# 4th Axis Build Help



## jimemack (May 14, 2013)

I am making a 4th axis spindle and have designed it with an aluminum housing/casing - 6" long x 5" high x 4" wide. Will aluminum stand up to those forces from an X2 mill? The housing will be 4" wide, perpendicular to the axis, along the "Y" direction of the table. I'm just worried that the forces might "push" the housing and temporarily, minutely deform it, either vertically or horizontally, creating inaccurate cuts. I probably should have purchased a block of steel, but I wasn't thinking. I haven't cut anything yet, so, worst case, I'm out $64, which is better than being out $64 _and_ having to rebuild it.

Thanks.


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## Codered741 (May 15, 2013)

Are you machining this out of a solid billet of aluminum?  If so, I would say that you are safe from deflections caused by cutting forces.  Give it a good base to sit on, and I doubt you will ever see a problem.  Your little X2 will have a hard time deflecting a 4 inch piece of aluminum.  

That being said, make sure that you leave as much material as possible, don't shave off anything you don't absolutely need to.  

Good luck!  I would love to see the photos when you are done!

-Cody


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## jimemack (May 16, 2013)

Thank you for the info, much appreciated.

Regarding the aluminum, would there be a problem pressing in the bearings at both ends, or would that potentially cause stress problems? Also, I'm not sure how much undersized I should make the interference-fit openings, which will both be about 2.83" (72mm) in diameter and 1.1" (28.75mm) deep.

As you can tell, I'm new at this.

Jim


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## Mid Day Machining (May 16, 2013)

I would use 7050 or 7075 aluminum. It will cost a little more, but they are much stronger materials.


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## jimemack (May 16, 2013)

I just checked the price of 7075 vs. the price for 1018 steel vs. the price for 6061:

4" x 5" x 6" 7075 = $162.20
4" x 5" x 6" 1018 = $114.84
*4" x 5" x 6" 6061 = $64.20* <--- what I paid.

I'll have to try and make the 6061 work.


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## Mid Day Machining (May 16, 2013)

You get what you pay for.


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## jimemack (May 17, 2013)

Steve Seebold said:


> You get what you pay for.



How does that help me?

Just because I paid less doesn't mean it won't work, right?


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## cjsamples (May 17, 2013)

Jimemack,
 I don't think he is bashing your choice but you are getting a weaker aluminum alloy. If you are building it as a tool for life, then maybe the added expense is worth it. If it is just a test or occasional use, you'll probably be ok.

Here is a quick "vs" between the 2.

Basically 7075 about 70% stronger and 63% harder. These numbers vary. It has zinc and copper added to it for strength and it machines very well, but its very difficult to weld with. It also dissapates heat a lot better than 6000 aluminum. 7000 series aluminum is stronger than mild steel.

So it does make it a little more apparent why it cost considerably more.

Chris


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## jimemack (May 17, 2013)

cjsamples said:


> Jimemack,
> I don't think he is bashing your choice but you are getting a weaker aluminum alloy. If you are building it as a tool for life, then maybe the added expense is worth it. If it is just a test or occasional use, you'll probably be ok.
> 
> Here is a quick "vs" between the 2.
> ...





Do you mean "70% stronger and 63% harder" than 6061? I'm not sure I agree with that. Can you show me your source for that info?

Thanks,
Jim


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## DMS (May 18, 2013)

Here is a page of stats of various aluminum alloys

http://www.onlinemetals.com/aluminumguide.cfm

Though I get about 85% stronger for 7075 than 6061 (for yield strength, which is what you care about) using these numbers. The thing is, you probably don't care about strength. I'm guessing you are going to have enough "meat" there that the material itself is not going to shear or deform. Your probably most concerned with 2 things, stiffness, and dampening. Stiffness is roughly the same for any aluminum alloy you get (take a look at the "modulus of elasticity" or "young's modulus" for materials to compare, bigger is stiffer). You can get stiffer by going to steel (it's 3 times as stiff as aluminum) or cast iron (about 1.5 times as stiff as aluminum).

http://www.engineeringtoolbox.com/young-modulus-d_773.html

Ok, now lets talk about dampening. I'm not aware of a metric for dampening, but cast iron is generally considered very good (one of the reasons machine tools are made out of it), and steel is considered poor. Try an experiment. Take a piece of steel and a piece of cast iron roughly the same size and shape and tap them against something hard. The steel will "ring". The cast iron will make a dull thud. Try it with wrought aluminum, and it will ring, but probably not as much as the steel. I guess what I'm saying is, aluminum is probably a "middle of the road" choice, and the alloy is irrelevant (though, cast aluminum _would_ be better, as it has better damping than wrought aluminum). 

Hardness may be a concern, but most of your wear is likely going to be on the bottom, and you could re-surface that. If you are worried about cosmetic damage on the visible portion, you could annodize it, and that will make the surface _real_ hard. You could also mount it to a steel or cast iron "foot" for mounting, I honestly don't think you are going to run into issues for years if at all.

As for pressing the bearings in, I think you will want 1-2 thousands interference. Make sure the bearing pocket is cool when you take your final measurements, aluminum expands a lot when heated. You will also want to chamfer the edges to ease entry. Make sure you press on the outer races when you press it in, not the inner race. If you are not going with shielded or sealed bearings, make sure you have enough room to work in an external seal.

Have you chosen bearings? Have you figured out how you are going to pre-load the bearings?


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## cjsamples (May 18, 2013)

Glad I took the time to read DMS post. I was just about to pull out the numbers but he did the work for me.
Chris

MANY people say 6061 machines "gummy". I agree.
7075 machines like a fine wine.........Sweet!


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## cjsamples (May 18, 2013)

All from Wiki:
T6 temper 6061 has an ultimate tensile strength of at least 42,000 psi (300 MPa) and yield strength of at least 35,000 psi (241 MPa).
T651 temper 7075 has an ultimate tensile strength of at least 67,000–78,000 psi (462–538 MPa) and yield strength of 54,000–67,000 psi (372–462 MPa).

Just wanted to add a source for these numbers.
Depending on T factors they can change drastically.
T4 temper 6061 has an ultimate tensile strength of at least 30,000 psi (207 MPa) and yield strength of at least 16,000 psi (110 MPa).
Mild steel (A36) runs around 400 to 550 MPa tensile and yield strength around 250 MPa.

If the 6061 will get the job done, then it will get the job done.
Chris


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## jimemack (May 18, 2013)

DMS said:


> Here is a page of stats of various aluminum alloys
> 
> 
> 
> Have you chosen bearings? Have you figured out how you are going to pre-load the bearings?




I have chosen 32306 Tapered Roller Bearings. The seals are Timken 473448. I will pre-load by tightening a 3/4" nut on the shaft.

This is really good info, thanks.

Wow...$162.20...I don't know if it's worth it.

Jim


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## DMS (May 19, 2013)

Tapered rollers should do well. Make sure you post some pics of the build


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## jimemack (May 19, 2013)

DMS said:


> Tapered rollers should do well. Make sure you post some pics of the build



I'm going to post pictures from before, during and after. It should be comical to watch someone who has no idea what they're doing actually construct something useful.

Jim


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## jimemack (May 25, 2013)

Somehow, I thought this board would be a lot more active. Is it the time of year? Is the hobby dying? Is it that my topic isn't interesting? Is it an after-effect of censorship? What gives? I was hoping for a lot more feedback before I start making chips.


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## Codered741 (May 25, 2013)

Kinda seems like we are waiting for you...  Give us something to go on, I am very interested to see what you come up with!  If you want more feedback, post a drawing, schematic, bar napkin sketch, etc. I will be happy to look at it and try to find problems! 

Hell, put up a photo of a big block of aluminum on your mill, and you'll have people drooling.  (Just me? Ok...)

Or just dive in and make some chips! Sounds like you have it all worked out, so go for it! And let us know if it worked! Or not! If it doesn't work, you didn't waste the time, or money, you just gained that much experience! 

-Cody


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## DMS (May 25, 2013)

Yeah, didn't mean to leave you hanging, but it sounded like most of your questions were answered (material, bearing fit..). I agree Codered, lets see that big old block of aluminum 

So, how far have you gotten on the design? If you haven't already done so, I would draw it out on paper or in cad just to make sure you have everything accounted for. The other thing to think about is the order of operations (what order you are going to machine each feature in). I have found that to be one of the biggest difference between someone with experience, and someone just starting out, and it makes a big difference. Specifically, you want to re-clamp your work piece the fewest number of times as possible. If you do re-clamp, you want to work to an accurate reference. For example, on that big block of yours, make one surface as flat as you can, then measure everything from there, and make sure that surface is one against the table of your mill, or against your fixed vice jaw. I would also recommend squaring up your stock, and then marking out all your dimensions before you start. It's very easy to miscount cranks of the handle, and drill a hole in the wrong place; marking out lets you see if you are "on" or "off".

I had assumed that you were off working, if you have other questions, or are stuck, just ask, people are always willing to throw in their $0.02.

Not sure if this helps, but here is a link to some pictures of a dividing head I built when I was first starting out. The body is 2x2x2"

https://picasaweb.google.com/113058612034694188913/DividingHead?authuser=0&feat=directlink


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## jimemack (May 26, 2013)

Well, being the idiot that I am, I didn't realize it was my turn. I do apologize - I am new at this. I have begun and will post drawings and progress. Again, I'm sorry for not understanding the 'process'.

Jim

- - - Updated - - -

Here is a hint:




This is my design that I created in Excel. Please bear with me.


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## DMS (May 27, 2013)

Looks pretty solid. What are you planning on doing for the spindle (construct, purchase)?

Not sure if you have seen this, but it's a 4th axis along similar lines. The guy integrated a brake into the assembly to help when doing heavy cuts

[video=youtube_share;b2-Kdud7eiA]http://youtu.be/b2-Kdud7eiA[/video]


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## Tony Wells (May 27, 2013)

I'm curious about your remark about censorship. If you have concerns, please send me a PM with details of what you believe to have been censored.


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## dustooff (May 27, 2013)

Hi all,
Jim great drawing, I'm lucky to get basic spreadsheet work done in excel.
I'm heading down this path also, a 4 axis build for indexing work.

Currently have most of the hardware,
Bits of Al stock, some bearing pockets machined
T5 pulleys, drive sizes are 15,20,30 teeth and driven sizes 30 or 40 teeth.
5A 570 Oz-in stepper with  2M542 4.2A microstepping driver. Only running at 30V supply to driver.
30204 tapered bearings x 2
ER40 collet straight shaft spindle.

I have a 2 plane design for the bearing mounts, with everything tied together in a box format.
I have drawn up some plans in CAD, great for visual assistance. Will post when I can.

I was going to have the two tapered bearings back to back at the inside of the shank and one
plain radial bearing at the outside end.
But now I think just the two tapered bearing one at either end of the shaft should be enough.
Any comments.

The pulleys I have I had to bore out to 20mm from 3/8". The size was no problem just a simple
pocketing operation on the mill. I centred the original hole as the reference, but got me wondering
about if it was a few thou off centre, the pulley now has an eccentric motion, this would mean
any job mounted now will have a varying surface velocity directly related to the pulley error.
Am I right?


regards
Andrew


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## jimemack (May 27, 2013)

Hi *Dustooff*,

Here are my specs:

Spindle: 1-1/4" D (before machining) x 6.25" L, Steel, Rockwell C60-C65
Bearings: SKF 32306, 1.1811" ID, 2.8346" OD, 1.1319" Thickness
Bearing Seals: Timken 473448, 1.750" ID, 3.001" OD, .375" Thickness
Large Pulley: 60-Tooth
Small Pulley: 10-Tooth
Gear Ratio: 10:1
Housing 6061-T6 Aluminum (might not have been a good choice), 4" x 5" x 6"
Chuck: 3", 4-Jaw, independent
Motor: KL23H276-30-8B, 1.8°, 200-Step, NEMA23 282oz-in 3A Stepper Motor ¼-Inch Dual shaft
Driver: M542 CNC Stepper Driver Controller 2/4 Phase, 256 Microstep, Multiple Subdivision
Theoretical Maximum Resolution: 50,000 Steps Per Revolution (1.8° Motor) = 0° 0' 25.92", or ≈ 26 Arc-Seconds

This is my first attempt at doing anything like this, so maybe it's impressive, maybe not.

As for the drawing, I've been designing everything in Excel - electronics, mechanics, woodworking, etc. - since the 90's. I find it to be a very useable drawing tool, but you have to create all the parts from scratch, and to perfect scale, for it to work. Additional benefits include parts lists, calculations, commentary, notes, etc. Also, the compatibility can't be matched - everyone has Excel. Therefore, I can send my work to almost anyone in the world and have no problems with compatibility.

*DMS*:
Very cool video!

Here is a drawing of the spindle before threading:





After threading with Taper (2MT):





Jim


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## DMS (May 27, 2013)

Is that 60 rockwell before or after machining? If before, that's not a trivial thing to do; if you are going to harden after machining, people usually leave an allowance so that the part can be ground after machining. Steel will often distort after heat treat, leaving an allowance for grinding lets you hit your target specs. Another option is 4140 pre-hard. It comes in a rockwell hardness of around 30C, but that's probably plenty. 60C is pretty dang hard; it may be overkill (and add a lot of points to the difficulty of this project).

For the spindle nose, I would recommend making it a little longer so you have enough to add a taper for registering the chuck mounting plate. Threads are not not particularly good at centering things. If you take a look at the picasa album I linked above, the chuck back plate I made for my dividing head uses a taper to register on the spindle. Once they are locked together, friction alone holds them tight. It is also dead straight and repeatable. The trick here is to cut both tapers (the one on the spindle, and the one in the chuck back plate) without moving your compound. It takes a little planning, but it's do-able, and the results are fantastic.


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## jimemack (May 27, 2013)

Do you mean like this:


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## DMS (May 27, 2013)

Exactly. Just remember, that taper is going to be cut into the back-plate, so it will take up some of your thickness.


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## geotek (May 27, 2013)

I think you are making this harder on yourself than I needs to be.  It is unlikely your little mill has enough force to hurt the aluminum housing, let alone a steel spindle. So 6061-T651 should do you quite well.
I would not thread the spindle unless you really wanted to mount other chucks.  In a lathe, the threaded spindle is always taking force from a single direction (unless you reverse too fast), so the chuck stays tight on the spindle.  But in your application, the forces can work of the chuck from either direction, and may unscrew the chuck from the spindle.
Instead, use a bit larger spindle diameter and bolt the backplate to a step on the spindle.  Just 1018 steel would work well.  Then mount the chuck to the spindle.  Go with as big a through hole as you can, and use an MT sleeve to sleeve it down to #2.  In this way you can use the system to cut shapes on the ends of long shafts.  Maybe even try some thread milling.


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## Codered741 (May 27, 2013)

Instead of changing the mount on your spindle, just make a way to secure the chuck.  Could be as simple as filing a flat on the threads, and putting a set screw in the mounting plate.  

-Cody


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## jimemack (May 28, 2013)

Interesting, Codered, as I was planning to use a setscrew and a tiny piece of brass to push between the threads to hold the backplate on. I wasn't sure if it would work.

Jim

- - - Updated - - -

George,

Not to get off topic, but I noticed the mention of your former life in your signature. I am a ham, who's built many things, some I've designed, and others that were sold by companies like Heathkit. I recently completed the Ten-Tec 1254 Shortwave Receiver; what a cool little radio.

I own an iCOM 746Pro and an iCOM IC-7700 <-- what a cool *BIG* radio.

I also just ordered the Elecraft K2/100 with most of the options.

Enough rambling about things that have nothing to do with machining. I just thought I'd mention it.

...and thanks for the tips.

Jim


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## geotek (May 28, 2013)

I'm a Ham as well, KC5RCC.  Hams don't build nearly as much as they used to, but the SDR has sparked the interest in Hams to start experimenting again.
I've got a FT-1000MP, but I don't get on the air much.  I always enjoyed the technical side more.


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## jimemack (May 28, 2013)

geotek said:


> I always enjoyed the technical side more.




Me, too.

Machining is pretty cool, though. I find it stimulating in that I don't have to strain my brain too much. I just watch this machine eat metal.


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## Codered741 (Jul 22, 2013)

Did you ever get this built?

I would love to hear how it turned out!  And see!!

-Cody


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## jimemack (Aug 19, 2013)

...still working on it.


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