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- Dec 3, 2014
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That is one heck of a crankshaft in photo above. You should be proud. Is there a write somewhere about its construction?
michael
michael
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Models for grinding HSS Lathe Tools
- Thread starter mikey
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- Dec 20, 2012
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My Emco 11" lathe manual says that if I want to go deeper than 0.200" I need to step down the speed one notch and then go for it. This is with a conventional tool so I figured a square tool would handle it and it did with no problem. It is a big cut, though, and we won't be doing this very often because its a waste of material but its fun to try it.
- Joined
- Dec 12, 2012
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- 109
Well I wish I could take credit for doing something to that crankshaft, but I had only mounted it up for fun! It's from my old Audi 5 cylinder.. a quattro, with 20 valve head... some would say, quattro 20 valve, or q20v... 
Mike, the biggest cut I've taken is about .075" DoC on heat treated 4140, bar was about 5/8" dia. using a carbide insert. It went pretty smooth and I had no real reason to go deeper at the time. But I'm anxious to give this HSS bit a try tomorrow. I will follow your guidance and report back. I'll even try taking a video.
To be honest I typically don't use feeds/speeds formulas but I suppose now is as good a time as any to learn.
Using 550 SFM for Aluminum (https://littlemachineshop.com/reference/cuttingspeeds.php) I'd be looking at 1400 RPM:
http://www.custompartnet.com/calculator/turning-speed-and-feed
That about right?
And for feed rate, the slowest my machine will go is 0.0025 IPR, should I try that or is there a more scientific approach I should be taking? I suppose it depends on what my machine can do?
Mike, the biggest cut I've taken is about .075" DoC on heat treated 4140, bar was about 5/8" dia. using a carbide insert. It went pretty smooth and I had no real reason to go deeper at the time. But I'm anxious to give this HSS bit a try tomorrow. I will follow your guidance and report back. I'll even try taking a video.
To be honest I typically don't use feeds/speeds formulas but I suppose now is as good a time as any to learn.
Using 550 SFM for Aluminum (https://littlemachineshop.com/reference/cuttingspeeds.php) I'd be looking at 1400 RPM:
http://www.custompartnet.com/calculator/turning-speed-and-feed
That about right?
And for feed rate, the slowest my machine will go is 0.0025 IPR, should I try that or is there a more scientific approach I should be taking? I suppose it depends on what my machine can do?
- Joined
- Dec 20, 2012
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Cutting speeds matter but I try to keep it simple. Instead of a calculator, I use the formula: RPM = SFM X 3.82 / D, where SFM is your cutting speed, 3.82 is a constant and D is diameter of the work. This works for both carbide and HSS tooling; the SFM will differ, with carbide being roughly twice the speed of HSS. Keep it simple.
The rpm derived from the formula is just an estimate of speed. Most folks go with the calculated value or the closest lower speed but with your modified tool, I would go with the next higher speed instead.
Feed is something you need to work out. It will vary with the gearing on your lathe and I would start with the lowest feed and work up until you get the result you want. When I evaluate a new tool, I don't power feed. I feed manually. I want to know what the cut sounds like, looks and feels like when I can feel a slight positive resistance to the feed. This tells me what to expect when things are right for that material, tool and lead angle.
Big depths of cut is an ego thing for the most part. We should be starting with stock close to our final diameter to reduce waste. However, its fun to see what a tool can do. If you like, try a 0.100" deep cut in aluminum and work up from there. I think you will be surprised how big a cut your square tool can handle in aluminum; I've gone up to 0.25" without even slowing down the lathe and I'm sure it can go deeper.
Do the same with mild steel; start low and go up. You will find that when the lathe slows or chatters, you need to drop down a speed but the lathe will make the cut. Play with it and see. Your square tool is capable of much more than you think.
Keep in mind that when a tool chatters you should first reduce your lead angle a bit. If that fails, reduce speed and increase feed and that will handle it.
Let me know if this is at all unclear.
The rpm derived from the formula is just an estimate of speed. Most folks go with the calculated value or the closest lower speed but with your modified tool, I would go with the next higher speed instead.
Feed is something you need to work out. It will vary with the gearing on your lathe and I would start with the lowest feed and work up until you get the result you want. When I evaluate a new tool, I don't power feed. I feed manually. I want to know what the cut sounds like, looks and feels like when I can feel a slight positive resistance to the feed. This tells me what to expect when things are right for that material, tool and lead angle.
Big depths of cut is an ego thing for the most part. We should be starting with stock close to our final diameter to reduce waste. However, its fun to see what a tool can do. If you like, try a 0.100" deep cut in aluminum and work up from there. I think you will be surprised how big a cut your square tool can handle in aluminum; I've gone up to 0.25" without even slowing down the lathe and I'm sure it can go deeper.
Do the same with mild steel; start low and go up. You will find that when the lathe slows or chatters, you need to drop down a speed but the lathe will make the cut. Play with it and see. Your square tool is capable of much more than you think.
Keep in mind that when a tool chatters you should first reduce your lead angle a bit. If that fails, reduce speed and increase feed and that will handle it.
Let me know if this is at all unclear.
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- Dec 12, 2012
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No, Mike, that is perfectly clear and is great guidance to follow. I'll play with it tomorrow and let you know how it goes. Many thanks for taking the time to explain everything in the detail that you do. I've been using the lathe for about 5 years now (intermittently) and although I feel like this is somewhat back to basics, it's obviously something I never had a good grasp on. I've been getting by for my non-critical parts, but now that I have a better grasp on what the lathe can do, I'm starting to think of more complex projects, and getting these basics locked down, I think, is vital.
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When I'm looking for an answer, the worst thing that happens is when someone tells me what but doesn't tell me why or how or when. I hate that. That's why most of my answers will be fairly complete so as to not leave you in a lurch. I mean no offense.
It's funny but whenever I have a machining issue, its usually something basic that I didn't attend to. So yeah, basics, I like basics.
And that's why this has been a very good thread with lots of good learning. This has been one of those learning experiences where the teaching vs doing it for someone has really paid off. ( Teach a man to fish...........)
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Thank you, Todd. I'm waiting for someone to modify a tool for specific material so we can go through the thought process. I mentioned it when I discussed the tools I made for @Bamban; he has a short video he can post if he feels it appropriate that shows how the chips come off (vs his carbide tool) and where the chips come off at the tip. The tool does what we wanted it to do and the video shows it. I will leave it to him.
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I'm looking forward to getting in on some of this fun. I've got some work in front of me but shouldn't take too long.
If you care to take a peek and confirm my dummy of the day,
http://www.hobby-machinist.com/threads/my-pm-1236-precision-arrived-today.63106/#post-519965
Q20V
I looked at the pic of your crankshaft chucked in your lathe and thought my eyes were playing tricks on me. I looked and counted and looked and counted but all I could come up with was five!!!
If you care to take a peek and confirm my dummy of the day,
http://www.hobby-machinist.com/threads/my-pm-1236-precision-arrived-today.63106/#post-519965
Q20V
I looked at the pic of your crankshaft chucked in your lathe and thought my eyes were playing tricks on me. I looked and counted and looked and counted but all I could come up with was five!!!