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Messages - simpson36

871
The disk brake caliper is mechanical from the git-go.  These are small calipers for bicycles, ATV's, mini bikes, etc. I purchased several varieties and the one featured on the 4th axis happens to be for what is called a 'pocket bike', which is a ridiculously tiny motorcycle. They all have similar internal cam arrangements.

I found the quality of the calipers to be unacceptable, so I had to extensively modify it. So much so that in the future, I plan to use the brake pads, but fabricate the caliper from scratch.

The disk is cut from 2024 of 7075 aluminium sheet. I must emphasize that this is a consideration for mass and these disks are not intended, nor capable of acting as brakes to slow a load. The disk on the milling machine spindle is another 'pocket bike' item. It simply needed a small hole for the sensors and have its mounting hub removed. It is the smallest pre made disk I could find at 5.5" OD

The servo motor will *try* to maintain one count on an encoder, but that is not going to happen if the load is too great and the amps too little. I have 35amps available and I can force the motor off center by hand with less than a 12" lever. The normal dithering is tiny with my 1800 line encoder (7200 with quadrature), but 'tiny' is relative. Cutting the teeth on the GT3 timing pulley was done with a tiny 4 flute ball end mil ll at 28,000 RPM. If you have a chip load of .0002, even a .001 oscillation is significant.

My 'anticipated' issue is off center drilling of fairly large holes in stainless or tool steel. The force needed for that would be greater than it takes me to move the spindle off hold.  This is a heavy unit intended for 24/7 production, so it needs to be able to handle tough jobs. 

872
IF you have no need for using your 4th axis as a lathe spindle, then it is a perfect application that takes advantage of a stepper motor's strengths, which have been discussed numerous times.

Flying Scott: You mentioned 'small' servo motor, but a direct comparison between stepper and servo power cannot be made based on published specs because they are not measured in the same way. Sort of like comparing Gallons to Feet.

Steppers are very good at holding (big steppers, that is). That is where the torque spec is measured and they do not dither or vibrate or have any 'slack zone'.

You need to also consider the drive mechanism involved. Many 4th axis are worm gear driven. I would speculate that this would swing the advantage back to the servo motor, where the vibrations would not be an issue, and the far higher speed of the servo motor would be a great benefit.

Hood: If we may refer to the drives that I reviewed as 'hobby level', then there are none that can have their amp output commanded in real time with Mach3 software. I'm not saying it is impossible, as there may be some method that I am not aware of, but I did investigate 'real time' reconfiguration via Mach3 at the time of the review and I know of none. CNCdrives is adding the capability and I don't know yet exactly how it will be implemented, but it will thru a macro for sure and will use  the currently unused 'aux' connector on the drive. . 

873
General Mach Discussion / Re: A Really Exceptional Vendor....
« on: January 26, 2010, 09:51:04 AM »

Here ya go. "Just the facts, Ma'am." 

Draw your own conclusion:


http://www.thecubestudio.com/KellingSupportEmailString.txt

874
Here are a couple pics of the new mill showing the spindle lock. In this case, I may want to use the brake for stopping the spindle, so it is a thicker steel part.





Next photo shows nearly fial assembly. Belt guards nor installed yet, etc.


875

It is a disk brake. The disk is .062" 2024 aluminum and is intended only for holding and not for stopping. The servo motor provides deceleration. The mechanical disk caliper is from a 'pocket bike'.

The lock was 'added on' and not part of the original design, so it could be better integrated, but other than having the disk extend past the frame (which requires an elaborate belt guard), everything worked out satisfactorily.

The servo drive is a 'Dugong' model from CNCdrive and they are modifying the firmware for me so that the drive's max amps can be set back a fixed amount under software control. This will coordinated with the lock event. The purpose of this is to prevent the motor from overheating if it disagrees with the location of the lock event. Keeping the amps below the motor's continuous rating will prevent possible overheating and damage to the motor.

876
General Mach Discussion / Re: A Really Exceptional Vendor....
« on: January 26, 2010, 07:58:14 AM »
Patience, Grasshopper. Things are not always as they seem. I see the question, but there was no urgency attached to it and I have only a very limited amount of time for forums, so I must prioritize. If there was an urgent need for an answer, then the error was in not stating so, methinks.

It would be a good strategy to determine the forum's policy on 'vendor bashing' before I get reprimanded for doing so, think? A moderator asking for clarification is an indication of that policy, one might imagine, so I will say that my issue with Keling is with their abysmal packaging resulting in damaged product (on three occasions) and my current gripe is with their sales/support which is completely incompetent and useless.

I will elaborate when I have time to choose my words carefully. Right now, as you may have guessed, I  am extremely annoyed with Keling . . . again . . . . I suspect you (Clemens) have some familiarity with that emotion . . . ;) , and it is important to be factual in such matters, you would agree.







877
Thanks!

The X2 featured here is now sold and gone. My new mill is scratch built completely from aluminum and is slightly larger than an X3. There are still some details to finish up and the high speed pulleys are not done yet, but I have just started cutting metal with it. I will be posting photos and videos soon. Unfortunately I do not have time to do a build thread on CNCzone or anything like that.

Here is the latest video which simply demonstrates the newly finished pneumatic spindle lock on the 4th axis. I now have a larger disk and an new belt guard (not shown in the vid)  extends to cover the new disk.

http://www.youtube.com/watch?v=glYDe94hxb0


878
General Mach Discussion / Re: A Really Exceptional Vendor....
« on: January 25, 2010, 02:49:40 PM »
On the other side of the coin are the Really Exceptionally BAD vendors, for which I nominate Keling Technology.

879
Thanks for all of the replies. I have the info I need now and a fairly good understanding of the various relationships I was asking about and everything makes sense.

Just a matter now of finding time to do the testing . . . .

880
The DMM products were good performers.

My apologies.

I have DMM confused with Leadshine. Everything I posted applies to Leadshine only.

I did not review DMM's products. These were AC servo drives that came with controllers and a non-optical encoder. I could find no references at all to anyone using these drives and they seem far out of the mainstream. I asked for references and/or interest in several places and got no response, so I decided not to review the products.

As I recall, they come with a money back guarantee and are claimed compatible with Mach3, so anyone who wants to give them a try, have at it.