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hoodlum
04-27-2012, 08:27 AM
I have a vernon borer/mill with a nice set of collets,but the largest collet I have is 5/8....I just scored on a nice end mill lot,but several have a 3/4 shaft,so I am planning on machining an arbor/holder for the 3/4 shaft mills....I am having a terrible time finding any hardened tool steel locally to make this from...Would some standard cold rolled be suitable for this? It would not be subject to any heavy strains,because my mill isn't big enough to take a huge cut with that size bit,but none the less,I still have a use for them....
Thanks!!!!

rickyb
04-27-2012, 07:14 PM
I have a vernon borer/mill with a nice set of collets,but the largest collet I have is 5/8....I just scored on a nice end mill lot,but several have a 3/4 shaft,so I am planning on machining an arbor/holder for the 3/4 shaft mills....I am having a terrible time finding any hardened tool steel locally to make this from...Would some standard cold rolled be suitable for this? It would not be subject to any heavy strains,because my mill isn't big enough to take a huge cut with that size bit,but none the less,I still have a use for them....
Thanks!!!!
It is generally not recommended to use collets as end mill holders. It is too easy for some circumstance to go wrong while milling, even with low power machines. You might think about making end mill holders for the sizes you need. It is easier than making collets.

When I make either I use drill rod and don't bother heat treating.

Ohio Mike
04-27-2012, 08:03 PM
Personally I want my tool holder softer than my spindle. After all which is cheaper to replace? I wouldn't use CRS simple because it doesn't machine as nice as a free machining steel. If I was doing this I'd get some 1144 Stress Proof. The stuff machines like a dream, and leaves an awesome finish.

What is the taper on the machine? If its Brown & Sharpe No 9 end mill holders (and collets for that matter) are available commercially from Tools4Cheap.

Forrest Addy
04-27-2012, 09:55 PM
Chocolate/peanut butter, paper/plastic, collets/emdmill holders...

Collets in good condition in a collet chuck or mill taper in good condition probably hold stiffer and more concentric than a setscrew (Weldon) adapter. The key words are "good condition". Collets when they wear, wear hourglass in the bore and internal taper and like the small end of an egg on the external taper. The wear is gradual, progressive, and goes un-noticed by the user until under heavier cuts the operator finds the cutter working out of the collet increasing the depth of cut. As wear progresses the work-out increases until even moderate cuts result in unpredictable depths of cut.

Summary: Collets wear. However much they wear, the cutter will still run pretty concentric. OTH in a worn collet the cutter can work its way deeper under the forces of the cut. That's a disadvantage of collets.

End mill holders: Endmill holders (Not an arbor. An arbor has a diameter and a shoulder gainst which a saw or wheel cutter is clamped axially with a nut and usually bushings. Yes this is a nit pick) secures the cutter with a setscrew from the side. They are often called “adaptors” (a more generic word) and are made with a small assembly clearance between the inside diameter shank fit and the cutter shank's outside diameter. When new the extremes of the fit runs between 0.0002" loose and 0.0007" loose. Any clearance at all allows the endmill shank to stir slightly in the adapter bore. Inserting a new cutter in a new adapter is often a struggle because the fit is so close. Minute cyclic movement under load results in wear over time. One indication of wear is ease of cutter insertion; if it's easy, the adapter is worn.

Try this experiment: Grip one end of a new pencil in your fist with the long end sticking out. Grasp the end and stir it around in a circle. The sensations you feel in your fist are analagous to the forces in the adapter bore. Thus the adapter wears more opposite the setscrew but the whole bore wears into an irregular hourglass. Sooner or later the adaptor that once held the cutter concentric with the spindle axis now holds the cutter eccentric and at a funny angle.

Summary: Staight shank adapters wear so the cutter runs eccentric and crooked so it cuts oversize but because of the setscrew retention, there is no end-wise movement.

You have a choice, concentric grip but axial cutter movement or eccentric running cutter staying put but running at a funny angle.

The point if all this discussion is that no tool holding system lasts forever. It will wear in use. Hardinge's finest $65 each R8 collets and Collis' finest $85 R8 endmill holders last only about twice as long as better quality imports: they will all wear eventually and if tool path accuracy and predictability is to be maintained, they have to be replaced when worn. It's a cost of business.

I worked in a big shop where the milling adaptors were years old and were worn - some to an unbelievable degree. Once made aware of the problem the management spent $120,000 and re-tooled in #50 milling tooling. Costs of damage and waste assigned to milling operations dropped to about 1/3 that of the previous year and the savings paid for the tooling several times over. Grins and handshakes all around. That was in 1988. When I left in 1993 the damage and waste figures were climbing to previous levels attributable to wearing spindle tooling. When I asked the shop supt about replacement he said no, we can't affod it. Thus avoiding a once in three year cost trumps containing continuing and increasing expense. Duh!

If your collets aren't holding well, maybe they or the collet chuck or both are shot. If your straight shank endmills are going grunkety grunk - cutting only on a few teeth - maybe your adaptors are shot.

The chain is only strong as the weakest link.

In answer to the OP question. Use either collets or endmill holders. Collets are shorter and stiffer but may allow endwise movement. Holders stick out further and may allow eccentric running. Both hold accurately and well when new.

I prefer collets unless I need extra reach.

Davo J
04-28-2012, 05:12 AM
I have a vernon borer/mill with a nice set of collets,but the largest collet I have is 5/8....I just scored on a nice end mill lot,but several have a 3/4 shaft,so I am planning on machining an arbor/holder for the 3/4 shaft mills....I am having a terrible time finding any hardened tool steel locally to make this from...Would some standard cold rolled be suitable for this? It would not be subject to any heavy strains,because my mill isn't big enough to take a huge cut with that size bit,but none the less,I still have a use for them....
Thanks!!!!

It will be fine to use. I have some steel here and was playing with the idea to make some, and after researching one guy over on CNC zone said he had made a few up and they worked fine. I also found others who had made them but mainly one offs.

In a home shop we don't have the luxury to harden and grind tool holders, but then again for our purposes cold rolled will be fine. As said above it will be softer than your spindle so it will damage first, so no harm done.

The way I was thinking of was to rough bore it out on the lathe, then mount it in the mill spindle to take the final pass. Either that or machine a piece of scrap in the lathe the same as you mill spindle and do them in that, though for a one off I would do it in the mill.

Don't forget to post it up if you make it, that way other guys down the track thinking the same thing will know how it all worked out and how you went about it.
Dave

John Stevenson
04-28-2012, 06:12 AM
It is generally not recommended to use collets as end mill holders.

Someone ought to tell the Machine Tool trade then. :rolleyes:

hoodlum
04-28-2012, 08:39 AM
OK...Thanks for the response....It seems some think I will be miling the spindle taper,which is not the case...It will have to be turned to fit in the 5/8 collet.....The collets are held in the spindle with a large not on the bottom of the spindle,and the hole in the nut is only 1"....It doesn't have enough room to pass a mill holder through and tighten onto the spindle....It will simply be a piece with a 5/8 shaft on one end,and a 3/4 hole in the other with a set screw....It will be simple to make....I could make another nut I guess,with a larger pass through hole,and machine the spindle taper....I will be sure to let you guys know which route I take.....
Hoodlum

Ohio Mike
04-28-2012, 10:11 AM
I see you're making a reduced shank end mill holder, what wasn't at all clear to me at first. I thought you were making a end mill holder to fit your spindle taper.

Davo J
04-28-2012, 10:46 AM
I see you're making a reduced shank end mill holder, what wasn't at all clear to me at first. I thought you were making a end mill holder to fit your spindle taper.

+1 so did I.
Just make sure you dont end up with to much over hange from the spindle nose.

Dave

bborr01
04-28-2012, 11:14 AM
Someone ought to tell the Machine Tool trade then. :rolleyes:

If I were still working I would let my Co workers in on this too.

Brian