I have a new project

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A friend owns a sheet metal shop and is constantly breaking nibbler bits. They aren't cheap and he goes through thousands of dollars each year. I promptly put my foot in my mouth. "I could make those bits for half that price." Suddenly, I have a new project.

This is a no stress, once a year, low volume task. I have equipment to manufacture the bits except for one item... a tool grinder. The first production run will pay for that. I'm looking for suggestions on machining and sharpening the bits. The best way to learn to swim is by getting in over your head. So, please feel free to tell me I'm ignorant. I probably am.

The bits are M2 HSS hardened to RC62. Cheaper versions are A2 steel and don't last. The bits are 1 3/4" long. Photos are posted. The raw material is 5/16" diameter M2 round stock (annealed). I plan to manually mill one bit at a time. I did say low volume production didn't I?

The holding fixture is two custom, 6" long V blocks which are bolted together, clamping the stock between them. The fixture is rectangular and held by the mill vise. That allows me to accurately roll the fixture and stock in 90 degree increments. The fixture is made, but not tested. About 2 1/2" of working stock will stick out of the fixture. I'm hoping the short length provides enough stiffness for milling. I'll modify the fixture to provide backing / support if needed. A few swipes with an end mill on the top, sides and bottom and I should be golden. I'm not sure if climb or conventional milling will be more appropriate for the side cuts. Climb milling produces more side pressure. Given the dangling nature of the piece, it may wiggle. What is you guys' experience with supporting and milling small diameter round stock?

The set screw hole is made with a combo drill bit. No sweat. Cut the bit to length (lathe or bandsaw), deburr, and it's ready for the muffle furnace.

M2 has to be hardened in an oxygen free environment. At high temperatures, oxygen bonds with the carbon in the steel making CO2 or CO. It sucks the carbon out of the steel. To prevent that, wrap the steel in stainless steel foil, double the seams and hammer them flat. Some people leave a piece of paper inside to suck up the last bit of oxygen. Bake the cookies.

Now I'm stuck. The hardened bits will need sharpened (flat ground). I'm considering buying a tool grinder. I've managed without one, but this is an opportunity to expand the tool collection. Enco has one for $250 (891-8106), Harbor Freight for $189 (46727). The HF will need reworked. Not sure about the Enco. Both are cheaply made. Does anyone have a better suggestion? Will the stock wheels suffice for grinding M2 at RC62 hardness? I'm not sure what wheels are on them.

This is not a big or sexy project, but putting money in my pocket does sound like fun. Plus I gain a grinder and a little machine time. Am I on the right track with all of this?

ShearBit2.jpg ShearBit1.jpg
 
I would try to find a small surface grinder if possible along with a bench grinder with a buffer pad on it. If you are patient you should be able to find a small surface grinder in the sub $500 range. I have bought 2 recently and am not too far from you so they do pop up from time to time.
 
HSS hardens at too high a temperature for any foil I know of. You need an inert gas oven. You might think about making the tools from D2,which is a high wear resistant tool steel used in exactly the application you are into here. However,you will not get the maximum performance out of D2 unless you can very accurately harden it within a 25º temperature range,let it cool until you can barely hold it for a few seconds in your hand,and put it into an accurately controlled oven at 400º to temper.

At least,you can use foil to harden it. I use a toaster oven with a Brownell's high temperature thermometer with a long probe on its back inserted into the oven. Do not rely on the built in thermometer. Professional hardeners often use the simple toaster oven with a decent thermometer.

I think you really have gotten into a tricky situation here. The only alternative without the right equipment is to grind them from pre hardened HSS blanks. Then,I think there's a hole to be drilled? I'd use straight flute carbide drills,but I don't know how long the carbide drills will last,if even for 1 hole. You could wear out wheels fast trying to grind that tool from round HSS rod.

I can't guarantee that D2 will be as good as HSS,but D2 is used in dies costing well into 6 figures. They can't use HSS for dies like D2 can be made into,so I guess that precludes HSS's use.

Try the D2 first and see how it does. Then,if no joy,you will need to get an inert gas furnace as well as your grinder. BTW,you'll need a tool and cutter grinder,not a simple double end carbide grinder. Frankly,I think you need to back out of this deal. Sorry. That's my advice and I'm a well experienced tool maker,retired.
 
We had that problem where I work tryed making bits from HSS D2 S7 nouthing lasted long. Then we got a larger nibler and solved that probleb. haven't broke a bit in two years .
 
i say go for it. whats the worse thing that can happen? you get a few new tools and some valuable experience. I agree with finding an older manual surface grinder. with all the new CNC crap out I have purchased two manual surface grinders for under $500 with about 20 wheels and holders. failure has taught me some very good things and big gains are rarely gotten without risk.

Roy
 
Thank you all for the replies and suggestions. George, I never retreat or back out. I just advance in the opposite direction. :)

I would love to have a surface grinder. I just haven’t had much need in the past. A tool and cutter grinder though, I could use. Lots of dull tooling laying around. This task is just one more reason to get one.

D2 steel is often used for punches and dies, but it losses hardness at high temperatures. It makes crappy drill and shear bits. I looked at a bunch of HSS options and talked with several engineers who deal with tool steel daily. It always came back to M2.

The Austenitizing temperature of M2 is 2050 to 2200 F. Maximum hardness is achieved between 2150 and 2200 F. Different steel manufacturers show different curves, but in general 2050 to 2200 F should give RC58 to RC65.

http://www.crucible.com/eselector/general/generalpart2.html

Stainless steel foil (#309) is good up to 2240 F. Knife makers use it for M2 all the time. No need for an inert gas oven. Hardening shouldn’t be a problem. Famous last words. :shark:

http://www.stainlesssteeltoolwrap.com/

This is a 10 gauge nibbler and I’m not sure they make a bigger one. The real plan is to build a 5x10 CNC plasma cutter table that will eliminate the problem entirely. That’s my spring time project. For right now, it’s time to make shear bits.

Does anyone have experience with the Enco grinder? Does it need reworked like the HF model? I’m starting to lean toward a used grinder in a quality brand.

Thanks again and keep those suggestions coming.
 
2 advices after 20 years in tooling, go for a universal grinder and sharpen the cutting surface on a 7 degree angle, v shaped if no pulling is allowed on the sheet....your friend will love how quiet the press runs and would like you to do this to all punches. The hit stress will diminish too, punches will stop breaking. A third will be to coat them with XADC or TiAlN.
:thinking:
 
Now we're talkin'. I hadn't considered a universal grinder, but it may be just what I need shop wise and task wise. I've never used one. I'll definitely look into it further. Thanks.

Syaminab, what do you mean by "v shaped"? The current cutting surfaces are flat on all sides. The leading edge and sides do the cutting. I'm assuming you mean to bring the tip to more of a point by tapering the leading edge and sides by 7 degrees (see sketch). That would allow the metal drag to gradually increase as the bit goes through the sheet. Is that correct?

BitTaper.jpg
 
McMaster sells stainless steel foil bags. I did a pocket knife last year out of D2 and tempered with the bags. Very nice, and you only need to worry about sealing one seam. Small strip of paper in the bag and a tight seal, and the parts came out bright and shiny. Never done M2, but for D2, you nead at least 2 tempers for maximum toughness, and 3 is preferred. I think this is common for chromium steels, not sure M2 falls into that category.

I have never machined HSS in hardened or annealed state, so I can't speak much to that. D2 machined easily with carbide. Needed diamond stones to get a good edge after hardening.

If you have the space, the surface grinder is probably more versatile than a T+C grinder. T+C is easier to store though. I have little free room, so I would probably go with the T+C.
 
I have got bought some grinders recently for the home hobby shop. Norton 6" x 32" Cylindrical, Landis Universal cylindrical, Cincinnati #2 cutter, Cincinnati Monoset, Kao Ming cutter and two surface grinders. I'm still wondering how I ended up with all these but thats another story. I am not too far from you so If you need me to grind the prototypes for you just send them over. I'd have to charge you $free.99 per pc though.
 
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