Home Made 4th Axis with Harmonic Drive Unit!

[widgitmaster]

As part of a favor to Justin (JUZWUZ), I have choosen to make a couple bases out of 6061 Aluminum to support a VEXTA stepper motor with a Harmonic Gear Reduction unit. The Harmonic Drive has a Ratio of 1/50, with a max Torque of 55Kgcm.

After I make the aluminum support bases, I will make an adapter plate to go between the Harmonic Drive and a 3" 3-jaw scroll chuck.

First I ordered two blocks of aluminum, 4x4x4 1/4

The next step is to machine the cube perfectly square, so the 4th axis motor will always be paralell to the base. The project begins here!

[widgitmaster]

The next phase is to machine one flat surface on each block, to do this I used my homemade Fly-Cutter, with a HSS tool bit sharpened just right!

Because my mill has a 4" vise, I had to remove the jaws to gain a little extra opening! Then I used a pair of "Starrett #54" hold downs to pull the block tightly to the floor of the vise, then I machined the opposite surface perfectly flat & parallel.

[widgitmaster]

Now that two sides are machined, the next step is to make o square corner. To do this, I put my 6x6x6 angle plate on the mill table. By clamping one machined surface to the angle plate and putting a dowel pin under the block to make it parallel to the machine table, I was able to machine a 90 deg corner. Then I placed the other angle plate on the machine, and clamped the block in such a way as to get a third 90 deg corner! Having a pair of 6" KantTwist clamps really helps!

[widgitmaster]

Now that I have a block with all the right dimensions, it's time to chop it up in the bandsaw!

First I scribed my lines on the appropriate surfaces with the carbide scribe attached to my little height gage, then I double checked the layout to avoid any mistakes.

Then I changed the blade in my bandsaw to a 6TPI, and set it at maximum speed. Then I took a wax stick and gooped up the moving blade! Next I pushed the block into the blade and with lots of noise, the corner was removed!

[widgitmaster]

The las part for the evening is to modify an endmill to be used on the inside corners.

A nice new 3/4" 4 flute endmill with a 3" length of cut will do just fine! But first I need to hand sharpen the corners of the endmill on my pedistal grinder, and a .1875 Radius gage. First I free handed the radius on all four flutes using the grinder, then I took a nice stone and honed the edge real keen while wearing an optivisor so my old eyes could see what I was trying to do!

Then I put the freshly saw cut block in the mill vise, and took a cut on one inside surface, to make it .750" thick. The radius on the endmill left a perfect fillet in the corner, to ensure strength of the drive unit! I'm hungry!


Total shop time: 4hr

[Enraged]

impressive work as usual!

[widgitmaster]

Then I flipped the part in the vise in order to mill the other inside wall to a 1.000" dimension

[widgitmaster]

Next I held the part sideways in the vise, and took a cut on both sides, flipping the part to ensure the hub would be central to the base.

Then I used an old .100 gage block to set the depth of the endmill equal to the floor of the part. This enabled me to blend the new cuts in with the exsisting surfaces.

[widgitmaster]

Next opperation requires a solid mill-stop, so the parts can be removed from the vise and put back in the exact same position over and over agan!

Then I used my dial indicator to place the spindle in the center of the part, by moving the table untill I had zero on both sides.

Then I used an old Toolmakers trick to put the spindle center equal to the edge of the part, by using a dial indicator and my .100 gage block! Simply the same as the previous step, except the zero from the back edge of the part, must be the same zero when the gage block is held against the part! This is a little more time consuming than an edge finder, but it is much more accurate!

Now that the part is on location, I drilled a 1/2" hole through each part. Then I used an 1 1/4" dia. 2 flute endmill to open the hole.

[widgitmaster]

The next step is to bore the hole to fit the protruding boss on the Harmonic Drive unit. For this I choose my little 2" boring head.

After several .100 deep passes with a feed of .003 / rev., at 1800 RPM The bores in both blocks are within .010 of finished size.

Because I was very rough with the machine and had removed the parts from the vise several times, I choose to clean up around the vise, and re indicate the part an take a final bore to size. This was done for each block.

They are now at the same level!

[widgitmaster]

Now that the bores are finished, it's time to drill and tap a few holes!

Each part gets 4 #10-24 threads through the part. then each side gets countersinked to make the threads look clean!

After assembly, the harmonic drive unit sits nicely in its new home!

Total Shop time today: 5hr

[widgitmaster]

This project was fun for me, it was not complicated or challenging, but as long as I'm cutting metal, I'm happy!
My methods were choosen to demonstrate a few basic procedures, they may not have been the best way, or the easiest way to produce these parts but they work!
A word of caution to the newbees amoung us, the use of long endmills can be extreemly dangerous! They can grab the part and rip it out of the vise, or they can snap or shatter in your face! After several years of experience on bridgeport mills, I have gained some knowledge as to the limits one can push a long endmill through a piece of metal!

I hope that everyone enjoyed following this post, as much as I have doing it!

Although the parts are not finished; consequently, there are still radius's to cut on the corners, and holes to drill in th base. The bulk of the project is done! I hope everyone can learn from this too!

But ther will be more, as I have to make the fixture plates too!

Sincerely,
Eric