Models for grinding HSS Lathe Tools

Thank you Mikey, I made a set of tools from your samples and they work great on my 12X36 Atlas/Craftsman lathe. I have had this lathe for thirty years I can hear and feel how much better these cut. A thank you to Jeff also for doing the mailing list. Thomas S.
 
thomas s said:
Thank you Mikey, I made a set of tools from your samples and they work great on my 12X36 Atlas/Craftsman lathe. I have had this lathe for thirty years I can hear and feel how much better these cut. A thank you to Jeff also for doing the mailing list. Thomas S.
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You're welcome, Tom. I appreciate the feedback and I hope they work as well for you as they do for me. The fact that you had an open mind and tried these tools says a lot about you!

And yes, Jeff has been a major help. Thanks, Jeff!
 
Well I tried the Worksharp for honing. It took a long time to get rid of the grind marks but the finish was like a mirror. I couldn't do the top of the tool on the Worksharp and did that by hand. I used the tool for a bit and noticed the cut was changing (getting dull). Could see a dull spot near the tip of the radius. So I decided to try honing on the little belt sander using progressively finer paper. Went up to 320 and got a very nice finish in less time.

This tool cuts very nicely and leaves a great finish. The HSS I am using must be poor quality though because the edge dulls quite easily and needs to be honed often. Where do you source quality HSS? I looked at q20v's post and noticed that with a grinder there is a hollow left in the middle of the faces, which results in only having to hone the top and bottom edges of the faces instead of the whole face. I think this would reduce the honing time significantly, unless I'm missing something.

I have a question about the feed rate? As you suggested I tried different feed rates with small DOC's and noticed I had to go very slowly in order to get small chips. If I went faster I would get long curling threads of mild steel. Is that ok for roughing cuts? I'm not sure what a chip should look like. What should I be looking for?
 
HBilly1022 said:
Well I tried the Worksharp for honing. It took a long time to get rid of the grind marks but the finish was like a mirror. I couldn't do the top of the tool on the Worksharp and did that by hand. I used the tool for a bit and noticed the cut was changing (getting dull). Could see a dull spot near the tip of the radius. So I decided to try honing on the little belt sander using progressively finer paper. Went up to 320 and got a very nice finish in less time.

This tool cuts very nicely and leaves a great finish. The HSS I am using must be poor quality though because the edge dulls quite easily and needs to be honed often. Where do you source quality HSS? I looked at q20v's post and noticed that with a grinder there is a hollow left in the middle of the faces, which results in only having to hone the top and bottom edges of the faces instead of the whole face. I think this would reduce the honing time significantly, unless I'm missing something.

I have a question about the feed rate? As you suggested I tried different feed rates with small DOC's and noticed I had to go very slowly in order to get small chips. If I went faster I would get long curling threads of mild steel. Is that ok for roughing cuts? I'm not sure what a chip should look like. What should I be looking for?
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Let me handle the tool-related stuff first.
  • The fastest way to a mirror finish is with belts. Jump up through the grits as you did to get rid of grind marks while maintaining your geometry. If you want to do very little honing, go up to 600 and you only need to do very light honing.
  • If the tool is dulling quickly I would suspect it wasn't quite sharp to being with. When honing, sight along the cutting edges. When the edge is sharp it will look like a sharp line. If the edge is not sharp you will see light reflecting off that edge. Your goal is to remove that reflection. When sharp, a HSS tool can cut a LOT of material before it needs to be touched up. Don't rely on your thumb to tell you if its sharp; use your eyes.
  • The choice between a bench grinder or belt sander is yours. It will come down to what you are most comfortable working with because both work. For me, the sander is much faster and more accurate, and changing grits takes seconds; not so on a bench grinder. Try stepping up through the grits and see.
  • The best and cheapest source for HSS bits will be ebay. You have to be patient and you need to know what you want. I would buy some Chinese import bits to play with and experiment with but once I found a geometry I liked, I would grind it from a good quality blank. See my End Notes post in this thread for suggestions. For now, stay with M2 or T1 HSS. Watch for auctions with new blanks; I do not buy used tools. If you're patient, deals come up. I just bought 8 new USA-made Mo-Max M2 bits for 40 bucks, which is more than I usually pay. A few days later, I bought 11 new DoAll T1 bits for $15.00. Not too long ago I got a box of 20 ETM M2 bits for $20.00. You have to watch, wait and then jump when you see what you want at a price you can handle. If you have the money you can still buy most quality tool bits from Industrial supply houses but it will cost you. Better to buy Chinese bits and use them while you're looking for a deal on ebay.
Chip formation is a function of depth of cut, feed rate, tool geometry and the properties of the material being turned. Many materials, including some mild steels, stainless steel and aluminum will produce long, stringy chips that can reach many feet long. These chips are sharp and dangerous; do NOT grab them with your hands and do NOT go near them with the lathe running. A long chip will often rapidly wrap around the work and can easily drag your hand into the chuck if you get close. If they wrap around the work or chuck, STOP the lathe and remove them with pliers.

You can avoid long, stringy chips in most materials by taking a decent depth of cut and increasing your feed rate when roughing. When roughing, you do not care about finish; you are trying to remove material in the least amount of time. For example, if you wanted a 0.500" OD final diameter but only had a 0.75" piece of 12L14, you can take a 0.100" deep roughing cut at a feed rate that produced chips. 12L14 usually produces stringy chips but it will come off as small chips if your DOC and feed rate are fast enough. The same is true for stainless and aluminum. I cannot give you numbers for these things because each lathe is different. The best way to find out is to burn some material and experiment.

When taking sizing and finishing cuts, you will be taking smaller DOC and your feed rate will be slower so you'll produce stringier chips at times. You learn to live with that but you can minimize them by altering your lead angle. You have to try different speeds, feeds, DOC and lead angle to figure out what works for you. I know this sounds like a lot of work but that is what you're trying to learn. Turning stuff is knowing about your materials and how it likes to be cut. Having a good tool makes things much easier and oftentimes a geometry made to work with a given material is the way to go. Remember that the square tool works well in most stuff but a tool ground to work with a specific material group will always be better. This is why I spent so much time going over tool angle modification.

The bottom line is that you need to buy some stock and spend some time messing around with your cutting conditions (DOC, speed, feed) to learn how your lathe and tools work with different materials. In general, rough at higher feed rates and finish at lower feed rates. Rough with the tool perpendicular to the work or maybe slightly toward the chuck; finish with the tool turned slightly toward the tailstock. And so on ...

These things take time. Having a good tool helps more than you know.
 
I should add to the above that the right feed isn't always going to be available on your lathe; depends on the gearing. Quite often, I will just feed manually when roughing to get the chips to come off the way I want. I may set the rpm for the material but I will feed manually to get chips instead of stringers. This is especially true of aluminum, which forms long stringers. When roughing, I may run my lathe at about 1100 rpm and hand turn the feed; with enough DOC and a fast enough feed the chips come off as chips, not stringers. Of course, this is with a tool modified to work with aluminum. Similarly, stainless steel likes to come off as looong stringers. My stainless tool has a lot of side rake and even with a moderate DOC, the chips come off as short curled chips, not stringers. This has more to do with geometry than anything else so, again, learn to modify your tools to work the way you want them to.

There is a lot to learn about turning but be patient and experiment with it; it will come.
 
Mikey,

You are so right about knowing your material and your lathe. I have some occassions, same material barrels from the same company don't always cut the same. For example, on same SFM, doc, and feed, one will string and the next one chips in 2 to 3 inch long when roughing.

I always make a short test cut, just to figure out what I am up against.

I am so afraid of those long razor sharp continuous strings, With a swarf tool I tried to break them at foot long and kind of swing them to the left of the operator to be collected on the floor.

Nez
 
Thanks so much for your response Mike. I really appreciate the time, effort and knowledge you have put into this thread and with guiding me. I've only been at this hobby machining for a couple of years, on a part time basis and it seems like the more I learn, the more I discover how little I know. I've struggled with finishes and getting to target depth for quite a while. Sometimes it seems to come together but I don't know why and most times I just accept the less than great finish and the close enough size. I have found that with this grind I get a far superior finish and it is waaaay easier to hit the target size. Also, very importantly, it is consistent, even for me. The only way I could get a decent finish with mild steel before was to use a shear tool with a very small DOC (0.001" or 0.002") and the slowest feed rate. Now I get better finishes consistently and I don't have to sneak up on the final size with a bunch of very small shear cuts.

I'm glad to hear the long strings are normal and will not concern myself with that when taking roughing cuts.

I'll take a closer look at my honing, especially the top surface, as that is where I think I may not be getting the finish right.
 
Bamban said:
Mikey,

You are so right about knowing your material and your lathe. I have some occassions, same material barrels from the same company don't always cut the same. For example, on same SFM, doc, and feed, one will string and the next one chips in 2 to 3 inch long when roughing.

I always make a short test cut, just to figure out what I am up against.

I am so afraid of those long razor sharp continuous strings, With a swarf tool I tried to break them at foot long and kind of swing them to the left of the operator to be collected on the floor.

Nez
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Yeah, you have to know your materials. That's where the pro guys have a lot more experience than us hobby guys because they work with bigger batches. Still, we can learn if we are willing to experiment.

I agree that some lots of the same material will cut differently and I'm not sure how to explain it. I know that with stainless, if I get the side and back rake correct I can avoid stringers to a much finer degree. Your Rex AAA tool does a good job of chip flow, right?

Like you, I am very careful around long stringers. You will find that if you manually feed, a very short pause in feed will break those stringers off. If you haven't done so, give it a try. Be safe, Nez.
 
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