Aluminum or Steel for 4th Axis?

[jimemack]

Hello,

I am acquiring all of the materials to convert both my mini mill and mini lathe to CNC machines. I have all of the electronics, all of the hardware and mechanics, most of the raw materials, and now I have completed my design of the 4th axis, which I plan to use for gear-making and other, more or less, light-duty stuff. It is a rotary indexer, of sorts.

My question is around what to make the housing out of. I am thinking I can use aluminum, but am not sure how sturdy aluminum really is when it meets up with milling forces, as I make things using it. Can anyone give me an opinion or experienced guidance?

I really appreciate any assitance you have to offer,

Jim

 

[8ntsane]

Hello Jim

I can only comment on what Ive seen on you tube vids. im sure you have looked at many as well.
From what I have noticed, they are mostly built from aluminum. If your building a indexer, I would think aluminum would do the job fine. I think many builders are thinking of the weight of the unit if built in steel. From looking at many, Ive seen some that were very compact, while others not so much. Some had used collets for main work holding , while others mounted a chuck to the spindle. With so many designs out there, the weight could easly become a issue, depending on a variety of things.


Is this something similar to what your building?
http://www.youtube.com/watch?v=9Sr9p8tCv_g&feature=endscreen&NR=1

 

[David Kirtley]

Personally, I am going a low tech direction with mine. I am just using a replacement spindle, a pair of pillow blocks and a 60 tooth sprocket. Just did the boring tonight for the sprocket to mount on the spindle. Will use #25 chain to drive it. Went with the big sprocket so my little steppers have more umph.

 

[Tony Wells]

If you want the best stability, and strength, find a chunk of cast iron or order from DuraBar. Next best would be steel. I would never, myself, make a machine tool accessory out of aluminum, if for no other reason, durability. Aluminum may be easier to work with, no argument there, but for longevity, iron or steel.

 

[Hawkeye]

For a middle-of-the-road option, you could use aluminum for the body, but use steel or cast iron inserts for the wearing surfaces.

 

[jimemack]

Thank you 8ntsane, David Kirtley, Tony Wells and Hawkeye for your diverse and insightful recommendations.

I feel that, being the middle-of-the-road kind of person that I am, I should consider a hybrid solution - an aluminum housing, reinforced with either steel or iron where the bearings will be pressed in. However, since I am using deep groove ball bearings with steel housings, do I even need to consider the wear factor with the main housing? The bearing housings are all that should come in contact with the aluminum.

I could just use a square aluminum tube of sufficient dimensions, reinforcing the walls that the spindle would be inserted through with a thick aluminum plate so that the bearing housing will be completely enclosed in aluminum, as the square tube walls are only 1/2" thick.

I don't know if that would work, since I'm rather new to this hobby. What do you think?

Jim

 

[Tom Griffin]

Tony has it exactly right, the most important factor in designing machine tools is rigidity and cast iron is the best candidate, followed by steel with aluminum a distant third. Another material being used lately in machine tool design is cast, reinforced concrete. A base might be fabricated out of sheet steel and filled with concrete, with re-bar placed in strategic areas for reinforcement. It makes for a very strong, rigid and inexpensive replacement for a casting. I know there are several blogs on concrete machine tool construction as well as a Yahoo group.

Tom

 

[8ntsane]

Jim

I can see your approach to the middle of the road thing. I also can see what Tony and Tom say with the use of cast iron or steel. I doubt your using this for any production work, and most likely occasional work. From what I have seen, it appears many are built from 3/4, or possibly 1 inch aluminum. Making a tube to encase the spindle is one approach. Though you may find it easyer to build the bearing walls from thick material, and machine up bolt on housings that would hold a seal. Ive also seen many that had anything from a plate for the top, to a piece of lexan to keep chips from entering the enclosure.

You might also want to look on E-Bay for other idea,s. I found many of these listed from several sources. David has certainly made a simple version of this. With bearings in there own housings, Im guessing he only needs to make a base plate. Keeps the parts to a min, but probably needs some sort of cover to keep chips out. No doubt just a tin cover will work well. Many variations of these out there, from super simple, to very complicated.

 

[PurpLev]

consider that 4th axis is usually used for lighter cuts and not for heavy shaping processes, Alum might be just fine for the housing - especially for a smaller setup (as in not a production house)

 

[David Kirtley]

People have been successful with AL for 4th axis on small machines. You just have to work within design parameters. What is right for a little mini-mill would be dead wrong for a large milling machine. With a mini-mill, you are going to have between a 350 watt motor to a 500 watt motor depending on the model of mill so you are not going to be really hogging out material regardless.

In my opinion, for a 4th axis on an X2 or smaller like the Taig or Sherline, the best solution is to bite the bullet and pick up one of the Sherline CNC rotary tables. Direct drive solutions will take up a lot of space. You would be hard pressed to come up with a better design that will fit the table and still leave you room to work. You can make one but if you buy a rotary table to modify, it will cost about the same as the complete Sherline unit.

I won't be putting mine on a mill. Mine is for a separate dedicated machine. I will have room to spare.