HSS blanks, QCTP, vs. inserts

[wawoodman]

I've read the instructions, and watched the videos, about sharpening regular HSS bits for the lathe. I think I understand clearance, side rake, and top rake. But I'm confused by a couple of points (no pun intended.)

The lantern-type tool holder puts the bit at an upward angle, about 10 degrees. But the QCTP holders keep the bit flat. Does this change the angles needed for grinding?

Also, I've looked at the Warner HSS insert kits. The inserts are flat. Is the bed angled to add the top relief?

 

[wawoodman]

Frank,
This is what I'm referring to.

http://www.arwarnerco.com/c-5-tool-kits.aspx

Thanks!

 

[Sandro]

Strictly speaking HSS toolbits need a generous top rake, about 15° if I remember correctly. But for the typical hobbyist a flatter top rake will work well enough that it doesn't matter.

Frank is right that most toolholders are now designed for carbide tooling. HSS tooling requires a bench grinder to sharpen, but with the advantage that you can grind the tooling into any shape you may need.

Insert tooling, whether carbide or HSS doesn't require a grinder for shaping or sharpenning tools, but the drawback is that you can't alter the shape if you need a different profile and once dull they are discarded.

HSS blanks allow you to grind custom shapes and for the same cost as an insert, individual HSS toolblanks can last for years or even decades so the savings in tooling can be very significant over time.

Hope this helps.

Sandro Di Filippo

 

[Rbeckett]

Also depending on the lathe size and horse power you may not have enough power to really exploit the Carbide cutters speed and depth of cut. I have a small 750 watt chiinese lathe motor and I just dont get the moneys worth out of buying carbide when HSS works as well or better in my little 7X10 lathe. And like Sandro said, the cost savings over time is pretty signifigant too.
Bob

 

[Bill Gruby]

The inserts are flat topped because they are universal. Any rake, angles, ets are built into the individual holders. I use the Warner HSS inserts and holders. They are "sweet".

"Billy G" )

 

[wawoodman]

Yes, they are. I'm just not there quite yet... Maybe next birthday, when I'm sixty-four. (cue music)

Bill, since you have the set, could you take a measurement or two for me? What is the angle of the side of the insert, and what is the rake on the toolholder?

Based on those angles, here's my idea: sharpen a 5/16 HSS bit as usual, with the correct top angle and side relief, but no top rake. Then, take a piece of 1/2" square steel stock, and machine in a 5/16 groove, canted over at about a 7 or 8 degree angle. Slip the bit into the carrier, and put it into the toolholder. The set screws should compress the carrier down onto the bit, and hold it fine. Does that sound reasonable, or am I breathing fairy dust?

 

[Tom Griffin]

Back rake is over rated for high speed tooling and generally unnecessary. I grind all of my tools with zero degrees back rake, use them in a quick change tool post and they cut just fine. About the only time I'll ever use back rake is if I'm machining something soft like wood or rubber or some plastics. Back rake when cutting steel is actually a bad idea because it removes material behind the cutting edge of the tool which allows heat build up. Another plus for tools with zero back rake is you'll get a lot more life out of them since the tool geometry doesn't change as the tool is sharpened.

Tom

 

[Bill Gruby]

Mike:

Relief Angle (side angle) is 7 degrees. Mine have no back rake at my request. As Tom said it is not needed. The radius on my inserts ie the standard .031.

"Billy G" )

 

[wawoodman]

Thanks to you both.

I'm currently working on a Cutter Bit Grinding Block (http://www.wswells.com/partslist/5910A.pdf) On a 2 x 42 belt sander, my initial test was VERY successful. Unfortunately, I didn't do a very good job of centering things up. It works, but I can do better. So, into the "premachined parts for future projects" bin, and I'll do it again.

Pictures will be posted when I'm satisfied!

 

[Hotbluechips]

HSS is great when you need a special radius or profiles.
Not all holders hold bit on angle some are straight with the shank, but those might be for brazed carbide tools.
QCTP is the way to go, check enco "hot deals".
Small shank toolholders will last a lifetime.
A DCMT or CNMG tool holder will give you thousands of insert choices.
NTK cermets work well on small lathes for finishing cuts.
With carbide inserts Use Small radius inserts with a top rake like sumitomo 431 size.
Brazed tools are fine also, But you will need a green grinding wheel or diamond wheel to sharpen them.
Also if your toolholder in rocker type toolpost is angeled to bring it up on center, you can make a big flat washer to fix that, just make same size as spherical plate and put under it.