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Author Topic: Adding a 4th axis to my mill  (Read 18616 times)

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Re: Adding a 4th axis to my mill
« Reply #10 on: March 17, 2012, 09:26:53 AM »
Nice work, Mike.

50% axial load for a deep groove ball bearing... sounds too much to me too. Hope he knew what he was saying ;)

Dan

The SKF bearing engineer sure sounded competent. He did specify that is was these larger 6200 series bearings that handle 50% of the radial load. Smaller bearings only handle 25% he said. I ordered the 45 x 85 x 19 bearings. Some of Mr. Simpson's bearings were 45 x 100 x 25. The ones I'm using are well within load and rpm specs. I just hope they are accurate and also that my spindle fits them well. Fingers crossed.
Re: Adding a 4th axis to my mill
« Reply #11 on: March 18, 2012, 01:59:27 AM »
The bearings arrived today. The one I tried appears to be a press fit on the spindle. I could push it on by hand about 1/8". So tomorrow I'll go into the shop and see how much of a press fit it really is.
Re: Adding a 4th axis to my mill
« Reply #12 on: March 19, 2012, 02:14:23 AM »
I tried to press one of the bearings onto the spindle. After I got it on there straight, it went on nicely. I pressed it on about 40% of the way and realized I need to probably press it into the front wall first, then press it onto the spindle. I have yet to machine the walls. At least the fit is good.

Offline Dan13

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Re: Adding a 4th axis to my mill
« Reply #13 on: March 19, 2012, 04:47:48 AM »
Check bearing fitting tables. The bearing fit in the housing doesn't have to be as tight as on the shaft. It's not an interference fit for that matter in most cases.

Dan
Re: Adding a 4th axis to my mill
« Reply #14 on: March 19, 2012, 04:27:24 PM »
Hi Dan,

I've not heard of bearing fit tables. I'll look into them.

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Re: Adding a 4th axis to my mill
« Reply #16 on: March 20, 2012, 09:33:43 AM »
I never knew there was so much science to press fitting bearings. I've always done it more or less by feel with success. Thanks for the links Dan.

I will be cutting up the pieces from the 1" stock here soon. Then we'll test my larger bearing press fit skills!

Re: Adding a 4th axis to my mill
« Reply #17 on: March 20, 2012, 09:56:49 AM »
I don't have any photos to post of it, but I added a 4th axis to my machine about a year ago. Basically, I just constructed an upside down U shape out of 2" aluminum blocks, and mounted the headstock shaft to the assembly using 2 pillow block bearing assemblies. (With eccentric collars on each). For the shaft itself, I used 2" diameter stock, and turned the ends down on my lathe to fit inside the eccentric collars of the pillow bearings. This created a shoulder on the shaft, which the collars seat against.

 Once I mounted everything up, I used a dial indicator the set the shaft to absolute center- then locked the set screws on the eccentric collars of each bearing. A tooth belt and gear assembly was used for installing the stepper motor to drive the headstock. I threaded a round-head bolt into the side of the shaft (between the two pillow blocks) which strikes against a microswitch to index the A axis to zero.

I used a similar construction in building the tailstock assembly. Both the headstock and tailstock assemblies are cradled between two pieces of angle steel. The headstock is of course bolted to these angles, while the tailstock slides along the length of the angles. The tailstock assembly itself is free to slide along the angle rails, and is adjusted by use of a lead screw threaded into the tailstock mounting blocks. The opposite end of the lead screw is inserted thru a second aluminum block upright which also slide along these rails. Two bolts pass through the aluminum block upright, (at the knob end) and thread into a piece of 1/4" flat stock suspended below the horizontal planes of the angle rails, which acts as a clamp mechanism to secure the position of tailstock.

This allows for easy (rapid) adjustments of the tailstock position from the top side of the machine. The lead screw has about 14" of travel, so plenty of adjustment capability. However, adjusting the position by turning the lead screw knob is a slow process. This was the reason I added the 1/4" threaded flat stock to clamp the assembly to the rails. For rapid adjustments, I simply loosen the two locking bolts, and slide the entire tailstock assembly to the desired position. Re-lock the two bolts, and then turn the lead screw knob to load the tailstock against the work piece.

The rails were added alongside the table, for the 4th axis assembly. Which allows use of the machine in 3 axis mode. I later added an adjustable limit switch (the positive Y axis limit) to allow for rapid setup for 4th axis use. I simply change the Homing from Negative, to Postive for the Y axis when preparing Mach3 for 4th axis work. This took some trial and error the set the Y axis positive limit switch in the correct position, so that the router's center is moved to top dead center of the 4th axis during Homing. Because of the distance Mach3 backs off the switch, once contact is made during Homing.

This assembly being a direct-drive system requires a LOT of torque! I originally had a 900 oz in stepper, which just wasn't up to the task. So I upgraded to a 1200 oz in stepper to drive the 4th axis -which worked.

After adding the 4th axis, and experimenting with it a few times, it has largely remained unused since. I do not have an encoder setup, but rely on the limit switch for indexing to zero on the A axis. Which of course, is not reliable enough for cutting gears, and such. But does function for doing things like small columns such as chair legs, etc. up to 30" long and 8" diameter. I use CNC Wrapper to create the 4th axis tool paths.
Re: Adding a 4th axis to my mill
« Reply #18 on: March 20, 2012, 10:10:26 AM »
Hi adprinter,

You really should post pics and a write up in your own thread. Great projects like that are a help to many folks.

Mike
Re: Adding a 4th axis to my mill
« Reply #19 on: March 22, 2012, 10:55:02 AM »
Found some 1.25" aluminum rod for the motor shaft adapter at a local supplier. Originally I was going to use steel. But a lower rotating mass is a better choice. And another piece of 1" flat stock for enough material to have enough for the tail stock. I'll lay out the parts on the flat stock to make sure I have enough material. I don't think my horizontal band saw is tall enough to hold a 9" piece. The standard back up plan is to use a hollow ground saw blade made for cutting aluminum in my circular saw.