Models for grinding HSS Lathe Tools

[q20v]

Hey guys,

I had a bit of time tonight to try the RH turning tool on a piece of Cleveland Mo-Max HSS that I had. I copied my copy of Mike's turning tool pretty much exactly, which took some time to accomplish considering my small grinder and Mo-Max is a tad harder than key stock... anyway, got it done and spent a decent amount of time honing, first by practicing on my key stock bit, then carefully on the HSS. Mike, I tried both honing techniques we discussed above and I felt I had better control doing it the way you suggested, basically piling up the burr (even though none really built up) on the cutting edge, then taking it off by honing the top.

The DMT plates I ordered arrived today and worked very well. (don't mind the shape of the back of the bit, I bought it used at a second hand store)


This is the new grind next to my previous attempt, using the South Bend manual as a rough guide. It worked with mixed results.


Please let me know if anything can be improved, particularly with the honing. I'm using a 6" grinding wheel so the hone is only really touching the edges.


Looking at this picture now, I kind of see a band of reflected light on the top edge. Is this what you're talking about trying to avoid, Mike?



I was almost going to stop there and go to bed, but I had to give it a try. The deeper cut is with very little lead angle (~10*) and the 1.25" piece of 6061T6 sticking out way too far. There are chatter marks on the surface as a result. Second cut (shiny one) is with a greater lead angle (as pictured) and the bar pulled into the chuck. Very very nice finish!!


Then I tried a piece of 1.5" mild steel. Same increased lead angle as before. Same impressive result on the surface finish. Then I put it to the test and successfully took less than .0005 off the diameter. Barely a hair of material came off the bar. Wow! Can't say I've ever done that before.



Maybe tomorrow I'll give the knife tool a try on some HSS. Gotta say I never thought I'd be putting so much time into grinding HSS, but I'm having a great time doing it now that I have some good direction!

Barry

 

[mikey]

Grinding HSS is a bit different than keystock, isn't it? There will be a tendency to push harder and grind faster but I suggest you not do that with a wheel. Take your time, dip the tool in water to keep it cool and it will get there eventually.

You need a larger nose radius on the tool, Barry. Try for a 1/64" to 1/32" radius and the tool will finish much better for you.

As for honing, yeah, when you grind with a small wheel it will tend to create a scallop on the flat. A belt will not do that. You need to flatten the entire side cutting edge, from the tip back to where the back rake curves up. This will give you the entire side cutting edge to work with. Same for the end face; you should catch the entire edge. The top should be honed so that the side and end edges are clean, sharp and do not reflect light.

The reflected light I was referring to will be on the edge created by two planes as they intersect, both the side and end.

Try honing the tool well, then align the shank of the tool perpendicular to the work to rough. If it chatters, which it won't, then turn it slightly more toward the chuck. If you want to size the work then turn it more toward the tailstock. You have to mess with it but the tool will tell you when its right; it will cut smooth and clean with a good finish.

As for taking a fine cut, yeah, this tool can take a very fine cut. I've dialed in a 0.0001" depth of cut (using a dial indicator) and cut it with the square tool so I know it can be done.

Good work, Barry! You went from newbie guy to tool grinder in a matter of days. It takes time to hone your skills so be patient and it will come.

 

[mikey]

I just re-read my post above and it is unclear. Barry, you need to hone the faces but you do not need to flatten the face with the hone. Only the upper and lower edges will be honed and that is just fine but try to catch the entire cutting edge. Sorry, Barry.

 

[mikey]

I was queried tonight about how a square tool cuts as you turn into a shoulder. As I stated before, most of the cut is made with the nose radius but the end cutting edge is also involved.

The tip geometry of a turning tool is actually rather complex but basically you have two cutting edges joined by a nose radius. You have the side cutting edge, which is comprised primarily of the side relief and side rake angles, and you have the end cutting edge that is comprised primarily of the end relief and back rake angles.

When turning normally, the side cutting edge is the primary edge used. However, when turning into a shoulder, the end cutting edge is primary. You can see this in the pic below; the side of the nose radius and the adjacent end cutting edge is in contact with the work:



What actually happens is that the end cutting edge cuts like a facing tool and this has the potential to produce very good finishes. However, there is also a fair amount of edge in contact with the work so cutting forces increase. Therefore, when turning into a shoulder, lighten up on your depth of cut and you will retain your accuracy and finish. Go too deep and you get deflection and can produce chatter due to the edge contact. What I do is rough until I am about 0.005 - 0.010" from final size and then change my lead angle like in the picture so I can get into that corner. Then I can reduce depth of cut and sneak up on the final diameter; works good.

This is one reason why I recommend you make the side and end relief angles the same; doing this reduces cutting forces and it makes a difference when taking light cuts into a shoulder. While this is yet another thing to remember, you will eventually learn to reduce your depth of cut in this situation without even thinking about it. At least now you know why you're doing it.

Edit: the work piece in the pic is a prop and was not being turned. An actual cut would produce a mirror finish.

 

[q20v]

Mike,

Thanks for the feedback!

Nose rad: Definitely agree with you. It was awkward trying to put the small radius I have on the tool, as I'm essentially freehanding it on the grinding wheel. Although the surface finish is pretty good in the pictures, that was at the slowest feed rate and there is still a discernible line around the work piece (more evident in person). Embarrassingly, I never thought to re-adjust my grinder tool rest angle so that I don't have to freehand the initial cut (small flat) for the nose rad. I'll try that tonight and carefully round the cut with the DMT plates.

Honing: I think I'm honing just the point of the side cutting edge because that surface may not be perfectly flat (not talking about the grinding wheel scallop, but the length from the tip of the tool, back), the pressure I was putting on the tool while grinding was likely inconsistent as I moved across that surface (grinder wheel is about 3/4" thick). I'll put a straight edge across it tonight to see how flat it is.

I'll try again tonight and report back with the results.

Barry

 

[mikey]

Mike,

Thanks for the feedback!

Nose rad: Definitely agree with you. It was awkward trying to put the small radius I have on the tool, as I'm essentially freehanding it on the grinding wheel. Although the surface finish is pretty good in the pictures, that was at the slowest feed rate and there is still a discernible line around the work piece (more evident in person). Embarrassingly, I never thought to re-adjust my grinder tool rest angle so that I don't have to freehand the initial cut (small flat) for the nose rad. I'll try that tonight and carefully round the cut with the DMT plates.

Honing: I think I'm honing just the point of the side cutting edge because that surface may not be perfectly flat (not talking about the grinding wheel scallop, but the length from the tip of the tool, back), the pressure I was putting on the tool while grinding was likely inconsistent as I moved across that surface (grinder wheel is about 3/4" thick). I'll put a straight edge across it tonight to see how flat it is.

I'll try again tonight and report back with the results.

Barry

Barry, I suggest you not use your grinder to put a nose radius on your tools; it is very difficult to do this under power. Use your fine or extra-fine diamond stone to do it manually. Just grind an even flat at the nose that extends from the top of the tool to the bottom, making it just slightly narrower than the nose radius you want. Then gently round the sides of the flat and blend it into the side and end faces.

Maybe consider using a belt sander as a tool grinder. I will try to find the time to use ceramic belts on my 1/3HP Craftsman belt sander to see if they will allow that machine to grind tools. If it does then we have a cheap and readily available option for a machine that will work. I'll get on it soon.

 

[q20v]

Hey Mike,

Okay, I follow you now. I'll give it a go manually. That edge is tricky to radius because it's curved (end and side faces are scalloped from the grinding wheel). And I hear ya about the belt sander. I will have to keep my eye out for one.

Barry

 

[Bamban]

Mike,

I have to admit, I learned from your posts and the personal messages you sent me. In the past I always use the indexable carbide bits with the holder just butted up against the inside of the wall of the cut out, basically straight forward into the workpiece and just let the holder and the bit design do their thing.

I have a barrel in one of the lathes, the 1236, that has been sitting there since I encountered the anomoly of the QCGB. Just out of curiosity I played with the bit angle of attack. Here is a short video as I made the finishing pass, cleaning up the previous roughing cut. Notice the bit holder is kicked back towards the TS side. Did not move the QCTP, just adjusted the angle of the bit holder. Notice the finish.

Thank you for all the tutorials.


Nez

Watch "Finishing Pass Cutter Towards TS" on YouTube

 

[Randall Marx]

Hi Mike
Thanks again for taking the time and putting forth the effort to help all of us with this endeavor! I have a question regarding the grinding tool. I am currently stuck with a bench grinder to use for grinding my tools. Using the periphery of the wheel to grind, where do I need to set the angle in relation to the tool? Does the 15-degree tangent need to fall at the top, middle, or bottom of the tool? In other words, If I match your example to my grinder, would I set the table angle with the wheel actually touching the ground face on the top or what? I ask because the tangent location will change the apparent angle of the ground face as seen by the workpiece being cut in the lathe.
Thanks again for your guidance.
Randall

 

[mikey]

Mike,

I have to admit, I learned from your posts and the personal messages you sent me. In the past I always use the indexable carbide bits with the holder just butted up against the inside of the wall of the cut out, basically straight forward into the workpiece and just let the holder and the bit design do their thing.

I have a barrel in one of the lathes, the 1236, that has been sitting there since I encountered the anomoly of the QCGB. Just out od curiosity I played with the bit angle of attack. Here is a short video as I made the finishing pass, cleaning up the previous roughimg cut. Notice the bit holder is kicked back towards the TS side. Did not move the QCTP, just adjusted the angle of the bit holder. Notice the finish.

Thank you for all the tutorials.


Nez

Watch "Finishing Pass Cutter Towards TS" on YouTube

Yup, lead angle is a real thing. Most guys who use inserted carbide don't even realize that just because the tool has clearance angles on the side and end, that doesn't mean you have to use the tool that way. Try using a CCGT AK insert turned toward the tailstock in aluminum - the finish will like to frost your eyeballs.