# Turning Aluminum at 1400??



## MWCurl (Feb 3, 2019)

Hi Guys

I am considering buying a new 1236 lathe that turns at a maximum of 1400 RPM.  When I use the formula for calculating recommended RPM’s for turning aluminum with a 1/2” diameter, I get a recommended speed of  2000 RPM. Does anyone have experience turning aluminum with that diameter or small at 1400 RPM? If so, what is the result?

Mike


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## derf (Feb 3, 2019)

It will work fine. I'm constantly turning small diameter pieces of aluminum at less speed than that just for the fact that I don't want to go to the hassle of changing speeds for such a short operation.


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## ttabbal (Feb 3, 2019)

It's fine. Think of it as a maximum speed rather than a minimum. I rarely go higher than 400 because I'm lazy and don't want to change the belts around. I mostly use HSS though, which likes lower speeds. 

The higher speeds are nice in that things happen faster with the power feed etc.. But it's often only a minute or two with the smaller parts I make, so I don't mind. 

If it's 3 phase you could use a VFD to speed up the motor if you want faster, but then you have bearings and gears to consider.


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## Mitch Alsup (Feb 3, 2019)

I have a 12-36 G4003G, I typically use 1/3rd the recommended speeds. Most of my 1" turning (inside and out) is done at 360 RPMs.

But I am NOT doing production work, nor is my time valuable. {It is to me, but that is a different story.}


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## P. Waller (Feb 3, 2019)

The spindle speed is dependent on the cutting speed required.
For .5" aluminum, say common 6061 rounds I would consider 2000 RPMs slow.
There is no reason that such a part can not be run at 5000 RPMs  using carbide tooling or 2000 RPMs with HSS tooling in general turning operations.

I use 600 FPM as a starting point with this material, this would be 4600 RPMs to start with a .5 diameter round.


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## T Bredehoft (Feb 3, 2019)

_*Speeds*_ are specified for those who need to spend as little time as possible, (production).
Those of us who play in the shop are not required to use the fastest speed. There is no penalty or reason not to go slower than the max. Finish will not suffer.

_Edit_: Speeds, not feeds. CSR kicking in. Mia Culpa.


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## P. Waller (Feb 3, 2019)

I fully understand this, do not however confuse cutting speed and feed rate.
Cutting speed is one parameter, feed is a completely different thing.


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## MWCurl (Feb 3, 2019)

T Bredehoft said:


> Feeds are specified for those who need to spend as little time as possible, (production).
> Those of us who play in the shop are not required to use the fastest speed. There is no penalty or reason not to go slower than the max. Finish will not suffer.


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## Dabbler (Feb 3, 2019)

I find that if you take your time, you get really good surface finishes in aluminum, _if_  you keep your tooling sharp - no really sharp, and you feed your cutter very, very slowly...

I never use carbide in aluminum so I defer to thos with more experience.  I use HSS for aluminum.


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## MWCurl (Feb 3, 2019)

Thanks guys.  I appreciate the comments.


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## magicniner (Feb 4, 2019)

I'm surprised anyone makes a small lathe with such a low maximum speed, the Myford Super 7 was capable of over 2000rpm and is a very old design.


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## P. Waller (Feb 4, 2019)

T Bredehoft said:


> _*Speeds*_ are specified for those who need to spend as little time as possible, (production).
> Those of us who play in the shop are not required to use the fastest speed. There is no penalty or reason not to go slower than the max. Finish will not suffer.
> 
> _Edit_: Speeds, not feeds. CSR kicking in. Mia Culpa.


Exactly, I was pointing out to the OP that slower is not a problem. 1700 RPMs at 1/2" diameter is 220 FPM.

I rarely run a lathe above 2000 RPMs with a 3 jaw chuck because this vaporizes the coolant, a collet chuck is a different ball game however, it has no fan blades (-:


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## magicniner (Feb 4, 2019)

Slower is fine if slow is fine for you. 
I've always had so many things on the go that it's been advantageous not to go slow just for the sake of going slow, I've never enjoyed doing anything in a sub-optimal way and I always enjoy learning and applying new things. 
That's not going to change if I retire unless I complete all the projects on my list, and it's a long and growing list


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## MWCurl (Feb 4, 2019)

I understand the desire to be as “efficient” as possible. However, I am retired and am not pressed to finish a project in the shortest amount of time. I recently purchased a mill and will use it along with this lathe to do small projects in my shop at the farm. I just want to make sure I am not eliminating the possibility to work on small diameter aluminum stock with a maximum of 1400 RPM.


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## Mark Needham (Feb 5, 2019)

32rpm. Is there really a hurry?


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## macardoso (Feb 5, 2019)

I run a 12x36 and rarely go into the high speed ranges due to a slightly annoying belt change. As such my top speed is 550 rpm. I do 100% of my aluminum turning with carbide aluminum specific inserts and get great results. When doing very small work I might hop up to 1200 rpm but that's rare.


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## hanermo2 (Feb 5, 2019)

Alu is soft as butter and will cut with most-any tools at whatever rpm, and doc.
Finishes are decent, not great.

High rpm has a big flywheel effect, and can result in exceptional finishes and accuracies.
The spindle stabilises, and thus the workpiece vibrates less, at high rpm.

It wont matter for hsm homeshop users, and any final sizing is easily done with abrasives.

I use ccmt 21.51 inserts for tool steels (98%) and everything else like alu and brass.

Biggest improvement ever was a 0-100% analogue feed and spindle speed override on a real servo motor spindle.
After some time, my rpms went way, way up, and the results got even better.

But you do not really _need_ a variable speed spindle for alu, at all, nor for steel - for decent results.

New ccmt inserts will leave mirror-like finishes on alu and tool steel, for a while.
The edges wear and the finish suffers, over time.
On alu the edges last very much longer.

I bought a 100-pack of inserts maybe 6-7 years ago and half are gone.
Around 2000 hours of cutting time in tool steels, mostly big stuff like 200x200x70-50mm blocks, in a 10" 4-jaw.
12x24 lathe, chester craftsman.


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## macardoso (Feb 5, 2019)

I'm a big fan of the positive rake high polish inserts specifically for aluminum like the CCGX and TCGX.


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## magicniner (Feb 6, 2019)

Always plenty of time left!


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