Models for grinding HSS Lathe Tools

[mikey]

A 0.350" radial depth of cut is a good cut in mild steel, Mike. That's almost 3/4" off the diameter. Good job on the tool!

The improved finish in the second cut is due to engagement of the end cutting edge. Remember, the side cutting edge removes material but the end cutting edge provides the finish. As you change your lead angle towards the chuck, more of the end cutting edge engages and the finish improves. This is why it is more accurate to keep nose radii small to reduce deflection from radial forces and involve your end cutting edge more to improve finishes.

 

[mikey]

Here is the pic, when I went back the bit had some weldment on the lead edge, how do you get away from that, lube?

Forgot to respond to your question re the built up edge (weldment on the tip). This suggests that temps got high at the point of cut. Normally, this is not an issue with steels and some lube would help prevent it. You can also reduce speed a bit and this will reduce temps at the point of cut. The other thing that helps is to increase side and back rake a little bit, maybe 2-3 degrees more. This will increase chip flow and thin the chip at the same time, resulting in reduced cutting temperatures. Lastly, a BUE can be due to a overly large nose radius so I suggest you add a bit more side and back rake and keep the nose radius small, then use some lube and I bet a BUE will no longer be an issue in steel.

 

[Aukai]

Thank you, I had to resharpen the bit , my first try had a small nose radius, and the finish was horrible. after resharpening the pictures is what I got. I'll look at the bit tomorrow again.

 

[Aukai]

I have a blank of T5 coming, what nose geometry for cast iron would you put on it? This can move if needed.....

 

[mikey]

I'm not familiar with T5 cast iron, Mike. What is your source and do you have any info on its machining properties?

There are four types of cast iron - gray, white, ductile and malleable. Most of the bar stock we see in a hobby shop is gray or ductile, with ductile being the most machining-friendly due to the ferrite and silicon content. I am not sure where T5 falls, Mike, and without knowing what it is, it is difficult to make a recommendation.

Quite often, we run into a cast iron of unknown type and this especially true when a hobby guy is trying to do something on the cheap. We know nothing of its composition, especially the carbide content, and then we wonder why we can't cut it. Some cast irons have a lot of pearlite/carbide in it and it will eat up HSS and some carbide tooling. In this case, it is best to pull it out of the lathe and dump it unless you're rich and can afford to experiment with inserts.

So, you need to find out what that T5 stuff is and we can try to go from there. An alternative is to find some Durabar ductile iron; you will really like turning that stuff. The last time I had some Durabar, I used a Square tool at low speed and it cut well with a nice finish.

 

[ttabbal]

Could T5 be the HSS type? I used something like that for cast iron and I was happy with the finish. I believe it was a 10 degree square tool.

 

[DavidR8]

ASTM T5 Tool Steel | 1.3265 | S18-1-2-10 | SKH4 | BT5

ASTM T5 Tool Steel is one of tungsten high-speed tool steel. It belongs to ASTM A600, together with T1, T2, T4 Tool Steel etc. They are also in T group in ASTM A600 standard. AISI T5 high speed steel contains Cobalt with range 7.0~9.5%. AISI T5 steel has better high temperature performance...

www.astmsteel.com

 

[mikey]

Okay, I might have misinterpreted the post. T5 HSS grinds like M42 cobalt HSS - takes more pressure to grind it.

Find out which kind of cast iron you have, Mike. For light cuts at low speeds a Square tool will work.

 

[Aukai]

It will be for the cast iron backing plates, the new one coming is fine grain, or something like that. The bit is a Rex supercut which it T5

T5 typical analysis (%): C 0.8; W 18.5; Cr 4.0; V 1.75; Co 8.0; Mo 0.8 – the ultimate in HSS for heavy duty cutting. Has a combination of red hardness and toughness that results in outstanding performance. Recommended for heavy duty lathe, planer and boring tools. Especially adapted for cutting hard, gritty material such as cast iron or steel, also heat treated alloy steels. Best used in tools that are well-supported and not subject to excessive shock or chattering. Cutting speeds can be about 25% faster than T1 with higher tool life.

 

[mikey]

Cast iron backing plates can really vary in their quality, especially if the plate is from China. They can have hard spots and sand and who knows what else is in there. You should be able to turn it just fine with your T5 bit. Again, I would try a Square Tool geometry and see how it works for you. I suggest a nose radius somewhere between 1/64" - 1/32" to hopefully enhance the finish. Cast iron tends to crumble and a bigger nose radius might help.

Keep you speeds low, like 25 sfm and use a lowish feed rate. Do NOT use lube or coolant.

Cover your lathe, Mike, and don't forget to plug up the spindle bore so you don't send dust into your gear train in back.