Vn12 Bent Knee Feed Screw

[gcaldicott]

Hi All,

I picked up a VN12 a couple weeks ago. I tore it down for restoration. Everything is in really good shape except the feed screw that raises the knee is bent. The threaded portion of the screw doesn't seem to be bent. The bend seems to be in the last 2" where the shaft fits into the knee. The bend is about .050" so the high to the low measures .100".

Any ideas how I should straighten it without breaking it?

Thanks,
Greg

 

[gcaldicott]

I tried to include a picture, but it keeps saying there is an error.

 

[Cal Haines]

Greg,

The basic way to do this is to hold the shaft using V-blocks, use an indicator to watch the deflection of the bent portion and apply a controlled force to push the shaft past the zero. You keep applying more force and pushing the shaft farther each time until it springs back where you want it. If it weren't for the fact that the knee elevation screw is the one you need to fix, you could do it using the mill itself. Your best bet is to watch YouTube videos and read forum posts until you understand what you need to do.

Here's a couple to get you started:

The second video is interesting because he's using a milling machine's table and quill to straighten a shaft. On a Van Norman, you could turn a rod to fit into the profile stud socket in the bottom of the ram and use it to apply force to a shaft by raising the knee. You can find the profile stud socket by looking on the bottom of the ram, near the drain plug for the ram gearbox.

 

[FOMOGO]

Being the bend is in the last 2" of the shaft makes it kind of tough. One solution would be to turn that section down on a lathe the .050 to make it true and then bush it back to it's original diameter. Mike

 

[gcaldicott]

Thanks for the input. Based on feedback that I have received, my plan is to make an aluminum block with a hole bored in it to fit the small end of the shaft. I will clamp that into a vise on the VN table. The bend is where the diameter first steps up in size. I was then planning to use another vise somewhere down the the threaded end to put a controlled force against the shaft to bend it back straight.

As it turns out, the bent shaft is of my own doing (stupidity). I transported the knee with the feed screw in it and left the casting that screws to the base hanging off the end. I'm not sure what I was thinking, but I'm sure that caused the bend.



I have a couple other issues that you might be able to help with. First, the bronze bushing that the feed screw connects to in the knee has a piece chipped off of it and seems to have a slot in it along the entire length (like a key slot). I'm not sure why the slot is there, but I am wondering if I should press the old bushing out and make a new bushing to press in.


Second, I would like to remove the chain sprocket from the feed box. It looks like I should be able to unscrew the hub of the sprocket with a spanner wrench. It does not budge. Any ideas?

Thanks,
Greg

 

[gcaldicott]

Thanks for the input. Based on feedback that I have received, my plan is to make an aluminum block with a hole bored in it to fit the small end of the shaft. I will clamp that into a vise on the VN table. The bend is where the diameter first steps up in size. I was then planning to use another vise somewhere down the the threaded end to put a controlled force against the shaft to bend it back straight.

As it turns out, the bent shaft is of my own doing (stupidity). I transported the knee with the feed screw in it and left the casting that screws to the base hanging off the end. I'm not sure what I was thinking, but I'm sure that caused the bend.



I have a couple other issues that you might be able to help with. First, the bronze bushing that the feed screw connects to in the knee has a piece chipped off of it and seems to have a slot in it along the entire length (like a key slot). I'm not sure why the slot is there, but I am wondering if I should press the old bushing out and make a new bushing to press in.


Second, I would like to remove the chain sprocket from the feed box. It looks like I should be able to unscrew the hub of the sprocket with a spanner wrench. It does not budge. Any ideas?

Thanks,
Greg

Why don't all my pictures show up in the message?

 

[gcaldicott]

Why don't all my pictures show up in the message?

Is there a file size limit?

 

[gcaldicott]

 

[gcaldicott]

 

[Cal Haines]

Thanks for the input. Based on feedback that I have received, my plan is to make an aluminum block with a hole bored in it to fit the small end of the shaft. I will clamp that into a vise on the VN table. The bend is where the diameter first steps up in size. I was then planning to use another vise somewhere down the the threaded end to put a controlled force against the shaft to bend it back straight.

That sounds reasonable to me, but I'm not an expert in this. Just make sure you use an indicator so that you can tell how far you are moving it each time, take your time and sneak up on it.

...

I have a couple other issues that you might be able to help with. First, the bronze bushing that the feed screw connects to in the knee has a piece chipped off of it and seems to have a slot in it along the entire length (like a key slot). I'm not sure why the slot is there, but I am wondering if I should press the old bushing out and make a new bushing to press in.

I'm guessing that the slot is to allow oil from the oil cup to flow down to the bearing. I doubt the slot goes all the way, probably just to the oil hole.

Second, I would like to remove the chain sprocket from the feed box. It looks like I should be able to unscrew the hub of the sprocket with a spanner wrench. It does not budge. Any ideas?
...

There's a threaded ring that holds the knob onto the sprocket. The thread is right handed. Yes, you need to remove the ring, the knob should come off, then you can use a puller to get the sprocket itself off.

Here's a drawing that shows the gearbox:

Here's what the shaft looks like: