# Change gears



## deadfrednc (Sep 8, 2014)

I'm turning a peice of 6061-t6 it's an 1 1/8 and I'm going down just below 1" spindle speed is around 1000 rpm and the back gears I'm not sure how there setup I'm not very familiar with that area. My cuts are very rough though but the feed is pretty slow so should I speed it up and if so how do I do that?


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## deadfrednc (Sep 8, 2014)

*Re: Back gears*

I apologize I meant to say change gears not back gears. I'm not sure how these are supposed to be setup it's missing the cover which apparently has a chart on it.


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## JimDawson (Sep 8, 2014)

*Re: Back gears*

If you can provide the model of your lathe, maybe someone can take a a picture of the their gear chart, or maybe do a Google search.

Given the information you have provided, the spindle speed might be a little faster that I would turn it, I would normally be in the 750 range mainly because the next speed on my lathe is about 1200.  Also, try some WD-40 as a cutting fluid, works great on aluminum.  6061 is kind of sticky, so a cutting lube helps a lot.  The other thing that comes to mind is the tool bit, make sure it's sharp, and is not rubbing behind the cutting edge.

Hope this helps.


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## Bishop (Sep 8, 2014)

*Re: Back gears*

Post a picture of your setup and I'm sure things can get figured out. Aluminium is quite easy to get a good finish on with the right tool and proper setup.

Shawn


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## Pat of TN (Sep 8, 2014)

*Re: Back gears*

If you're using an HSS tool, figuring 300 SFM - which is slightly conservative, but regardless - I don't see much wrong with your RPM, assuming the lathe is in decently good shape as far as spindle bearings, gib adjustment, rigidity, etc.

You will have to figure out your feed in IPR - inches per revolution - before we go further, and describe how the finish is rough... is it simply rough, ridged? Or perhaps, is the tool feeding fast enough to cut threads, leaving evenly-spaced grooves?

There is also your tool grind as well. Again assuming high speed steel, aluminum cuts best with cutters that have a higher back/side rake and relief than steel. It's not entirely necessary, but it helps. A slight radius on the tip is a must as well.

Your setup is also important. Even if it's a 1" piece, if it were sticking out three or four inches - especially if you have a smaller lathe, another unknown factor - that would certainly cause chatter due to workpiece deflection.

When you get time, feed us some more details - we hunger!


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## deadfrednc (Sep 8, 2014)

*Re: Back gears*

TH42 is the model number and yes I've checked it over.  Everything is in good operating order. I'm also using carbide tooling. No pics at the moment


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## deadfrednc (Sep 8, 2014)

*Re: Back gears*

Ok I found what I believe to be the correct chart online and from what I see on it my lathe the gears are configured for  .0035 ipr


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## Pat of TN (Sep 8, 2014)

*Re: Back gears*

Carbide, I see. Fred, I would check the tool for any kind of damage or excessive wear. .0035 IPR isn't an extraordinary number by any stretch, so that isn't the issue. I've never had a great deal of luck with carbide on aluminum - usually to get anywhere close to the "proper" SFM, you gotta be flying. Figuring 1000 SFM on a 1" diameter, part, you're looking at 4000 RPM, so... but, aluminum is forgiving enough you don't really need to get scientific with it.

So, take a glance at how your tool is ground. See if it has any chips in the tip (bad), or if it has a slight radius or chamfer on the tip (good)...


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## kd4gij (Sep 8, 2014)

A pic of your tool and setup would help. I use carbide inserts on 6061 all the time I usley run around 300-500 rbm at the same ipr. Make shure your tool is on center line. And use wd40.


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## wa5cab (Sep 9, 2014)

Threading charts for all 10" and late 12" and speed charts for all 16-speed machines except the 6" are in Downloads.  In the Maintenance and Tech Bulletin folder.  I see that I need to add the ones for 6" and both early 12" groups.

Robert D.


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