Taking more aggressive cuts

[AmericanMachinist]

I've got a logan 200, 3/4 horse 10" lathe. Carbide tipped tool. Turning down 1.5" round 1018. Taking 0.004" per rev. I can take about 0.015" off the radius, 20 thou works but is pushing it. I think i could up the 0.004 cut a bit but without mist the tool gets super hot as it is (i am applying oil to the stock).

I need to have half the diameter off, so at 0.030 off the dimater per pass, this will take a while.

Is this about the best i can reasonably expect to do?

Thanks!

 

[mikey]

Which tool are you using? Got any pics of your set up?

I will say up front that on an older lathe like yours that is not overly rigid or powerful, you will be much better off with HSS tools. Carbide needs rigidity, speed and horsepower to cut as it should and you just don't have it. What you can do is to take lighter passes and increase your speed and just accept that it is going to take a lot of cuts to whittle the piece down to size.

It is also possible that you can look at tightening the gibs and belts and try to eke out more rigidity and power transmission. I don't know if that will make a difference but it's worth a try.

Or you can grind a good HSS tool and I bet that will work better for you. I say this because my little Sherline has only 0.08HP and can take a 0.050" deep cut off the radius in mild steel with a decent HSS tool. With a HSS tool optimized for mild steel, it will take a 0.060" deep cut off the radius. I cannot even approach these cuts with an inserted carbide tool on this lathe; I can maybe go half that at best and even then the finish will suck. This is why I think HSS might just be a better bet for your lathe, not just in this instance but in general. Just an opinion, of course.

 

[ThinWoodsman]

What's the rule of thumb for lathe size and carbide?

I couldn't get carbide to work on my 7x16 bench lathe, but on the 14" it just chugs merrily along making chips no matter what the tool material. I'm surprised a 10" wouldn't be solid enough, as those make the 7" lathes look like children's toys.

Lower bound would be a 12" lathe then? Barring customizations like a gibraltar toolpost and whatnot.

 

[AmericanMachinist]

I don't know that the carbide is an issue but I'll try HSS.

It cuts, just gets hot quickly and starts to approach stalling the motor (if i go to .025" or so.) If its because of thr physics of the carbide cutting vs. HSS cutting then i guess that makes sense.

Thanks!

 

[ttabbal]

I use both, but almost always run HSS because it cuts with less force, so my smaller lather runs better.

If you are running a normal insert, it's likely not very sharp. It relies on general shape and being harder than the work. HSS is usually honed to be very sharp and it helps more than I thought it would. There are some insert grades that are honed like that. I've never been willing to pay for them, so I can't say if they are as easy to cut with as my HSS tools though.

 

[ThinWoodsman]

That's a good point, I haven't tried using the carbide in the bench lathe since I started honing both the inserts and brazed tools. Might work a lot better; I've pretty much demoted the 7x16 lathe to wood turning until I can find a way to make that saddle stable.

 

[BtoVin83]

You are short on HP, not a put down just a fact.
What eats up HP
1. Negative rake carbide
2. DOC which you have experienced
3. Feed rate
4. Material
To mitigate the negative rake issue change to positive rake either HSS or carbide. The beauty in carbide is you can run the RPM probably as fast as that lathe can go and carbide will live. Running high RPM allows to to remove material fast without a deep DOC or high feed rate plus it will probably put the heat in the insert rather than the stock which is what you want. once you have established your RPM play with the feed rate and DOC until you optimize your removal rate which may be small cut fast feed rate or maybe just the opposite. The beauty of HSS is that you can go slow and have a high positive rake, this may be a better solution. .004 per rev is a pretty small cut. Good luck

 

[benmychree]

I absolutely agree with Mikey, HSS tools are the answer on small lathes.

 

[macardoso]

I use carbide on my 12" lathe very successfully. Ground periphery inserts are available inexpensively if you know what to look for. I do stick to positive rake tooling as it cuts with less horsepower. I mostly buy import inserts and have had solid luck with them.

I have used HSS and it works great, however I do not do any grinding in my basement shop because it makes a mess and would get sucked into the furnace. I am not going to carry the bench grinder outside every time I sharpen a tool. I like that the performance of the carbide inserts is very consistent and many different tools can be used without rotating the toolpost.

 

[mikey]

I don't know that the carbide is an issue but I'll try HSS.

It cuts, just gets hot quickly and starts to approach stalling the motor (if i go to .025" or so.) If its because of thr physics of the carbide cutting vs. HSS cutting then i guess that makes sense.

Thanks!

There are a fair number of Logan users on HM. It might be good to ask them for their opinions on this. It could be that there is an issue with your lathe that can be corrected to improve the results you're seeing. Just keep in mind that tooling does make a big difference in performance.