1. We have switched to XenForo forum software. If you are having trouble accessing the site, please email support@hobby-machinist.com and we will get you fixed up ASAP!

Tool Grinding...How'd I Do?

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by pburns, Feb 1, 2013.

  1. pburns

    pburns New Member

    Likes Received:
    0
    Trophy Points:
    0
    City:
    FLAGSTAFF
    State:
    Arizona
    Here are some pictures of my first attempt at tool grinding. I'm pretty new to machining and I have never ground a tool before today. I don't have anyone to ask on how well I did or on what mistakes I made and/or corrections to make so I thought I would ask you all? I tried to follow these four steps


    1. Grind the end relief
    2. Grind the left side relief
    3. Grind the tip rake
    4. Round the tip

    My first attempt was to create a rounded tip tool...see pics. My second attempt was to create a sharp pointed tip and my third attempt was to make a cut off tool. All tools were created using HSS bits. I tried all three tools on some 1 inch round aluminium. They all cut pretty well, nice smooth finish with the round tip and good facing with the sharp point. My only problem came with the cut off tool. It seemed to work ok, but it would leave a very small raised section on the inside top piece that was cut off, also it would leave a slight hump on the inside of the cut off piece. Let me know what you think. Thanks

    Patrick
     

    Attached Files:

  2. Ray C

    Ray C Moderator Staff Member Supporter Moderator

    Likes Received:
    3
    Trophy Points:
    0
    City:
    Crofton
    State:
    Maryland
    Very nice! They will cut well.

    Hope you don't mind but, I'd like to pass along a tip... When you have to do deep grinds, there's a tendency for the metal to discolor. This is a sign the metal is annealing which will make it a softer. Tip #1. blanks with a little cobalt (2 to 5%) are less prone to this and cuts just as well (if not better) than normal HSS. Tip #2, get a cup heavily loaded with ice water next to your grinder and chill the bit till it's cold before making any grind. When doing the grinds, leave a little water on the bit and as soon as you see it start to evaporate (just shy of 212 degrees) dunk it in the cold ice water until it's completely cold again. HSS starts to anneal around 300 degrees so watching the water evaporate is a good sign of the temperature. Those levels of hot/cold swings will not impact the natural hardness in the least.

    Ray
     
  3. DMS

    DMS Active Members Active Member

    Likes Received:
    3
    Trophy Points:
    38
    City:
    Santa Clara
    State:
    California
    The turning tool looks pretty good to me. Don't know much about grinding cuttoff tools as I have never had to patience to do it myself ;)
     
  4. rgray

    rgray Active Members Supporter Active Member

    Likes Received:
    3
    Trophy Points:
    18
    City:
    Helena
    State:
    Montana
    Looks good. On the cutoff tool if you mean the little tit that remains on the completion of the cut....I read (on this forum) that the tip of the cutoff tool can be angled to control witch piece the tit ends up on either the part in the chuck or the cut off part. I haven't tried this myself but it sounded like it made perfect sense.
    As far as the rounding I'm wondering if the tool is slightly wider towards the base..as you cut if you see cuttings coming off the side of the tool then narrow the tool behind the tip.
    If not cutting straight in the same thing will happen...again look for cuttings coming off the side of the tool..may have to slow the speed down to see it happen and get a good light on the subject.

    Russ
     
  5. Hawkeye

    Hawkeye Active Members Supporter Active Member

    Likes Received:
    5
    Trophy Points:
    38
    City:
    Kelowna
    State:
    British Columbia
    Good start on the grinding. If you can find a small diamond hone, your final step will be to lay the cutting edge on it and take out the grinder marks. Just a short section right at the cutting edge, top and sides. It makes the working part really sharp and only takes a few rubs to do it. You'll get better cuts and finishes, and the edge will last longer.

    You can see the shiny areas from the hone. The grinder hollow is no problem. The bit is sitting on the hone, so you can see how fine the grit is.
    P2020775a.jpg
     
  6. Tom Griffin

    Tom Griffin Active Members Active Member

    Likes Received:
    0
    Trophy Points:
    0
    Good start! It definitely looks like you are on the right track.

    A few things you may want to consider:


    • Watch the size of the radius on the turning tool, unless you need that large a radius for a specific purpose. Large radii greatly increase the chance of chatter but contribute little to surface finish. A 1/32" radius would be appropriate for a tool like that.
    • The sides of your parting tool should taper slightly. If they are parallel, there will be too much drag and the tool may bind in the slot and break.
    • Stoning the cutting edges will give you a better surface finish and create less heat, which will make your tools last longer.

    Now all you need to do is practice to develop your skill. One of the hardest parts of hand grinding is laying the tool back on the wheel in the same position after you take a peek at it. A good way to do that is to watch the sparks. They will tell you when the tool is aligned with the wheel and when they start going over the top of the tool, when it is flat on the wheel. Keep your wheel dressed and use the entire face of the wheel when you grind, don't just hold it in one place. And as has already been mentioned, keep it cool!

    Tom
     
  7. george wilson

    george wilson Global Moderator Staff Member Global Moderator Supporter

    Likes Received:
    10
    Trophy Points:
    38
    City:
    Williamsburg
    State:
    Virginia
    Sorry,it is a BAD idea to quench HSS in real cold water. Some don't quench it at all because it may cause small cracks since it is an air cooling steel,meaning it hardens when cooled real slowly. Quenching it in water would best be done at room temperature at best.

    Personally,I have not cracked a HSS lathe tool dipping it in water,but I dip quickly,take it out,and dip again. Plus,I don't let the bit get REAL hot to begin with,to avoid cracking in the quench. I'm saying I know how to quench at the grinder,by cooling HSS a little slowly.

    Cooling ANY tool steel in ice cold water,even water hardening tool steel,is a bad idea as it causes too much shock,inducing warping and possible cracking. Old blacksmiths would start their cold mornings by heating up a steel bar good and hot and putting it into the quenching tub(slack tub) to take the chill off the water.

    There is NO trouble letting HSS get blue when grinding. It is TEMPERED at at least 1000º(lots of different HSS's here),which is a good red heat. HSS will still cut while being heated orange with an acetylene torch in a lathe. This was an old advertising piece years ago:"Red hot and still cutting". I think South Bend ran this picture of the torch heating the bit as it cut.

    If you want to make cut offs leaving no teat on the workpiece,grind a slight angle so that in use,the side of the cut off tool cutting the workpiece is slightly longer than the side cutting the parent metal. The cut off tool must be exactly at center height to work properly in any case. After you make your first cut off,you can carefully adjust tool height so that when you advance the cutoff tool,it completely cuts away the teat left on the parent metal. Then,the cutoff will leave no teat on what you're cutting off. If you have an a loris type tool post,it is a big advantage to leave a cutoff tool properly adjusted for height in one of the tool holders. As mentioned,grind clearance on the sides and front of the cut off tool. If you don't grind the sides,the cutoff tool may cut sideways,leaving a cut off that is not straight in. It finds the path of least resistance.

    A cutting tool with that large a radius,as stated,will be very prone to chattering unless you are using it for very light,finishing cuts on a decently rigid lathe. If you are using a fine feed of a few thou per revolution,a large radius is not necessary. The radius needs to only be large enough to "bridge the gap" between revolutions of the lathe when fine feeding. You don't even really need a top rake angle if you have a lathe larger than a mini lathe. Leave the top flat,and grind a chip breaker groove along the top edge. It should be close to the cutting edge,but doesn't need to be right at the cutting edge because the quickly built up "false edge" of compacted metal really does the cutting. The chip breaker needs to bend the chip enough to break it into short,curled chips,avoiding the long,hot,sharp snake of a chip that can be dangerous and in the way.
     
  8. pburns

    pburns New Member

    Likes Received:
    0
    Trophy Points:
    0
    City:
    FLAGSTAFF
    State:
    Arizona
    Wow...All good feedback. So let me see if I have this straight. On HSS, no cold water quenching use room temp. I feel like I need to quench just to give my fingers a break. I would quench just when I started to see some discoloration forming using room temp water. On cobalt use cold water? How much better is cobalt then HSS for cutting?

    Use a smaller radius...got it. Stone the tips...check. Thank you for your input.

    Patrick
     
  9. george wilson

    george wilson Global Moderator Staff Member Global Moderator Supporter

    Likes Received:
    10
    Trophy Points:
    38
    City:
    Williamsburg
    State:
    Virginia
    Actually,not ALL good feedback!! Don't worry about a little discoloration,Burns. If you're holding the lathe bit in your fingers,nature will force you to quench it soon enough!!

    Cobalt is better,but it costs a LOT more than HSS without it. Cobalt drill bits are really high,and I would NOT advise you to buy Chinese "cobalt" bits. I don't bother with cobalt in my home shop. Didn't bother with it during my career as master toolmaker at Colonial Williamsburg,either. We weren't in a high production situation there. We did some pretty heavy work,like all the axles and wheel bearings for the carriages that roll around town every day. The stage wagon's axles were 2 1/2" square and about 6 feet long. Large by any standards most home shops would be doing. Cheap brazed carbide bits are needed for things like taking a facing cut across a large face plate,to make sure it is dead true with no wobble.

    Those brazed carbide bits actually require honing before use in case you all don't know it. I have the black and the white Spyderco. ceramic stones. I also start with a diamond bench stone. Less hard stones won't do much on carbide.

    The cost of cobalt is why the use of alnico magnets turned into using ceramic magnets in speakers.

    BY THE WAY: COBALT is VERY harmful to breathe. Unless you have a dust collection setup at your grinder,I'd just use regular HSS. The older I get(have copd) the more careful I am about what I breathe.
     
  10. Bill Gruby

    Bill Gruby Administrator Staff Member Administrator Global Moderator Supporter

    Likes Received:
    14
    Trophy Points:
    38
    City:
    Bristol
    State:
    Connecticut
    Yes, the grind looks good from here. But one thing I will say is the a pretty grind is not always a good thing. The proof of the grind is in the cut. If it works, you did well, if not, try again. If I grind a tool here, and someone grinds one in California, and we send them to someone in Texas, I'll bet the Farm they are not the same, if hand ground. It takes practice. When you think you have it, practice some more. You are on the right track.

    "Billy G"
     
  11. Ray C

    Ray C Moderator Staff Member Supporter Moderator

    Likes Received:
    3
    Trophy Points:
    0
    City:
    Crofton
    State:
    Maryland
    Hi George... I hear what you're saying about creating stresses and am aware of that. The outside surfaces expand/contract many times faster than the core and this places pressures indeed. But they are just that, pressures... because at these temperature ranges the metal is no where near any boundary from spheroidized structure to austenite structure -not by many hundreds of degrees. At the temperatures we're talking about, in the eyes of metal, that's like the difference between a human walking from a room that's 75 degrees to a room that's 65 degrees. Do you feel it? yes. Does it make a difference? No.

    Most tool steels have annealing temps that don't start until 400. -That's why I leave a little water on the bit because it starts to slowly evaporate around 150 degrees and at that temp, there's no harm in dunking in very cold water. Consider that car engines in Minnesota can go from -20 to 350 in a matter of moments... (the stresses of rapidly going from hot->cold or cold->hot are identical). And the reason all but the most critical parts of an engine are kept at/under 350 degrees is because that's approaching the annealing point. As far as cryogenic structure change, the first signs of crystalline reorganization occur at -150 and occurs fully at -320.

    Dunking warm HSS in cold water is +/- 200 degrees from any boundary of crystalline change...

    One thing for sure, if you warm it up till it's blue (or even dark amber) that's a sign that atmospheric oxygen has started to bind molecularly -and that occurs WELL after the annealing point so, by definition, it has become softer.

    Respectfully...

    Ray
     
  12. Ray C

    Ray C Moderator Staff Member Supporter Moderator

    Likes Received:
    3
    Trophy Points:
    0
    City:
    Crofton
    State:
    Maryland
    I'm definitely with Bill on this one... As mentioned before, if those are your first grinds, YOU DONE GOOD! -And to further bolster Bill's commentary, the reason I mainly started using carbide was because I spent so much time grinding and more often than not, struggled to get consistent results. For the simple bit styles (LH, RH, Threading), I could do those repeatably but anything more complicated than that... -Forget it! It took me way too much time.

    Now please don't abandon HSS because of what I said. Please learn how to do HSS right because it will come in handy.


    Ray


     
  13. Tony Wells

    Tony Wells Administrator Administrator

    Likes Received:
    17,543
    Trophy Points:
    113
    Location:
    Tyler, Texas
    City:
    Tyler
    State:
    Texas
    I seriously doubt you could hurt HSS with a grinding operation. Tempering after the initial quench (>2000°f generally) during manufacture happens around 1000°f or a little more. It's tough to properly anneal HSS. In fact, I have melted some, and later found it to be just about as hard as it was. It's pretty hardy stuff. One of the things that earned its name is the fact that it will retain its hardness running at speeds that no other material at the time could approach. In fact, even at red hot, it is still harder than the carbon steels is soon replaced and will cut many materials. So even if you get it red at the grinder, it's not hurt........unless you quench it. Stay away from the ice-water for sure, and even the thermal shock dunking it in room temperature water from red or near red temperatures causes micro-crystalline fractures that will ultimately result in chipped and broken tools. They will fail not because they got too hot in grinding, but because the oft recommended water quench. Best way to grind it is to use an open, coarse wheel, substantial pressure and get with it. Ignore the temp. When you get it close to size/shape, etc., slow down to a finer wheel, then hone an edge on it. You will do less damage to the tool, and save tons of time if you are aggressive with the initial grinding and skip the water altogether.

    A lot of this thinking has probably come from the slow, wet grinding done in surface grinding of other metals, and the production grinding of most HSS tools. However, the reasons for all the light touch and flood coolant is not to protect the metal from heat effect but to provide a stable, non-moving part to grind. Cooling it accomplishes this. Offhand grinding has no such need.
     
  14. Ray C

    Ray C Moderator Staff Member Supporter Moderator

    Likes Received:
    3
    Trophy Points:
    0
    City:
    Crofton
    State:
    Maryland
    Thank you... Exactly my point. Yes, when going from many hundreds -or thousands of degrees to cool/cold water, bad things are going to happen. But going from 150 to cold... No problem. As mentioned, if you leave a little water on the metal, it starts to evaporate at/around 150 (just about the time it feels uncomfortably hot). When it starts changing colors, you're getting waaarrrmmmerrrrr... By the time you say, CRAP and your brain figures-out this thing is too hot to hold... That's when you don't want to dunk the thing.


     
  15. Tony Wells

    Tony Wells Administrator Administrator

    Likes Received:
    17,543
    Trophy Points:
    113
    Location:
    Tyler, Texas
    City:
    Tyler
    State:
    Texas
    My point was that at 150°f, you don't need to cool it. Go ahead and grind it until it gets red.....still no damage, unless you quench it. Of course, you shouldn't hand hold a piece and grind it until red, use a holding device of some sort. If you do grind to 150° and cool, true you won't do any damage. In fact, this is a good practice for nice high quality woodworking edged tools. But we are talking about HSS metal cutting tools. Different rules apply. If you do take such a slow approach to grinding lathe tools, you will waste time, and grinding wheel.
     
  16. Ray C

    Ray C Moderator Staff Member Supporter Moderator

    Likes Received:
    3
    Trophy Points:
    0
    City:
    Crofton
    State:
    Maryland
    So, I hate to say this but, what other way is there? You got my curiosity going now. Don't clam up on me.


     
  17. george wilson

    george wilson Global Moderator Staff Member Global Moderator Supporter

    Likes Received:
    10
    Trophy Points:
    38
    City:
    Williamsburg
    State:
    Virginia
    Let me clarify why I quench at all. I,as I've stated,know that red heat doesn't hurt HSS,in full agreement with Tony. I make repairs to mechanical antiques and do other work wherein I need special shaped miniature form tools like ogees,etc.,which I need to inspect carefully and diddle around getting them just right. So.I quench in order to hold the bits and closely inspect them.

    If I can find the pictures,here's a model cannon barrel I made recently with moldings all over it. I made form tools to speed up the process of making repetitive moldings. This cannon is about 8" long. It has not been polished yet in the picture. Just from being turned.

    Also,a pair of wax seals I made from brass,with buffalo horn handles. Typical of orders I get from customers. They are about 6"" overall length.

    I'm not the usual type machinist. Most of my work is artistic in nature,especially from being the toolmaker for an 18th.C. museum setting.

    For ordinary left and right hand turning tools,etc.,no need to quench.
     

    Attached Files:

  18. Ray C

    Ray C Moderator Staff Member Supporter Moderator

    Likes Received:
    3
    Trophy Points:
    0
    City:
    Crofton
    State:
    Maryland
    Beautiful, George... Really beautiful! You're right, I don't see how you could do that with typical carbide inserts of the usual variety. Definately a job for custom HSS. Like I said, it took too much time when I tried to make complicated bits so, you must have the knack down pat.
     
  19. Tony Wells

    Tony Wells Administrator Administrator

    Likes Received:
    17,543
    Trophy Points:
    113
    Location:
    Tyler, Texas
    City:
    Tyler
    State:
    Texas
    I'll give you an extreme example. I wanted a 2.000 radius slab tool. I had a piece of 1" HSS. I took a oxy acetylene torch and burned it in according to a scribed line, then took it to a 10" 36 grit OA wheel to get it close to profile. Then I used another trick (to be given at some later date) to finish the radius with a smaller grinder. Never touched water with the tool. Never had a problem cutting 4140 @36 Rc.
     
  20. Bill Gruby

    Bill Gruby Administrator Staff Member Administrator Global Moderator Supporter

    Likes Received:
    14
    Trophy Points:
    38
    City:
    Bristol
    State:
    Connecticut
    George, your work is impecable. Simply amazing.\

    Ray -- Take a piece of 1"X1" Steel. Cut a slot length-wise to fit the tool. Use setscrews to hold it fast and have at the grind. Length is up to you. Old school technology come full circle.

    "Billy G" :))
     

Share This Page