How To Get Accurate Milling- Vn16 Bad Collets-what To Do?

[Bob V]

Hi,
I'm new to milling-- got my VN 16 last April and have been tooling it up.
It seems to me that the main factor limiting my ability to do precise work with this mill is the collets I got with the mill (about 25 of them). The spindle runout about 1 inch up inside the spindle is .0005. I don't think there are burrs or other problems inside the spindle.
However as I go through the collets-- they almost all have variable and significant runout when I put a gage pin or precision bar in a collet and pull it up into the spindle the runout are .005 and higher when measured only about 1/2" below the collet. most of the collets have burrs inside the bore of the collets where tools have slipped etc.
New 5v Hardinge collets for this mill are about $150 each-- so this is not an option for me. Used VNc and Hardinge 5v collets are available on eBay -- usually one at a time for about $50--- and I have no idea if these collets are any good at all. I'm guessing at least half of them have runout problems.

--I have an accessory adaptor that adapts from the VNc collet to a Morse 2 taper-- so I was thinking of getting a 5c collet holder (I have a set of 5c collets-cheap imports but pretty true).

What do you guys think?
How have you guys used the VN C spindle to mill without runout bordering on "wobble"?

Thanks,
Bob

 

[Bob Korves]

You don't "think" you have problems in the spindle. What have you done to check it? I noticed when I looked up 5V collets that they have an unusual anti-rotation keyway in the taper of the collet. Make sure whatever key or pin that fills that keyway is not too tall or wide to fit the available space, or it could be pushing in on one on the collet grip segments. The key needs clearance all around it. Clean the spindle collet seat really well and lightly stone any burs. Try not to remove spindle material at all except the high spots of any burs and corrosion. You are trying to save the original accuracy as best as possible. Take out or pull back the drawbar temporarily so it does not interfere. Get some Dykem Hi-spot blue, and put a thin coating on the taper and shank ring of a CLEAN good and bad fitting collet and seat them fairly lightly with the nominal size dowel pin or other accurate size shafting in the collet bore. Take the collets out and look at them carefully for even contact, and see if there are any contact pattern problems repeating from collet to collet. If so, try to find what is causing it. If all seems good, then it probably is. You may just have worn out collets. If so, you could try to find a good collet in a common size in your set, perhaps 3/4 or 1", and use it to mount something like an ER collet chuck for tool holding, avoiding buying a set of expensive collets but losing some headroom in the process. If the spindle turns out to be damaged, it can probably be ground to new tolerances.

Edit: also make sure that bad or loose spindle bearings are not causing your problem.

 

[Bob V]

Bob K,
Thanks for all the advice-- I will check out all the things you mention in your post--I've saved the post.--
--You say that if the spindle is damaged

can probably be ground to new tolerances.

Do you mean it can be ground to the original VN C taper? If it is ground to the original min runout tolerances, then I still have the problem of almost no useful collets to pull into the spindle.

Assuming the spindle is OK (after a thorough check as you've outlined) do you have any suggestions for removing the high spots inside the VN "C"collets that I have that are damaged?-- or is that simply not possible? I know most "worn out" collets are simply discarded and replaced-- but most collets are MUCH cheaper than the Hardinge 5c collets (same as Van Norman "C"). So it might even be worth maybe $25 per collet to have the collets reground/honed instead of paying $155 each for new collets. I'm guessing that the collets can't be saved since you suggested the ER collet chuck solution.
Any and all advice appreciated
Bob

 

[Bob Korves]

I know that Wells-Index grinds spindles to various oddball tapers, and can even change the taper to a different one where possible. Costs $200+ IIRC, plus freight. They want the spindle and quill as a complete assembly for vertical mills. I am not quite sure how the VN16 is built.

Once collets have had the slots placed in them so they can contract to fit a tool, they are not really machinable by any method I know. Maybe someone else here knows better than I. Regardless, it would be fussy and expensive hand work, and would probably equal the price of a new collet. I have found that Ebay prices for rare collets are not necessarily what they are selling for. I have some 2VB collets that I would like to sell, and a guy is trying to sell them on Ebay for $125 each. New ones from Hardinge are ~$200 each. But the fact is that those collets are not selling, a permanent ad. You can do an advanced search on Ebay and check the "sold" box to find out what has been selling recently and what the prices were. There are no sales. Try it with your 5V collets and see. Sometimes a private message to the seller explaining the facts of life can get him to see reality, but often they just don't seem to want to sell it to a real buyer at a real price. I agree with you about used collets. Sometimes the ones you buy are worse than the ones you have. Are you sure you are looking at high spots in the collet bores? If so, you might try to stone them, but it would be fussy work and would require a lot of retesting...

But, you are getting ahead of yourself. Get your Sherlock Holmes hat and a magnifying glass and see what you can learn about your spindle and collets. "A single well thought out test is worth a million expert opinions."

 

[Glenn Brooks]

Cal, the thread moderator has told me the drive slot in VN collets isn't necessary when the collets are used with the VN 12. I think They are needed for work done in the VN 16 - a slightly larger machine. The collets themselves only have a unique taper on the lip, where it draws up into the spindle, so this area could perhaps be honed - very gently - to remove any dings or high spots. Most likely, from your description the collets themselves are chewed up, perhaps ID made oval or egg shape - out of round in any event, through long useage. One option is to have the collets re ground , take each bad collet up one size e.g. 1/2" collet re ground to 5/8", and buy a replacement for the one or two that will not be able to be sized up.

Certainly, if you know a collet is bad, it can't hurt to try to lap or grind out the imperfections in an effort to save the piece. Otherwise set it aside for re grinding at some future point.

Cal and several others are a wealth of knowledge about these things, perhaps he will be able to add a useful approach.

Don't despair, everything is fixable!
Regards
Glenn

 

[Cal Haines]

Cal, the thread moderator has told me the drive slot in VN collets isn't necessary when the collets are used with the VN 12. I think They are needed for work done in the VN 16 - a slightly larger machine. ...

Glenn,

What we were talking about is arbors and such that have the drive lugs, not collets. So if I were going to make say a ER25 collet holder, I wouldn't bother with the drive key, since the holder would be driven by the lugs. But when you're using the "C" collets you do need the key.

The No. 16 (not to be confused with the 16L, 16M or 16S) is basically a redesign of the No. 12 and is a similar sized machine. It added things like a coolant pump, optional universal table, moved the table feed motor to the knee, etc. During the years when the No. 12 and the No. 16 were both produced, Van Norman used the No. 16 cutter-head on the No. 12. The 16L/16M/16S were the next generation after the No. 16 and featured bigger table, taller column; the 16M had a NMTB 40 spindle and the 16S had a quill.

 

[Bob V]

Hi Cal, and thanks--
I hadn't thought about the lack of need for the key in the spindle taper when using the "Van Norman Style "C" Taper Collets (Cal-- these are actually called "collets" even though they don't have the slits in the sides) I have these with M2 tapers as in the attached pic with my drill cluck on it).


These are essentially "collets" with drive lugs, and without the slits in them-- so I am thinking these would be less prone to deformation and I might put some Dykem blue on these (pictured at the bottom of the top pic) to help assess the runout in the spindle that Bob Korves was helping me with.

Cal:

What we were talking about is arbors and such that have the drive lugs, not collets.

I appreciate you pointing out the difference between the slit-type collets and the lug driven adaptors such as I am using for my drill chuck, BUT, I still have about 25 Van norman "c" (slit type) collets many of which have burrs inside them, and I would still like to know if there is a way to hone or lap out the burrs to return the collets to near their original runout. Bob Korves has suggested that an outfit called Wells-Index might be able to rehab these collets- and I plan to give them a call. I'll go the ER collet route with an adaptor to my spindle if I have to-- but would rather use the collets- for three reasons: 1) the collets would be IN the spindle so I would have about 4-6 inches more headroom, 2) because the collets would be in the spindle-- I would not get "stacked runout" from multiple adaptors between the spindle and the tool, and 3) the setup would be much more rigid with the tool shank essentially inside the spindle bearing-- not 4-6 inches below it. --So while I don't want to pay $200+ for a new set of Hardinge v5 collets for this mill-- I would easily pay $20+ to have the collets I have trued.

For honing-- has anyone heard of "flex hones"? --These were recommended to me by a friend who has a lot of mechanical/engine/machining experience.

Does this make any sense to you guys? I am well aware I'm a rookie here.
Thanks for all your help-
Bob V

 

[mattthemuppet2]

whatever you do not start removing material from the spindle! You mentioned burrs inside the collets in your first post. Removing these would be my first priority, before doing anything else, as they'll completely screw up your accuracy.

 

[Uglydog]

Before you do anything...
I had a similar problem with my VN6.
There is a little removable key which has a small metal dowel pin to hold it in place.
Check to make sure the key isn't burred.
I had to fab a new key. Then make sure that the slot in the collet lines up with the key. If the collet doesn't seat correctly then you'll get runout.
Every collet and arbor I had was bad. Fixed them all by fabbing a new key.

Daryl
MN

 

[Bob V]

Hi Daryl,

What kind of runout do you get on a pin in a collet in your spindle-- measured about an inch down from the bottom of the seated collet?

I'll check the removable key-- I've been careful to make sure it's not burred, since some of the keyways in my collets were damaged when I got them and I had to dremel off a small amount of metal on the sides of some of the collet keyways. I've been really aware of this key and I make sure it's in the collet keyway before I tighten the drawbar. I'll recheck this, but I don' t think this is the problem (I wish it were!). I think the problem is burrs inside the collets-- I can see them in some of them where tools have turned and gouged the collets.

Have you ever heard of flex-hones?
I'm going to call Wells-index, too, to see if they can rehab my collets.

Any and all ideas appreciated--
Bob V