Polychain belt conversion for VMC15

[Edster]

I have a 1994 vmc15 with a 7500rpm belt driven spindle. I'm converting the belt to the polychain cogged version on newer models. I have all the parts I need, but I'm running into a slight problem. The new poly chain pullys are the same size for a 1 to 1 ratio. The old pully has two sets of pullys one looks to be a 1 to 1 ratio the other looks like it's got some reduction on it. My old belt happens to be on the upper set with the reduction.

Here's my problem, is my spindle actually running slower that it's supposed to? If so how can the rigid tap option still work? If anyone has a fadal like mine can you verify which set of pullys your belt runs on.

Thanks,
Ed

[Edster]

I got a non-contact tach today and verified the spindle speed. Half of what the control was displaying. The previous owner must have switched the position of the belt on me. Rigid tap was working before despite of what speed the control was programed at. Does this mean the machine is counting the spindle revolutions at the spindle? Will switching the belt over mess with the rigid tapping?

[HuFlungDung]

Can you tell where in the drive train the spindle encoder is being driven from? If it is after the power belt pulleys, then it would not be affected by the input ratio.

Alternatively, providing that there is no belt slippage, and the encoder index only serves to provide a start signal for the initiation of threading, would it really matter what the speed was? The precaution for most automatic threading is that the speed command must never be changed during a multi-pass threading procedure. This leads me to think that the engagement point for rigid tapping is not absolutely fixed, but it will repeat at a given rpm and given start point.

Edit: BTW, good luck with your Polychain conversion. I found mine got to be quite noisy at high speed....so much so that I hated it. I switched to an EaglePd drive, with herringbone style pulleys and belt. Much nicer, much quieter.

[Edster]

I think the encoder is driven off the spindle. There is a small magnet in the spindle pully and a sensor in the orientation bridge. But I'm not 100% sure.

I would think the machine would have to know the exact spindle speed so it could feed x ammount per turn for rigid tapping. It will pickup the the same thread. I've had to adjust the thread depth before and it had no problems tapping the same hole a second time.

I did switch the position on the pullys and the spindle speed is right were it's suppose to be. I also tested the rigid tapping. Cutting air only. I'm still waiting for a part for the drawbar from fadal. It looks like it works fine. In fact I would get spindle motor overloads above 1000 rpm when the belt was in the wrong position. Now It will tap at 1500 rpm no problems, which seems to be the max for the machine. I tried a few speed settings above 1500 and it reverted back to 1500.

Initially I was switching to the polychain because the belt would occasionally slip when using a 1/2-13 thread forming tool in copper. Maybe I can get away with a new belt on the quieter pullys now that there is more surface contact with the belt. I have two haas lathes with the polychain belts. They are really noisy and I rarley run the sl-10 over 3000. I bet it would be really loud at 7500rpm.

The real kicker is the fact that I've had this machine for over 3 years, and the spindle speed was 1/2 what I thought it was.

I just thought the machine was kinda weak. .002 chiploads were really .004, .003 chiploads were really .006. I wonder how much better cycle times I'll get with the correct sfpm and chipload

[Neal]

The Encoder is mounted on the spindle motor shaft. The line count is sent to the Vector drive and is used to verify the RPM. If the count is too low then the vector drive provides more voltage to keep the RPM up. This is how a closed loop system functions. An open loop system, no encoder, simply sends a predetermined amount of voltage out to the motor and does not monitor whether the RPMs vary or not.
The Encoder is also used in rigid tapping to syncronize the spendle motor and axis motor.

Neal

[Edster]

So if my rigid tapping was working before with the 50% reduction will I have to change some settings when I'm using the 1:1 pulleys?

[Neal]

Once you have the RPM issue corrected, I would advise that you have the Rigid Tap function re-calibrated. The Gain and ramp are very important fro proper tracking.

Neal