Offline Mosey

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Re: Mill Creep
« Reply #14 on: January 04, 2015, 07:32:20 PM »
Hi Mosey.
is it possible you can put up a picture of the W20-ER collet-holder that you have. My be you have a drawing too :naughty:
CS
Sorry CS, if I mislead you, but I don't have an W-20 ER collet holder, I want to make one. My new metric change gears might make it possible.
Mosey

Offline sshire

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Re: Mill Creep
« Reply #15 on: January 04, 2015, 10:51:27 PM »
It's 2015. I thought we had put the "end mill/slot mill" thing to bed in 2013.
In the interest of repetition, here's one more try  In the Colonies, you can buy two types of end mill.Center cutting and non center-cutting. It's rare to see the non center-cutting variety. Both varieties are called "end mills."
I just checked my end mill drawer. 100% center cutting. I'm assuming that slot mill is the U.K. name for center- cutting.
Hopefully, the next time someone posts about milling a slot with an end mill, it won't be necessary to bring this up again unless they are from the U.K. In that case they should be carried of in someone's boot and deposited in the nearest tip.

Best,
Stan

Online Allen Smithee

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Re: Mill Creep
« Reply #16 on: January 04, 2015, 10:55:24 PM »
In that case they should be carried of in someone's boot and deposited in the nearest tip.

Well we would, but we'd need an air or sea ferry to get the car boot over to america.

AS
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Offline Alan Haisley

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Re: Mill Creep
« Reply #17 on: January 05, 2015, 12:28:27 AM »
From the introductory statement, I'd look to see if the collet was "well oiled" when the error occurred. There are places that need lube and places that need dry and collets are one of the dry ones - as mentioned by Jo.

Mosey, if you have another go at it, take some alcohol or acetone (or your favorite strong degreaser) to the collet, mill, and spindle nose socket before starting. I suspect that all of the creep will be gone.

Alan
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Offline Jasonb

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Re: Mill Creep
« Reply #18 on: January 05, 2015, 08:03:02 AM »
It's 2015. I thought we had put the "end mill/slot mill" thing to bed in 2013.
In the interest of repetition, here's one more try  In the Colonies, you can buy two types of end mill.Center cutting and non center-cutting. It's rare to see the non center-cutting variety. Both varieties are called "end mills."
I just checked my end mill drawer. 100% center cutting. I'm assuming that slot mill is the U.K. name for center- cutting.
Hopefully, the next time someone posts about milling a slot with an end mill, it won't be necessary to bring this up again unless they are from the U.K. In that case they should be carried of in someone's boot and deposited in the nearest tip.

Its not the fact they are centre cutting that Jo is on about its the fact they are TWO Flute which for various reasions I won't go into do tend to cut to their nominal size unlike cutters with 4 or more fluted which can cut overwidth.

Offline sshire

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Re: Mill Creep
« Reply #19 on: January 05, 2015, 11:57:52 AM »
Jason
Please go into the factors (or physics/geometry) that cause the end mill with more than two flutes to cut over nominal size. It's part of my "apprenticeship." I'm genuinely curious.
Thanks
Best,
Stan

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Re: Mill Creep
« Reply #20 on: January 05, 2015, 12:08:34 PM »
I'm sorry some folks don't agree but I rather like the obvious difference in the name "Slot Drill" and "End Mill" and hope the convention continues, over here at least.

The only slight confusion is that you can get three flute cutters and I don't know where these fit in the scheme of things. Are they suitable for slot cutting?

There was a very good description and diagram of why a slot drill is used to cut slots  :facepalm: will someone post the link when they find it. :naughty:

Offline Roger B

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Re: Mill Creep
« Reply #21 on: January 05, 2015, 12:33:38 PM »
A quick internet search showed this to be an endless topic  ::) . The attached document is from the Central Washington University and seems to make sense to me as a novice.

Best regards

Roger

Offline Ian S C

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Re: Mill Creep
« Reply #22 on: January 05, 2015, 01:31:43 PM »
I find that a two flute Slot Drill is best for aluminium as there is a bigger gap between the flutes for the swarfe to exit.
Ian S C

Offline Mosey

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Re: Mill Creep
« Reply #23 on: January 05, 2015, 01:35:38 PM »
The chat about center-cutting v slot milling is interesting, but not germane to my posting. I do find it informative though and will retain the information.
After checking, I find my much-used 1/2" W-20 collet measures .5022" ID, and the roughing mill shank is .4998. I believe that explains most  of the creep.

I have cleaned them both, and the inside of the spindle, as Alan wisely suggests. The spindle of this machine requires oiling, not greasing up high between the bearing races through a zerk type nipple, 2 pushes of an impossibly expensive Swiss hand oil gun.
I would replace the collet if I could, but these W-20 collets are unavailable in the US from Schaublin, nor anyone else. I may have to import one from them in Switzerland if I hit the lottery.
 
I think we have obtained much help from all of the issues in the discussion already, I know I have.
Mosey

Online Allen Smithee

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Re: Mill Creep
« Reply #24 on: January 05, 2015, 02:46:12 PM »
A quick internet search showed this to be an endless topic  ::) . The attached document is from the Central Washington University and seems to make sense to me as a novice.

What's bizare in that document is the way the section of 2-flute mills has the picture of a 4-flute one and vice versa!

AS
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Offline Jasonb

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Re: Mill Creep
« Reply #25 on: January 05, 2015, 03:30:04 PM »
Jason
Please go into the factors (or physics/geometry) that cause the end mill with more than two flutes to cut over nominal size. It's part of my "apprenticeship." I'm genuinely curious.
Thanks

The second page on Roger's link covers the reason.

J

Offline sshire

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Re: Mill Creep
« Reply #26 on: January 05, 2015, 05:32:42 PM »
Thanks Jason. I missed that link and it is an excellent explanation.
Jo.
You quote Tubalcain, but isn't he on the same page as you re: slot cutters vs end mills. My understanding of his quote is that end mills are not center-cutting while slot cutters are.

I'm calling a truce on this one. When someone over here says "end mill" it's quite likely that they mean the same thing as slot cutter.
I'm sure you have no problem putting a suitcase in your boot. Over here it's a struggle to fit one's foot in.
Best,
Stan

Online Dan Rowe

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Re: Mill Creep
« Reply #27 on: January 05, 2015, 05:38:41 PM »
Stan,
The KEY word is slot DRILL. It has to be a center cutting end mill to be a slot drill.

Dan
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Offline Jasonb

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Re: Mill Creep
« Reply #28 on: January 05, 2015, 05:52:38 PM »
Stan,
The KEY word is slot DRILL. It has to be a center cutting end mill to be a slot drill.

Dan

Not so over here, to be a slot drill it has to have two flutes as well. Take a look at the picture below , both are centre cutting but we would only class the two fluted one on the left as a slot drill as generally a two flute cutter will give a more accurate slot width in a single pass. You really only need it to be ctr cutting if the slot does not extend to one end of the work.

Take the shaft below, both were cut with a slot drill to get an accurate width but the centre cutting facility is only needed for the longer slot where the tool need sto be plunged if you have not predrilled wither end.

But all this is of littel relevance now as cutter technology has advanced so much you can get 4, 5 or 6 flute cutters that will give an accurate slot and they can be plunged or ramped.

Quote
quite likely that they mean the same thing as slot cutter

Stan I think you meant slot drill, a slot cutter is another kettle of fish entirely :-[
« Last Edit: January 05, 2015, 05:56:01 PM by Jasonb »

Online Allen Smithee

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Re: Mill Creep
« Reply #29 on: January 05, 2015, 06:11:35 PM »
Stan I think you meant slot drill, a slot cutter is another kettle of fish entirely :-[

Shirley you mean a woodruff cutter?

AS
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Offline Mosey

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Re: Mill Creep
« Reply #30 on: January 05, 2015, 06:17:17 PM »
Why don't we rename this thread to Slot Drills and End Mills, and I can repost my question?
My question has nothing to do with either. I asked about milling cutters that creep out of their (collet)holders, and why they do.  :noidea:
I too looked at  my mills and find that flutes run from 2 to many and all are center cutting.
I gather that some prefer to talk about slotting.
Or better still, why don't we put it to rest.
Mosey

Offline Roger B

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Re: Mill Creep
« Reply #31 on: January 05, 2015, 06:37:12 PM »
I have had a quick look here and metric W20s are easy to find but I am still looking for imperial sizes. There are a couple of other places I will try.
Best regards

Roger

Offline Jo

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Re: Mill Creep
« Reply #32 on: January 05, 2015, 07:00:40 PM »
Muddled Engineer had a large ice cream tub full of them thrown in for free with the Schaublin 12 milling machine goodies he shipped back from the states as the guy couldn't find any one who wanted them  :shrug:

Jo
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Offline Mosey

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Re: Mill Creep
« Reply #33 on: January 05, 2015, 07:04:58 PM »
I cleaned the collet, mill shank, and spindle and retested the roughing mill with a 5/8" deep 1/16" cut, and found that the mill still creeps out of the collet. Tomorrow I will install a new collet and retest.

W-20 x 1/2" collet is now in stock in the US!!  :cartwheel:
It is on the UPS truck to me for tomorrow.
They come in Standard and Ultra Precision grades.
Mosey
« Last Edit: January 05, 2015, 07:21:19 PM by Mosey »

Offline Bluechip

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Re: Mill Creep
« Reply #34 on: January 05, 2015, 07:07:48 PM »
Why don't we rename this thread to Slot Drills and End Mills, and I can repost my question?
My question has nothing to do with either. I asked about milling cutters that creep out of their (collet)holders, and why they do.  :noidea:
I too looked at  my mills and find that flutes run from 2 to many and all are center cutting.
I gather that some prefer to talk about slotting.
Or better still, why don't we put it to rest.
Mosey

I've no real idea whether this is relevant but ...

When I first got a mill I always used parallel shank cutters in a ER25 collet holder and the larger diameters tended to walk out of the collet. Presumably because the helix tries to ' drill in' ??

A Professional geezer said to use threaded shank cutters in a suitable chuck, in my case a Posilock.

This one:

http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Posilock_Collet_System_105.html

Problem goes away. Still use the ER25 for small stuff though.  :)

Dave

Offline Mosey

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Re: Mill Creep
« Reply #35 on: January 05, 2015, 07:25:14 PM »
Bluechip
I have never had a mill creep out of an ER collet on the old mill. Unfortunately, ER collet holders are not easily found for a W-20 spindle in the US, so I will make one eventually, as they are so  convenient and I like to use them.

Online Dan Rowe

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Re: Mill Creep
« Reply #36 on: January 05, 2015, 08:12:51 PM »
If you are making holders anyway put end mill holders on the list. End mill holders with a set screw are very handy and they will not slip or creep if the set screw is tight.

When I started I used collets only for the mill then I had a job that required several tooling changes. The z height is locked with the set screw with an end mill holder so it is the same each time it is installed in the spindle. So I could alternate between two cutters and not have to reset the z every time I changed end mills.

Dan

 
ShaylocoDan

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Re: Mill Creep
« Reply #37 on: January 05, 2015, 08:37:06 PM »
If you are making holders anyway put end mill holders on the list. End mill holders with a set screw are very handy and they will not slip or creep if the set screw is tight.

Remember, when you install the endmill in the holder, to pull it down against the nearly tightened setscrew before fully tightening the setscrew.  DAMHIKT.
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Arbalest

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Re: Mill Creep
« Reply #38 on: January 05, 2015, 08:51:26 PM »
I've got a small end mill with absolutely no teeth on the bottom at all, it's perfectly flat. Is this normal or has it missed a stage in production? It's brand new, never been used.

Offline Roger B

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Re: Mill Creep
« Reply #39 on: January 05, 2015, 09:03:35 PM »
I've got a small end mill with absolutely no teeth on the bottom at all, it's perfectly flat. Is this normal or has it missed a stage in production? It's brand new, never been used.

It's called a reamer  :stir:  :)  :mischief:
Best regards

Roger

Offline Mosey

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Re: Mill Creep
« Reply #40 on: January 05, 2015, 09:21:41 PM »
I've got a small end mill with absolutely no teeth on the bottom at all, it's perfectly flat. Is this normal or has it missed a stage in production? It's brand new, never been used.
Might need a picture of that

Offline PStechPaul

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Re: Mill Creep
« Reply #41 on: January 06, 2015, 05:32:42 AM »
Like this?



McMaster does not have "slotting drills", but they have planty of two, three, and four flute center-cutting end mills, and tight tolearance two-flute mills made for slotting. There are "finishing" end mills with four and more flutes, that are not center-cutting. I have some large end mills that are end-cutting but not center-cutting, because with higher flute count it becomes impossible to provide effective cutting edges at the center.

http://www.mcmaster.com/#end-mills/=vcd1rl





Some of what I have that I thought were end mills turned out actually to be counterbores with removable (and in some cases broken) pilot drills and plain pilots:


Offline Mosey

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Re: Mill Creep
« Reply #42 on: January 06, 2015, 07:18:34 PM »
To reach closure on this thread, I bought a new collet and installed the roughing mill in it today, taking a good cut of 5/8" deep by 1/16" feed. There was no creep of the mill! None.
The new standard precision Schaublin collet measures 0.505" ID at the nose, considerably larger than an old one. I suspect it holds so well because when tightened against the mill shank it contacts evenly along the length of the shank. Perhaps that is what makes it more successful than a worn collet. What Bogs  said.
I learned a lesson from this about work holding.
Mosey

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Re: Mill Creep
« Reply #43 on: January 06, 2015, 07:36:22 PM »
So, you didn't buy the ultra precision collets,  you saving the money for "cutters :lolb: :lolb: :lolb: :mischief: :Jester:"

Cletus

Offline Roger B

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Re: Mill Creep
« Reply #44 on: January 06, 2015, 07:37:16 PM »
Glad you reached a good solution  :ThumbsUp:  :ThumbsUp: Do you think that the old collet had worn to a taper?
Best regards

Roger

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Re: Mill Creep
« Reply #45 on: January 06, 2015, 07:52:47 PM »
I've got a small end mill with absolutely no teeth on the bottom at all, it's perfectly flat. Is this normal or has it missed a stage in production? It's brand new, never been used.
Might need a picture of that

Judging by the weight it's solid carbide, about 5mm.


Offline smfr

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Re: Mill Creep
« Reply #46 on: January 06, 2015, 08:20:32 PM »
Looks to me like it's been ground down. Did you buy it new?

Simon

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Re: Mill Creep
« Reply #47 on: January 06, 2015, 08:21:24 PM »
Glad you reached a good solution  :ThumbsUp:  :ThumbsUp: Do you think that the old collet had worn to a taper?
So, you didn't buy the ultra precision collets,  you saving the money for "cutters :lolb: :lolb: :lolb: :mischief: :Jester:"

Cletus
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Offline Mosey

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Re: Mill Creep
« Reply #48 on: January 06, 2015, 08:21:59 PM »
Glad you reached a good solution  :ThumbsUp:  :ThumbsUp: Do you think that the old collet had worn to a taper?
It would seem so!
Mosey

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Re: Mill Creep
« Reply #49 on: January 06, 2015, 11:00:32 PM »
Looks to me like it's been ground down. Did you buy it new?

Simon

Yes. That's how it came, never been used.

Online Allen Smithee

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Re: Mill Creep
« Reply #50 on: January 06, 2015, 11:14:29 PM »
I've got a small end mill with absolutely no teeth on the bottom at all, it's perfectly flat. Is this normal or has it missed a stage in production? It's brand new, never been used.
Might need a picture of that

Judging by the weight it's solid carbide, about 5mm.



Is it just me, or does it look like the flutes spiral in the wrong direction as well?

AS
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Re: Mill Creep
« Reply #51 on: January 07, 2015, 12:03:45 AM »
I agree Allen...that's a strange one. I can only assume it was designed for a specific purpose though I have no idea what that is  :headscratch:

Bill

Offline GailinNM

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Re: Mill Creep
« Reply #52 on: January 07, 2015, 01:26:17 AM »
It's a Right Hand cut Left Hand spiral.  They are used extensively for profiling thin materials as they tend to force the work downward against a support so less clamping is required.  The profile is typically only a little oversize from the support.  They also have the advantage of the swarf is directed downwards where it can be collected easier. Since they are only used for profiling there is no need for cutting edges on the end.  I have used several of them.

Gail in NM
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