CNC 4th Axis Issues

[JeffJ]

New to this forum and hoping someone can guide me in the right direction.

Our company recently purchased a new ACT DMCIII milling machine with an added 4th axis. The rotary table was appealing because it was advertised as having "zero backlash". 2 tables later we find this is not the case. In fact, the backlash was so bad that we actually tried to secure $3000 part with bungee cords to stabilize it.

What I am wondering is if anyone can recommend a good 4th axis that has very little or no backlash (or at the very least is adjustable down to 0). I am not an engineer and am not looking to redesign an existing part. I just want to find the best possible, out of the box 4th axis rotary table that will work with our new machine.

Thanks for your comments!

[txcncman]

All mechanisms have some backlash. I am surprised you cannot adjust for the backlash with the machine parameters. Have you attempted to measure how much backlash you actually have? Is the 4th axis drive mechanism adjustable for backlash (through shimming a pinion or such)?

[fizzissist]

Their own ad for the 4th axis says: (emphasis added mine)

"The speed of the step motor to the turntable is 90 to 1 reduction with no measurable backlash. A high precision infra rate optic sensor is used for home position. The system is not using the conventional worn gear design which will produce the backlash and wear out. It is a high precision planetary gears for the speed reduction. This high precision design guarantees no wear out or backlash. The resolution of the turntable is 7.2 arc sec or 0.002 degrees."

DMC-III Milling Machine | Desktop CNC Milling Machines | DMC-III CNC Mill

Right there in black and white, their own words... GUARANTEES...
They said it, hold them to it. NO MEASURABLE BACKLASH.

Either you're abusing or misusing the hardware, or they're lying.

In any case, if you're doing $3000 parts, this AIN'T the machine to be using.

[JeffJ]

Their own ad for the 4th axis says: (emphasis added mine)

"The speed of the step motor to the turntable is 90 to 1 reduction with no measurable backlash. A high precision infra rate optic sensor is used for home position. The system is not using the conventional worn gear design which will produce the backlash and wear out. It is a high precision planetary gears for the speed reduction. This high precision design guarantees no wear out or backlash. The resolution of the turntable is 7.2 arc sec or 0.002 degrees."

DMC-III Milling Machine | Desktop CNC Milling Machines | DMC-III CNC Mill

Right there in black and white, their own words... GUARANTEES...
They said it, hold them to it. NO MEASURABLE BACKLASH.

Either you're abusing or misusing the hardware, or they're lying.

In any case, if you're doing $3000 parts, this AIN'T the machine to be using.

The people at ACT have actually been helpful about this. Unfortunately, they are guaranteeing a part that they don't manufacture. Apparently, the manufacturer of the axis took an "Oh well" attitude. ACT readily took back the part so I have no criticism of them. The machine itself is actually really good. It's just the rotary axis that is giving us the blues.

I just need a good 4" rotary table to add on since the machine doesn't do us any good without the 4th axis.

[JeffJ]

All mechanisms have some backlash. I am surprised you cannot adjust for the backlash with the machine parameters. Have you attempted to measure how much backlash you actually have? Is the 4th axis drive mechanism adjustable for backlash (through shimming a pinion or such)?

Actually, I was talking about using the machine parameters to adjust the backlash. I do realize that there really isn't such a thing as true zero backlash. I am just trying to find a decent rotary axis that someone knows will operate efficiently with minimal backlash.

We run three Maxnc-10 table top machines that cost us a lot less than our ACT machine and we have no backlash issues.

[fizzissist]

Sorry, then I can only offer what I did long ago with my first CNC retrofit and the 4th axis issue... make your own.

I bought an extra stepper, and made mounting brackets and adapters for both a large rotary table (for a vertical 4th axis) and a small dividing head for use as a variable angle/horizontal 4th axis.

Since the control didn't care what the 4th axis was actually doing, I was able to use either component and just adjust a parameter in the software and run.

In your case I would have possibly suggested just making your tool moves always in the same direction to compensate for backlash...but too late now. Would've been a programming PITA anyway.

You might give these guys a call, since they deal in Kitigawa, Troyke, Hardinge, and Tsudakoma 4th/5th axis rotary tables Tsudakoma, Troyke, Kitagawa and Hardinge Rotary Tables from CNC Engineering
I didn't see anything smaller than 5".... but it won't hurt to ask.

Some misc. ideas for DIY 4th axis..
CNCCookbook: 4th Axis for the IH CNC Mill

[awerby]

Actually, I was talking about using the machine parameters to adjust the backlash. I do realize that there really isn't such a thing as true zero backlash. I am just trying to find a decent rotary axis that someone knows will operate efficiently with minimal backlash.

[What was the symptom that led you to suspect backlash was the issue? What were you trying to do with that bungee cord - keep the rotary table from wobbling during the cut? There are other kinds of looseness besides backlash, which only shows up when you change directions.]

We run three Maxnc-10 table top machines that cost us a lot less than our ACT machine and we have no backlash issues.

[The Max-NC uses a 4" rotary table made by Sherline, which is a high-quality unit, although relatively inexpensive. It actually does have a little backlash (which really can't be eliminated entirely in a normal gear-driven machine). But if they worked fine for you, it tends to confirm my suspicion that you were experiencing some other kind of problem. You could probably put one of those rotary tables on your ACT machine. I'm not sure if anything bigger will work, though.]

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[Tkamsker]

Hi
I use the 4th Axis at cnc-step.at
It is an german product and not expensive
How heavvy is the Part?
Cu
Thomas

[JeffJ]

[The Max-NC uses a 4" rotary table made by Sherline, which is a high-quality unit, although relatively inexpensive. It actually does have a little backlash (which really can't be eliminated entirely in a normal gear-driven machine). But if they worked fine for you, it tends to confirm my suspicion that you were experiencing some other kind of problem. You could probably put one of those rotary tables on your ACT machine. I'm not sure if anything bigger will work, though.]

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

Here is an interesting twist. I am already running 3 Maxnc-10 mills. I never knew that the rotary tables were Sherline. Sherline is one of the rotary tables that I have a bunch of info in front of me to look into.

They are very good rotary tables. Very adjustable and do a pretty decent job.

Guess I've already had a 5 year test run with them!

[SStra]

I just need a good 4" rotary table to add on since the machine doesn't do us any good without the 4th axis.

Lehmann offers the EA-510 (new generation)... compact / small unit with a load capacity of 250lbs.

pL LEHMANN AG - 500 Series

Contact the Lehmann USA Rep. Ivo Straessle (914)941-7311

[mrprecise]

Little Machine Shop sells a pretty good 4" rotary table CNC ready without motor, or with a motor. I believe the make of the unit is PhaseII; adjustable backlash, hardened and ground worm screw, tailstock. tooling, parts, and accessories for bench top machinists - LittleMachineShop.com

[Tkamsker]

I hava tested an roundino from cnc-step.AT or .de
Worked verry well