Fixing Milling Arbor Runout

[Mywayornoway]

I have several CAT50 horizontal milling arbors, mostly 1 1/4" diameter, of various lengths. They came used with my B&S 205 so I don't know their history, but every one of them runs out between. 010" and .100" at the outer (small) bearing surface near the tip. This is when mounted in the taper, but otherwise bare.
Is there a way to true these arbors to the taper so then I can move on to straightening the shafts themselves?

 

[magneticanomaly]

Straightening shafts is a bit of an art. Your arbors may have one simple bend near the shank, or may be pretzels. If you mount the arbor in the machine, and indicate it
at every couple of inches from outboard journal to shank, marking the high-spots and the value with a Sharpie at each station as you go along, you will know what you have.|
If you have a simple unidirectional bend, you could gamble that you will not brinnel thge spindle bearings by usng a floor-jack and a 2x4 to bend upward. in the machine. Of course the careful way would be with vee-blocks (padded with aluminum scraps) on the bed of a press
However you set up, always use an indicator to record how far past straight you are pushing, so that you can add deflection on successive tries and get it straight without overshooting.

 

[eKretz]

Straightening shafts is a bit of an art. Your arbors may have one simple bend near the shank, or may be pretzels. If you mount the arbor in the machine, and indicate it
at every couple of inches from outboard journal to shank, marking the high-spots and the value with a Sharpie at each station as you go along, you will know what you have.|
If you have a simple unidirectional bend, you could gamble that you will not brinnel thge spindle bearings by usng a floor-jack and a 2x4 to bend upward. in the machine. Of course the careful way would be with vee-blocks (padded with aluminum scraps) on the bed of a press
However you set up, always use an indicator to record how far past straight you are pushing, so that you can add deflection on successive tries and get it straight without overshooting.

I like this, other than the bit about trying to straighten the arbor in the machine. I sure wouldn't risk the spindle bearings.

 

[Donkey Hotey]

If you're really intent on trying to straighten them, I would make an aluminum 50-taper outside bushing for the holder to screw into. I'd put each arbor into that pocket and fasten it, then take that assembly to a hydraulic press. The bushing will protect the taper while you support the ends and push on the middle.

 

[pmtool]

Straightening shafts is a bit of an art. Your arbors may have one simple bend near the shank, or may be pretzels. If you mount the arbor in the machine, and indicate it
at every couple of inches from outboard journal to shank, marking the high-spots and the value with a Sharpie at each station as you go along, you will know what you have.|
If you have a simple unidirectional bend, you could gamble that you will not brinnel thge spindle bearings by usng a floor-jack and a 2x4 to bend upward. in the machine. Of course the careful way would be with vee-blocks (padded with aluminum scraps) on the bed of a press
However you set up, always use an indicator to record how far past straight you are pushing, so that you can add deflection on successive tries and get it straight without overshooting.

Really? Risk an expensive spindle to fix a cheap arbor? If they really run out as much as you say why even try to save

Straightening shafts is a bit of an art. Your arbors may have one simple bend near the shank, or may be pretzels. If you mount the arbor in the machine, and indicate it
at every couple of inches from outboard journal to shank, marking the high-spots and the value with a Sharpie at each station as you go along, you will know what you have.|
If you have a simple unidirectional bend, you could gamble that you will not brinnel thge spindle bearings by usng a floor-jack and a 2x4 to bend upward. in the machine. Of course the careful way would be with vee-blocks (padded with aluminum scraps) on the bed of a press
However you set up, always use an indicator to record how far past straight you are pushing, so that you can add deflection on successive tries and get it straight without overshooting.

Trying to straighten an arbor while in the machine spindle with a floor jack is a bad idea on multiple levels unless you care less about the spindle than the arbor. Why risk it? Buy a new old arbor on eBay and be done.

 

[rwilliams]

What is the run out when filled with good spacers and the nut torqued down?

Bob

 

[Bill D]

First measure the runout on the bare spindle.
Bill D

 

[michiganbuck]

QT magneticcanomaky (However you set up, always use an indicator to record how far past straight you are pushing, so that you can add deflection on successive tries and get it straight without overshooting)

That is the way I was taught to straighten, push the straightening bend to a certain shim stack, and then try a little more. Agree that I would not straighten out of a machine spindle. One job I had included straightening long spline round broaches. They were about 5 or 6 feet long would come in with multiple bends and had to be <.001 for their length before sharpening. We used an air hammer and carbide chisels to put small dents on the hard steel. Different direction bends were all along the tools so I would straighten one 3" long section and then move to the next section..a real bugger of a task.

 

[rjwalker1973]

I agree with Bill. Check the bare spindle first if you have not already. Then mark the arbor incrementally like magneticanomaly said. If it is multidirectional bend it would probably be less time consuming then getting an used one . I have straightened arbors with a small bottle jack and aluminum shims before. Not good for the bearings, so these days I really recommend against it.

 

[magneticanomaly]

Maybe I am crazy to consider straightening an arbor in the machine, and maybe not. My milling machines have plain bronze bearings. Yours probably ball or roller.
But consider how much force it might require to straighten a simple bend near the shank..the only kind it would be geometrically practical to try to fix in the machine. Your rolling-element bearings are probably larger but a mere 6308 (40mm bore 90 mm OD) has a static load capacity (the load that will NOT brinnell) of over 5,000 lb, according to a New Hampshire Ball Bearing co data sheet that was easy to pull up. You can figure the leverage based on the length of the arbor and spacing between front and rear bearings of your spindle.
The suggestions of checking runout with good spacers torqued up is good, because they will tend to straighten the arbor, and also to check the bare spindle.
I seem tgo remember another thread on same subject, which eventually agreed with my experience that it is unrealistic to expect a cutter on an arbor to run perfectly true, same depth-of-cut per tooth all around...unless you grind it in place. This is more noticeable with light cuts and flimsy setups...like most of mine.
With the cost of arbors, IMO it is certainly worth invesing a couple of finicky hours on the press with aluminum shims and indicator IME .002 TIR is attainable most of the time.