4th Axis Build Help

[Tony Wells]

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.

 

[dustooff]

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

 

[jimemack]

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

 

[DMS]

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.

 

[jimemack]

Do you mean like this:

 

[DMS]

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

 

[geotek]

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.

 

[Codered741]

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

 

[jimemack]

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

 

[geotek]

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.