I've a used 1/2" MT2 end mill holder that I'd like to bore out to 3/4". The problem is that the holder seems to be hardened throughout. A small file won't scratch the bore of the holder. It seems that my options would be to bore it out as-is with carbide or anneal it and bore. I suspect that grinding would take forever and am not real thrilled with the idea of grinding on the lathe, though I do have a decent toolpost grinder.
For annealing, I have available a toaster oven (500 °F) or gas barbecue, a propane torch, or a 1-hour round trip to a friend with a small heat treating oven. If scale is likely to be a problem with annealing, what is the best way to deal with that? I don't much care about the appearance of the end mill holder end, but don't want to screw up the MT2 end.
Does anyone have any thoughts on the best approach?
I'm not familiar with that particular holder, Mike, but I'd be cautious about opening it up for a larger shank unless the exterior is fairly large diameter. If it compares favorably with the typical 3/4" holder, I wouldn't hesitate, but it could prove a mistake if you put it to work with a slender body. Screws may not hold, and it may offer chatter that a more robust one wouldn't. I'm assuming it looks similar to a cat 30,40 or 50 holder.
Assuming there's no good reason to not open it up, the first thing you need to determine is if it is hardened through. It may be induction hardened, which often controls heat treat depth. If that be the case, you may get through the hard layer and it will machine better, although you would then be faced with a soft interior when finished. Regardless of how hard it may be, I think I'd hesitate to anneal it in any way, not being able to control where to stop, and scaling.
Grinding the size larger would be the ideal way to go, assuming it is hardened, and it wouldn't be much of a job on a proper internal grinder, where you have more power and rigidity and can keep the thing cool while grinding. If push gets to shove and you can't do it otherwise, you may be able to bore near finish size, then grind for size and finish. Carbide should cut it, even if it's in the low 60's, Rc scale. I'm not suggesting it would be easy, just possible. One thought could be using a carbide end mill held in your toolpost, not the tailstock. Just a thought.
I'll gladly buy one, but no one seems to make Morse Taper 2 end mill holders for 3/4" shanks any more. Someone (the VersaMill guy?) once offered to make a few specials in that size but ISTR that he needed to get around $200 each in small quantities just to break even. That's a bit over my tool budget.
Mike, I can only speak to the annealing question, Harold gives excellent advise as to the other considerations. He and others also cautioned me about annealing a MT2/J33 adapter so that I could remove the tang and drill and tap for a drawbar for use on my Clausing 8520 mill. I never heat treated the adapter after finishing it and it seems to be holding up well under my light use. I annealed as follows:
I put the adapter in a piece of copper pipe with one end pinched off and the other sealed with a brass plug. Put the whole thing into a charcoal fire and let it burn until the coarcoal was gone. Perhaps an hour total burn time as I added charcoal at one point. Fished it out when cool and it had turned a nice blue-grey color and was well annealed. There was virtually no scale except where air had leaked in a little at the crimped end of the pipe. I finished drilling and tapping and can now use my new Rohm chuck. I haven't tried to reharden and temper it as it seems to work well as it is. For my hobby use I doubt it will matter. YMMV. If I had thought of it at the time I'd have put some paper in the pipe with the adapter to burn up the oxygen in the pipe. Better yet would have been to seal the pipe better in the first place.
I would avoid annealing and the potential of scale ruining the MT2. My approach would be to try tempering it back to about 600 degrees F (pale blue) and then bore it out with a carbide tool. If you try this, let us know if this works.
The MT2 is Morse Taper #2, which is the spindle taper on my Clausing 8520 mill. You probably know what that is, but if not the shank that fits into the spindle tapers from around 0.7" to 0.59" over a length of about 2.5" and is internally threaded for a 3/8-16 drawbar.
The tool shank end of the holder is 1-1/4" OD by 2", so the OD would leave a
1/4" wall for the set screw after boring it out to 3/4" ID. Possible applications include a Rotary Tech carbide insert flycutter and a Tree boring head, both of which have 3/4" shanks. The mill is a bit beefier than the import benchtop mills, but no where near as stout as a Bridgeport, so I figure that fairly light cuts would be required in any case and that 1/4" wall for the set screw won't be a problem in that sort of duty. That could be wrong but I'll only be out the cost of the EM holder and the time to "adjust" it. Please let me know if that analysis is likely to cause problems to the mill.
Is there an easy way to tell if the hardening is through the part or not? Annealing doesn't really appeal to me. The holder end has a lot more mass than the spindle arbor end so I suspect that it would be tough to use a torch to anneal just the EM end without affect the spindle end. A Clausing
5914 (12" lathe) would be used to bore it out with the MT2 arbor inside a MT2-MT3 sleeve and that inside an MT4-1/2 to MT3 sleeve. All of the adapters are in good shape with no corrosion, dings, or galling. I'd rig up a drawbar to help prevent any of that from slipping. The number of adapters needed does have me a little concerned though.
What sort of cut(s) should be taken if boring with carbide? The 1/2" ID of the holder has about a 0.050" chamfer so I assume that a first pass should have at least that much DOC to get it started properly. I also seem to recall that carbide likes healthy cuts and that sneaking up on a dimension doesn't work very well.
Grinding it out myself with a tool post grinder really doesn't appeal to me as I don't like the idea of all that grinding diust flying around, even with proper precaustions. If that's the best choice it might be better to find a local shop that can do it.
That has to do with the ability of an MT2 (a small taper) to resist spinning at the torque a 3/4" shank bit might put on the holder. Even with a tanged holder it might spin a few degrees before the tang stops it; you're likely to nasty-up the socket with too small a holder. It's not NICE to bugger up a taper socket! (bad machine operator! BAD machine operator!)
MSC lists 3/4" holders in MT3. Their MT2s go up to 5/8 shank, only.
I gather that you think a 3/4" end mill holder will put too much torque on the MT2 spindle. My primary application would be for occassional fly cutting of aluminum with a 3" insert fly cutter with modest DOC. Is that too much to expect?.
That's what I wondered about. That's a relatively thin wall, and is likely the fly in the ointment, but that doesn't mean you can't do it. Possible future problems would include thread failure because of the thin wall and the amount of torque you may need to prevent end mill slipping, but on a light duty machine as you've described, it may not be a problem. Assuming there are no 3/4" adapters available, I'd think that's an indicator that you're bordering on a bad setup, but Bridgeport also stopped at 3/4" for R8 collets, but the aftermarket supplied the size. With care, they work fine, as would your modified adapter.
I'm having a hard time thinking of how it could affect the mill, the only scenario being that the less than rigid enough adapter might spring enough to cause a crash, but that's a risk we take anyway, especially on light duty machines. In my opinion, so long as you worked within the capacity of the machine and didn't crowd it, there's no reason it wouldn't work It's just a matter of how long it might last once modified, and how much chatter you're willing to tolerate. We all have to accept some on these small machines, Bridgeport included. I hear the smart guys talking about the fact that steel is the same where deflection is concerned, heat treated or not, but the fact that tensile increases with heat treat tells me that hard is better than soft, requiring more effort to deflect. Maybe I don't understand how it works.
I'm not aware of any simple indicator, Mike, but reading the response about annealing an adapter, plus thinking about my post after making it, I can't help but wonder if you might have success annealing only the end. If you submerse the shank in water, securely, and heat the end with a torch, it would prevent scaling and annealing the part you'd like to protect, and soften the part that needs modifying. The transition zone could be trouble, but you maybe could have that just behind the area needing modification. Overall I don't like the idea, but that doesn't mean it wouldn't work. I'd also consider the idea of drawing it back at 600°, which, if it's high carbon steel, should make it soft enough to machine, and still retain a trace of hardness, with no scaling. It's not anything I've tried before, but sounds good.
I recommended the use of an end mill to start opening the bore because it could be a real bitch with a boring tool, if nothing else, because of the interrupted cut. The starting diameter limits the size of a bar so much that it would be quite slender, so I'm not convinced you'd have great luck while it's still in the heat treated state. Once you had it roughed and the bore was considerably larger, you may be able to change to a boring bar and achieve size, but if it's hard through, it isn't likely to cut well enough. All depends on how hard it is. If it's 50Rc or under, no big deal.
I share your concern where the multiple adapters get involved. You're at the mercy of several things beyond your control. Could turn out fine, maybe not. If I had the job to grind, I'd want to be able to dial it in instead of trust multiple adapters.
If you haven't ever tried machining something hard, I suggest you tackle a dowel pin. Once you see how they respond, it will snap right into focus. Hard stuff often will cut OK for a moment, but tip failure usually causes a rapid cascade to the point your tool goes from cutting to broken in a very short interval. When material is (very) hard, you have to rule out healthy cuts, too. The material doesn't cooperate, it breaks your tool instead. I'm assuming you have nothing at your disposal than typical carbide. Iscar sells tools that are capable of machining hard things, but it's a real good idea to have rigid machines with proper spindle speeds. Light duty machines are likely to disappoint.
I'd probably feel the same way, Mike. That's a lot of grinding to do dry, and I'm not convinced you'd have good luck, anyway. Internal grinding on a blind hole takes a little skill if you expect a straight bore. Grinders are adjustable, lathes are not. Grinders run coolant, on a lathe it would be a mistake, even though it would help tremendously....
Chuckle! Just had a thought, Mike. What a great excuse to buy a nice Heald internal grinder!
For the tool manufacturers, apparently yes.........'modest cuts" no......"very light".....perhaps......realize that many shops would fire your butt due to the hazard and possible liability....
But since you seem so determined, why not just turn the shank down on your flycutter, or maybe even make up a new flycutter--one that actually 'fits' the holder you already got ???
My budget (financial and space) is a little tighter than that would allow.
I wimped out and ordered a 3/4" EM holder from JTS following email from a kind lurker. I'd be inclined to try carbide on the 1/2" holder anyway, just for the experience, but there is a full weekend of work planned anyway.
I would buy a blank MT2 arbour (actually I keep a stock of them for similar emergencies). The I would turn the end down to 1/2", bore a bit of 1 1/4" bar
1/2" and braze or Loctite 603 it onto the arbour. Then I would bore the resulting assembly to 3/4" and fit the lock screw. I'd keep the 1/2" holder, or sell it if it was a spare.
You can order one from JTS Machinery in Ohio for $20.00, and take 10% off every Tuesday for a final cost of $18.00. The part number is MT2-34, their phone number is (800) 321-3566. I'm picking up an MT-3 end mill holder for a
1" shank, they are the only source for them also. Be sure and get their catalog.
I don't know, Tim, my Shoptask's milling spindle is MT3 and I run 1 1/4" multi-flute end mills and 1 1/2" indexable carbide end mills in mild steel without any trace of a problem. They have 5/8" and 3/4" shanks respectively. Lovely cuts. I would think a 3/4" cutter width would work in an MT2 holder. I did manage to stop the 1 1/4" once, but that was because I didn't snug it up enough.
I now do most of my heavy cutting with M-42 cobalt roughing/finishing cutters from Production Tool (page 182 of their 2005 catalog). The staggered teeth give low chip loads and the wide flats in between the teeth produce a nice smooth finish. Man, they just run through steel and iron with a neat buzzing sound.
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