Trying to prevent ribbing on tapers

[tornitore45]

There is a fundamental difference between a torque and a force. A force applied to the handle of a crank results in a torque BUT it also applies a force to center of the crank wheel. The wheel rotate but the axis is forced to attempt movement up and down left and right as the the hand pushes the crank around. A pure torque as is applied by any kind of rotating shaft is equivalent to two equal and opposed forces applied to two points diametrically opposite. The shaft has no resulting force applied.
A power feed is ideal since it apply a pure torque and has uniform speed, the next best thing is to turn the dial between fingers like winding a wing nut. The side force component is eliminated but uniformity is still difficult, it can be improved by transitioning from one hand to the other ... before your arm twist like one of those ornamental candles.

[Harold_V]

Thanks, Mauro. Very eloquently stated.

H

[Russ Hanscom]

A long time ago, when I had a related problem, I made an aluminum yoke that slipped over the cross feed handle. The center of the yoke was broached 3/8" square so it would take a 3/8" socket drive U joint and speed handle. With that combination, you can turn the cross feed dial with no extraneous lateral forces. It worked well for me. Sorry, but I was not able to find the yoke to take a picture.

No need to remove or modify the cross feed handle and it goes on and off in seconds.

[RSG]

The side force component is eliminated but uniformity is still difficult, it can be improved by transitioning from one hand to the other ... before your arm twist like one of those ornamental candles.

This is exactly how I did it the last time I was faced with it and thought I got a very smooth travel with minimal stutters and speed variations however after further processing I found it was no better. But I do appreciate the suggestion.


I think the take-away here is power feed, simple as that. I will work on a simple version based on the suggestions I've received here in this thread. Thanks for all great responses!

RSG

[Jorg50]

Mauro addressed the issue correctly. It is not easy to use a compound and achieve a uniform cut, due to deflection of the slide as you apply pressure. You may find that loosening the gib so the slide moves easily may improve the finish, but don't count on it. Best way to eliminate the problem is to apply power feed to the slide. Some creative thinking could prove to be a solution; a simple speed control of some kind with a flex coupler attached to the screw, with no handle present. Might be worth the effort.

You may enjoy success by simply spin polishing the area in question, using a flat surface covered with abrasive cloth. A file, for example. You'd have to spin polish until all traces of irregularity have been removed, and that can be challenging.

H

Harold in one of your posts do not remember which you have said never to use a file in a round stock to polish in a lathe because the piece isn't going to be round it would be better to wrap a strip of sand paper ( which I do agree) why don't you recommend doing the same procedure in the tapper. Please don't this as criticism, I like to learn and know the reasons why.

[Harold_V]

Harold in one of your posts do not remember which you have said never to use a file in a round stock to polish in a lathe because the piece isn't going to be round it would be better to wrap a strip of sand paper ( which I do agree) why don't you recommend doing the same procedure in the tapper. Please don't this as criticism, I like to learn and know the reasons why.

In this instance, I didn't make mention because it doesn't solve the problem being experienced. A permanent solution that doesn't add time to each piece would be desirable.

When one must polish an uneven surface in the hopes of leveling, the process slows as the surface improves. The first half thou goes rather quickly, but as the leveled surface area increases, the low areas that remain are slower and slower to be removed, as it's the high areas that must be leveled to their depths. Eliminating them is the best choice, although for a one-off it may not be worth the effort. Filing offers the opportunity for further damage, as file pinning, especially with aluminum or mild steel, is an ongoing problem. A flat surface covered with abrasive strip would yield acceptable results. It's just slow business.

H

[ptross]

one other suggestion is to alter the way you are sanding with 240 and 600 grit paper. If you hold the paper stationary against the surface (even when backed with a file) you will not remove the grooves. It is helpful to apply the abrasive diagonally across the ribs you are removing- across the furrows rather than along them. while this isn't easy on a spinning surface, moving the abrasive up and down the taper or swiping slightly diagonally will help. Another useful thing is to go to even finer grit abrasive than 600. This will show remaining ribs better before you start polishing.
Peter

[John Hasler]

Harold writes:
> Filing offers the opportunity for further damage, as file pinning, especially with aluminum or mild steel, is an ongoing problem.

"File pinning"?

[GlennW]

"File pinning"?

Swarf lodged in the file.

[GlennW]

I'm in total agreement with Mauro, but I'd also try a smaller radius on the tool. Maybe about half of the radius you are using to start.

[ctwo]

I was taught that with hand finish feed, don't use the knobs, but rather use a two-handed hand-off on the wheel and keep the feed constant. Most of the time, both hands are on the wheel. I've always done it that way, even on the carriage, but I don't do a lot of production. When I worked in a commercial shop, I was young and a cheap automatic feed for the owner.