Taig mill vibration

[jarkman]

I've just finished a Taig mill CNC conversion, which I intent to use for engraving & some small robotics work.

I'm having finish problems with the engraving, with consistent ripple marks in brass and silver. I'm using a single-spiral-flute 60 degree cutter at the highest speed I have available, which is 8000rpm (I'm in the UK, so I am running Taig's CNC-ready motor on 50Hz instead of 60Hz).

Running the numbers, my ripples are all at a frequency in the region of 2Hz. And, my machine does vibrate a a bit, even when the motor is running but no cutting is going on. It is sat on the kitchen table, and the vibration is enough to make small tools walk slowly off the edge of the table.

I'm beginning to wonder if the ripples and the vibration might be related. Is that level of vibration normal ?

Thanks,

Richard

[jarkman]

A couple more observations ( I should have thought of these before ):
- The vibration doesn't change too much when I switch pulleys, but it is a bit more severe on the faster pulleys.
- With the belt removed, there's almost no vibration.
- When I power down the motor, the vibration stops instantly, even though the motor keeps spinning for a few seconds.

Thanks,

Richard

[lsces]

What do you have the machine bolted down to? Something with a bit of 'mass' like an offcut of kitchen worktop will probably help, and fit some rubber feet, or a bit of rubber matting for it to sit on.

For fine engraving a faster spindle is much better, and the Kress produces some nice work for my jewelery type customers.

[jarkman]

Lester - thanks. Right now the machine is not bolted down at all, and I ought to fix that.

But I suspect the real problem is that the motor is generating so much vibration. I don't know if it's faulty or if the Taig-supplied CR motors always do that. Any thoughts ? Is it perhaps a consequence of running a 60Hz motor on 50Hz ?

Yes, I know I need some higher speeds, one way or another. Take a look at the lamentable finish on this for an example:
http://picasaweb.google.com/lh/photo...eat=directlink

The Kress is certainly an interesting thought. I had been imagining I would just swap the pulleys or the motor to get up to 18k RPM on the Taig spindle, and I expected I'd find someone selling a simple conversion kit somewhere, but I haven't found one yet.

[lsces]

Since there is no mass to the Taig, it HAS to be bolted down to something even if just for safety. The kit I was bringing over from the US came nicely secured to a 3/4" ply panel which was very useful for initially setting up. Peter does not get his machines in this format. In addition, I would not take the Taig motor, since it is NOT really suitable for running on a transformer. The Kress spindle has been my preferred basic spindle for the last couple of years, and the new 5k to 15k model looks like it will fit the bill.
Samples from customers has a few real jobs, but I must add some pictures of some of the other bits from the display cabinet.

[lsces]

Knew I had some pictures ...
Nice way of shipping Taig Mill
You used to just undo the other bolt and drill a new hole so that the bed was square. And fit four big rubber feet ....

[jarkman]

Is that Kress 5 to 15 or 5 to 25 ? It does sound tempting, albeit expensive.

Do you have any feel for how the Kress runout will compare to the Taig ER16 spindle ?

Thanks,

Richard

[lsces]

The 800 watt unit is 10k to 30k. They have recently modified the 1050 Watt unit to provide 5k to 25k as an alternative. I've not needed to drop below 10K yet, but I understand that the 5000 RPM lower limit may be useful to some people. Run-out wise ... can't measure it with my dial gauge. These units are designed to handle large profile router cutters on wood, so our smaller cutters are a little light relaxation

[Andre' B]

But I suspect the real problem is that the motor is generating so much vibration. I don't know if it's faulty or if the Taig-supplied CR motors always do that. Any thoughts ? Is it perhaps a consequence of running a 60Hz motor on 50Hz ?

The motor was designed for 120/240 at 60Hz it should work fine at 50Hz but may run hotter and a little rougher.
Ideally when changing the frequency the voltage would be changed by the same ratio.

50/60 = 0.833
0.833 * 240 = 200

So if there is anyway you can drop the voltage to about 200VAC it should run as smooth as it would over here.

If you have an electronics surplus place near by they usually have these http://www.variableautotransformer.com/ fairly cheap.

Note that they are not isolated and so present all possible the shock hazards.

[themedulla]

You might also want to check your pulleys and make sure they are running parallel. There is some info on Nick Carter's website on a couple of ways to check.

If your spindle and motor are out of parallel, you could run into some vibration issues as well as trashing belts.

[jarkman]

That's a happy thought. I just lined the pulleys up by eye, so they could well be a bit out.

Thanks!

[TOC Admin]

If you are engraving from a DXF file make sure its a clean cut copy...

Some DXF to Gcode converters save a DXF file with very small increment cuts and make it look like its chattering or vibrating..

What are you using for your Engraving G code...?