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Uneven Bottoms! Help Me Out


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Hey, 

 

I am having trouble with the bottoms of my pots. They tend to come out uneven so the pot is wobbly. When it sits on a table it wobbles back and forth rather than firmly and evenly resting on it. 

I don't trim feet on most of my pots, I leave the bottoms flat. I have seen a few different methods for evening the bottoms out like sanding, grinding, trimming, etc. 

 

So my questions are: Throughout the entire pot making process how can I ensure that my bottoms will be evenly flat? and How should go about evening out the bottoms on the pots I already have fired and finished?

 

Thanks!

 

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Once the pot is fired, grinding the bottom even is your only option, unless you want to try and glue something on. I have used a belt sander with 60 grit carbide.

 

Did you check for flatness before the piece was fired ? Are you throwing or hand building?

 

I always wait till my pieces are leather hard and then rotate the bottom on a plaster bat, with a little even downward pressure. That evens out any early warping that might happen because of moisture difference between the walls and the base. This should do the trick, unless the warping is occurring during the firing cycle.

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When pots dry they have a tendency to cup upwards at the base. If you give the middle of the pot a very slight press in the middle (on the underside) when it’s soft leather hard it counteracts this. I compress the base, either on the wheel or by hand with a rib, press the edge with my thumb or gently roll the edge on the table top to create an undercut then use the heel of my hand to slightly indent the bottom, just in the middle. doesn’t show from the inside of the pot.

 

For wobbly pots already fired I think the best option would be to sand / grind them flat. A diamond lap disc attached to your wheel head with clay would work or a grinder with a silicone carbide wheel. If it’s just a little bit wobbly you could probably just use a coarse stilt stone or diamond sanding pad.

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Have a look at the containers for sale in the shops, and the containers in which yoghurt, dips and icecream are sold. Every single one has a foot ring of some kind. The bottom of a vessel MUST be concave. I have a plastic cup that has a foot ring of tiny half domes, which I consider to be ideal for dishwashers, because they don't collect grotty water.

Vitrified stoneware has a tendency to slump a little when there is a wide span of bottom unsupported between a foot ring. I give plates a double foot ring, one on the outside and another small one closer to the centre point.

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i just took out a load of mugs that every one of them rocks.. I haven't had a rocking pot in a while, not sure what I did wrong, but I was going to list them on etsy and now they are all getting el hammerzor. Going to have to figure out where I went wrong, because none of them rocked until after fired. I feel your pain.

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Uneven bottoms can be really annoying. It appears that many of the steps I

do to insure the bottoms of my pottery is flat have been mentioned.. These are the steps my OCD requires me to do for just the foot and bottoms.

 

When the vessel is almost finished on the wheel, I sponge off the bat, then

take a needle tool and score around the base. This gives the wire tool a place

start, so the wire tool won't ride up the back side of the foot, cutting off a chunk of the base/foot. A clean bat will leave evidence that a wire tool was used.

 

I seldom if ever wire off a vessel twice. When the vessel is leather hard, I'll

bend the bat, and lift off the vessel. At this point, I'll palm in the bottom, making it concave. Making a concave bottom insures that the vessel won't become a lazy Susan and spin. A concave bottom also gives the option to trim a foot or not.

 

If by chance, the bottom is not palmed, and is not concave, it is soaked back down,

to be made into something else later regardless how well the vessel turned out.

 

To trim a concave bottom, take the triangle end of the trimming tool and trim down to the depth of the lowest point of the foot and trim towards the center until the bottom is flat. Shouldn't take more than 9 or 10 seconds. Don't follow the curve of the concaved bottom, that defeats the purpose.

 

If I think there is a chance the vessel will warp if moved, I move the bat with the

vessel on it.

 

When the vessels are bone dry, and either before or after they are smoothed over with a scotch brite pad, I place a known flat bat on the wheel, dribble water on it

and while the wheel is spinning, place the bottom flat down. The water will soften

the clay and it will conform to the flatness of the bat. If you allow the vessel to sit on the bat too long without spinning, it will stick and become ruined.

Start in the middle then slide the vessel off the bat. Sometimes a 7 inch square bat will do, sometimes a 13 inch round bat will have to be used. A bone dry

works better for me, because of the difference in color between the dry clay body

and the wet clay. A leather hard vessel is more tricky, and requires more skill and finess.

 

As for the pots with the bisqued uneven bottoms....if you sand them or try to

Dremel them smooth and even, it will be a dusty mess. The time spent trying to sand them could be spent making several other vessels.

 

Hope this helps,

Alabama.

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I made up a sanding bat that works great. The best is to sand before the bisque fire.

The bat is ½" MDF board with 60 grit sand paper. The sand paper  can be rinsed off and will work for a long time. I had some paper left from when I used to sand hardwood floors. You can usually buy a few sheets from a rental shop that rent the sanders. This is Very heavy duty stuff and comes in 8" or 10" width. I glue it on with some spray contact cement.

Think I will post this idea under the equipment section for others to see.

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One thing you can do if the piece is already dry is to grind the bottom in a circular motion on a cordierite kiln shelf until it's not tippy.

This can make the bottom a bit rough depending on your clay and if it has grog in it.

You can smooth a bit more with a 3M pad.

 

I have to keep real close attention to drying and warping due to my studio being outside.

 

I've tried cutting pieces of the bat, and the wheel, and using several different bats with frustration and loss.

Pot lifters are going to warp your piece automatically.

The blue plastic bats won't release the piece by the time the it's leather hard and ready to trim, and cutting them with a wire doesn't help when you cut through the bottom.

(Note,: I'm working with mostly large bowl shapes).

 

I'm finding that the answer for me, is the plaster Hydrobats from The Ceramic Shop.

They release the piece just at the right time for trimming, and leave the bottom completely flat. They also stick alot better when centering. Pricey, yes, but I wish I had the $$$ I spent on plastic and masonite bats and spent it on these.

They've really speeded up my (limited) throwing time and solved so many issues.

 

I'm leaning towards not trimming a traditional inner foot now. I can still trim a clean outer foot but the bottom remains flat.

A bit of  pressure towards the center during the trim will help concave the bottom ever so slightly.

After that I set the pot on a piece of stone marble top and compress the bottom to insure flatness.

Then onto the drying shelf upside down. Later I'll flip it and check the bottom again for flatness.

 

I know potters that say 'You trim? No trimming!', but I learned to trim as being part of the deal as a student.

I like it, it's part of the finishing process for me.

 

Hope that helps.

 

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I like trimming a lot too, I found when I trimmed I never had rocking feet, but I stopped trimming some of my mug forms because it just looked incorrect, now I think I will go back to trimming feet on everything again. If it requires that much effort to get a pot to stop rocking with a flat bottom, I can trim with an extra minute added to that time. 

 

Pottery.... so much to learn every single day.

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Rex, why don't you just make some batts with No.1 Pottery plaster? About $15 for a 50 lb bag, enough for plenty of batts. Cake or springform pans for the mould to cast them in, super inexpensive and they work.

 

Agreed, I gave that a (small) thought. It's a messy process and not something I want to tackle for a so-so outcome.

 

That said, since my studio time is weekends and whatever is left at the end of my day job, trying the Hydrobats was an easier option. As a student and with my first studio I used plaster bats. But all I recall is they were lumpy, heavy, and took up alot of space.

 

I like well engineered tools. These are well thought out, don't require attaching an centering on the wheel head with clay (they have built in pin-holes), and are relatively thin and light. For now, since time is at a premium for me, they're worth the money.

Just a good tool for me.

 

hydrobat-12-5-.jpg

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Rex, why don't you just make some batts with No.1 Pottery plaster? About $15 for a 50 lb bag, enough for plenty of batts. Cake or springform pans for the mould to cast them in, super inexpensive and they work.

 

Agreed, I gave that a (small) thought. It's a messy process and not something I want to tackle for a so-so outcome.

 

That said, since my studio time is weekends and whatever is left at the end of my day job, trying the Hydrobats was an easier option. As a student and with my first studio I used plaster bats. But all I recall is they were lumpy, heavy, and took up alot of space.

 

I like well engineered tools. These are well thought out, don't require attaching an centering on the wheel head with clay (they have built in pin-holes), and are relatively thin and light. For now, since time is at a premium for me, they're worth the money.

Just a good tool for me.

 

hydrobat-12-5-.jpg

 

 

Umm, i wouldn’t say that batts made from #1 pottery plaster are so-so or lumpy. 

 

I agree clay pancakes are messy to use to attach plaster to the wheel head, so I don’t use it. Xiem Bat Mate works, dip it in water and the plaster batts stick to it, no clay. It is more of a pain to recenter a batt on the wheel without pins but I rarely do that so not an issue for me.

 

#1 Pottery plaster batts could be heavier I don’t know. I weighed one of my14†plaster batts and it is 3lb10oz, have no clue how much that size  Hydrobat weighs.

 

Anyhow, I’m glad you are happy with your Hydrobats, I'm just throwing out another option for anyone who has the time or inclination to make their own. 

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post-747-0-54474400-1442948595_thumb.jpg

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