#40 NMTB mill arbor

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earlgo
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Joined: Sat Jan 29, 2011 11:38 am
Location: NE Ohio

#40 NMTB mill arbor

Post by earlgo »

Recently a new Polish Made mill arbor followed me home. It is a #40 NMTB 1.25 dia arbor with keys and spacers. I thought it looked odd when I bought it but took it anyway. When I got home I realized it was 18" long from the outboard face of the flange to the outboard end of the threads. The end pilot is 0.718 diameter. The arbor is too long to be used on my small horizontal mill which uses 12" long arbors. I set it up anyway to see if it could be used and discovered that the overarm was too short, too. Right now the arbor has about an hour's use.
I am willing to trade this 18" long 1.25 dia arbor for a 12" long 1.25 dia arbor, if any one has one in good shape and is willing to trade.
Arbor Tag
Arbor Tag
Arbor in box
Arbor in box
Please PM me.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
Russ Hanscom
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Joined: Wed Mar 15, 2006 11:10 pm
Location: Farmington, NM

Re: #40 NMTB mill arbor

Post by Russ Hanscom »

What about putting the running bushing at 12" and letting the remainder just hang out?
pete
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Re: #40 NMTB mill arbor

Post by pete »

Afaik Russ that won't work, there's generally a reduced ground area on the arbor end that runs in the bushing. The picture seems to indicate that's true for this one as well. It probably could be shortened if it's not too hard and a new plain end turned as well as new threads added for the tightening nut. There doesn't seem to be many here with horizontal mills Earl, you might get lucky but a post on the PM forum here https://www.practicalmachinist.com/vb/t ... or-wanted/ might get more results?
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rklopp
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Re: #40 NMTB mill arbor

Post by rklopp »

Russ Hanscom wrote:What about putting the running bushing at 12" and letting the remainder just hang out?
That’s how I run my arbor. I do have to be careful around the rotating shaft sticking out. You likely will find that the arbor is harder than the hubs of Hades, so not amenable to easy shortening. BTDT, have video of orange-hot lathe chips to prove it. I annealed one to allow it to be machined into a boring bar, but it warped enough to ruin it for use as an arbor any more. It was fine as a boring bar.


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earlgo
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Location: NE Ohio

Re: #40 NMTB mill arbor

Post by earlgo »

Thanks fellows. Pete is right about the end bushing. Here are pics of the problem.
18 in arbor
18 in arbor
12 in arbor
12 in arbor
I discussed cutting this shorter with a machinist friend and he was not enthusiastic about threading the hard arbor and he doesn't have a thread grinder. We thought it might be easier to fill the keyway before threading but that still doesn't reduce the hardness of the rest of the arbor, but it would stop the interrupted cut.
He suggested I look for a trade instead.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
Ken Schroeder
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Location: Gardnerville, NV

Re: #40 NMTB mill arbor

Post by Ken Schroeder »

I bought a Cat40 arbor for my horizontal mill that I cut down. It was case hardened and once I got through the hard layer I was able to turn it down and single point the threads for the running bushing.
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liveaboard
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Re: #40 NMTB mill arbor

Post by liveaboard »

I did that too.
I bought a box full of 1" cutters for cheap on ebay, so I bought a 1" arbor to carry them, but it was too long.
And I needed a different bushing that I had to make too.
There was nothing particularly difficult, just paying extra attention to concentricity.
I use carbide thread cutting inserts for single point threading.

The newly threaded section is within the key slot zone, this caused no trouble.
It's actually still a little too long, I cut off the minimum amount instead of the optimum amount.
horizontal milling.jpg
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