Trying to buff primary cover- not coming out to good

[ecollins]

Small parts come out good, larger parts do not. I am trying to buff my aluminum primary cover that is from my triumph motorcycle. Here's my setup and technique.

1) 6" buffing wheel set from caswell (sisal, spiral, cotton, canton flannel).
2) compound set bought from sears (black, brown, white, red).
3) no-name 3/4 hp bench grinder bought from joblot for $30.

I wet sand up to 600 grit. Take the piece to the sisal wheel w/black compund. I use a left to right motion. It looks a little shiny after this.

I then move to spiral wheel with brown compound. Again using a left to right motion. I expect piece to look much nicer but it looks duller with more noticeable scratch lines.

I wonder if my cheap bench grinder is too weak to properly cut or if the compound that comes from sears sucks or if it is my technique. It is pretty easy to bog down the grinder (I can almost stop it with my hands!) Before I lay down money for a new buffer, I was hoping someone could tell me my cheapo bench grinder is fine and my technique needs to be changed. Thanks!
-ethan

are you sure it is not chrome plated? but as for the compound caswell got the better of the 2 .... and for grinder ... what amp is it running ?

[ecollins]

This grinder does list the amperage just says 3/4 HP. I will double check tonight when I get home from work. The cover is definitely not chrome plated.
-ethan

[fxstcguy98]

First I think you need to spend more time on the black/sisal combo, that will be the majority of the buffing. Buff until it looks close to the finish that you want. Second make sure you a cleaning all the compound off the part before switching to brown. Use brake parts cleaner, then Dawn and HOT water, and make sure it is completely dried. Third, rake the spiral wheel before you put on the brown to make sure the black dust hasn't gotten all over the spiral wheel and will make scratches. And remember use a little compound and use it often. Keep practicing, it will get better.

if it is chrome plated watch so you don't mess up the plating ...

[BrassLover]

Here is the formula for finding amps when horsepower is known.

Horsepower x 746/Volts x Efficiency x Power-Factor

Sometimes the tag or name plate on the motor will have the efficiency and power rating rating (both expressed in percentage).

.75hp x 746 = 559.5

120volts x 90% x 80% = 86.4

559.5/86.4 = 6.475 amps

I'm guessing at the Efficiency and Power-Factor. Your motor probably draws 5 - 7 amps.

how is it coming on this project ?

[ecollins]

First off, the piece has small casting pits that can't be sanded out, without really deforming the shape of the piece. I tried w/an orbital sander and 100 grit sandpaper. They are pretty deep. I think that might be the main problem. Anyway, I'll live with the pits and I just sanded over them. It looks pretty good after the white and loose cotton combo. But then I go to the rouge and canton flannel combo and I still can't get rid of the swirl marks. I wish I had digital camera to post.
-ethan

[rotorman]

Originally Posted by ecollins

Take the piece to the sisal wheel w/black compund. I use a left to right motion. It looks a little shiny after this.

I then move to spiral wheel with brown compound. Again using a left to right motion. I expect piece to look much nicer but it looks duller with more noticeable scratch lines.

you need to change the angle of the pice to 90' from the black compound step.

This applies to every sanding step also. each finer stage must be applied in a direction perpendicular to the previous stage.

What is probably happening is that you aren't removing the scratches from the rougher stages - in fact you are just making them more pronounced, as the finer grits with just run themselves along the existing scratches. So, when you reach the polishing stages it is just exposing the scratches that are already there.

Sometimes when the piece is big or a weird shape, its hard to do each stage at 90'. The way I get around this is as follows (feel free to suggest a better way though!)...

eg if its a long thin piece...cut on a 45' angle with black compoound, pulling the piece against the flow along its length so that the direction of the wheel is at 45' to the piece.

then with tripoli, do the same but at 45' the other way. the buffing ends up being at a 90' to the previous stage.

hard to explain.

[ecollins]

I know you are supposed to sand and buff each stage at 90 deg to each other. But it was too hard to do with this particular shape... so I didn't. I will try your technique and post.
Unfortunately, my cheapo bench grinder has burnt out after less than a month of use. I think I will get a the craftsman 1 amp model from sears. Thanks for the advise.
-ethan