Drying border tiles without them bending

[e.s.malte]

I've started making tiles and am successfully keeping them flat during drying by sandwiching them between pieces of plasterboard (drywall). All of my tiles are about 3/8" (10mm) thick.

However, when drying border pieces, say 1" x 4" x 3/8", although they stay flat (in the z-axis), they nearly always bend upwards or downwards (in the y-axis).

I'm using molochite-grogged clay appropriate for tiles and using a wall mounted extruder to make the borders. I'm drying the borders very slowly,  say for a couple of weeks, but they nearly always bend by the time they've dried.

Does anybody have any suggestions as to how I can stop this? I've tried using pieces of wood between the plasterboard to constrain the bending and butting many rows of the border tiles up against each other to try to keep them straight, without much success. I'm trying to make several feet of the borders at a time.

There must be an established way to do this, judging by the amount of straight border tiles I see almost every day! Perhaps a dedicated type of drying rack? I've searched in vain to find one.

Thanks in advance for your help.

[Mark C.]

Are they staying completely flat coming out out the extruder or are they slightly curved and yiou flaten them as you cut them.

Clay has memory

if you weight the drywall they cannot bend up or down

if they are going sideways  between the press its because they are curved coming out of extruder is my guess.Is your die hole center in extruder? off set? need more info on that part

how about rolling the border and and cutting them and seeing if they stay flat.

[Chilly]

Commercial tiles are pressed from dry powder, therefore no drying out, therefore no shrinkage.

When I made border tiles, I don't remember them changing shape, in fact, I think I had fewer problems that the actual tiles.

Can you use drier clay?

 

[e.s.malte]

Thanks for your replies Mark C and Chilly. 

I've attached a picture of two of my border extrusion dies. I haven't paid any attention to the alignment of the apertures when extruding, and I guess the extrusions are probably coming out with a slight curve if I haven't aligned the apertures with the axis of the extruder handle. I thought that if I straightened them on placing them on the plasterboard that they would stay straight.

I'll try ensuring that the extrusions are straight when they emerge from the extruder and see how they dry.

I will try cutting from a sheet as well, although as you can see, most of the extrusion are not simple rectangles in cross-section.

I'll also try varying the consistency of the clay (thanks Chilly)  to see whether that helps.

I'll report back to this thread in a few days - thanks for your suggestions. 

[neilestrick]

The warping is most likely due to particle orientation from the extrusion process. Lots of directional forces at work there as the clay goes through the die, especially with such small shapes, and even if they come out of the extruder straight. The process is fast, but not ideal for trying to keep things flat. Plus long narrow things seem to like to warp regardless of how they're made. I would try to do some additional compression of the forms before they dry too much and see if that helps- rub a soft rubber rib over them. If that doesn't help I would consider a different method of making them, such as a press mold.

[Pres]

I helped one of my adult students taking the Saturday classes with a tile project. She wanted to make particular border tile for her bathroom with a matching color and style that she had had before. We had a Bailey, so extrusion was the best bet. I cut the first die with the scroll saw set to 90. The tiles seemed to come out well, but did warp slightly, and she was not satisfied. I thought about it for a while, and thought maybe more compression. I cut a new die with about and 8 degree angle. Using this with stiffer clay, we found that we had fewer warped tiles and were able to finish the project to her satisfaction. You might try the angle on the die.

 

best,

Pres

[Min]

On 5/9/2021 at 7:12 AM, Pres said:

You might try the angle on the die.

 

+1 for this. Have a look at some of the commercially made dies, they are tapered downwards like the ones below. I'ld also toss the first few inches of the extrusion if it has a bend or curve to it.

 

[Mark C.]

The more compression the better-so the angle on the die is a must . If they are curved coming out they will later curve again (clay has memory)

If you extrude them center the hole in die.I think slab made will be easier than extruding to keep them flat .

 

[e.s.malte]

Thanks for the replies everyone. I knew that the ready-made North Star dies had an angle on them. Unfortunately my extruder is fairly basic and only really has room for a 3 or at most 4mm thick die (most of my dies, including those in the photo above, are 3mm aluminium). I'm in the market for a new one - either a Bailey or North Star I think - I will definitely make the new dies with an angle.

I extruded a few feet of clay through one of the apertures in the first die in the photo above this afternoon, ensuring that the axis of the aperture was at right angles to the extruder handle. It came out reasonably straight after the first couple of inches; I'll report back how it dries!

I also take the point that extruding may not be the best method for making these forms and I'll investigate other techniques as well.

Thanks again for the guidance everyone.

[Mark C.]

Bailey and Brent extruders are top of the line-Northstar no so much- also one made in Northwest called If I recall Big Blue? Laim has info on it.You want one that holds at least 10#s of clay

I use a breant and a highly modified Scott Creek -redisigned the handle and weilded a Brent cap on it. I favor the quikness of Brent caps

[neilestrick]

6 hours ago, Mark C. said:

Bailey and Brent extruders are top of the line-Northstar no so much

Huh? NorthStar work great! The barrel doesn't hold as much, but as far as performance goes there's nothing wrong with them. The thing I don't like about Bailey and Brent extruders is the sliding yoke. Lots of bonked heads and pinched fingers with those when we had them in school. The North Star has a fixed pivot point so it can't slide down and pinch or bonk. I think the Scott Creek extruders are the best because they have a larger barrel and the handle doesn't slide.

[e.s.malte]

I dried the tiles that I carefully extruded at right angles to the handle of my extruder so that they came out of the extruder straight.

They have remained pretty straight after drying . I'll try the other suggestions such as using drier clay but for now I'm quite happy - thanks for your help everyone

On 5/9/2021 at 6:29 PM, Mark C. said:

Northstar no so much- also one made in Northwest called If I recall Big Blue?

The Big Blue is made by North Star - it looks great but is quite expensive and takes an age to get in the UK (I've been quoted August / September for delivery).

Thanks again!

[Pres]

i have used the old screw on cap Brent extruder in the early days. The screw on cap was a DUD! One of the reasons I purchased a Bailey with a 5" barrel I think, and the larger barrel with the plywood die set. I had a band saw at the school, and a drill press, along with a scroll saw and belt sander. These allowed me to make dies for both, usually out of 1/4 to 3/8 plastic, or plywood.

@neilestrickI know what you mean about the clevis and handle. I was dangerous for someone that did not know what they were doing. That is why my demonstration for the extruder had the first 10 minutes stressing that it could bite you if you didn't handle if with respect. I pointed out the web of the hand getting pinched by someone holding the clevis, and the possibility of getting rapped by the handle overhead. I should mention however, that all of my demos of equipment included the "what coulds". Especially the slab roller, and potters wheel. In cases with the extruder and the slab roller I encouraged students to pair up with another student. I have never used a Scott Creek extruder, but have seen them in catalogues and such.

best,

Pres

[Mark C.]

My modified Scott Creek has a fixed pivot point and a Brent cap so its the best of both worlds. I had to weld the pins on the barrel for the cap change and make a new handle as well. Twist on cap that takes about 1 inch of twist to get on and off so its fast. I also have a straight unmodified Brent (we use a lot of extruded handles here every week). In a community studio situation I can see the sliding yoke be an issue just like in retail with the general public  where just about everything is an issue. But in a private studio we never pinch out fingers or get bonked  so that why I recommend them to private studios. The more clay (10#s a minimum ) it holds the less hassle in my view as charging  the extruder takes time. Brent now makes a new non yoke style extruder that takes out that yoke with sliding shackle design so folks can now buy that one now as well as community studios.They did the R&D on it so its solid.

I do not know if northstar has changed their design but the early ones held hardly any clay. In fact Northstar made slab rollers with pastic gears that stripped out as well. They fixed that I'm told but I have a pet peeve about doing the R&D for company's with poor designs . Yes they are cheaper and many choose that over other factors.

Northstar makes some very nice plastic Bats which are blue. You need to store them flat but thats not a problem . They hold up very well-recently they switched to a thicker bat as well.