4th axis - spindle or lathe head?

[erikjgreen]

Hi again;


I'm looking to build a 4th axis for my CNC mill in my upcoming machine shop (I'm excited, I haven't had a dedicated space for my shop until now). I want a 4th axis for a number of projects, including milling out some marine propellers.

I've looked around at the various projects out there that add these to home shop mills, and I've decided that what I want is an axis that can run high speed to perform lathe type turning operations and also run indexed at slow speed for simultaneous motion with the other three axes.

I'm thinking I don't want to just make up my own design for this, I want it more rigid and precise than I could make without a lot of trouble. I'm also pretty sure I can't make a better spindle than companies who have sold them for years. I think that setting up a servo based belt drive with a mechanical brake/lock mechanism is what I want. I'll use the servo's encoder for position feedback plus perhaps a tach on the actual spindle.

The question is, which would be a better starting place for this? Should I get a surplus/used milling machine/VMC spindle and mount it horizontally, or should I convert a lathe head for this? The electronics and software are easy (or at least handled at this point), but I don't know all the pros/cons of these tool parts.

The spindles are easier to find, but the lathe head has a hollow bore, which might be nice for some things.

I'm basically planning on mounting the spindle/head on the left side of my mill's table, along with the servo coupled by timing belt to the head. The head will have a dovetail fixture on it and/or a lathe chuck.

Thoughts/comments/opinions wanted,

Erik

[Bob Adams]

Hi,
For an Idea checkout this one at:
4th Axis/ Mill/Lathe
Bob A

[Cartierusm]

What I did was buy a replacement head for my Harbor Freight Converted CNC Lathe 9x20. What I didn't want was to buy a rotary table and have to deal with the cost and backlash from the worm gear. If you build one or retrofit one yourself then a good worm gear is pricey.

What I did was just add a type L timing pulley 8.5" or so Pitch diameter to the lathe head spindle and add a stepper motor with a 2.2" or so Pitch diameter pulley. The first time I did it I uses a 1:4 ratio for the reductions and it would move if I was milling so I found an 8.5" pulley on ebay cheap, normally they are $150. Now it's rock solid.

If I were you then use a servo that can double as a motor if you use it as a lathe, then find a cheap used lathe head that serves your size requirements, add the motor and pulleys and be on your way.

I don't use a dovetail on my mill and leave it setup, as you said, on the left side all the time. I just put a gound shaft in it lined it up with my mill by way of a dial indicator and set a position in my Mach3 Off sets, G58. I don't ever remove it or need a dovetail to position. I could use a tail stock but don't have an extra one or had a need yet, but if you can find a used lathe head then buy the tail stock too and work with that.

Hope that helps, seems like rambling to me, today as it's friday, if you need a pic let me know and I'll post one.

[mrcodewiz]

I would like to see a picture. I made one from a 7X10 headstock and spindle but as you say, it moves unless I am taking very light cuts.

[Cartierusm]

Here's some pics.

[boaterri]

Here is a link to another idea. The builder has done quite a high end job with this project. It is a long read but worth it.

Success! Mini Machining Center under Mach3 control - Video link

Good luck,

Rick