How to build a 2 spindle diy CNC machine?

[hanermo]

Some additional comments.
The spindle mount in use needs to be "stout and rigid" .. but it does not need to be too fast or rigid when switching spindles while moving.

One could use any cheap acme rod, and some igus drylin or similar plastic slide under the body, preloaded via a thin rubber sheet etc.
Or just the cheap igus slides, *while moving* the spindles.

Then run the active spindle into a hard stop via a cheap small stepper.
The hard stop could also perhaps be a wedge, helping rigidity.
Then you need a tiny movement of very high force to clamp the active spindle rigidly.
The hard stop would give excellent repeatability for nominal cost.

A cam, or a split collar, operated by air, or a solenoid, or a tiny motor with linkage via moment arm or gear or worm gear.
Perhaps a click-type ratchet.
Drive the spindle past the ratchet link downwards until it hits a sensor.
Now drive it up into the ratchet hard stop.
This would preload it and give excellent repeatability.

Or optionally a geneva-wheel type mechanism if using rotary switching.
Some toolchangers used this geneva-wheel type, e.g. on lathe turrets.
Its very rigid and does not need the extra cam or mechanism.

All sorts of mechanical latches could also be used for catch/release functionality without an extra motive bit for the tension/catch/release functionality.
Or a 30$ auto-type solenoid driving a cam, on-off, via 24V DC power.
The lock just needs to try to move about 0.02 mm, to positively lock and register the spindle.

Even purely mechanical solutions exist, like tripping a mechanism when driving down further past the sensor, to release a catch/cam/clip allowing upwards movement.
Look at old turret lathes for example, for inspiration.

[Goemon]

if you really want to get into a complicated machine build im going to suggest that you look at the various open source G-Code interpreter solutions out. The old stand by here is LinuxCNC but you may want to look at GRBL. Then you have derivatives that are slowly coming along like the various attempts to get GRBL running on ARM and things like Machine Kit.

I mention this because at some point you will need to become a programer if you want to implement something that hasn't been done before. As mentioned above there has to be a million ways to do dual spindles but not one of them already implemented may be suitable for your specific solution. For example right off the top of my head i cant remember anybody doing a dual Z axis machine off one Y axis saddle, if you did something like this you would need a G-Code interpreter modified to be aware of the two axis. This likely isn't a trivial programming job to get to a technically correct and bug free solution. Im sure the community would love to see such a solution though.





Actually many G-code interpreters out there can already handle tool changes and the associated offsets. From the software standpoint much of the work is done. It would be a lot like a tool changing carousel, but you rotate spindles instead. The real trick is in doing that carousel in a mechanically sound way. You would likely need to consider various machines like lathes with live spindles and some of the CNC drilling machines out there.

An ATC might be a better choice than going dual spindle in your case. Im not convinced that a high torque spindle supplementing the high speed spindle makes sense. Sure it can be done but I'm not convinced of a pay off for the types of molds you are talking about. It really comes down to the number of expected tool changes per run.

An ATC wouldn't help for what I would want to use dual spindles for. I was thinking more along the lines of using the same machine for multiple purposes instead building or buying a second machine, or carving 3 or 4 identical parts at the same time.

For example, maybe when my machine is not making molds, I could be making 3 or 4 wood stocks on a set-up like this:



Or, if I wanted to add a titanium milling capability for bottom metal , I could add a high torque low speed spindle like the one I posted a link to on the first page of this thread.

I don't think either of those option would require custom programing. I would have to borrow some ideas from Ger21 on the wiring though.

ATC doesn't feel like a priority for me right now but I haven't yet experienced how annoying tool changes are maybe I'll feel differently in a few months. PDS called this morning to let me know my spindle was finally on it's way! At the same time, another vendor emailed me the best deal I have ever seen on an ATC spindle and I won't be able to take advantage. Typical...

[Goemon]

Here's a single Z axis, 3 spindle machine.

That's so cool! I want one!

The weird thing is, I bet it is cheaper to make than buying a single ATC spindle... we need someone to at least make a motorized torque wrench that is compatible with ER25 and ER32 collet nuts to allow faster tool changes like they do for R8 drawbars. Having to use two manual wrenches is just barbaric.

[Goemon]

Goemon... if you don't mind redoing your gantry, the easiest solution would be to make a gantry that extends well past the upright on each side, and have two spindles on two carriages, mounted independently, using a dedicated ballscrew for each spindle. One spindle would be "parked" to one side while the second spindle ran. Or you can "slave" the other spindle and run them in tandem.

I wouldn't have to redesign my gantry for that. I decided a while ago to make it wider than I needed to allow for future upgrades. I'm actually curing a second gantry as we speak because I had second thoughts on the design I chose. I am making a fixed gantry and the Y axis will the long one. The X axis will be a moving table (going under the gantry beam) as my table is long an narrow (to fit my molds).

My fixed gantry is 48" wide, the rails are 40" with only 30" of travel required so there would be room at the size for a second spindle. I would have to switch back to the old design if I wanted multiple spindles running the same time though.

[louieatienza]

If you want to gang rout something, you don't need a separate Z axis for each spindle. Simply make a mount that holds multiple spindles a specific distance away from each other on center, then mount your work the same on the table. As long as your axes motors are strong enough to move it, and the frame rigid enough, the computer don't care. You'll need a separate VFD for each spindle though.

[Goemon]

If you want to gang rout something, you don't need a separate Z axis for each spindle. Simply make a mount that holds multiple spindles a specific distance away from each other on center, then mount your work the same on the table. As long as your axes motors are strong enough to move it, and the frame rigid enough, the computer don't care. You'll need a separate VFD for each spindle though.

In my case I would need to get extra 50amp 220v breakers and outlets installed too. I am already worried if the ones I have are enough to run one spindle. I could buy lower power spindles I guess. A double wide Z plate would take some design thought to make it stiff enough too.

Net, net, there probably aren't any issues that can't be solved with a little time and money.

[wizard]

There was a time when many a job shop ran on Bridgeport type mills with an occasional horizontal. Machinist simply matched the horspower available to the tooling and material removal rates used. While maybe not the case now, i know of several machine shops that ran with no CNC equipment at all when i left high school. One guy was extensively involved in tool and die work for die casting.

The point here is that a lot if interesting stuff was built on machines with less than 5HP available to them. These days high horse power is pretty common in CNC machinery but that doesnt mean it is required. Further some of those machines are high horse power due to high spindle RPMs. In a nut shell high horse power in your spindles isnt a requirment to getting the job done.

In my case I would need to get extra 50amp 220v breakers and outlets installed too. I am already worried if the ones I have are enough to run one spindle. I could buy lower power spindles I guess. A double wide Z plate would take some design thought to make it stiff enough too.

I try to stress to people to be conservative when loading a branch circuit with a CNC machine. Loading a breaker to no more than 80% of its rating is a good idea and possibly a lot less than that.

The thing here is that blowing a breaker mid job on a CNC machine can really ruin your day. How effectively you can recover depends upon what exactly happened and your ability to get precisely back to start.

Now in normal operation with decent CAM software and proper material removal rates spindle overloads shouldn't happen. We all know that shouldn't and reality sometimes dont mix. In any event you dont want normal operation of the machine to put you near a breakers trip point and have a transient load shut the whole machine down.

Net, net, there probably aren't any issues that can't be solved with a little time and money.

Oh so true! I might add that experience is a big factor here. Once you have access to a CNC you will learn quickly how well a specific machine fits your needs. Experience will tell you what features you need and dont need and inform your specifications for the next machine you build or buy to replace this one. You might even consider a horizontal solution.

[Goemon]

There was a time when many a job shop ran on Bridgeport type mills with an occasional horizontal. Machinist simply matched the horspower available to the tooling and material removal rates used. While maybe not the case now, i know of several machine shops that ran with no CNC equipment at all when i left high school. One guy was extensively involved in tool and die work for die casting.

The point here is that a lot if interesting stuff was built on machines with less than 5HP available to them. These days high horse power is pretty common in CNC machinery but that doesnt mean it is required. Further some of those machines are high horse power due to high spindle RPMs. In a nut shell high horse power in your spindles isnt a requirment to getting the job done.


I try to stress to people to be conservative when loading a branch circuit with a CNC machine. Loading a breaker to no more than 80% of its rating is a good idea and possibly a lot less than that.

The thing here is that blowing a breaker mid job on a CNC machine can really ruin your day. How effectively you can recover depends upon what exactly happened and your ability to get precisely back to start.

Now in normal operation with decent CAM software and proper material removal rates spindle overloads shouldn't happen. We all know that shouldn't and reality sometimes dont mix. In any event you dont want normal operation of the machine to put you near a breakers trip point and have a transient load shut the whole machine down.



Oh so true! I might add that experience is a big factor here. Once you have access to a CNC you will learn quickly how well a specific machine fits your needs. Experience will tell you what features you need and dont need and inform your specifications for the next machine you build or buy to replace this one. You might even consider a horizontal solution.

That's all true although those old Bridgeport 1hp motors are considerably more powerful (in terms of material removal) than your typical 5hp 18,000 or 24,000 rpm spindle. You would need even higher HP to reach 1 hp at 1000 or 1500 rpm.

You only have to look at the Datron spindle choices to see that you are correct about how little power and torque is really needed or even recommended for milling aluminum (or even steel) at high speeds with smaller end mills. I didn't choose my spindle for the high HP. I chose it because it was a good deal on a spindle with other features I wanted (and a good brand). If I was in a position to buy exactly what I wanted, I would have chosen one with lower HP and lower top speed.

The reality is that at the speeds I'll be using my spindle, it is really a 3-5hp unit. I'll never run it at top speed because I don't want to blow the VFD and I don't need the high rpm. I think I'm safe running one spindle like that. For two or three at that power, I would want additional breakers for each.

[louieatienza]

That's all true although those old Bridgeport 1hp motors are considerably more powerful (in terms of material removal) than your typical 5hp 18,000 or 24,000 rpm spindle. You would need even higher HP to reach 1 hp at 1000 or 1500 rpm.

You only have to look at the Datron spindle choices to see that you are correct about how little power and torque is really needed or even recommended for milling aluminum (or even steel) at high speeds with smaller end mills. I didn't choose my spindle for the high HP. I chose it because it was a good deal on a spindle with other features I wanted (and a good brand). If I was in a position to buy exactly what I wanted, I would have chosen one with lower HP and lower top speed.

The reality is that at the speeds I'll be using my spindle, it is really a 3-5hp unit. I'll never run it at top speed because I don't want to blow the VFD and I don't need the high rpm. I think I'm safe running one spindle like that. For two or three at that power, I would want additional breakers for each.

Depends... on an older machine the speed changes via belts, on later machine via gears. The 1HP is generated at 1750rpm which is typically the speed of the motor, and all speed (and thus power and torque) changes happen via gears or belts. So if you set the spindle slower you'll have inversely more torque and vise versa. Power is simply a measure of work over time. Whether you take big chunks slowly, or small chunks fast, if you remove the same amount of material over the same time period you've generated the same power, period. The difference is, some materials cut better at slower speeds, and some at higher speeds. Some tooling works better and are designed for slower speeds, and some at higher speeds.

It's the same with automobiles. You can have an F-250 and a Porsche 911GT, each with 400HP. But you wouldn't tow a boat with a Porsche; that HP happens at about 8000rpm, where on the F-250 it's about half that. But the F-250 also weighs twice as much.