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RonSa

Bottom Depth Tool

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Here's a tool that I've made years ago for turning wooden bowls to help me find how thick the bottoms are.  I slightly modified it to work with clay pots. I know I can tap the bottom and hear if I'm getting close to the thickness this is just another method that I like to use to prevent me from making funnels.

This tool is made from a 9" x 1" x 3/8" piece of scrap walnut I had. Any size would work as long as its long enough to touch both sides of a bowl. I drilled 5 snug holes for the two chop sticks.

DSC_1294.jpg.76124c61a8a59fd35c176fa33c9ace33.jpg

 

 

Just lay it across the top  rim and adjust the rim and push the stick until it touched the bottom

DSC_1295.jpg.baffa6e33962950b52a143e51a7915a8.jpg

 

I reverse the pot  so the rim is on the wheel and I lay the stick on the bottom and measure the distance form the stick to the wheel. I find the space is 10mm

DSC_1302.jpg.aba3c9bb287fdb0e15e0b2749ad12f2f.jpg

 

Since I like my bottoms around 4mm thick I measure off 6mm on the other stick.

DSC_1304.jpg.c6ab716d6393f5b26023ba4af211d65a.jpg

 

When the short end of the stick touches the bottom and the walnut board rests flat on the foot I know I've reach the depth I need. The glass bead is a counter weight since I didn't have enough hands to hold both the camera and the depth tool.

DSC_1306.jpg.63c10b94a018020ce3ac7e3ded241f41.jpg

This thread is in response to Min's thread found here  http://community.ceramicartsdaily.org/topic/16839-handy-techniques/  thanks Min

 

Thanks for looking and comments welcome

Edited by RonSa
Min, synj00, Tyler Miller and 4 others like this

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I never heard of a tombo, I had to google it. Thanks for bring that tool to my attention. 

While looking at I can see how my newly christen Ronbo can be used while throwing to set a height and width of a pot

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After some practice thowing many  many forms you get a feel for this bottom thickness deal and a tool will not be necessary .

If you throw and trim say 50 bowls you will get this feel at the end. Nice tool but never needed it. At least with this tool you can eat some hot noodles in a bowl  as well .

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I agree with Mark on the getting the "feel for this bottom thickness" from practice.  Practice may not make perfect, but it does lead to consistency.  
 
As a beginner, and I found that a couple of wooden coffee stirrers from the famous coffee shop will work just like Ron's.  Lay one stirrer horizontally across the bowl, cup, etc. as in Ron's and drop the other stick vertically in the lowest point inside the pot, make a mark on the stick where it crosses the top of the horizontal stick.  Then do the same outside the pot so that the stick rests vertically on the bat surface (wheel if your work bat-less) and again make a mark on the stick.  The difference between the marks is the thickness of the bottom. 
 
I use coffee stirrers for lots of chores and nearly always have several either in my pocket, or handy in my tool kit. 
I tend to evaluate the bottom thickness against the width of the coffee stirrer and estimate how many stick widths I need to remove by trimming.  I then trim the inside area of the foot so that the amount removed is appropriate.  Then I trim the rest of the foot. 
My mentor always (except when he didn't) marked the position of the inside bottom on the outside of the pot with a line of some sort.  Then when the pot needed trimming this line was used to guide the trimming. 
 
Trimming is related to throwing by forming habits that get's the job done efficiently for the person doing the job.  It is easy for me to trim my pots because I generally know what expect in the bowl.  Trimming another potter's pot (as is often the case at bowl-a-thons) requires deliberate attention to certain steps at the right time to avoid ruining a pot.  This situation is where my coffee stirrers really pay off.

LT
Rae Reich likes this

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Thanks for you input Mark and LT. It is appreciated.

I get what you guys are saying. 99% of the time when I check the thickness of the bottom it comes out as 10mm and I can visualize 6mm (1/4") easy peasy. I typically turn wooden bowls so the bottoms are 1/4" and the walls to 1/8".

In order to engrave the design in this woodturned form the walls needed to be 1/16" thick and the base 1/8" thick. Unlike clay if you make a mistake with wood the only way to recycle it is to toss it in the fireplace (or fuel a roko kiln). But everyone needs a little help now and then.  You never know what you may learn by looking at different ways of doings thing. Heck, because of Min I even learned a new way to use this tool that I've used for better than a decade.

5a1606f03be15_maplehollowform-s2.jpg.866195acbbdeaef18382856e89f9ee75.jpg

 

Edited by RonSa
Rae Reich, glazenerd and oldlady like this

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Unlike wood, a leatherhard pot can easily be pierced with a needle tool to measure the thickness. The tool looks very useful for wood, but too complicated for pots. 

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Thanks for replying Mea and thanks for the tip.  I know there are dozens of good techniques that a potter can use to determine how thick the base is. I'm just suggesting that this may come in handy for others to try and in light of sharing tips on this forum I thought I'd share how I do this.

I can see that this tool wouldn't be useful for those that can throw 50 pots then take a break for lunch and come back to trim those 50 pots before leaving after putting in an 8 hour day. This technique might be more useful for beginners and intermediate potters and other mere mortals that may only throw a couple pots each session.

If one finds this complicated just take a look at photo 3 and imagine that the rule is not there and notice the space from the end of the stick to the wheel then guesstimate how far you can trim the base based on your observation.

 

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interesting.  why not push the outside stick in the 2nd picture, until it touches the wheel head.  The difference would tell you exactly how thick the untrimmed base of the pot is and what you have to work with, take out all but 1/4 " of the difference.  

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Hey Biglou

chopsticks do not come in a standard size you'll have to measure the ones you have.

1 hour ago, Biglou13 said:

and my home made danish oil mix

ThumbsUp.gif.9be5936782244ed1a1693bd1ef2002bd.gif

1/3 mineral spirits
1/3 Boiled linseed oil or tung oil
1/3 Poly or varnish.

Edited by RonSa
Biglou13 likes this

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15 minutes ago, RonSa said:

Hey Biglou

chopsticks do not come in a standard size you'll have to measure the ones you have.

ThumbsUp.gif.9be5936782244ed1a1693bd1ef2002bd.gif

1/3 mineral spirits
1/3 Boiled linseed oil or tung oil
1/3 Poly or varnish.

Hey don't give out the secret recipe..... Yes pretty much same recipe...  I up the spirt or other thinner to get a deeper penetration on earlier coats.  But finish with thirds.....    I really like the way. Walnut finishes with the  danish oil....  I also use it in all my wood pottery tools 

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