Sanding issues

[William McAloney]

I am a novice at turning, having been at it for a couple of months. I have been steadily ascending the learning curve and have arrived at a place where I can usually produce bowls with pleasing shapes, smooth curves, and thin, uniform walls. Sanding, however, has me flummoxed.

I start with 80# to 100# grit, both by hand and with 2" discs under power, and continue up through to 320#. Somewhere along the way a condition often occurs. Rough spots appear which get worse with continued sanding. I back down a grit and attempt to clear it up by sanding with the lathe off, sometimes without success. The surface turns white colored and feels "fuzzy". It looks like galling on metal. I'm currently unable to post a pic of this condition.
I turn on a Delta-Homecraft which has a lowest speed of 900 RPM and no reverse capability.
Thoughts or advice, anyone?

[Dave Fritz]

What is the wood your working with? Many times aggressive work with the lower grits cause more trouble than good. The standard answer is to learn good tool control so you don't have to start with such a low grit. Easier said than done.

[Chris A Lawrence]

Try hand sanding the trouble spots with the lathe off at a different angle then the lathe is spinning. Your sanding could be lifting the end grain fibers instead of cutting them.

[Paul Williams]

You could try wet sanding. I use BLO, but suspect that any finish or solvent works for the "wet" lubricant. Another thing I do on wood that is soft, partially spalted, or gets fuzzy is to apply a liberal coating of thinned shellac. Then return or sand.

[Reed Gray]

I did this one a while ago, but it may be helpful...

https://www.youtube.com/watch?v=s4Pkr89STGY

My first thought would be that the rough spots are tear out. Some times that comes from the wood, some times it is tool technique, and some times it is a dull tool, or all of the above. My favorite finish cut is usually a shear scrape (video on that one tool) If you don't get it out with the 80 or 100 grit before you step up to the next grit, it will never go away. Some times it takes a practiced eye to tell you have more sanding to do. Some times you need better light and glasses too. I do consider the 900 rpm a bit fast for sanding. I do keep the drill speed down too, half speed or less on a slow speed angle drill. You may need to sand with the lathe turned off. An arm rest for your arm holding the drill, and rotate the bowl back and forth for the trouble spot. Some times just a light wiping with water can high light the tear out.

Some one once said, 'Never take a finished piece from the shop to the house on a sunny day. Sun light causes scratches."

robo hippy

[Richard Coers]

There is a technique called "whiskering". You take a damp rag and with the lathe shut off you dampen the surface of the wood. This swells the fibers. Then let it dry and sand again. The swollen fibers cut off very easily. I really like using the technique with cherry because some small scratches are hard to see. The moisture will even swell a small scratch and make it easier to sand. Also some turners will mix up a very thin sanding sealer to do the same thing. The lacquer sanding sealer flashes off very quickly with lots of thinner added. This seal the fibers and again they cut off easier. But the sanding sealer may effect any other finishing or dyeing technique you want to do latter.

[Alex Zeller]

Is it happening on the end grain? That's what gave me problems. When I first started turning I was pulling out the end grain. It wasn't exactly at the end grain but just past it. As I got better technique I got much better so I really couldn't see it but it was still there. When I would sand it would raise up. What I found that worked for me is to sand in one direction only (the opposite way that the tool was going) with the coarser grit sandpapers in just those spots. I also rarely use anything less than 120 grit.

[William McAloney]

Brethren,
I think you are all spot-on with your assessments of the situation.
I believe it is end-grain tearing. It happens in all of the species that I turn: maple, ash, cherry, cedar, rosewood, bloodwood, mahogany, and white pine. I also think spindle speed is a factor.
I will try the wet sanding method as well as doing more stationary sanding away from the direction of spindle travel. I'm a little leery of stationary sanding because of the possibility of creating a divot which will then require yet more work.
Improved tool technique will undoubtedly help as well. I'm working on it. One can pick up much from videos, but I really need a couple of hours with a mentor.
Thanks to everyone who contributed. I'll post updates when I figure this out.

[Alex Zeller]

A sharp bowl gouge with an Ellsworth grind using the wings more than the tip to take very thin shavings on the final passes made a world of difference for me. Whether or not I think it needs it I touch up the edge before making the last few cuts.

[William McAloney]

Brethren,
I tried some of the suggested techniques today on a couple of curly maple bowls. On the first one I tried moistening the wood, then let it dry before sanding. Some of the tear out remained, but yielded to hand-sanding in the opposite direction with the lathe off. After removing all traces of tear out and switching to the next higher grit, the tear out returned. This happened with 120#, 150#, and 180#. Finally at 220# the tear out sanded out and stayed out. Finished up at 320# and the bowl looks acceptable.
I would like to learn shearing techniques as you suggested, Alex. I have watched a number of videos and read descriptions of the technique, but I need to see it done live, in person.
I plan to attend the next local club meeting, if it doesn't get snowed out again.
Thanks again for the input.
Bill

[Chris A Lawrence]

Once you learn to shear scrap life will get much easier. When i take lite cuts shear scraping i get nice thin shavings that float in the air. They are probably so thin they only have one side.

[Alex Zeller]

......I plan to attend the next local club meeting, if it doesn't get snowed out again.
Thanks again for the input.
Bill

It may seam like forever waiting until you can get to the next meeting but I think it'll be worth it. I was only able to attend one meeting and even then when I got there it was already half over. I only had my lathe for a week so it was all new so mostly watched and really didn't talk much about actual turning with members. They meet on the 1st and 3rd Wednesdays and it either works out great or terrible for my work schedule. In the winter they meet further away from me at a school (which I don't think it has a lathe). Hopefully this summer I'll be able to get to more. So I've done exactly the same as you. Watched videos, lots of reading, and asked questions here.

[Brice Rogers]

I believe that what works for one person may not work for another person. So, I'll share some of my own thoughts, knowing that others may not have had the same success.

If I have tear out problems, I often switch to a negative rake scraper. That is, a NRS that was sharpened about 15 seconds ago. The burr only lasts a short time and needs to be renewed. If I am getting whispie shavings that float on the air, then it is working fine. If I'm getting sawdust, it is time to resharpen. Also, I also use the water technique to raise the grain (and use the NRS). That often helps at least a bit. If that doesn't work I sometimes apply a sanding sealer (and NRS). If that doesn't work, and even when it does (at least a little) then I resort to "wet" sanding with an oil like walnut oil. BLO and real Tung oil would also work. I think that some of the wood flour fills some of the pores. Also, when I've applied oil, it sometimes makes the NRS more effective. I shouldn't admit it, but I've even just squirted some WD40 on the tear out and seen some improvement. I've seen some demos (from turners who are miles ahead of me) applying an oil and then re-turning.

If the original poster tries any of these things, I'd appreciate feedback.

[Stan Calow]

Isn't 80-100 grit pretty rough to start with?

[John K Jordan]

Isn't 80-100 grit pretty rough to start with?

That's what I was thinking. If I use the negative rake scrapers I usually start with 220 grit. If followed by hand scraping (my usual method) I might start with 320 or 400. Much of my sanding is by hand.

The wood itself can make a huge difference as does the tool sharpness and experience level. Some species of wood are prone to such problems and perhaps not worth the time to turn.

The tool sharpness and experience with cuts can make all the difference. What seems like a sharp tool to one person may be hopelessly dull to someone with more experience. There should never be tearout. If I see tearout I sharpen the tool, swtich to a different tool, make lighter cuts, treat the wood with sanding sealer or somesuch, or unless the wood is spectacular or has some sentimental value just throw it away if it's punky or something and start over with some better wood. As the other JJ is credited with saying, life is too short.

On bowls and platters I always use the NRS and always follow with hand scraping. I never power sand with rotating disks, coarse or not. When appropriate I'll use a small pneumatic random orbital sander with fine paper as the last step. I do often wet sand with danish oil.

To the OP, if relatively experienced, try to spend some time with an experienced turner/mentor/instructor, attend club meetings. It may be immediately obvious that some basic things could be done differently.

I didn't read the whole thread so sorry if this is repeating what's already written.

BTW, I use negative rake scrapers a lot but don't rely on the burr from the grinder. I find that a burr raised with a burnisher lasts far longer. I have scrapers ground different ways but these are what I use the most on bowls and platters. I grind them a differently at the tip than most turners.

scrapers_neg_rake.jpg

JKJ