put a "finished" bowl through a drum sander?

[Dan Gaylin]

So I made a nice(ish) 10" wide bowl, 2" deep and steeply sloped so that it is about 2.75" at the bottom. For those of you who saw my earlier post where I was contemplating this project, I did not succeed in getting an even narrower (2" or less) base. But I learned a lot in the process and can try it again hopefully with better results now that I have a feel for it.

Unfortunately I did not get the bottom perfectly flat, and I have no way to remount it on the lathe. How risky would it be to put it through my drum sander? I could use my Festool RTS 125 hand sander, but I'm worried about slipping and hitting the side of the bowl with the sander. I could wrap the bowl except for the bottom but then it's hard to keep the wrapping out of the way of the sander, which is how I ended up with a slightly less than flat bottom in the first place.

So: drum sander yes or no? And if not, other thoughts?

Thanks!

-dan

[Walter Mooney]

I say NO WAY! Make a jam chuck, or a donut chuck and remount it to flatten the bottom. If you need a couple 12" pieces of mdf for remounting purposes, send me a PM and I'll send some to you. I thick putting it through a sander is a terrible idea! My $0.02

[Bernie Kopfer]

If you were to glue it down with double sided tape to a large piece of MDF or plywood you would have much Less chance of it tipping. Multiple light passes and it would be parallel to the top and flat

[John K Jordan]

Unfortunately I did not get the bottom perfectly flat, and I have no way to remount it on the lathe. How risky would it be to put it through my drum sander? I could use my Festool RTS 125 hand sander, but I'm worried about slipping and hitting the side of the bowl with the sander. I could wrap the bowl except for the bottom but then it's hard to keep the wrapping out of the way of the sander, which is how I ended up with a slightly less than flat bottom in the first place.
So: drum sander yes or no? And if not, other thoughts?


Other thoughts:

Do you have a vacuum chuck or can you make a jam chuck to hold it and turn the bottom again?

BTW, I never make the bottom flat since there is too much chance for a small amount of warping causing it to rock. Probably better to make the bottom slightly concave. If that rocks from movement, it's easy to flatten a narrow rim with sandpaper fastened to a flat surface.

Some examples. In each case the only thing that touches the table is the relatively narrow rim on the base.

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JKJ

[Alex Zeller]

You could make a sanding disc for your lathe. I made a 20" one for my Grizzly and find I use it all the time. I actually made 2, one for 120 grit and one for 180 grit. I use it with and without a table I made from an old Craftsman table saw. It works great for blanks that were rough turned while green and have dried.
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[Kyle Iwamoto]

Make a sanding board? Easy, 3/4" plywood that is FLAT, MDF or whatever you may want to call it works also. 4 square feet should do it. Get adhesive sandpaper, stick it on the board. One side 80 the other 180 or what ever suits.
I would NOT put it through a drum sander. Since you have one you can make any piece of plywood FLAT.

[Dave Mount]

Superglue a small waste block to the bottom of the bowl. Put a scrap in the chuck and turn a dome shape, then put a pad on it and hold the bowl in compression with the inside over the piece in the chuck (padded to protect the inside) and the tailstock live center in the waste block, then re-turn the bottom concave as John discusses. Turn away as much of the waste block as you're comfortable with and clean up with a chisel and sandpaper.

Or. . .put some adhesive sandpaper on a flat surface (e.g., wing of a table saw, or just a piece of flat ply or particle board) and rub the bottom on it until it is flat. Have to be very careful while doing this that you keep the piece in the desired orientation and don't dub the edge.

Best,

Dave

[Brian Brown]

which is how I ended up with a slightly less than flat bottom in the first place.


I have a slightly less than flat bottom too. I blame the doughnuts.:D

[Gustav Gabor]

I'd recommend making and using a quick router sled jig such as what I used below or something similar.
Perfectly flat, and easy to do once the bowl is clamped down.

https://live.staticflickr.com/4785/26021836657_f1146a5e37.jpg (https://flic.kr/p/FDsHsa)

This was used in milling an automotive supercharger cover, but the idea is the same.

[John Keeton]

Like JKJ, I never make a bottom flat and there is no way I would run a bowl through a drum sander. There are many ways to finish the bottom, including simply using a pad between the chuck jaws and the inside of the bowl and using the tail stock to press it against the chuck. Turn the bottom leaving a small nub and remove the nub with a chisel, sand the spot and call it done.

[Dan Gaylin]

These are all good, helpful suggestions. Thank you all for your replies. I admit I was being lazy in contemplating the drum sander. I do have a donut chuck but it is too small (will only work for an 8.5" or small diameter bowl). So I would need to make a bigger one and buy the hardware. Probably worth it The problem with the jam chuck for me on this one, is that the bottom is pretty small. I find that my live center gets in the way of proper tool technique in that I end up with the tool angled to the point that I get worried about a catch. The router sled is an interesting idea but seems no less risky (possibly more so) than the drum sander set for very tiny little passes. I know many of your recommend against it, but I may just test it on a old bowl that I don't really care about and see if it will work. I'll report back with how I resolve it. Thanks again

-dan

[John K Jordan]

... I find that my live center gets in the way of proper tool technique in that I end up with the tool angled to the point that I get worried about a catch. ...

One comment that may help with that. I use several live centers but one of my favorites is the Nova. It accommodates a short #2 Morse Taper to hold various points. I turn various things from wood that will fit into the MT socket. Often useful is a long piece turned with a short MT on one end and a flat on the other end. This puts the live center far enough away so it gives me much more working room. Since it's made out of wood instead of metal you can get very close or even cut into it with the lathe tools.

This picture shows one of the long pieces mounted with some other custom attachments in the foreground. In the back are some that come with the live center.

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I make a variety of attachments for specific tasks such as to fit into holes.

Another option is to make an attachment for the Oneway live center or the Oneway clones that come with some lathes. Drill a hole and thread it with a 3/4"x10tpi tap. Turn it to suit and fasten it to the live center.

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I don't have a photo of a longer attachment for this center but one is easily made. One hint - to shape any attachment from wood so it is perfectly concentric with the lathe, I first drill and tap the wood and mount it on the live center. Then I use the live center as a drive center by putting a piece of wire through the holes on the side to lock to keep it from spinning.

Here's the Nova on Amazon. https://www.amazon.com/NOVA-5015-Center-System-Stepped/dp/B0064JIZGC
The price is high right now but it's often about $20 cheaper. You can check price trends or set a price watch on camelcamelcamel.com

JKJ

[Zachary Hoyt]

They're not bowls, but I routinely run banjo rims through the drum sander to ensure the bottom is perfectly flat after turning on the lathe. These are segmented turnings, 3 or 4 layers of 18 blocks each, 8-16" in diameter and generally 2-3" deep, like a bowl with vertical sides and no bottom.

[John K Jordan]

They're not bowls, but I routinely run banjo rims through the drum sander to ensure the bottom is perfectly flat after turning on the lathe. These are segmented turnings, 3 or 4 layers of 18 blocks each, 8-16" in diameter and generally 2-3" deep, like a bowl with vertical sides and no bottom.

I put turning blanks through a Performax 22-44 often to flatten them, make both sides parallel, and to better see and evaluate the wood. These are usually 8/4 around 7-9" across. I use 80 or 60 grit sandpaper.

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The only problem is if not I'm not careful the blank can lift a little when leaving the sander causing what would be called snipe on a planer. I prevent this by holding down the emerging edge as it's about to exit contact with the drum.

I do think a finished bowl could be passed safely through the sander to flatten a base if the rim is held down to the belt by hand or if fastened to a board and the board held down, and with light passes. However, as I mentioned, I'm not a fan of having a flat bottom on a bowl.

[Richard Coers]

If the bottom is not flat after turning, the rim isn't either. So no way to start with anything flat. I have a 24" disc sander and flatten the base by hand. All bases are turned concave before drying and all I am sanding is the outside rim of the base to flatten it.

[Prashun Patel]

How close to flat are you? Can you post a picture?
Also, is the base a flat plane, or is there a recess?

I always turn the foot slightly concave to insure the only contact points are along the rim. If you do it this way, then HAND sanding the foot level becomes a breeze - assuming you are within shooting range off the lathe and only doing micro-adjustments.

Re-mounting a bowl without a center reference mark isn't always fun (for me!) and often leads to bigger probs than just tweaking it by hand.

Even better than hand sanding is using a rasp. Even better than that is using a block plane, router plane (for me).

[John K Jordan]

...
Re-mounting a bowl without a center reference mark isn't always fun (for me!) and often leads to bigger probs than just tweaking it by hand.
...

That's the truth!

Although my remounting got a lot easier when I carried a dial indicator from my little machine shop to the wood lathe:

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I usually adjust by measuring the rim but in this case I only needed to turn the transition where I glued together the 3-cornered top and base. I usually check in several places.

JKJ

[Dan Gaylin]

Thanks all for the additional responses, you guys are great. John, I aspire to have my bottom look like your bottom :-). And yes Brian I appreciated the humor. I usually make the bottom of my bowls slightly concave, although not a work of art like John's. Because of all the effort I went to to get this bottom narrow, and my problems with the live center, I ended up sanding the last bit of the tenon off by hand, again because I was worried about a catch. I should look into the various special live centers that John suggested. The bowl is pretty close to flat, it just rocks a tiny bit, so I could just leave it. Most people wouldn't notice it. It sucks to be a perfectionist with intermediate (at best) skills. It didn't occur to me to try to hand sand it concave. I just went for flat.

[Mike Nathal]

Free hand sanding using a 2 inch sanding mandrel in a drill press (or your lathe) also works well. I have a flat glass plate that I use to check that the piece doesn't rock. Also, even with a concave base, sometimes I find that a piece that I thought was complete, several months later it is rocking again. (This is with my hollow forms with 1~2 inch diameter bases.) In this case I place some 320 grit sandpaper on the glass plate, and hold the vase firmly on the paper and slowly rotate it.

[John K Jordan]

Good point.

Someone gave me a roll of 29" wide 220grit and later somewhere I stumbled on a 12" wide roll of 240 grit Klingspor gold sandpaper (probably in the discount bin in the Klingspor store)! These are excellent for dealing with the slight warping you mentioned, common to both rims and base due to change in environment (shop vs house, etc.) or piece not completely dry when finish turned.

[Dan Gaylin]

Mike — sanding mandrel in the drill press. I have actually done this before and it worked great. Totally forgot about it!! Thanks for the suggestion. I have float glass plates for plane blade sharpening so that’s a good idea too.

-dan

[John C Bush]

Use your left over belts from your drum sander. 3M #77 adhesive spray on plywood scrap, stick on the paper, clamp it to the bench and start smoothing. Works for the rim as well. I used one to finish sand a bunch of French pastry rollers on the lathe.