Help with making a 4th axis

[Archer60x]

Hello, i have not done any lathe work. So bear that in mind.

I am designing my own 4th axis for my Tormach 770.

I have lots of experience with Stepper motors and harmonic gears that i will be using to make the 4th axis as i build astronomy mounts that use them.

My questions revolve around putting a Lathe Chuck and Collet chuck on the end of the harmonic gear box.

I do not know anything about spindle noses that 3/4/6 jaw chucks and collet chucks attach too.

I attached the bolt pattern that is on the harmonic gear box to this post. You can see the bolt pattern has a diameter of 54mm or 2.126 inches.

I would be using a 4 inch chuck most likely.

If anyone has suggestions on the best nose to buy/make/use for this application please let me know.

Thanks!
Chad

 

[markba633csi]

You will need to fab an adapter to mount a scroll chuck or collet chuck. I assume you want the assembly to be concentric within some
tolerance specification (need to specify). Essentially you would be making a disc with a shoulder/step on each side and some bolt holes, possibly threaded.
There should be a flange or step on the gear box hub to register the adapter exactly. You can't rely on the mounting bolts to do that.
Some precision lathe work will be required; this looks a bit involved for a beginner project, but why not? You would need a
few measuring tools: caliper, dial test indicator. If you could get away with making the part in aluminum it would be easier.

Does the harmonic drive have bearings that can handle machining forces? Side loads especially? Something to consider

 

[Archer60x]

Yes, i need concentricity.

Here is a cross section of the harmonic. You can see the bearings and the right side is the face i will be making something to attach the 3/4/6 jaw chucks and collect chuck.

I need to figure out the best adapter to use to mount these chucks. Do i emulate an existing nose like what is on a Lathe?

THanks
Chad

 

[Archer60x]

Maybe what i need now that i am googling things is to use front mount chucks.

This one is super expensive, but it looks like it is front mount and adjustable for concentricity.

Pardon Our Interruption

 

[Archer60x]

Then again i see little macine show has these that i can drill a my harmonic hole pattern into.

Lathe Chucks and Adapters

3-Jaw and 4-Jaw lathe chucks and lathe chuck backplate adapters for small lathes at LittleMachineShop.com

littlemachineshop.com

 

[homebrewed]

Make sure to provide a ground connection that prevents welding currents from flowing through your gears/bearings.

 

[Archer60x]

My research today i am just down to not target any nose style. There is enough choices out there in 4" chucks i am just going to buy one that had drawings or CAD files and design an adapter to my harmonic bolt pattern.

 

[markba633csi]

I don't think you want to emulate a screw-on type lathe spindle, but instead, a flange which a front mount chuck would mate up to.
Certainly if you are looking at 3-jaw chucks you would want a "set-tru" type and they are pricey, if they are even available in 4" size

You could accomplish roughly the same thing with a conventional chuck by deliberately leaving some play in the mounting, but aligning the
assembly would require a dial indicator, a precision pin or dowel and lots of patience-

Pratt-Burnerd and Bison make good chucks

 

[Archer60x]

OK so the chucks that i can adjust concentricity are relatively pricey. I will need to spin the harmonic to see if it is concentric with and without a load on it.

If it is not then an adjustable chuck will be the way i go. From what i understand they are basically a 4 jaw chuck type adjustments inside of the back of the chuck so you can get your concentricity dialed in.

I am going to start with a ER40 collect chuck and make an adapter for it. Then i will move on to making an adapter for a chuck.

OK thanks for everyones help and input. I was just hoping there was some standard nose pattern i could follow that lathes use and there are... but some of them seem to complicated for my application.

 

[RJSakowski]

I have a 770 with a Tormach 6" 4th axis. The RT they used is q Phase II H/V and it has a 5" 3 jaw chuck. The chuck is mounted on the RT with a backing plate which provides a .6" wide flange to mount the assembly to the RT using four screws and Tee nuts in the four Tee slots on the RT. Concentricity is provide by a mating boss on the back side of the backing plate which matches the socket in the RT.

IMO, using the 4th axis in horizontal mode offers little advantage on a CNC mill. The few times that I have used it has been in the vertical mode. The one problem that I have encountered with it on the 770 is it isn't sealed so there is an ingress of coolant when using flood coolant which requires draining and cleaning. I don't leave the 4th axis on the table as it takes up a fair amount of precious space so it only goes on when truly needed.