VN Van Norman # 12. Collet questions.

J

John TV

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I have had my van Norman #12 milling machine for more than two years now but I still consider myself a complete beginner. Each time I use the mill there’s a new learning experience. I have most of the original van Norman 5V collets but I do not own any end mill holders at this time.

Recently I was using a half inch roughing end mill to clean up some rough edge cuts on hot rolled 3/4” steel (conventional not climb milling) and the end mill kept slipping down in the original Van Norman collet. I removed the collet, checked the spindle and the collet itself for cleanliness and oil and made sure the cutter was clean of oil and re-tightened the end mill with a significant amount of force. Again the end mill slipped.

I tried a different cutter and that also slipped in the collet. The collet was tightened with enough torque to bend my “pin” made from a grade 8 bolt that I use to hold the spindle. I realize that speed, feed and depth of cut and cutter condition all play a roll here and as I said I’m learning so they may have all played a roll in my problem.

I am also wondering about other issues. How do you know if a collet is too worn? Spindle taper wear ever an issue? Other thoughts? As you all know these collets are getting hard to find and new from Hardinge they are north of $200 each so before I order a new collet thought I would check with you more experienced VN owners.

Appreciate your thoughts.

John in Minnesota


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Hey John. Since nobody offered any thoughts, I thought I'd give you mine.....

My VN16 does the same thing when I get impatient. I have a couple sets of collets and have same results. I assume you have key for your collets. You might check diameter of endmill, some "1/2" stuff is really 12 (mm).

I have thought about getting one of the new hardinge 5v collets. If I was, it would be a 3/4 inch collet. This is what my Tormach uses to hold the TTS holders which are readily available. See ebay "Tomrach" or c3/4. Even the genuine Tormachs are cheap compared to VN....
 
Thanks for the response. Appreciate your thoughts. I will check into those tormach collets.

When you said you had the same problem when you were impatient...
Did you mean taking too large a cut or too fast? I assume that’s what you meant.

I love this old mill, just wish I had a bit more knowledge to bring her back close to speck. Still, really fun to learn.

John


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John. Both too big cut and too fast. I'm mostly a novice and inpatient.

To be clear, the TTS holders are not collets. They are 3/4 inch shaft tool holders. There are set screw endmill holders, chucks and ER series collet holders. On the tormach mill, the spindle taper is r8 and a modified 3/4 collet is fitted. The various holders sit in the 3/4 collet allowing for a variety of tools. The downside is there is loss of available z axis and more possible sources of runout. So for the VN you'd need a 3/4 collet to start, then some tts holders.

You might also check your drawbar, it could be stretched or wrong length if shop made and not allow full draw on collet.
 
Yes, I get impatient too and add inexperience to that ...and I have broken a few end mills way before their time.

Thanks for the clarification on the tool holders. I hate to use up valuable z travel but most of the time it’s not too big an issue for what I have made so far.

I think I have the original draw bar and it seems to be able to exert a great deal of pulling force, but as already stated I’m not sure about collet or spindle wear. Right after I got the mill I had to make a new key for the spindle. The old one was so worn it wouldn’t engage in the collets and maybe years of use like that damaged the spindle some.

I don’t know if Cal Haines is still checking in here from time to time but his knowledge of VanNorman equipment has been so helpful to me and many others. Wish I lived closer to that guy so a little more would rub off.

Good luck with the 16, I’ll keep knocking on the 12.

John in Minnesota


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It's fairly common for end mills to walk in collets. If your working the cutting tool hard the tool can walk. The best solution for this is an end mill holder. I've had it happen on new collets. The issue is there are pretty much no source of end mill holders for the VN machines. You can roll your own though.

Jason
 
Thanks Jason,
I’m working up to trying a collet but my skills and Logan may not be up to the concentricity I would hope for.
Willing to give it a try tho!


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Collets are made of spring steel, I don't know how easy or hard they would be to make.

I've made several arbors, and this is what I did.

Use 4140QT. I turn everything thing I can on the lathe via a 4 jaw, get your run out as close to 0 as you can. I grind the taper in with a tool post grinder. Once this is done, rough in the bore on the tool side. I then mounted the new tool holder in the mill set in the horizontal position. I then mounted the tool post grinder on the table and grind to the final dimensions. This will ensure that your tool run out is the same as your spindle.

Jason

IMG_20160422_174535643.jpgIMG_20151211_164152496.jpg
 
How much are you leaving to grind? A few thou? I have a chinesium tool post grinder I have not fully set up yet. Think that might work. Pics are awesome. Did you cut the key seat on the mill or leave it out?

John in Minnesota


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You can get more clamping load by lubricating your drawer thread and the shoulder. A little lube on the collet taper will also help. The collet to end mill interface wants to be dry.

If you want the ultimate grip you can put a little diamond powder between the end mill shank and the collet bore. Of course, this is going to wear anything that moves... at one point I was making a tensile tester for ultra-strong wire (MP-35N). I used ER collets set so that the pull tightened the grip, ball bearing nuts, torqued the #%^ out of it, and still had to step up to the diamond to get it to break instead of slip!

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