Erik Barrett was kind enough to gift me with his extra knife edge balancer (on the understanding it will be passed on to another T man when I'm through with it). I have found that it takes much more time to level the balancer than to use it!
Just to add to the roaring response on this thread I would like to add my experience today of working on the balance of my drum. Eventually it won't be "my drum" but will be "my transmission" and "my motorcycle wheels".
I have had a bit of insight whilst balancing my first drum. First, for background, the reason to balance is obvious. The vibration of our T engines can not only be annoying but is a symptom of wasted energy. If rotating parts are well balanced they will not oscillate around their center of mass but will run smoothly. (Simply stated the center of mass will coincide with the geometric center of the component.) Hence a major source of vibration will be eliminated.
Another major source of vibration is the reciprocating masses; the pistons, rods, piston pins etc. These can be made to vibrate less by the use of counter weighting adjusted with... you guessed it... dynamic balancing.
Well enough of this what have I found with my crude dynamic balancer? Right no I am probably 90% done with the first drum balancing. I reasoned where I should remove mass (or where I should add mass) in my previous post. Before actually grinding my drum I decided to test out my assumptions. By wrapping one spoke of the reverse drum with solder I made that spot significantly heavy. Then by spinning the drum up I could visualize the position the drum was in when the commutator (Model T lingo) made the drum appear to stop. Next I stopped the drum and placed it into the position which the strobe light had identified and, on the machine, marked where the heavy spot was located. In the future this index identifies where the drum is heavy and needs lightening.
What I found was I that my assumption of location was 60° off! No matter the correct position was located.
Next I removed the solder and started balancing the drum. By grinding selectively on the drum the oscillation noted when a drum spins is decreased as you progress. Soon the oscillation becomes very small and you are almost done. Good enough for model T use, but I can keep going. Tom Carnegie says that with his home brew machine he can remove all out of balance.
So there you have it!
I never said that! You can make it pretty good though. The reason it is 60 degrees off is because you have spun the rotor past its point of maximum imbalance. It must be allowed to slow through that point to visually see the spot where it needs to be lightened. As it slows, the spot will appear to move one direction, stop, and then reverse. The point where is appears to stop is where the heavy spot can be detected. As the balance gets closer and closer, that spot is hard to detect because it moves through it so quickly. What I wound up doing was guessing and using modelling clay on the opposite (light) side as a way to test.
The 60 degree spot will change as the balance changes. So don't assume it will always be 60 degrees off. That is a function of rotor speed vs. imbalance.
Ah... Tom once again it is better to learn from others experience than it is to learn from my errors.
I have seen that reversal as it spins down without understanding the significance. I will re-weight the drum and experiment with that tomorrow. I am very happy with the progress I am making on this.
Keep it going Terry, I'm coming up on this very operation next. PK
Terry, perhaps you could see to it that Pat could be the next user of the balance rig if he needs it and you are done with it.
leveling the knife edge is easy by installing four bolts with jam nuts at the corners of the knife edge like a washing machine setup.
I use a high end level for the first check then switch to a machinist level for the final check. The machinist level is very sensitive to a change
The knife edge is fastened to a heavy bench when level because any movement from setting or re setting drums on it will give a false reading if its not solid.
Erik, Pat, you bet.
Paul, I use a level salvaged from an alignment set up. My trick with levels is to level it once and then turn the level 180° and then split the difference in that direction. Then I go back and check it. (my level is in a gear adjustable housing which allows a bit of error). I level the first blade then across one end of the two blades. Next I level the second blade. To check it all I check across the other end of the two blades. I am then very careful not to move it. I like your idea of bolting (or clamping) it to the bench!
I'm not ready to send the knives on yet, I still have to select which drums I want to use and to balance them.
for interest it would be fun to send some drums to someone like Tom for comparison of balance if he cared to check balance with his method. there is more then a few ways to balance drums and my method is a little different from the posts I have read. My knife edge is made from two new Home Depot hand saw blades turned with the teeth down bolted to a frame similar to the picture posted. I balanced a set of Dun weights on that setup then took the crank to a professional spin balance shop who had first said my balance method did not mean much then after checking said I was within the limits of high speed cranks and did not know how it could have been static balanced that close.
I seem to remember (see above to calibrate my memory) that Tom has checked the accuracy of his balance with a pro. Rather than me reporting his results in error maybe he will chime in on that.
I wrote an article for the Montana 500 newsletter about balancing. The purpose of the article (actually a series of articles) was to show that with a little bit of work a guy on a limited budget could do stuff to make his motor better. Most of the stuff in this series of articles is kinda crude, but it is also effective. I don't have a balancer other than this home made thing. I generally pay a local guy to do my balancing.
Here is a link to the original article where I think I explain it a little better than I did above.