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Bowl Sanding (Read 1,643 times)
 
Mike Turner
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Bowl Sanding
Oct 27th, 2020 at 4:01am
 
I seem to always have trouble sanding bowls. I tried sanding with the lathe running but it wasnt good.So I have gone to sanding by hand going with grain or the way it appears I need to sand. (I am always hesitant to sand a bowl...ran into the same problem with having sanding marks showing) The wood I have a bunch turned is spalted maple (thats what I think it is..beautiful wood) from my yard that I cut down years ago. I go through a progression of grits but am not satisfied with my results.......sanding marks ,swirls etc. Any suggestions ?

This bowl has been removed from the lathe and bottom cleaned up so I can't remount it. I thought it was good until...like I have seen before when you put finish on it Boom there are the scratches.The grain on these bowls from this tree seems to be all over the place or to me its hard to figure out how to sand.

There are light sanding marks swirls etc.

I make flutes and never have any trouble sanding them but the grain is pretty much straight on them
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« Last Edit: Oct 27th, 2020 at 4:02am by Mike Turner »  
 
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Grant Wilkinson
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Re: Bowl Sanding
Reply #1 - Oct 27th, 2020 at 7:03am
 
Others with more experience will, no doubt, add to this. You've seen that sanding bowls is much more difficult than sanding spindles, because you are sanding side grain and end grain both. For me, the key is to be more patient than I am normally. I need to progress through all the grits and make sure that I remove the previous grit's scratches before moving on. Wiping with spirits before moving on can reveal scratches that I've missed. Good lighting is key. Finally, there is a saying about using sandpaper like someone else is paying for it. I struggle with that, since I'm the one paying, but it makes sense to discard sandpaper before it's dull and causing scratches rather than removing them.
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Grant Wilkinson
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Glenn Jacobs
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Re: Bowl Sanding
Reply #2 - Oct 27th, 2020 at 9:15am
 
First, I would recommend getting your sanding discs from Vince.  Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register
For me, when ready to sand, I put a coat of finish on the bowl let dry then sand. This shows the marks that need to be sanded out. I also do a lot of wet sanding. IE: reason for using Vince's blue discs. Another idea is to take the bowl into a different light. This will show more finish imperfections. I'm amazed at how this shows up imperfections.

Glenn J.
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Ed Weber
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Re: Bowl Sanding
Reply #3 - Oct 27th, 2020 at 9:26am
 
Grant Wilkinson wrote on Oct 27th, 2020 at 7:03am:
progress through all the grits and make sure that I remove the previous grit's scratches before moving on. Wiping with spirits before moving on can reveal scratches that I've missed. Good lighting is key. Finally, there is a saying about using sandpaper like someone else is paying for it. I struggle with that, since I'm the one paying, but it makes sense to discard sandpaper before it's dull and causing scratches rather than removing them.
Glenn Jacobs wrote on Oct 27th, 2020 at 9:15am:
Another idea is to take the bowl into a different light. This will show more finish imperfections.


I recommend all of the above.  Thumbs Up
You say you go through progressive grits but how exactly are you sanding?
Are you using a sander, backing pad, by hand, etc.
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Robert Evans
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Re: Bowl Sanding
Reply #4 - Oct 27th, 2020 at 9:58am
 
Spalted wood can be a challenge.  I've had some luck in sanding up to about 220 grit and then applying sanding sealer.  It will firm up and fill in some of the softer areas.  Then start sanding at 220 grit and move up from there. 

I also use Vince's blue sanding disks on a Harbor Freight angle drill.  It works pretty good.  Just let the sandpaper do the work.
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robo_hippy
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Re: Bowl Sanding
Reply #5 - Oct 27th, 2020 at 10:50am
 
Another vote for Vince's blue discs. They cut longer and faster than any other disc I have used. Maybe not best price, but best value for sure.

As for the mystery scratches, well, even I, after 20 years of turning and thousands of bowls, some times have to go back and sand some more... Good lighting and good glasses, if you need them, are essential. Some one on this forum said "Never take a finished piece from the shop into the house on a sunny day. Sunlight causes scratches." True, but mostly it is because our eyes evolved to see in natural sun light and most shop lighting is not in natural spectrums.

Sand with both your drill and lathe in low speed range. I keep my slow speed drill at half speed, and my lathe at 50 rpm max. Abrasives cut better at slow speeds because they have a chance to dig in and cut, where at high speeds you are spinning your wheels but not going/cutting very fast. I spend more time with grits up to 120 or so, than I do with grits over that. The coarser grits are for smoothing things out and removing light tear out. The higher grits are for removing scratches from the lower grits. If I start at 80, then I go to 100, and 120, and 150, and 180. According to most, I can skip some grits in there, but I think it saves time. If I see a scratch that needs to be sanded out, it is faster to sand out 80 grit scratches with 100 grit than it is with 120 grit, and yes, that includes time spent with the extra grit in the rotation. I try to use different parts of the pad so I can get contrasting sanding scratches/arcs. So, on the outside of the bowl, with one grit I sand with the upper part of the pad, and with the next grit I sand with the lower part of the pad. I wipe the surface down with my hand, and the sanding dust will work into the scratches of the lower grit and high light them. This works better with higher grits than with lower grits... In the inside of the bowl, I tend to sand with the sides of the pad so I get scratches like this ( on one edge, and like this ) with the other side. Generally I sand till I think I have all the scratches out, and then hit it one more time. I do use a firm/hard pad on grits up to 180 or 220. I use a medium pad on grits up to 400. If I go over that, then I use a soft pad.

robo hippy
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David Moeller
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Re: Bowl Sanding
Reply #6 - Oct 27th, 2020 at 12:18pm
 
But Mom, I'm done. I turned a bowl, I'm done! Why I gotta sand it? Mom! It's done Mom. MOM!!!
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Al Wasser
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Re: Bowl Sanding
Reply #7 - Oct 27th, 2020 at 1:07pm
 
Woodturning is a three step process .....  turn, sand, then finish.  Mess up on any of the steps and you have a less than desirable product.
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Mike Turner
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Re: Bowl Sanding
Reply #8 - Oct 27th, 2020 at 6:33pm
 
Thanks everybody for all the help.I have some of Vinces  disks.They are good.Im sure it is just me.
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Don Stephan
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Re: Bowl Sanding
Reply #9 - Oct 27th, 2020 at 6:57pm
 
When sanding with grits like 80, 100, 120 I am sometimes working a small radius transition zone where it is hard to get to the wood and I am more likely to press harder on the wood.  Which I think is going to leave more prominent deep swirl scratches.
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Mike Turner
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Re: Bowl Sanding
Reply #10 - Oct 28th, 2020 at 3:22am
 
Don Stephan wrote on Oct 27th, 2020 at 6:57pm:
When sanding with grits like 80, 100, 120 I am sometimes working a small radius transition zone where it is hard to get to the wood and I am more likely to press harder on the wood. Which I think is going to leave more prominent deep swirl scratches.

I probably am doing the same thing..
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Re: Bowl Sanding
Reply #11 - Oct 28th, 2020 at 7:48am
 
On the outside of bowls I have recently been noticing at about 150 or 220 grit some small circular scratches on the convex surfaces, which I would have expected to be removed with 120 grit.  Probably sanding these areas with just the small center area of the firm pad and so not getting a full eight passes over each spot.  Fortunately these scratches are easy to see in a strong raking light.
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Re: Bowl Sanding
Reply #12 - Jan 16th, 2021 at 7:02pm
 
Make sure the lathe is on very slow speed when sanding. I had problems because I was sanding around 1500 rpms. I turned the lathe down to 250 for sanding and it made a world of difference.
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Glenn Jacobs
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Re: Bowl Sanding
Reply #13 - Jan 17th, 2021 at 12:14pm
 
On spalted or soft woods, I apply a finish before sanding just to firm up the fibers. Let finish set before sanding.

Glenn J.
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Re: Bowl Sanding
Reply #14 - Jan 17th, 2021 at 1:45pm
 
Strange, but true, you can get 80 grit scratches from the edges of your discs. This is worse if you have pads that are the exact same size as your discs. With this, you can get scratches both from the edge of the disc, and the edge of the hook part of your pad. At least, that is the best excuse I have come up with for some times finding these scratches after I have sanded to the point where I know I have removed all the lower grit scratches. I find these most often in the transition area of the bowl.

robo hippy
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