Jump to content
Sign in to follow this  
hershey8

How Forgiving Is Placement Of Posts Under Shelves?

Recommended Posts

Everything I've read-there I go again, believing everything I read-says that when shelves are stacked, the supporting posts must be vertically aligned with each other. Sometimes it just ain't gonna happen, though. Has anyone ever lost a load of pots because of improper position of posts or imbalanced weight on a shelf? Ever had a shelf warp or crack because you didn't follow the book? Some say place posts two inches in from the edge of your shelf, which can certainly encroach on much needed space in some cases. I guess I'm trying to figure out how far I can push the envelope without messing up big time. Also interested to know if you always use a shelf on the floor of your electric kiln. One manual I've read says to put small ware right on the floor, under the first shelf. But I think I'd rather grind glaze off of a shelf than from the floor of my kiln. Also my kiln floor has developed some cracks, as I guess most do,and I really would prefer a more stable platform for my posts, ie., a full shelf. But, then you always put posts, even short ones, under the lowest shelf. Right? And why can't the lowest shelf just sit on the kiln floor without posts?  Have you ever bent the kiln loading rules?    Has it ever cost you?       john a.

                                                     

 

Share this post


Link to post
Share on other sites

Lots of questions. Maybe a few answers from me to start. Lots of times the whole shelf on the bottom is a bad idea if you have a heated bottom. Also remember that your elements start pretty close to the bottom so that space might get heated up more than you would want, warping a shelf-but I can't really attest to that. I do use two half shelves on the bottom at the same 1" posts all around-3 per shelf.I have found over the years that I really don't warp shelves if I am off on placement of stilts by a few inches. I have often done a rotating shelf set up where the shelves and shelf parts help me stack in a spiral. Is it suggested any where? NO, did I have any warping of shelves-no. Did I get all twenty plates/patens and all chalices in the load-yes. I pat myself on the back for those. I fire to cone 6, so I do not put as much stress as someone will at 10. I really don't know how correct I am in my loading of the kiln, but I load solid-no wiggling of post under shelf, entire structure solid from top to bottom with no movement on the shelf when I put a new pot down. I keep my shelves washed, on top, keep them stacked neatly, and have some that from age have cracked that I use as 1/4 shelves or smaller. Some get broken down to use as spacers for things like the spiral stack, or for a spacer for an extra 1/2" or so.

 

Not a pro, not really trained as none of my college classes early on covered kiln stacking. Later/grad courses assumed you knew, or did the stacking/firing for you. Only one course  touched on all of the particulars I felt I was missing, and that was a visiting prof-Ron Gallas. Great experience.

 

Hope this helps, and does not raise more questions.

Share this post


Link to post
Share on other sites

there is a simple way to keep the posts lined up.  i use full shelves and so only need 3 posts and i prefer the triangular ones.  forgot to say there are 3 half inch ones holding up a full shelf on the floor.

 

to keep them lined up i drew 3 triangles in marker on the top rim of the kiln walls at about thirds of the way around the kiln.  very seldom do i need to put posts outside these marks by more than an inch or two. i put them at the edge of the shelf so i can use every inch of space.  after a year or so i re-draw the marks because they do fade over time.

 

when i get toward the top, i sometimes use a half shelf for leftover small things or to allow a lower shelf to hold something tall on the opposite side of the kiln.  still put two of the posts close to the original spot and a centered one on the outside diameter of the half shelf.

Share this post


Link to post
Share on other sites

I have a story about posts not lined up back in collage.

Another person loaded the bisque (36 cubic foot alpine kiln) He choose to not align the posts much near the bottom and changed the pattern 1/2 way up. He lit the kiln and left. I was throwing late that night when we heard a huge strange noise from th kiln room-as we approached the room was a mix of fine dust and the feeling something was off. We turned off the kiln and let it cool after opening the door the whole load had collapsed with very little greenware left whole.Seems the top shelve was now near the bottom shelve and all the pots where back to smaller clay pieces once again.

 

Years later this same guy blew up his home built catanary arch kiln-the two end walls blew out and the arch went up then down into a pile.

 

Years I bought all his materials as he gave up working with clay.

 

Now you can fudge some for sure on line ups but do it near the top of the load.

As to shelve on bottom-mine is a full with 1/2 broken shelve pieces on floor under it-the floor is always cooler and a shelve up helps with more heat.I only bisque in this kiln occasionally . I do not have a vent or heated floor

With my 35 foot car kiln to cone 10 or cone 08 the posts all line up always. I take care of my shelves and get long life from them this way. Theres not much reason ever not to have posts line up. Maybe large sculpture and if thats the case fire it on top.

One last note we all learn from our mistakes you will not know your limits until you have exceded them.

Mark

Share this post


Link to post
Share on other sites

I keep a full shelf on the bottoms of my kilns, sitting directly on the kiln floor. My reasoning is the same, I'd rather have a glaze accident on a shelf than on the kiln bricks. As Pres said, you can't do this if you have elements in your floor. And if you have an undermounted vent (I don't) then you need to prop up the bottom shelf on 1 inch posts to allow air flow to the vent.

 

As for lining up the posts, I always line them up, except when I use a half shelf or two on the top of the stack. I've never felt it necessary to not line them up. But then again I am the type if potter who considers kiln shelf space availability when designing pots. ie, some pots are designed to fit exactly two between each post with no wasted space, and I make plenty of small items to fill empty spots.

Share this post


Link to post
Share on other sites

Always put a shelf at the bottom. It's cheaper to replace a shelf than a floor. I would also put the bottom shelf up on posts- even very short ones like pieces of broken kiln shelves- as this will help to insulate the bottom a little better, and get the bottom of the pots up closer to the first row of elements.

 

You can have unsupported posts, but only near the top where they're not carrying much weight. An inch or two on the way up won't matter though. and they don't need to be two inches in from the edge. I always put mine right at the edge and have never had a problem.

Share this post


Link to post
Share on other sites

If your kiln is vented through the bottom, you'll want to place your bottom shelf at least 1/2" off the floor; am guessing 1" might be better.  I use  I " supports beneath the bottom shelf because it allow for the vent to do its job and puts the shelf just a bit below the first row of elements.  As others have said, easier to scrape or replace a shelf than a kiln floor.

Share this post


Link to post
Share on other sites

I saw a whole load melt together because the post from the first shelf up were in the wrong place..not over the supports. That was in 1968. It was enough to remember and I never made that mistake..ever! his was done by some fellow students. Large gas kiln firing to ^10.

 

 

Marcia

Share this post


Link to post
Share on other sites
Guest JBaymore

When the posts line up over each other, a given shelf is only "carrying" the weight of the ware ON that shelf. If a post from shelves above is placed on a shelf and not aligned over the lower post, then that shelf is bearing a portion of the weight of everything above it. Worse, all of that weight is concentrated on a surface area that is the square area of the post itself where it contacts the shelf it is on.

Easy to get a failure of a shelf in a large gas, wood or electric kiln (BIG one)if you do this.

No magic to 1" or 1/2" or 3" in from the sides of the shelves as far as support goes. For small electric kilns...... this practice tends to get the posts a bit away from the elements...... which transfer heat energy mainly by radiant means. This improves the radiant heat transfer a small bit.

best,

.................john

Share this post


Link to post
Share on other sites

I've honestly never thought too much about loading the kiln.  I place the shelves and posts, so they are stable, with the least amount of wobble.

 

I use a full shelf, on the bottom, because it's solid, heavy, and doesn't need to be moved very often unless it gets dripped on, or I have to clean the kiln.  I have my bottom shelf on short posts, because that's how I was taught.  I never questioned it.  So I could gain another bit of space, since I don't have to do that.  I have no bottom elements, nor a vent.

Share this post


Link to post
Share on other sites

I did what my L&L kiln book said to do.  Put a full shelf on the bottom on 1/2 in posts.   My kiln isn't that large so I pretty much have to align my posts...it sort of just made sense to me to do that.   You had some good questions, John.  Made me think about things.

 

Roberta

Share this post


Link to post
Share on other sites

there is one tip you might find helpful.  when placing a shelf on the posts, put it down, try moving it gently with one finger, if you feel any movement, lift slightly at each post until it settles firmly and you can tell when the shelf is solid.  sometimes tiny spots of kiln wash get under a post and it feels unsteady. there is a knack to setting posts and shelves and practice is what makes it easier.  

 

if you are new to this, practice with an empty kiln just to become familiar with the process.  notice where you are going to put the next shelf and lower it carefully, at an angle so you clear the thermocouples above where it will go.

 

also, the marks on the top help a lot.  make sure you put them where the posts will not line up with thermocouples or peepholes. if using whole shelves and adding a half near the top, put the half shelf on the opposite side from the thermocouples.

Share this post


Link to post
Share on other sites

Great replies everyone!! Very helpful information from you all. Very thoughtful answers. Thanks for the help. I appreciate you.

 

                                                                                                                  john a. :rolleyes:

Share this post


Link to post
Share on other sites

 

to keep them lined up i drew 3 triangles in marker on the top rim of the kiln walls at about thirds of the way around the kiln.  very seldom do i need to put posts outside these marks by more than an inch or two. i put them at the edge of the shelf so i can use every inch of space.  after a year or so i re-draw the marks because they do fade over time.

 

 

I do this with a "permanent" marker pen but the marks burn off in every firing, (I expected them to) what are you using as a marker?

 

 If I used an oxide based stain, would that be bad for the kiln (bricks)?

Share this post


Link to post
Share on other sites

One final word on my spiral stacking. I use a 1/4 turn on each of the 1/2 shelves and as it works out, the stilts do sit very close if not over the stilts below. This stacking allows me to place more patens/plates on a layer than with traditional.

Share this post


Link to post
Share on other sites

i use a fat Sharpie.  do not know the UK brand name.  underglaze, perhaps??  it doesn't stick so your lid will not be stuck down.

Permanent marker is the exact same thing as a Sharpie, I'm amazed that yours doesn't just burn off.

 

Underglaze is a good idea though, I'll do that tomorrow.

Share this post


Link to post
Share on other sites

.....

Years later this same guy blew up his home built catanary arch kiln-the two end walls blew out and the arch went up then down into a pile.

.......

 

Mark

I'm assuming he blew up a gas kiln..... I'm planning on building a wood fired ( maybe ocassionall gas fired) cant'. I don't want to blow it up!!! What did he do wrong?

Share this post


Link to post
Share on other sites

just like when you build a tower out of anything, you want all the supports vertically inline.

 

i've seen a few times what happens when you don't line up your supports.  both in gas and electric kiln firings.  hopefully it's just a small crack that forms where the supports were offset and you replace the shelf.  can be as drastic as the shelf shearing instead of a crack, and the load falls onto whatever's below...and hopefully it's at the top of the kiln and gets stopped by the next level, not at the bottom where your support tower begins.  haven't seen that one happen and don't plan on it ever happening under my watch!  keep in mind that my studio makes large-scale, heavy ceramics; not lightweight functional wares.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.