What am I doing wrong?

[Jerry Toschlog]

I am somewhatnew at turning and I have a question. When I turn a bowl and I am at thesanding stage, sometimes a nice surface starts getting rough and pitted spotson the bowl. I had assumed it was the wood. Today I turned my first segmentedbowl and much to my surprise it happened again. It crossed into both types ofwood in the areas it was happening in, so it has to be my technique. I am at atotal loss, the wood was not green by any means. ..EDIT I typed this in word and the words wore not ran together, not sure what happened, sorry guys..

[Harry Robinette]

It sounds like end grain tear out to me.

[Josh Bowman]

Jerry, I start my sanding with 80 to 120 at about 500 to 600 rpm with an angle drill going in the opposite direction. I use only lite pressure, avoid any heat. Then I go up though all the grits to 400 or 600, slowing the lathe down each step and getting lighter with my touch as I get finer.
Vince at http://vinceswoodnwonders.com/ has solved a lot of folks problems here. Give him a call, he's a very personable guy. He knows a lot about sanding and most likely will solve you issues.

[Jerry Toschlog]

Harry, that was what I thought until today. Josh, You may be right I really push when sanding and yes it gets warm, never thought that could be the issue.

[Scott Hackler]

Jerry, when sanding you should use light pressure and slowed down to a speed that allows for sanding without the generation of heat (or much of it). You should also start at the appropriate grit and don't skip grits. Keep in mind that the next grit is scratching the wood and only used to remove the scratches from the previous grit. The best advise on sand paper I can give is to use sand paper as if someone else is paying for it. On any given piece I will use 1-2 discs of each grit and they get thrown away after use, unless they are completely clear looking and I can physically feel the grit with my fingers. Go to Vince's site and learn more or better yet call him and get schooled in proper sanding! He's a good guy and a lot of us use his products.

[Jerry Toschlog]

Thanks guys I have been reading since I seen Josh's post and yeah I have been really over doing it... I do use all the grits but I need to lighten up and slow down... I am so glad I ask. I did check his site ...

[Reed Gray]

Slower speeds on both the lathe and drill let the abrasives cut much better. It seems to be just the opposite with your lathe tools in that they seem to cut better at higher speeds, though you still can cut efficiently at lower speeds. High pressure, high speeds, and dull abrasives generate enough heat to cause heat checks, which are a bunch of tiny lines, and are cracks.

robo hippy

[Jerry Toschlog]

Heat checks!!!!!! So that must be what I am calling rough spots and pits.. Ok, nice to know. I have been back on Vince's site reading, etc. I am now excited to turn something and to get to the sanding part. I had a mindset that faster was better with sanding...

[Faust M. Ruggiero]

Jerry,
Somehow all the comments revolved around sanding but I believe Harry may have hit the nail on the head when he said tear out. There is a place on a side grain bowl where the cutting edge is cutting directly into the mouth of the grain. Imagine what would happen if you tried to slice a bunch of straws that are leaning toward the cutting edge. The grain gets disturbed and unevenly cut resulting in a rough area that almost no amount of sanding will remove. If I am correct that this is your problem, you need to begin learning a technique to deal with that grain. In some woods, even the sharpest tool may still "bruise" the grain. Often a light touch with a freshly burred scraper will clean up the end grain but sometimes scraping makes it worse, especially is you present the tool to the wood with too much pressure or at an improper angle. Some people talk about a negative rake scraper that handles this grain better. Either way, begin your search for a way that eliminates tear out before you begin sanding. If not you will have to sand so deeply to eliminate it you will spoil the flow of the bowl.
faust

[John Beaver]

Faust. If you read the post closely you will see that he says "a nice surface starts getting rough during sanding." It may be happening more in the endgrain area, but I agree with the others, that it sounds like sanding too aggressively.

[Reed Gray]

Well, without actually seeing the piece, or a picture, I can't say for certain. He did say he was doing a segmented piece, and cutting technique is a bit different for those, and generally there is no end grain, it is all pretty much side grain.

robo hippy

[Jerry Toschlog]

I can get you some pictures... Here is why I think it is not end grain, please correctly me if I am wrong as I am always open to suggestions as I am new. The last bowl was segmented and lets say I have a spot the size of a quarter. The roughness was on BOTH types of wood and in a somewhat oval shape. Faust, I just re-read your post and what you are saying also has happened while turning. such as with the bowl being smooth then as I am about done it starts getting rough. I want to thank everyone who has responded here, as I wish I would have ask this question a year ago. I have leaned a ton about sanding in the last 24 hours.

[Jerry Toschlog]

Ok here is what I am talking about, and a lot of times it starts showing during sanding. Several times I am very happy with what I am getting when sanding then all the sudden these start showing. Last night I did another turning with very slow sanding and same thing... DSC_9762.jpg

[Reed Gray]

Jerry,
That is tear out, and it is in the end grain. If you divide a bowl up into 15 minute sections of a clock. for each rotation, 1/4 turn is cutting down hill with the grain, and 1/4 is cutting up hill against the grain, then it repeats. There should be tear out 180 degrees around the bowl from what your picture shows. Some times it is invisible till you go up to a fine grit, then it highlights. If you spin the wood slowly, by hand, both forward and backward, you can feel it. So, high shear angle, and very light cuts. Shear scrapes will do it as well, and it takes several passes to remove the tear out. Cut from the base to the rim for best results. If there is any one to mentor you where you are, it is a huge help.

robo hippy

[Jerry Toschlog]

Mentor... I wish there was !!!!!! I keep asking if anyone turns around here... I will check the bowl and see about the 180, BTW that is a close up pic with low angle lightning, that pic makes it look horrible but either way I wanted to show the issue as I want it perfect as it can me. I want to lean to correct or not have these issues. Thanks Reed