Grinder design questions: tracking wheel & drive wheel position, over-center tension, etc.

A motor running on a VFD will sometimes have a band of vibration when running on bench with no load. Once you've got on 2X72 that provides enough load to smooth motor out - most of time. If not you can always program the VFD to skip the freqs that give vibration. I've never had to do that with any of the cheap Chinese VFDs I've got. Programming VFD to display belt speed in SFPM is one of the things I really like about the VFDs with display.

I put off buying a mill for 3 or 4 yrs, just didn't think I'd have enough use for a mill. Now I've got a mill I don't see how I got by without. Just like the lathe, always using for something you'd never thought of before.

I think the cooling tower mention was from industrial days when Fitzhugh was using VFDs in industry. Cooling tower fans where a popular use to save power. With the mention of reactors I suspect there were some long motor runs also, and had to worry about standing waves on the motor power leads. The last chemical plant I was responsible for I passed on use of VFDs because I had some 500 to 600 ft distances from MCC to motor. The problems of long distances just didn't justify use of VFDs. AND getting the expensive armored/shielded power cable made the use of VFD not a good choice due to cost.

Good to be retired {yea, I'm bragging} :)
 
I see, he was joking.

A lathe would be nice, I have almost convinced myself that I need one.

Ken, could you tell me how far from the pivot point the spring is on your tension arm? I am struggling a little bit with the design of my tracking system since I have very little room. I have to put the spring in front of the pivot point for sure, or use a different mechanism altogether if I cannot get enough leverage.
 
Sorry, yeah, those were other reasons I saw given for motor vibrations. The description of those issues did make me realize that a pulsing motor that isn't well anchored could appear to be vibrating like it was out of balance (if it's relatively minor and you don't have instruments). Likewise, Ken, thanks for explaining about that - this one is NOT bolted down to anything unless the tiny pallet (palletlette?) it came on counts (which it doesn't).

I want a mill, though I'm human so that probably goes without saying. I've only used a cnc benchtop mini mill but it was fantastic.

I was looking at my design and realized the gas shock could mount on the belt side of the chassis and stay within the belt path, making it more in-line with the forces it's countering, if it attached below the tracking pivot. Might work, if it doesn't interfere with the locking handles.
But wait, do you need a spring in addition to the cam?

I got a kbda-27d. It comes with the display and a jog and reverse button, and I'd rather press buttons than turn trimpots and move jumpers like the KBAC (input voltage is still via jumper). One potential drawback I overlooked is that you need an $80 optional IO board if you want to add external controls, as I understand it. (Not needed for optional power switch, obviously).
I think Ken has shown you don't need a fully enclosed vfd if you do it right.

I just saw the photos on my computer monitor instead of my phone. The countersunk holes look great. I've had trouble getting them consistently sized. Guess I need a better depth stop.
 
Fitz, the cam mechanism does not need a spring for tightening the belt. A very soft spring might be helpful to keep the whole mechanism from lifting before the wheel touches the belt. The wooden prototype would do this, the metal one so far not. I think in the horizontal orientation, that might change and I will need a spring.

I thought I saw a potentiometer for speed control on the kbdas when I looked at them a while back. What does the I/O board add to that?

The countersinks turned out better than expected, but you can see some inconsistencies from up close. Like I said, I would probably skip it next time and use different fasteners.
 
I have been thinking about the yaw tracking a little bit more. It seems to me that the force from the belt would always make the whole assembly want to turn clockwise around its pivot point, looking at it from the top. If this is correct, the spring force in the Reeder design always has to be higher than the force from the belt. In my design, the force from the belt pushes against the adjustment bolt and I should be able to use a very soft spring to keep the arm in place while not loaded.

In other words, the Reeder yaw tracking mechanism seems to be the equivalent of a roll tracking mechanism where the adjustment knob is mounted above the hinge point and a very strong spring is used in the normal location for the adjustment point.

Am I understanding this correctly, or is there a flaw in my thinking?
 
Hubert S. said:
I see, he was joking.

A lathe would be nice, I have almost convinced myself that I need one.

Ken, could you tell me how far from the pivot point the spring is on your tension arm? I am struggling a little bit with the design of my tracking system since I have very little room. I have to put the spring in front of the pivot point for sure, or use a different mechanism altogether if I cannot get enough leverage.
Click to expand...

Everyone needs a lathe and a mill.
I don't know how they exist without one.
 
Oh, you're talking about the spring in a yaw tracking assembly, not tension spring. That makes more sense.
I think you're right about most yaw setups I've seen, and you're looking at moving the spring to the other side of the pivot? I just looked at a Reeder video where it looks like he uses two counter-acting socket head screws and no spring. I'll try and post a screenshot shortly.

The kbda does have a potentiometer, though it's configured by default to use the up & does buttons to set frequency.
The IO board is for integrating it with broader systems and automation, from what I can tell, but you'd need it (I think) if, say, you run multiple machines off the vfd and want controls at each. It gives control of relays triggered by vfd frequencies, various vfd status and condition signals, provides external control of parameters. API on a board, I guess.

Here's a good description: http://www.electricmotorwholesale.com/KBDA-9668.html
 
Fitzhugh said:
Oh, you're talking about the spring in a yaw tracking assembly, not tension spring. That makes more sense.
I think you're right about most yaw setups I've seen, and you're looking at moving the spring to the other side of the pivot? I just looked at a Reeder video where it looks like he uses two counter-acting socket head screws and no spring. I'll try and post a screenshot shortly.
Click to expand...
I think there was a v1 that did not have the springs. There is a video linked somewhere in this thread that shows a tracking arm with a compression spring acting on a long lever behind the pivot point and a yaw adjustment knob in front of the pivot point.

I think if you put the adjustment bolt where the spring is in the Reeder design, the bolt would always be pushed against the tracking arm by belt tension. A spring placed where the tracking knob currently is in their design could be very weak, just enough to keep the arm from flopping around when not loaded. In other words, I think the Reeder design is backwards and that is why a long lever and a strong spring are required to overcome the force generated by belt tension.

If you draw a line from the mid-point of the segment where the belt touches the wheel to the axle of the tracking wheel, you get the approximate direction of the belt force. I cannot imagine a belt configuration where this line would tilt past vertical towards the user. This means, looking from the top, there is always a clockwise moment around the yaw axis.

What I want to do is thread the tracking arm and push against a plate in front of it to stop the rotation and adjust tracking. This vertical plate would be attached to the horizontal plate that pivots around the yaw axis and sits on top of the tracking arm. A weak tension spring through both plates keeps the yaw tracking assembly from flopping around when the belt does not provide any load.

I am just questioning whether my analysis is correct, since there is a commercially produced grinder where they do it the exact opposite way.
 
On second thought, there is a configuration where the force vector could go past vertical and push the tracking wheel towards the back. That would be a small wheel holder with additional wheels to pinch the belt together. If those wheels are put far enough behind the small wheel, I think one could make the belt steeper in front of the tracking wheel than behind.
 
What is wrong with this ?
DZENMZI.png
 
Ah, the video I saw was the old one. I did not recall that the photo in the thread was from a Reeder.

I don't think you'd cross the point where it would push the other way even with a small wheel. I used a cad sketch to check the belt path on a variety of different wheel positions & tool arm heights, with contact wheels, platten and SWA just to be sure I was not missing something. (It was lazier work in CAD than actually thinking).
 
Fitz, thank you for checking. When you modeled the small wheel, did you have an additional wheel that runs on the grit side of the belt behind it? By itself, the small wheel seems to be no problem, but with the pinch wheels behind it is not so clear. I made a crude sketch to guesstimate, and I think there is a possibility that the force vector will tip over if the additional wheels are mounted a few inches behind the small wheel. My geometry is different from yours, though. I have the motor a bit further back because of the tilt stand and the 7" wheel adds to that versus a 4" wheel. I have not cut the motor mount yet, so I can still move it up a little bit and change the tilt stand design.
 
Hubert S. said:
Ken, could you tell me how far from the pivot point the spring is on your tension arm?
Click to expand...
Hubert, we've talked about so much here I'm not sure which spring you're talking about. The spring that puts tension on the belt wouldn't be needed with the cam design that's been talked about.

Ooops, got this far, went to measure distance and forgot all about it. Center of spring to center of pivot bolt is 6".
 
Natlek said:
What is wrong with this ?
DZENMZI.png
Click to expand...
Thank you very much for the drawing. I never thought about turning things by ninety degrees. I think there is room to use a much longer spring there without needing a stand-off. This arrangement could work nicely with a couple of modifications. I'm not sure where the motor is in this setup. If it's on the left, the tracking bolt should be on the other side I think, or be threaded through the part you have drawn and react against a plate on the left side. The other issue is that there is not much room in front of the pivot for a spring and a very short lever. But the spring could easily be moved on the other side of the pivot. I have to think about it a bit more and see if I can make things fit.
 
Ken, I was confused as well. It's the spring in the yaw tracking knob works against, not the tension spring.

Hubert, I did check it with the three wheel SWA, but I'm going from memory and I can't say it fit yours. Easy to check though. I need the size of your wheels, their relative locations, and the height of your tool arm.
Looking from the side let's use X,Y, call 0,0 the axis of your drive wheel. What is the X,Y of the tracking wheel axis, the Y of the tool arm centerline, and the wheel sizes?
 
Hubert S. said:
Thank you very much for the drawing. I never thought about turning things by ninety degrees. I think there is room to use a much longer spring there without needing a stand-off. This arrangement could work nicely with a couple of modifications. I'm not sure where the motor is in this setup. If it's on the left, the tracking bolt should be on the other side I think, or be threaded through the part you have drawn and react against a plate on the left side. The other issue is that there is not much room in front of the pivot for a spring and a very short lever. But the spring could easily be moved on the other side of the pivot. I have to think about it a bit more and see if I can make things fit.
Click to expand...
This is how it would work , tracking wheel will go left -right , not up - down.......short strong spring will work .Position on motor don t change anything .............
mc8nycv.png
 
Ken H> said:
Hubert, we've talked about so much here I'm not sure which spring you're talking about. The spring that puts tension on the belt wouldn't be needed with the cam design that's been talked about.

Ooops, got this far, went to measure distance and forgot all about it. Center of spring to center of pivot bolt is 6".
Click to expand...
Thank you, Ken. That is the spring I was talking about. I definitely do not have the room for that. Since I asked about the distance, I have convinced myself that this arrangement is backwards from what it should be. If the adjustment bolt was behind the tracking pivot, it could take up the load from the belt. Do you think that is correct?
 
I think I spoke too soon, going from memory. The vector could potentially cross the pivot. Here's an older check, not even sure what layout it was for. Belt path is 72" (f360 can't use multi-segment line lengths as parameters to fit to, so I just alter the line that is currently 16" until the loop is 72" (or 72.082" in this case, it's an iterative but quick process)
47saopl.png


Edit: If it's any help, I can change the parameters and check, just tell me which to change, and to what
 
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