Tool life

[RJSakowski]

There is a big difference between a large lathe and a hobby class lathe regarding available hp and rigidity and the rules are different. What works well regarding feeds and speeds on a large lathe will simply stall out on the smaller lathe. As you become more familiar with your lathe, you will get to know what works for you. My advice is to be conservative rather than aggressive in your approach working your way up.

When stalling the lathe while using carbide, you can sometimes save the tool be stopping the machine and reversing the chuck by hand to clear the jam. It doesn't always work though. High speed steel is more forgiving and better suited to small lathes. It is also much cheaper since tools can easily be reground and put back in service. For a small lathe 1/4" tool bits work well. Any larger sizes offer no real useful improvement in rigidity as they aren't the week link. They are also easier to grind and considerably less expensive.

 

[rabler]

Hi all, just starting to get to work with my myford ml7. Had a small project with some 1045 and killed 4 carbide tips. First was when I got a bit too aggressive with my cut and stalled the lathe. (Belt slip) in fact might have done a couple this way before adjusting the belts ... I was trying to be aggressive as I've always been told these tips like to be worked hard.
Next was when I tried to face right to the center of my job, pushed in a bit hard and lost the tip.

Just seems these tips are too brittle for a learner like me.....

Any tips on using carbide tips for a beginner? Or are you going to say, sick with tool steel?

Cheers Dave

Lots of good advice and thoughts here. One additional thought: Carbide inserts come in various grades of hardness/toughness. Harder inserts tend to take longer to get dull, and are favored especially for high alloy steels, etc, but are more prone to chipping. Tougher inserts are favored for interrupted cuts. They are also a bit more tolerant of things like cutting past center when facing, and thus more beginner friendly.

 

[nzlowie]

Thanks guys. All part of the learning.... Yea I understand, just get a bit frustrating. Next tip order I'll confirm with the supplier and maybe get some tips that are a bit more forgiving. Or just the right ones for the job!

 

[compact8]

I am also a beginner and my experience with carbide insert is that the machine must be powerful enough to maintain a steady speed when under load. If the machine stalls and the speed becomes erratic, the insert tip will break for sure.

Regarding your question about boring bars and holders, yes, the insert tip points downward when viewed from the end of of the bar. I believe the need for extra shims is because the hole of the bar holder is centered instead of having an offset. Try to get one with an offset like this. The shim at the bottom is just 0.9 mm thick.

 

[brino]

@nzlowie,

Hi Dave,

We have all been there.
Keep at it everything you spend time learning now will make the future easier.
Lots of good advice above. Keep practicing.

I have no advice on carbide. I use HSS 99% of the time, on a Southbend 9" lathe.

Welcome to the group!

-brino

 

[addertooth]

I am a full supporter of HSS tools on smaller lathes. Usually trouble for a novice starts when you don't calculate what "feeds and speeds" the charts indicate, and instead choose to "use the force". As others have said, many mini-lathes don't have the stiffness and Horsepower to support the sweet-spot of feeds and speeds that carbide enjoys.

Now for the flip-side of that record. I do sometimes use carbide on a mini-lathe, especially when toughing my way through something like a cast-iron outer layer. I may use it when I am making a Batch of identical items, to simplify hitting the same cutting depths. If the carbide fails. I can rotate the insert, and be back in action. For one-off stuff, it is hard to beat HSS.

 

[MrWhoopee]

Asking your supplier about types and grades of inserts is sound advice, but it also suggests that you are probably paying a high price for those inserts. While you are learning, it might make more sense to get your inserts off eBay or Aliexpress. Trashing a $1 insert is far less traumatic than doing the same with a $10 insert. I have over 20 years in the trade and, while I don't claim that they are equal to the brand name inserts, I find the cheap ones to be quite acceptable for the less than optimal conditions encountered in a home shop with an underpowered lathe.

 

[nzlowie]

Thanks again for your tips guys, appreciate it!
I'm sure there will be more questions coming......

Cheers Dave