CNC - 4th Axis Build Log

I didn't find a too many 4th axis builds when I searched in the past and none of the ones I did find were like this so I thought I would share what I have done.

A 4th axis has been a day dream for a little while now and I am working on a product design that it would be a great help to have a 4th axis when it comes time to prototype the design. I have researched several different options, import rotary table, import super spacer, harmonic drive, used industrial 4th axis. The used industrial unit was my most desirable path and I went and looked at a couple pallets of them that I could have had for $200 each but they were 12" units and just too big and heavy for my machine. The next most favorable was the super spacer based design that Tormach has, in fact my plan was to wait until I had a need for one and just buy a Tormach unit.

A few weeks back I was at the local used tool store when I stumbled upon a used Rutland 8" Super Spacer with a nice 8" 3 jaw chuck and the price was less than half of what a Taiwanese 8" super spacer is going for now. The unit appears to be several years old, by the overall quality of it. All the machining and parts seem to be superior to the quality of current import items. So I bought the super spacer and immediately started working on the CNC conversion.

Attachment 336422
Attachment 336424

-Dan

First step was to tear it all apart and clean it, followed by documenting all the parts with 3D models in Solidworks. Which I don't have any pictures of at this time.

This is the solid model of my final design.

Attachment 336426
Attachment 336428
Attachment 336432

The final design has the following features
-Pacific Scientific NEMA 34 stepper motor (because it was free)
-2:1 belt drive with a 15mm wide 5mm pitch HTD belt (because one pulley was free)
-A new backlash adjuster cylinder with reamed to size bronze bushings and a pilot added to mount the motor to
-A folded back motor mounting position to prevent the motor from hitting my mill enclosure
-Built in homing sensor
-Spindle/Table axial pre-load spring to reduce moment error durring unlocked motion
-Spindle bearing to reduce moment error during unlocked motion


I will cover each of the above items in more detail as the build progresses.

-Dan

I can't tell, but if you are blocking the through hole with the motor you may want to modify that. There will be times you want something to stick all the way through.

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Originally Posted by mcphill

I can't tell, but if you are blocking the through hole with the motor you may want to modify that. There will be times you want something to stick all the way through.

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The motor does clear. Below is a picture from the back. The motor is hanging just a hair over the edge of the hole but the motor mount is at 90* to the back in this configuration. It will actually be able to rotate up a little and clear the bore once built. Additionally I can turn the motor bracket so it is straight up at the 12 o'clock position with this design.

Attachment 336436

-Dan

LOL.....for one moment I thought there had been a breakthrough with a new 4th axis design solution......"a super spacer".....now I've heard it all......it's just a common or garden rotary table that can work in the vertical or horizontal mode, (only horizontal in this design build) and still has backlash due to it being a worm drive design.
Ian.

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Originally Posted by handlewanker

LOL.....for one moment I thought there had been a breakthrough with a new 4th axis design solution......"a super spacer".....now I've heard it all......it's just a common or garden rotary table that can work in the vertical or horizontal mode, (only horizontal in this design build) and still has backlash due to it being a worm drive design.
Ian.

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Whoa simmer down fella, crazy thoughts of new fangled backlash free 4th axis setups imported from overseas, could get you thrown in the loony bin.

From what I have read the name "Super Spacer" started with the "Hartford Super Spacer" which has the form of a rotary table but fixed detent angles like a collet based spacer fixture or maybe a indexer. It then seems someone in one of the "ese" countries decided it to add the worm drive to the design.

While this is still not a perfect design and it far from backlash free, the price was right for me and unlike the relatively cheaper import rotary tables which have a very small mounting surface when used with the axis of rotation horizontal, these "super spacers" have a much larger foot print and generally have a decent sized through bore.

For my use this 4th axis is being used to build several prototype parts and all I need it for is strictly indexing at this point so no live motion cutting. Once I get the design proved out I will send it to a machine shop to be made in quantity.

-Dan

Hi....yes I realise a name is only a name in kind only........if it identifies the object as something remotely similar to the same thing it'll sell for those that are not in the know.

I've given up relying on EBAY for an accurate description of the sellers goods.

I was under the assumption that this was a 4th axis not just a spacer device.......the sketch showed a motor drive........further reading and I see you are going to use it to work on the eventual design for commercial;l purpose.

However........if your design is going to incorporate a worm drive device.......that is a dead end path as you cannot eliminate the backlash that is inherent in such a design.

I have a design that I want to make, purely for a 4th axis drive, and that does have a worm and worm wheel, but the worm assembly is pivoted and spring loaded.

This will enable it to be metal to metal meshed with the worm wheel and allow the worm to slightly ride up and down in the worm wheel without binding on a tight spot that does occur with a fixed worm due to uneven wear rates of the steel worm and bronze worm wheel.

I'm talking about a miniscule amount of worm pivot movement and a fairly strong spring, as a tight spot in the worm wheel is only a few thou at most.

For normal running, dividing heads and rotary tables all have some freedom with the worm mesh....or they soon will have when the device is used a bit and this normally cannot be eliminated by adjustment.

That's how I'm going to make it work for a backlash free 4th axis, built from the ground up with a 1:60 worm ratio.

It'll have a 5C collet spindle bore size.....I already have a set of 5C collets for a T&C grinder....... and a 3 and 4 jaw chuck.
Ian.

Ian all I need it for is strictly indexing at this point

No major updates on this project right now. Right now I am focused on finishing the operator control panel on CNC mill, until that is finished I can't use my mill.

These pictures are basically exploded diagrams of the Super Spacer as I bought it.

Attachment 338102
Main Spindle assembly

Attachment 338104
This is the "Backlash adjuster", the worm screw is mounted eccentrically in the cylindrical body (2 shown). I made a new main body because the dimensions of the factory cast iron were a little small and allowed for too much play in the system

Attachment 338106
Wedge brake assembly

Attachment 338108
Indexing Pin assembly

-Dan

Updates?

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Originally Posted by mcphill

Updates?

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The project has been side lined, its available for purchase if anyone is interested. A paying job expedited the need for a 4th axis, so I bought a used one this last spring and have not looked back.

I think all that is left is bore a pulley and machine a belt for the timing cover.

-Dan