Tool Grinding...How'd I Do?

pburns

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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

2013-02-01_10-49-28_496.jpg 2013-02-01_10-50-08_637.jpg 2013-02-01_10-50-17_814.jpg 2013-02-01_10-51-01_640.jpg 2013-02-01_10-51-29_440.jpg 2013-02-01_10-51-48_558.jpg 2013-02-01_10-52-00_297.jpg 2013-02-01_10-52-18_485.jpg 2013-02-01_10-52-53_339.jpg 2013-02-01_14-49-48_643.jpg 2013-02-01_14-50-01_734.jpg 2013-02-01_14-50-33_729.jpg 2013-02-01_14-52-01_221.jpg 2013-02-01_14-52-26_512.jpg
 
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
 
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 ;)
 
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
 
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

P2020775a.jpg
 
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
 
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.
 
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
 
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.
 
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"
 
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