I did the same calculation on DMM's next smaller motors and came up with the same figures. The smaller motors when geared down with at least a 2 to 1 ratio have more torque and a higher RPM to the screw than what their larger motors have.
I look at the constant torque ratings of these motors as what the sustainable constant feed torque is going to be. 1125 in/oz sounds like allot, but that's peak torque. The constant torque rating is quite a bit less.
I have 25mm dia. by 5mm, or .196 inch pitch screws. I am doing a 3 to 1 reduction. The keling motors have a max RPM of 3200 divided by 3 is 1067 RPM to the screw, times .196 for the pitch of the screw gives me a top rate of 209 ipm.
I could more than likely get by with smaller motors for the X and Y axis, but I need the power on the Z axis. My head assembly will weigh in approximately 75 to 100 pounds heavier than the stock head. As I wrote in another thread, I am building a new Z-axis head slide assembly using heavy duty 35 series linear rails and bearing blocks. The new head mounting slide or plate is 1.50 thick by 11.50 wide by 16.00 inches long. The column is going to have the sides machined for the mounting of the rails and the 4 bearing blocks will bolted to side plates that will be screwed and doweled to the new head slide.
I still have quite a few components to fabricate yet, and then there's all the re-machining of the table and saddle ways before I can even think about installing any CNC parts.
But this is getting way off the topic of my original post.
I think it would be a good idea to calculate the order of magnitude of the torque applied by your intended milling processes. You may find that a brake is essential. Without some form of calculation you are just guessing that your 6:1 will hold the spindle.
You could start by calculating your maximum case horsepower applied at the cutter. Then assume this horsepower (converted to force at the cutting edge) is applied to the work piece at 90 degrees to the indexer axis and at the maximum intended workpiece diameter. This would put you in the ball-park of applied torque. If nothing else it would help you to design/select an appropriate brake.
The machining work that I am considering for this fixture would be mostly continuous radial motion with small or tiny cutters .125 dia. or smaller on parts 2 inches in dia. or less. Primarily in the X,Z and A axis. Some operations that I have in mind involve small abrasive tooling. The idea of a break is a good one. I agree it would be a necessity if one were doing heavy cuts on larger pieces than what I am considering in static indexing situations. Working with 4th axis rotary motion is a funny duck with trying to figure cutting force. Since force is never a constant in rotary motion in relation to the center of the rotational axis. This fixture I am working on is not a substitute for an actual vertical worm drive rotary table or one of the fine examples shown Mr. Warfield's site. Although this fixture does have a possibility of having some type of a brake system applied to it. But this all defeats my intent of KISS. The reason I decided to use a spin fixture in the first place.
Well I ordered the stepper motor and the driver for this 4th axis thing I am building. I also ordered all my pulley's and belts for my machine as well as this 4th axis thingy. I did do some work on the 4th axis fixture. I put the housing in the lathe and opened up the diameters of the existing c'bores front and back to accommodate the needle bearing thrust washer sets I am putting at each end of it's spindle. I also did the mounting holes for the stepper motor bracket on the back of the housing. There was enough meet around the front c'bore of the housing that I could totally enclose the front needle bearing set below the front face of the housing. I did not have to make the c'bores any deeper than what they already were. I've got the mounting plate for the stepper motor on the mill right now and I'm getting that made. Just a couple of pic's as to what the fixture is looking like.
The last pic shows how the front bearings are recessed. That should keep the chips out.
I'll have to edit this post latter and try inserting the pic's. For whatever the reason the pictures are not uploading. All pic's are under 325K in size and there is only 4 of them. It just says Uploading Files please wait and just sits there.
Oh one more thing. I will be installing a drip oiler where you see that aluminum thumb locking screw.
Last edited by duwayne.; 12-30-2011 at 05:59 PM. Reason: pictures would not upload the first try
The photos are very useful for understanding what you are doing.
I still have a couple of questions, though...
How are the needle bearing thrust washers tied to the shaft? Is the bearing ring itself a loose slip fit, while the washers are a tight interference fit? Or is there some other method for handling that?
I understand that your goal is to prevent any axial back-and-forth slop, and so my guess is that in order to accomplish that, the bearings on either side of the housing need to be pressed tightly against the counterbored surfaces of the housing, but I'm not sure how that is done.
Lastly, do I understand correctly that your chuck is designed for mounting in a 5C collet, or does the chuck back plate have the same profile as a 5C collet, or did you make a custom back plate for it?
Not being a machinist (and having taken only a couple of machine tool technology courses), the ins and outs of working with different styles of bearings is somewhat of a dark and mysterious art to me.
As far as the 4" 3 jaw chuck I have, it came with a 5C adapter plate already mounted to it. I have a Clausing 12x36 variable speed lathe that has a 5C collet adapter for the spindle. I use that chuck on there at times when I have small parts that I cannot grab properly in my regular 8" 3 jaw chuck. The spin fixture seems to support it very well also.
I hope that answers your questions
Yes, indeed that answers my questions, thanks...
Well I got a little further on it. I ordered all my pulley's and belt's for the machine the other day and got them yesterday. Only thing is the belt that I spec'd for the 4th axis is on back order. I still need to order a drip oiler from McMaster Carr and I also need to get a 4 pin jack and plug and mount it on the stepper bracket somewhere. The large pulley needs to have the screw holes transfered and drilled and tapped for the QD bushing. The stepper motor is a KL23H2100-30-4BM and the driver is a KL-8060. So far so good.
Here's a couple pics.