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Bent Arbor on Horizontal Mill?

WakelessFoil

Aluminum
Joined
Aug 18, 2020
We test fired our Cincinnati No. 2 horizontal mill today. We had a large 8 inch, 32 tooth (HSS?) cutter that we were gonna use to cut a simple 1/2” deep slot in a piece of steel. We chose a very conservative chip load with low spindle RPM and even lower feed rate; well under book recommendations.

When we went to make a cut, it sounded as if the cutter was not concentric with the spindle. We listened to the sound of what appeared to be an interrupted cut.

Brrrp… Brrrp… Brrrp…

This led us to take a runout on the spindle in a couple of places. Right in front of the cutter we got 0.005” total RO. Not good but it got even worse when we moved out dial to the end part of the spindle that sticks out past the head; .015” TRO!

Could this be a bent arbor? Or maybe worn out spindle bearings? What does it sound like to you? This is a 70+ year old machine.
 

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FamilyTradition

Aluminum
Joined
Feb 24, 2018
Location
Greenfield, Mass
What is runout right at the spindle, or in the spindle taper itself?

Check to make sure you didn't get any chips in the spindle taper or on the taper on the arbor when you put it in. Cleanliness is next to godliness.

Do you have another arbor to try out? If you have cleaned off this arbor good and it's still funky, but the next one is fine, bad arbor may be your problem.

Also check cutter itself, could be out of round or not concentric.

Basically process of elimination to figure out the culprit.

I have worked with Cincinnati horizontal mills that have done a similar thing. Never looked too far into it, kind of just ran with it.
 
Joined
Apr 19, 2006
Location
Manchester, England
What is runout right at the spindle, or in the spindle taper itself?

Check to make sure you didn't get any chips in the spindle taper or on the taper on the arbor when you put it in. Cleanliness is next to godliness.

Do you have another arbor to try out? If you have cleaned off this arbor good and it's still funky, but the next one is fine, bad arbor may be your problem.

Also check cutter itself, could be out of round or not concentric.

Basically process of elimination to figure out the culprit.

I have worked with Cincinnati horizontal mills that have done a similar thing. Never looked too far into it, kind of just ran with it.
Just picking up on your “ cleanliness is next to godliness “. Absolutely dead right. Not enough people in engineering take cleanliness seriously enough.

Regards Tyrone.
 

kootne

Aluminum
Joined
May 11, 2009
Location
montana,usa
My experience with a horizontal mill led to these conclusions;
1. Every thing, arbor, cutter, spacers, spindle, outboard bushing, must be absolutly clean.
2. Check the runout at the outboard bushing without the outboard support in place. If it's off, try rotating the arbor 180 degrees in the spindle. Mike all the spacers and cutter for uniform thickness. Swap spacers and cutters if possible.
3. If nothing else works, a paper shim in the spindle/arbor interface may get things to run true and cut evenly. I thought that was a bubba idea but two different guys who definitely not bubbas told me it can bail you out. I was running 3-4" diameter form cutters and doing finish cuts, not big hogging stock removal cuts.
my 2 cents worth.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Good to map it while it is still mounted and tight, sharp zeros mark + and - highs and lows...Then break spacer stack lose and check it again -> That may suggest a bug in the assembly.
A bad spacer or chip between spacers can put a temporary bend in an arbor.
Inspect arbor between centers to prove arbor OD and mounting hub are good..

There are some arbor straightening threads here on PM, and arbor straightening services in the USA
 
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guythatbrews

Cast Iron
Joined
Dec 14, 2017
Location
MO, USA
Also do a very close inspection of the spindle taper. Chips could be mashed in there.

A good idea to check the arbor in vblocks to see if it is straight. Check the arbor taper too. Mark the arbor runout in the mill before you do this and see if anything makes sense.

Non-parallel spacers and dirt your worst enemies. Amazing how much a crooked spacer will eff stuff up.
 

WakelessFoil

Aluminum
Joined
Aug 18, 2020
Thank you all for the input. We don't have much experience operating horizontal mills.

We suspected that the spacers were not perfectly concentric with the arbor so we stripped them off, cleaned everything, and remounted the arbor. We took a RO reading just behind the front support. We got about 0.003" TRO.

Not bad considering the age of this machine and definitely an improvement over our initial readings on the spacers. Upon examining the taper attached to the arbor, we found a possible issue. The very base (largest dia.) appears to be very shiny while the rest of the taper is dull and scarred. Could this be indicative of an issue with the taper? Maybe someone ground the taper incorrectly? Could this likely be the cause of our RO of a few thou?

Thanks again for all the input!
-Justin
 

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boslab

Titanium
Joined
Jan 6, 2007
Location
wales.uk
I haven’t seen a straight horizontal mill arbour in, any years, they all come bent imho, I have 3, not straight, horizontal = brrm brrm brrm, standard operating condition, often the cutter is tiny off centre, they aren’t interference fits, just sliding so rarely concentric
Mark
 

M.B. Naegle

Titanium
Joined
Feb 7, 2011
Location
Conroe, TX USA
Can't really tell the fit from the shin of it, since both surfaces have an unknown history. I'd use blue Dykem ink (the stuff in the tube, not the spray or bottle stuff) to check the fit if it's a concern, but it sounds like your arbor and spindle are typical condition. If you need/want better, I think a brand new arbor would be the first step.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Arbor spacers are tricky to inspect because sometimes they are ground on the ends not quite perfect/square. On a day with nothing to do one might set the whole bunch each in a good V block and check the ends, good that they don't run out over .0002
 
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Jaxian

Hot Rolled
Joined
Feb 24, 2013
Location
Santa Cruz
I have had a few Cincinnati horizontals. They always make that thrumming sound. I assume all arbors are bent, or shims are off, or spacers. Just too much stuff that has to be perfect. I just touch off, call that zero and go. Play with the feeds and speeds to get a nice finish if you want but with that many teeth the cut will be fine dimensionaly.

I have two arbors that came with my most recent No.2 Cincinnati that I bet have never been used. I could check them to see how straight they are and how hard it is to keep them that way once set up. I do also have, no joke, a new in box arbor from Cincinnati. Never used, was ordered by a university, Ball or Bowling Green can't recall. That would be the one to test. If it's not perfect from them new then nothing is. Very cool looking custom printed box with all the Cincinnati logos and stuff on it. Circa 1966. Shipping filler was like shredded wood/tinder. I should post a picture at some point.
 

Mechanola

Stainless
Joined
Mar 21, 2011
Location
Äsch
For geometry’s sake you investigate the tool holder and spindle tapers, then the plain bearing in the counterarm, and lastly the arbor. This should be placed in a taper that meets the specifications of ISO 7388. The general tolerance for the 50 taper major diameter is five microns or two tenths (0.000196 in.) on both sides, combining mathematically to 0.0003136". There are precision ground test arbors.

Push-on cutters always run with a little runout unless you pay extra money for high-grade stuff. In that case you have a shorter arbor, else you won’t be able to bring the cutter in place and take it off.
 

Cannonmn

Stainless
Joined
Jun 25, 2016
“Wakeless” replaced cutter, put same spacers back, etc. and did another test run, and machine + arbor performance was ok, no more intermittent cutting.
 

Richard King

Diamond
Joined
Jul 12, 2005
Location
Cottage Grove, MN 55016
From the look of the cutter you were climb milling? Try it conventional milling. Climb milling on a worn machine will pull the work into the cutter as the lead screw and nut are loose. Lots of cutting oil or coolant. Also make sure the knee and saddle locks are on. Also check the table gib to be sure it's snug. I used to have a Cinc universal horz. with a swivel vertical head. It was a great mill. Also check the inside of the spindle taper if you suspect bad bearings. Also put the indicator on the end of the spindle and push it to and fro. It should not have any play.
 








 
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