[harveyjbarrow]

Hi,

I am looking at machining some intricate patterns in copper. I have tried but the standard sherline stepper motors do not seem to be up to the task as well as the standard spindle. The only modifications to the machine are the kerk motion leadsrews and anti backlash nuts.

I am after some advice on what is best. I am looking at possibly upgrading the spindle to a VFD running up to 24000 RPM ( 0.75 - 1KW and am unsure of the best brand ) and then a G540 driver with keiling stepper motors.

I do currently have the 10000 RPM kit but from reading some forums it looks like I might need more RPM hence im looking at the VFD. The only other material that I machine is tooling board.

I would really appreciate some help as I do not have a local shop that specializes in mini mills in New Zealand.

Thanks

Harvey

[mhackney]

Harvey, it would help if you described - in detail - what you did and what the results were. I can state definitely that you can mill copper with a Sherline mill. I can also state definitively that you can not mill copper with a Sherline mill. "It depends". Tell us what you are trying to do.

cheers,
Michael

[harveyjbarrow]

Hi Michael,

I am machining some copper waterblocks ( similar to a CPU cooler ). They are 60mm x 48mm x 5mm thick. I am using 1mm bit for the detailed channels and then a 2mm bit to create some inlet and outlet holes as well as finishing off the edges.

The issue that I am currently having is that it is very slow and also in the 5 attempts that I have made the stepper motors are skipping so I am always loosing my origin. My feedrate is 100mm/min and stepdown on both the 1mm and 2mm bits is 0.5mm and I am using kersone as the lubricant ( this is manual with myself and a spray bottle ).

I am thinking that with a faster motor as well as higher torque stepper motors then I could at least double my feedrate but most importantly not to lose my origin.

Thanks

Harvey

[mhackney]

Harvey, is your plunge federate 100 mm/sec also? You might need to slow that down to 50 mm/sec or less. With an end mill that small, I would think the end mill would break before the motor stalled or skipped. Have you successfully milled other materials? Do you have some experience under your belt? It might be that your gibs are too tight, causing the skipped steps.

regards,
Michael

[harveyjbarrow]

Hi Michael,

Good point, I forgot to mention my plunge rate is 25mm/min.

Yes I have done quite a bit of milling of tooling board, machining wax, and some urethane.

I actually purposely loosened the gibs off for my second round of testing.

[Fastest1]

I suspect another issue. You should be able to break those end mills and never lose position.

Could it be something else? A loose coupler? Do the Kerk screws (I am guessing you have the A2ZCNC base) use the same Sherline coupler that has a taper? That taper has given me many issues over the years.

[mhackney]

I agree with Fastes1, a 1mm end mill should snap before a stepper stalls. Something else seems to be going on.

[Fastest1]

Upon further inspection of my now neglected A2ZCNC mill. It uses the Sherline CNC stepper mounts and tapered ended leadscrew and coupler. There is a miniature screw inside that coupler that threads into the screw. Check it, make sure it is very snug ( I hate to use the word tight on such a small screw). I have loctited the screw and the taper a few times. It works for a while but eventually breaks free.

I have since gone to boring my coupler, threading it 1/4-20 and screwing it on the leadscrew, then tightening the clamping screw onto the now threaded shaft. Seems to work.

Could it be your acceleration is too high not really the velocity?

[harveyjbarrow]

Thanks for the reply. Yes I am using the A2Z kerk motion lead screws and anti backlash nuts but only in the X and Y axis.

I have been breaking the 1mm endmill bits but not the 2mm. On my final pass I lost origin on the y axis which has never happened before. I did check the coupling and all is OK and I have also reviewed the G-code and the Y position is exactly how it should be.

Last night though I was checking how bad the vibration was from the spindle and I noticed the Z axis handle moving and the Z axis was actually dropping!! This will be what is causing me the biggest issue especially because I normally switch the motor on before I enable the stepper motors. This might also be the issue with the Y axis.

The reason why I wanted to fit a VFD was to reduce the weight on the Z axis but also reduce the vibration but give me more that 10000rpm but I do not think that the higher rpm is necessary.

I was also thinking about the Z axis rail. When I first got the machine the only way that I could get the collet lose was to essentially use a rubber mallet. So initially I did not tighten the collet up too tight but then the endmill bits were working lose. So by the time that I tightened the collet and then used a hammer to loosen it I think that the Z axis is now bent. I have now tapped the end of the spindle and I have a bolt and pin that pops the collet out.

My plan going forward is that I will order the A2Z Z axis as well as a G540 plus some new Keiling stepper motors and I will somehow create a anti vibration mount for the motor.


Fastest1 - How do you find the A2Z Z axis?

[Fastest1]

I bought the whole Monster Mill. Tim (of A2Z) would probably work with you to get you going if that was the route you choose to take.

Regarding the collet releasing, first i would use a dead blow or brass hammer, while supporting the spindle head with my hand. It should take a short but firm rap on a slightly loosened draw bar bolt. The rubber mallet would take a violent blow to exert enough force.

Sherline parts are interchangeable and inexpensive enough. If it is the column by it direct and reuse your other parts. I might even have 1 in a box around here somewhere. I am not likely to use it though I do always derive a way to use their parts. I just got a shipment of Moglice today. I plan on doing a write up of some kind.

Dont replace the steppers right off. I agree on the G540 (and preferably a 48vdc power supply?) With a proper drive and power supply your existing steppers might perform to your liking.

[pippin88]

What software are you running?

I used to lose steps on Mach3 if I had 3 axes moving fast. Fixed with moving to LinuxCNC. Was likely a kernel / parallel port speed problem

[harveyjbarrow]

I use emc2. Hopefully won't be too hard to integrate the G540.

[pippin88]

G540 is easy to get going with LinuxCNC

Have you done the LinuxCNC latency test?

[Fastest1]

Most likely a corrupted version of Mach.