[mesyin]

Hi everyone,

I would like to build a 4-axys DIY CNC milling/router machine using single-shaft NEMA 23 stepper motor.

So far I only know 3-axys DIY CNC milling/router machine.

They are X (horizontal, left and right motion), Y (horizontal, back and forth motion), and Z axys (vertical, up and down motion).

Can anyone please tell me what is the 4th axys and what additional parts I need to buy in order to build a 4-axys, medium-size DIY CNC milling/router machine?

Thank you very much for the help.

[Fish4Fun]

mesyin,

Welcome to CNC Zone!

A typical 4th axis is a rotary table/ spin index. As far as "parts to buy", you could buy a complete assembly like this : Weiss TC 150T Rotary Index Table | eBay or you could build one from scratch or you could convert an existing manual table/index. A great deal depends on your machine and requirements. There is a HUGE difference between a "mill" and a "router machine". A router based machine implies you are working primarily in wood, and "medium sized" is almost meaningless as typical wood working machines range from a 6" x 6" work envelope to 5ft x 12ft work envelope. A mill typically implies a machine capable of machining metals and is typically made from cast iron and steel. While mills range from "desk top" sizes with 6" x 8" work envelopes to huge industrial machines, a very common size is the Bridgeport style mill which typically has a work envelope of ~9" x 42".

Things to consider in a rotary table/spin index wrt your mill or router: 1) Weight 2) Height 3) Accuracy 4) Intended use 5) budget. Since it does not appear you have a specific use in mind for a 4th axis as of yet, I would urge you to focus on your machine until the need arises for a 4th axis.

Fish

[rmwarren]

mesyin,

There is a HUGE difference between a "mill" and a "router machine". A router based machine implies you are working primarily in wood, and "medium sized" is almost meaningless as typical wood working machines range from a 6" x 6" work envelope to 5ft x 12ft work envelope. A mill typically implies a machine capable of machining metals and is typically made from cast iron and steel. While mills range from "desk top" sizes with 6" x 8" work envelopes to huge industrial machines, a very common size is the Bridgeport style mill which typically has a work envelope of ~9" x 42".

Fish

Fish - can you expand on the mill-versus-router question? Specifically, I am new to CNC but I have a small Seig mill and a couple of little lathes. I am more of a woodworker than machinist and a hobbiest at both. I am interested in making some woodworking jig components that will be small, perhaps 25mm thick by 160mm max width/length. I will probably sell some items to other hobbiests.

I am considering either building a small CNC machine or perhaps buying one of the cheaper ones. My question is whether a machine such as those typically found described on this site is capable of milling mostly plastic however I would like to be able to use it with 6061. Is this an unreasonable expectation?

I am only looking to maintain a tolerance acceptable for jig parts. I am willing to sacrifice size capacity for accuracy and speed. I don't see this as high precision machining but since one part will have to clip or mount to another there is some need for accuracy. Apologies but I do not know how to properly describe the needed tolerances.

I am not looking at high production rates but some components I may want to make in runs of 20 - 50 pieces. I would appreciate any input you or anyone else may have.

Thanks in advance,

RMW

[Fish4Fun]

rmwarren,

Most machines described in the woodworking section of this forum are quite capable of cutting common plastics. The feed rates, spindle speeds and tool geometry typically combine to differentiate the quality of the cuts. 6061 is fairly easy to machine, but it is at the outside edge of many woodworking CNC routers and beyond the reach of others. At the top of the list of things that differentiate a typical router based CNC machine and a true CNC mill is rigidity. The rigidity in a true CNC mill comes from massive cast iron and steel components. A "Bridgeport" style mill typically tips the scales at over 4000lbs and has a working envelope of ~9"x42" to 10"x50". A typical CNC router of the same working size might weigh an order of magnitude less. Typical CNC routers achieve fast feed rates with nominally sized steppers or servos, while a CNC mill requires much larger drives to achieve typically much lower feed rates (due to a combination of the mass to be moved and the increased friction components of a bed & way system as opposed to rails and trucks.) 6061 can certainly be machined with many router based machines, but if the machine lacks the requisite rigidity, tool breakage will be a common occurrence. If the drives lack the the power to handle the cutting forces, "missed steps" will cause inaccurate cuts. If the Z-Axis is not sufficiently rigid, the deflection will become a real problem. Finally, the spindle itself needs to be up to the task; ideally this would mean higher torque at lower RPM with heavy-duty bearings, uncommon in consumer routers.

Having said all of the above, please bear in mind that many, many people report success milling aluminum with their CNC routers. I would suggest you read through some threads where the author(s) discuss their success with milling aluminum and research the machines they are using. As a general rule, the smaller the working area and the stronger the machine, the better success you will have. Once you decide on a machine and get it set up, do some test cuts in aluminum. I would start with very shallow cuts, perhaps 10% depth to tool diameter (for a 0.25" tool, try a pass depth of 0.025) and do numerous cuts at various feed rates. Repeat the process increasing the pass depth by perhaps 0.005" at a time. Use of forced air or liquid coolants should improve results dramatically. Finally, experiment with various tool geometries (number of flutes, roughing, up spiral, down spiral etc etc); the goal is to find a tool, feed and pass depth that best suits your particular machine. In a machine that is sufficiently rigid the ideal spindle speed, feed rate, pass depth and coolant are available from the tool MFG, but with machines that are not sufficiently rigid, results can vary widely and a fair amount of trial and error is frequently the best approach.

It might be best to start a thread and specifically ask members to describe their machines that they have had good success using on Aluminum, then look carefully at the machines they describe and the tools, feed rates and pass depths they use.

Fish

[cyclestart]

If a 4th axis is being considered make that decision now, it will effect some other decisions such as z clearance and overall design.

For a small work area a moving table has a potential rigidity per dollar advantage. Some discussion of basic design in this link:
The Hobby CNC Router: Builders Guide Step 1

[cyclestart]

I am new to CNC but I have a small Seig mill .........am interested in making some woodworking jig components that will be small, perhaps 25mm thick by 160mm max width/length.

Have you considered a cnc conversion for the Sieg ? Parts that width are a stretch for a small Sieg but it has been done. Check out Hoss's creation for a walk on the wild side
Hossmachine Homepage

[rmwarren]

Fish, Thanks for the detailed response, that makes a lot of sense to me.

Cyclestart, thank you for the input and links, I am reading the CNC Router Basics page now.

RMW

[mesyin]

mesyin,

Welcome to CNC Zone!

A typical 4th axis is a rotary table/ spin index. As far as "parts to buy", you could buy a complete assembly like this : Weiss TC 150T Rotary Index Table | eBay or you could build one from scratch or you could convert an existing manual table/index. A great deal depends on your machine and requirements. There is a HUGE difference between a "mill" and a "router machine". A router based machine implies you are working primarily in wood, and "medium sized" is almost meaningless as typical wood working machines range from a 6" x 6" work envelope to 5ft x 12ft work envelope. A mill typically implies a machine capable of machining metals and is typically made from cast iron and steel. While mills range from "desk top" sizes with 6" x 8" work envelopes to huge industrial machines, a very common size is the Bridgeport style mill which typically has a work envelope of ~9" x 42".

Things to consider in a rotary table/spin index wrt your mill or router: 1) Weight 2) Height 3) Accuracy 4) Intended use 5) budget. Since it does not appear you have a specific use in mind for a 4th axis as of yet, I would urge you to focus on your machine until the need arises for a 4th axis.

Fish

Do I really need a rotary table or just a rotary jaw chuck as the 4th axis (sorry for the misunderstanding)?

The 4th axis I've meant is such as below video, the one that rotating the wood in horizontal position:

[nomedia="http://www.youtube.com/watch?v=O-RzYjSPzP4&feature=related"]YouTube - ‪CNC 4th Axis at work‬‏[/nomedia]