VN VN 16 Overarm Woes

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kb3guy

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Mar 29, 2017
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Hi All,
I have a VN16 mill with an overarm that won't fit back in its bore, and I'm trying to figure out how to approach the problem. This is probably out of my league, but I'm betting on taking my time. When I first got the mill, everything was very rusty:

2017-03-17 21.25.40.jpg

With a liberal application of WD-40 and some time, I was able to get the overarm bar out with a mallet and a bolt of hickory as padding (trying not to mar the ends of the bar.) The overarm let go all at once and ended up on the floor, no doubt putting it further out of dimension. I spent some time with some scotchbrite to try to clean all the rust that was on it, hoping it would fit back where it was meant to:

2017-03-19 16.43.11.jpg
2018-01-13 18.13.23.jpg

The overarm is bent longitudinally maxing out at about 0.010 TIR in the middle (I put it in some v-blocks on the table under the ends of the bar, and put an indicator on the top of the bar, in the middle - not sure how accurate this would be, but that's where I got the number.) There are also a few hammer marks on the ends of the bar from some prior owner which may have upset the end of the bar. The bar will now only go about 3/8 inch back into its bore by hand, and I'm sure I don't want to drive it in.

I'm pondering a few different paths of action, sort of depending on what the problems are:

0) Should I just buy a piece of turned and ground 2.375 stock and call it a day?

1) Measuring and dealing with potential mushrooming / upset ends: Do I just take some calipers and compare the ends of the bar with the bore? If it is too big for the hole, do I take this somewhere to get ground, or is it something I could turn a few thousandths off of on the lathe? What kind of fit should I be looking for? I would like to do some horizontal milling on this machine someday, so getting it right is probably important.

2) Dealing with the longitudinal bending of the bar, should I get it pressed straight at a shop, or maybe flame-straightened? I don't think the bar being 0.010 out in the middle would cause the very end not to fit more than 3/4 inches (at that distance, it would be a deviation of less than 0.0003, right?) But again, I'm not sure how straight an overarm bar needs to be to work properly on a machine like this.

I'm sure I have overcomplicated this - this is a round bar that needs to fit in a bore, at a certain level of accuracy (which I don't know how to measure.) Any advice on how best to tackle this would be much appreciated. Thanks!

2017-03-21 19.01.34.jpg
 
The bend in the middle will not affect the entry into the hole. The upsetting will. It will, however, affect where it holds the support for the end of the arbor. You can use the machine without the arbor support if you use a tool mounted in the spindle, not on the arbor. Do you have the arbor support? if not use your bar as a rusty paperweight, there's no other need for it.
 
I think that a purchase of a piece of TG&P would be the best thing to do, what with the bent part. I think that also you should do some clean up on the bore that it fits into, perhaps with a cylinder hone, which would clean things up without increasing the bore size. It seems likely that the hammer marks are indicative of some mushrooming of the end of the existing overarm, you could have a go at it with a sharp mill file, which would show you where the high spots are, then carefully remove them by hand with the file. The old bar will be fine material for other projects.
 
If you think any mushrooming is your problem, I would just take a file to it. Even if you filed enough to put a noticeable taper to the ends, it will not hurt anything, as the ends are not used for anything. The length of your arbor determines what sections of the support are needed.
 
Just my opinion:
You have way to much rust on that bar. And probably too much in the bore. I would take some 600 wet dry paper with oil on it and work that rust off. Then I would stone any burrs.
Next I would pick up a ball hone, or small engine hone and hone the taper. You are looking to get rid of the rust and come up with a shinny metal surface. use plenty of oil and keep it wet.

Then make your decision. As as straightening the rod, I would look into Keith Fenners videos on how to straighten a shaft. Very knowledgeable.
https://www.youtube.com/user/KEF791/
 
Did you try both ends of the bar? Did you try loading it in from the back? Make sure that you're not running into the blind half of the split-cotter clamp.

You probably damaged the ID of the hole in the ram on the way out. As the bar tipped down, the end of it put a lot of pressure on the bore at the top, check there.

0.010" is absolutely not a problem here; that's probably well within the original specifications for a bar that long. In any case, you can rotate the bar and move the overarm support to get the centerline of the support exactly on center.

The best way to find any bulges/burrs on the support bar is to use a large (6" plus), fine India or Arkansas oil-stone. Glide it along the bar and you'll feel any burrs or bulges. Stone/file them down, take your time, be patient. Keep the stone/file in light contact with the bar, working parallel to the long axis of the bar. You can work helically along the bar, but the key is to keep the stone in light contact with the bar so that it can guide you. Stop as soon as you no longer feel the drag of the bump. If the end of the bar is badly mushroomed, wrap the end in a piece of stainless steel shim stock and use that to guide your stone/file until you get close. Watch the shape of the shiny spot that emerges as you stone off the bump, if it starts to turn into a line along the axis of the bar, you've gone too far in that spot. If you don't have a suitable oil-stone, you can use a fine, sharp (new) file, but a stone is better. Large defects will require some file work, then finish up with the stone.
 
There is a lock and cam which secures the ram. Is it completely clear of the ram?
Are there palpable burs on the roundstock?
How about the hole?
I had significant issues with the ram lock/cam mechanism on the 22LU. Disassembly, cleaning and lube made the difference.

Daryl
MN
 
The first thing you need to do is find some patience and not do anything rash...
 
Agree with what Cal said about the cotter clamp. Put some dykem or hi-spot blue on the bar as you twist it in- that will tell you where the tight spot is- you could also use a sharpie pen
in a pinch- then carefully file the high spot off, checking frequently
Mark
 
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