Horizontal milling arbor modification?

[ISEN AG]

Have a Bridgeport with a Erickson 30 spindle and use a nmtb 30 1” stub arbor every once in awhile for various projects. I would like to add similar stub arbors in 7/8” & 1-1/4” but these simply do not exist or are prohibitively expensive for a home workshop. I do see standard length horizontal arbors from European manufacturers for reasonable prices and was wondering if there were any drawback to purchasing one of these standard length arbors and machining them down to 2-3” for my purposes?

Has anyone ever modified a horizontal milling arbor in this way? Are there any problems/obstacles I’m not seeing in going this route?

 

[crickets]

I think the main caveat is about hardening. Not necessarily in terms of machining difficulty, because usually they aren't hardened beyond of carbide cutter limits (and even then you can go with CBN). I am mostly thinking some could be just case hardened, and machining down will expose softer parts and potential stress issues that can cause for the thing to deform some. If you have a grinder, you can likely correct the last problem.

Check out this related video :
Modifying the shank of a boring head - Abdrehen eines Ausdrehkopfes - YouTube

 

[rklopp]

I tried modifying a 1-1/4" NMTB40 arbor to make a stiff boring bar with long reach. I needed to turn it down to about 1-1/8" and I suffered. The keyway was the problem. The interrupted cut killed whatever inserts I threw at it. I ended up annealing the thing. I probably could have gotten away with it if the keyway weren't there.

 

[Bill D]

Would filling the keyway with something like solder or jb weld help. Then burn it out when done machining?

 

[Greg Menke]

I bought a ebay cheapie import 40-taper shell end-mill arbor, turned and threaded it to take BS#21 collets - it was pretty hard going until I could dig through the outer surface, inside was a lot more machinable. I bought some for-realsies $ inserts for the job, inexpensive ones couldn't take the interrupted cut or the hardness.

I wouldn't try turning down a full length horizontal mill arbor without a follower rest and a convincingly good setup. If such an arbor cuts as hard as my shell end-mill arbor did I doubt something soft like solder/jb weld would do much in the keyway until you're past the case. OTOH if filling the keyway helps it run smoothly in the follower then it might be a win.

 

[crickets]

I would either [Tig] braze or Tig weld the keyway. Another option is just to go straight to a tool post grinder and... keep grinding the thing

Also carbide may take a bit more interrupted beating when it's not as sharp. Brazed carbide cutters may be better suitable for this - just touch up the tip on the diamond wheel for a more liberal radius.

 

[neanderthal mach]

European sourced probably or almost for sure means metric for the draw bar threads. That may or may not be important to you. I'm vertically challenged in my home shop and just changing a draw bar to a metric version would mean tilting the head and dialing it back in. So it's just a detail I make sure to check before buying.

 

[ISEN AG]

To provide a bit more clarification on what I am looking to do. I have found both a 7/8” & 1-1/4” diameter arbors both with roughly 12” of arbor length on each of them. I would like to buy the correct diameter arbors, cut them to the length I need, then machine a new threaded portion for the nut.

I figure a chop saw will make simple work of cutting off the extra length i dont need & I am only looking at machining roughly maybe an inch to re thread the new end of the arbor. Might go through a few inserts for that inch but nothing like turning the entire shaft.

Another question I had was would the current key ways be too deep to machine the new threaded portion for the end nut?

 

[Ray Behner]

I don't see why the key cut would care if it had some threading done to it. Yup, interrupted cut, but a couple resharps on HS or a couple corners on an insert should do it. If you do consider welding the key cut, please re-consider. There will be a "HAZ" (heat affected zone) . The welding will have drawn considerable carbon to the area. Very hard! Or make a smaller nut.

 

[wood2steel]

ISEN AG,
Was curious if that occasional milling project would require more stability than you could achieve with a nmtb 30 ER collet arbor; you could possibly machine whatever reduced shank diameter stub shaft with key slot and threaded end and hold it in place with the largest collet available for 30 taper arbor.
It does sounds like a weak configuration, but you would have to be the judge based on your proj needs. Just throwing some ideas out there----

 

[4GSR]

I have a couple of "made in Poland" horizontal mill arbors. They are case harden on the shank end. The arbor end is hard but machineable. At lease a file will cut the surface. If this helps you any. Ken

Oh, they do have inch draw bar threads in them.

 

[ISEN AG]

ISEN AG,
Was curious if that occasional milling project would require more stability than you could achieve with a nmtb 30 ER collet arbor; you could possibly machine whatever reduced shank diameter stub shaft with key slot and threaded end and hold it in place with the largest collet available for 30 taper arbor.
It does sounds like a weak configuration, but you would have to be the judge based on your proj needs. Just throwing some ideas out there----

Rigidity is the reason. In all honesty I could probably get away with home made shanks but If I can get 30 taper stuff cheap enough then I thought it was worth looking into if a project like this was even possible or if the arbors were just to hard to machine to justify.

 

[Shaybuilder]

Should not be a problem. I cut a 1" cat 40 arbor down for my mill and it was easy. The arbor was case hardened so it didn't take to much to get through the case and single point the thread.

 

[wood2steel]

I know there are a few 40 taper mill arbors here; will check this week to see if any 30 taper were left in the mix.