Shrinkage/Machining?

Can you file or sand clay to get an exact size after the first firing? IOW, will it shrink more during the second firing?

Reply to
Noname
Loading thread data ...

yes you can sand bisque although it may take a lot of time if you need to take a sizeable ammount off( and there are a lot of dust particles as you can imagine) so wear a mask and goggles as bits tend to fly off and go straight for the eyes.as for more shrinkage this should not happen if the clay was bisqued to maturity.

Reply to
paula

That depends on how high a temperature you to fired it to initially. If there is to be a second firing and the succeeding temperature is the same or less than the first firing, there may be a small increase in shrinkage due to the increase in heatwork. If your first firing was low, to enable you to work on it, and you are going a lot higher second time around i.e. to stoneware, then the increase will be substantial. Total shrinkage with stoneware clays is generally in the region of 12 + percent, but this does depend a lot on the composition of the clay used; some shrink more than others. Porous Biscuit Fired ware is theoretically able to be sanded or filed.

Steve Bath UK

In article , Noname writes

Reply to
Steve Mills

I recently read a great idea on one of the poster's site (I will have to look it up on a different computer). Take a strip of clay that has been rolled/flattened out the size of a ruler. Take a ruler that has raised marks on it and push it into the clay. Fire it and then used the initial ruler to mark the original inch markings on the fired ruler or just use your original ruler to find the size you want. So if you want the opening to be

4" when finished use your fired ruler and find what measure on it reaches the 4" of the original ruler. If you are getting around 12% shrinkage, your fired ruler would show about 4.5+" on the unfired ruler at 4". I imagine you would want both a bisque fired and a glaze fired ruler. Though I can't say how much variance there is going to be in firings and shrinkage. This probably isn't much help for the moment but maybe something to use in the future.... DKat

Reply to
D Kat

Most people bisque to about 1000C and glaze fire considerably higher than that. Which means that you will get shrinkage in both firings. If you want to make things exactly the right size you need to make a slab, mark ruler marks on it and bisque and glaze fire it, find out the shrinkage rate of your clay in your kiln and then calculate the size you need to make to get the size you want.

Reply to
annemarie

Rats!

That seems to be the consensus.

I think I am trying to do something that can't be done. I want to make my product fit a pre-made base, to do that it needs to be PRECISELY the same size every time. I have adjusted for the preliminary shrinkage, and was hoping I could machine the relevant portion to the correct size before the final firing. But if it is likely to change size again, I will have to rethink the whole process. Even one tenth of an inch would be way over tolerance, and so far I am adjusting for over 1/4 inch..

Reply to
Noname

Clever idea, useful

NJ

v
Reply to
Nancy Albin

ceramics have been used in engineering applications for hundreads of years. when i worked in a pyrotechnic company - some 17 years - we only used ceramic "headers" - the part of the pyrotechnic that has the firing charge & bridge wire. you get a very strong material, electric insulation, hermetic sealing, with high temperature & shock resistance.

we held machined tolerances down to +/- .0002 inches.

the manufacture of these parts was slip cast, limited firing, machining, with a final firing near the same temp as the initial firing. in the pottery world these parts would be considered bisque fire temperatures.

see ya

steve

steve graber

Reply to
Slgraber

InspirePoint website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.