As I was watching a rod dry in my power wrapper I was wondering why you guys thought that manual drying (turning by hand) produces a better looking finish job? I would think that drying under power would turn out better but that is not what I have heard from those that do it manually, i.e. Tom.
Any thought??
Thanks,
Noel

I've always felt that the slight centrifical force generated by constant rotation of the rod causes the finish to draw in toward the center and then outward - a very slight but definitie football shape. Of course, this happens either way if you apply too much finish. But I still suspect that centrifical force is going to affect the finish every so slightly.

Most people who move from powered rotation to doing it by hand will report that their finish jobs just seem flatter and smoother, although they also mention that they have to babysit the rod for a couple hours, which many don't like.

............

Everything has it's good sides and it's bad sides. I started building and finishing by hand. After several years, I built a 2 RPM drier out of an old humidifier motor. I now wonder how many hours that bugger has turned a rod 'round & 'round?? After all those years (nearly 20), it still is going strong. I built a back-up several years ago because I knew that black cloud over my head would come in to effect, but it's still in the drawer where I put it after I was done.

I think a slower RPM motor does at least as good a job as hand turning (but it's really hard to remember that far back) and it really frees me up from babysitting the rod.

Putter
Williston, ND



Edited 1 time(s). Last edit at 07/19/2005 06:58PM by Randy Parpart (Putter).

I am making this post in honor of Emory Harry. Someone must take Tom to task during Emorys' stay in the hospital. Now for the rest of the story. In Mr. Kirkmans' post a word was used and probably miss spelled, to wit, centrifical. There are far to few opportunities for anyone to edit anything Tom writes so I will have fun with this one.

This brings up a very interesting story. The first time the word "centrifugal force" was noted was in a Flash Gordon Comic Strip in the 1930s. It was defined and thought to be the force that holds rotating bodies out when they are spun around an axis. In Mr. Harrys' world of scientific fact there is no such force. The real force is the other way around. If you are slinging a rock around your head tied to a string what would happen if you cut the string. It is obvious that the rock would fly off in a tangent to the arc. The real and correct force is properly spelled "centrepital" and is defined as the force that holds a rotating body in!

Contemplate that for a few minutes and conjure up all sorts of reasons that the finish turns into the shape of a football. Mr. Seider makes a comment in his Flexcoat lectures that internal forces, due to the initiation of polymerization, of the the finish components, can cause funny movement of the curing finish. I am just glad that the finish does not resemble vollyballs!

I am presently at the stage of high speed finish application after watching Sharons' people, at All Star, AKA Shakespere, apply finish at 200 rpm. I presently do not have to worry about leveling - it is a simple matter to scrape the "excess" hard finish off the walls weekly. Drying speed then becomes a rather moot point - hand turn, slow turn or let it rip with the right amount of finish applied will self level.

Emory, take another happy pill and go to sleep - the board is in good hands!

Gon Fishn



Edited 2 time(s). Last edit at 07/19/2005 08:36PM by Bill Stevens.

I'm with Putter! I switched from 30 to 3 Rpm although, I still prefer to let it level by itself and hand turn for an hour or two first

Mike

I've only ever owned one dryer and it's been running at 3 RPM for over 15 years. I use it because it turns out good work and it's convenient. I've seen stunningly beautiful work from people like Tom who always turn by hand. I'm tempted to try it myself sometime when I'm able to babysit the process properly and compare the results.

Hey, Putter - I guess you're babysitting something besides rods now, aren't you?

Yes sir, Sam! The girls are back!!!

Putter
Williston, ND

Bill is correct, the correct spelling is centrifugal (as in centrifuge), not centrifical. A dumb mistake on my part, but I believe it is the centrifugal force rather than the centripetal one that helps creates the footballs. Centrifugal forces are those used to explain objects in a frame of reference that is in rotation. Now if you're outside that frame of reference, looking in, then I suppose you could say you're witnessing a centripetal action. But I think centrifugal would almost certainly be considered that which moves away from a center while centripetal would be considered that which moves toward a center. When Emory gets back we can argue this some more.

Either way, too much finish certainly causes the football effect, whether rotated by hand or machine. I can only suspect that the constant rotation of a rod also tends to help create the same effect. I have no proof, however, it's just been something that I've long suspected might be one culprit.

.........

Tom, I've noticed one brand of rod finish in particular, when too much is put on and it starts to football, it pulls the finish right off the threads on each end of the guide wrap leaving them "bumpy" where I can feel each of these threads like not enough had been put on. Have you noticed this with that one brand of finish??

Putter
Williston, ND

I've noticed it with all of them, but maybe a couple more than others. I can only surmise that the formulation is somehow one where the attraction between molecules is stronger - more adhesion, so that when any of the finish moves, the rest tends to move with it.


..............

I'll go along with Mike on this one. Hand turn for the first hour or so, then finish up on the 3rpm dryer.

The best finishing advise I ever got from this board was to put it on, then leave it alone!

Regards......Doug@
TCRds

Doug,

AMEN!!!!!!

At least check it once for drips

And by the way, by move "away from center" I'm talking about it moving away from the center as in the "axis" of the rod. Not away from the center of the wrap.

..................

Tom consider this little caviet.

The angular velocity at constant rpm is controlled by the diameter of the circle at any given point. This velocity can be calculated by the arithmetic expression of velocity equals 2 (3.1416) radians. If you have a rod on a turner say at 3 rpm, as the learned Mr. Puter espouses the angular velocity at any given point along the x axis of the guide wrap is a function of the diameter of the segment in question. The smallest diameter of the wrap in question is at the end where the thread is only wrapped around the blank, i.e. both ends, if a security wrap is used on a single foot guide. The largest diameter is where the thread encloses the blank and guide frame at its highest point. Even at a constant speed of a turner the center of the guide has a higher angular velocity than the ends. With the small molecular forces that are in play it is highly possible that the small differential in velocity at any given point will tend to "football" the level of the finish.

If you think about the reality of this being factual it may provide an explanation why so many people have a problem with "bumpy" fnishes on long butt wraps. The thread crossings provide points of greater diameter which slightly increases angular velocity of the finish at that point. The only real way to get a level finish is to let the liquid finish seek it own level when at rest .

This complex logic by a builder of rods from de bayou is fully intended to represent the position normally taken by Emory Harry. Back to Flocking & Sniffin Solvents

Gon Fishn

WOW, Bill!!!!! I actually understood that (some of it anyways) and what's scary about it is that it makes sense!!. Please Emory, Hurry Back!!!!





Mike (Southgate, MI)
If I don't want to, I don't have to and nobody can make me (except my wife) cuz I'm RETIRED!!

So it sounds like either turn it by hand and babysit, or a very slow turning dryer.

Exactly. You will find however, that even on a purely decorative wrap or a long trim wrap where there is no guide and thus the diameter of the wrap is the same over its entire length, you'll still get the football effect in many instances. Not that your own suspicion is wrong (in fact I think it makes sense) but overall the simple act of spinning a rod tends to throw anything on it away from the center axis. Due to the adhesion of the finish, as it moves outward it also pulls finish from each end of the wrap into the heavier area now formed in the center. I would think that the greater the rotation speed the greater this problem would tend to be.

I wouldn't ever go so far as to say that you can't get a nice level finish if you use a dryer to rotate the rod constantly, and you can certainly foul up a finish even when hand turning every few mintues. But generally speaking, there is an inherent difficulty in getting a perfectly flat, level finish with the use of any sort of constant mechanical rotation device. If you use such a thing, you need to be very careful of the amount of finish you apply and you still need to check back after the first half hour or so and continually until the finish tacks up just to make sure what you have is what you want. If you get those footballs, you can usually just remove them and be fine.

...........

Another thing I have noticed is the finish should not set too fast.
I was using glass coat in the winter and it was OK but!
I then started to play with LS again, and found that the slower time it takes this finish to set up gave it time to also level out.as long as you say it is not loaded on

I think it's important to recognize that there are TWO forces operating on a spinning rod that can cause the finish to move around. The first, thoroughly discussed above, is the 'centrifugal' force, a reaction force opposed to the centripital force that is due to inertia and depends on the rotation rate squared. This is the force that would spray your walls with epoxy if you used a very low-viscosity finish and rorated the rod really fast. The second force is of course the weight of the finish, due to gravity, which will cause it to sag but also to even out laterally. The weight force is always present, regardless of whether the rod is spinning or not.

There is also a third force at work, the internal cohesion of the epoxy, but that doesn't cause the finish to move around, it causes it to stay put.

When we apply a finish we want the weight force to eliminate any horizontal imperfections by causing the epoxy to "flow out", but without sagging to the bottom of the rod. When we rotate the rod we produce an outward 'centrifugal' force that serves to counteract the force of gravity. There will ALWAYS be a slightly larger downward force than upward force, because the forces are additive and the centrifugal force is independent of radial direction, but gravity is not.

If you are intent on constantly rotating a rod, it seems logical that you would want to rotate it as rapidly as possible, subject to the constraint that the cohesion force is sufficient to keep the finish from flying off or oozing up the guides. This is because the 'centrifugal' force depends on the rotation rate (squared) while the weight is constant. The disparity between the total force up and down will therefore decrease as the weight becomes smaller and smaller relative to the 'centrifugal' force. Perhaps you can see this best if you envision a rod turning so slowly that there's a constant sag on the bottom that the 'centrifugal' force can't distribute outward. As the rod turns faster, the 'centrifugal' force increases rapidly so that the difference between the upward force (C-W) and the downward force (C+W) isn't very significant.

All fo this really doesn't apply when you hand-turn a rod. Here, you are manually attempting to compensate for the sagging produced by gravity by reversing the direction of force, not by inducing another, extra force that will govern the distribution of finish. Skill and experience will come into play, but if you're good at it (like Tom K) then you can manipulate gravity to produce a finish that is radially symmetric. It may be too that by relying on gravity to shape the finish and not the 'centrifugal' force you can better remove those horizontal imperfections that give a finish that wavy and uneven look.