"Reverse Boring" (Horizontal Mill) Sanity Check Requested

[mattthemuppet2]

Funny, I was just typing that I'm going to try 32.50 CCGT/CCGX inserts and reducing the stick out next. I don't remember who recommended them to me first (may have been you actually) but they're handy to have. I was actually turning some 7075 aluminum to make an outboard spindle spider for my Sheldon over the weekend and was shocked at the finish I was getting.

Might have been me, but there are several others that recommend them too. They last pretty well if you don't get to greedy with the DOC and feed.

I was playing around yesterday rough turning a piece of alu (6061 most likely) at 35 thou DOC, 500 rpm @3" diameter and feed as hard as I could without causing the belts to slip =
I needed to wear a hat, those were going everywhere, even with the chip guard (off, on right)!

It would cut at 50thou but I couldn't feed fast enough to break a chip without stalling the lathe, so got nasty ribbons instead. Shallower cuts with the same feed produces the long spirals you can see at the back

 

[G-ManBart]

Is the arbor Morse or Brown & Sharpe? You can tell with a couple quick measurements

Dimensions of Standard Tapers

This page give the dimensions of Morse, Jacobs, Brown & Sharpe, and Jarno tapers.

littlemachineshop.com

Is an NMTB 50 to 'whatever the arbor is' an option? Seems much easier than trying to turn down that hardened German arbor.

50 NMTB Adapter to Brown and Sharpe 9 Taper | eBay

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I'm not sure what the taper is right now, but I'll take some measurements. I know it's 1.5" +/- a touch at the big end since I had to know that to pick an end mill holder. It's a long taper, so at least 6" and has no provisions for dogs...just a tapered section that is threaded for a draw bar.

NMTB to X isn't a great option. If the taper goes into an NMTB holder it would lose a lot of prime work area. Normally usable arbor starts just forward of the dogs. With the end mill holder I lose about two inches for the end mill holder section, then maybe another inch to get to usable arbor, so around 3" lost. If the arbor is mounted to an NMTB holder I'd have a couple of inches lost to the holder and then another 4" or so lost to the long taper, so 6-7" lost in prime work space.

If I go with turning the arbor I'm going to have to shorten it quite a bit. The end mill holder only has about a 2" deep bore so I'd really only be turning a 2" long section and max going from 1.5" to 1.25". I think I could anneal the tapered portion if necessary...much like doing a differential heat treat on a blade.

 

[Mill Lee farm]

I'm not sure what the taper is right now, but I'll take some measurements. I know it's 1.5" +/- a touch at the big end since I had to know that to pick an end mill holder. It's a long taper, so at least 6" and has no provisions for dogs...just a tapered section that is threaded for a draw bar.

Sounds like maybe BS-11 taper? Most (but not all) BS arbors I've seen don't have dogs. They just use the taper. In fact, most don't need a drawbar (from what I've been told). I know my BS-10 taper arbor did not use a drawbar when I picked it up. Took some solid whacks to get it loose! (of course some sort of sturdy drawbar would make removal easier and safer)

Could possibly be a Jarno #12?....

I understand about losing work envelope. My arbors have 1-1/2 to 2 foot of cutter bar so I was just figuring you would have enough room to move out 6"-8".

Also, I'm not trying to talk you out of it! I just thought I'd throw it out there in case it hadn't occurred to you.

 

[Mill Lee farm]

OK... thought experiment here... I'm looking at the NMTB50 dimensions.
Is there not enough room to have most of a BS-11 taper in one? Especially if you went all the way to the rear and used a new drawbar that grabs the BS taper instead of the NMTB50? Just thinking out loud here...

 

[Mill Lee farm]

BS-9 seems to leave a lot of room left. BS-11 is a good bit bigger but it seems reasonable? Am I just ignorant?
Of course finding one is the issue.... or making one and getting both tapers right?!?

Adapter, 50 NMTB, 50 NMTB to Brown & Sharpe #9 BS

Cincinnati 50 NMTB to B&S #9 Adapter

lostcreekmachine.com

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[G-ManBart]

Sounds like maybe BS-11 taper? Most (but not all) BS arbors I've seen don't have dogs. They just use the taper. In fact, most don't need a drawbar (from what I've been told). I know my BS-10 taper arbor did not use a drawbar when I picked it up. Took some solid whacks to get it loose! (of course some sort of sturdy drawbar would make removal easier and safer)

Could possibly be a Jarno #12?....

I understand about losing work envelope. My arbors have 1-1/2 to 2 foot of cutter bar so I was just figuring you would have enough room to move out 6"-8".

Also, I'm not trying to talk you out of it! I just thought I'd throw it out there in case it hadn't occurred to you.

I think BS-11 or Jarno #12 are the most likely going off the specs....I'm going to take a few more measurements tonight just out of curiosity.

I don't think losing 6" would be the worst thing ever, but it would also push out the arbor further so the supports would have to be pretty far forward. Going off memory it has 22" of cutter area, so add some for the nut, plus the taper/adapter/etc and it probably would be something like 30+ inches...so long, but within range for the machine.

I've searched through NMTB 50 adapters on eBay and Lost Creek and haven't seen anything I think would be a direct fit.

If the German arbor is too hard to turn I have a DuMore tool post grinder that would probably be better in every way except for mess and cleanup. If I can't turn it, and don't want to grind it, I already have some 1144 stress proof I can use to make an arbor that would fit the end mill adapter. I'd be able to use the spacers, running bushings and nut from the German arbor and still be ahead financially. I was originally going to make the arbor and spacers (and probably buy a new running bushing) until i found the German arbor.

Decisions, decisions!

 

[pontiac428]

My reason for purchasing EM holders is I can't bore/grind a perfectly parallel-walled bore. Let those ops be done on the right equipment for centerless cylinder grinding. Even with a carbide bar, there will be taper. The difference is worth paying for, even if it's a Chinese approximation of a parallel hole- it's probably better than I can do on a lathe. In tool holding, we're talking about a much higher level of precision than general machining- 10x-50x finer work is needed to pass.

 

[G-ManBart]

BS-9 seems to leave a lot of room left. BS-11 is a good bit bigger but it seems reasonable? Am I just ignorant?
Of course finding one is the issue.... or making one and getting both tapers right?!?

I did some measuring and I think it's BS-11. The ground tapered section is 6.5" long. At the big end it's 1.530" and at the small end it's 1.260". My guess is if I measure in a quarter of an inch from each end it would match the 1.4978" and 1.250" listed for BS-11. I didn't think to check the thread for the draw bar, but I will....if it's BS-11 it should be 5/8-11.

 

[G-ManBart]

My reason for purchasing EM holders is I can't bore/grind a perfectly parallel-walled bore. Let those ops be done on the right equipment for centerless cylinder grinding. Even with a carbide bar, there will be taper. The difference is worth paying for, even if it's a Chinese approximation of a parallel hole- it's probably better than I can do on a lathe. In tool holding, we're talking about a much higher level of precision than general machining- 10x-50x finer work is needed to pass.

I won't argue that a bit. I just figured the bore is fairly shallow, and the end mill holder was cheap, so it was worth a shot. If I can't get a decent bore on the end mill holder I won't progress to working on the arbor. I can always buy a 1.25" diameter end mill holder if needed.

 

[G-ManBart]

Slight update: I moved things around and shortened up the boring bar quite a bit (at least an inch). I also switched to a CCGT 32.50 (1/128" radius) insert. I only had time to make two passes, but I got actual chips this time....still small, but chips rather than dust/sludge. I made a cleanup pass then another pass .010 DOC and there was still a bit of deflection through the hard spot (what I'm calling it for now) but nowhere near as bad, and the amount of taper is way, way better. I'm going to measure it with a telescoping gauge to get real number, but using calipers it seemed pretty straight going back about half way.

I'm going to make a few more passes this weekend and see if it continues to get better. If not, I'm probably going to wait until the CBN inserts show up. I'm still considering annealing the nose of the holder....submerge it in oil up to the flange and then heat it with an oxygen-acetylene torch. I already have a fair amount of experience heat treating and annealing tool steel with that method, so I think I can pull it off without turning it into a pretzel.