Mud Lathe

[Pete O]

There was a fair bit of machining to do on the throwing-head casting, I started by chucking it by the outer rim to machine the underside on the lathe, made the central spigot round and square (confusing?) and bored the blind centre bore to take the 25mm shaft. I made the outer rim thicker than the spoked section so that water coming over the sides would not run into the centre and down the axle. I left enough rim clear of the chuck jaws so I could turn a face to indicate off when I flipped it to face the top. I turned it over and chucked it by the centre spigot so I could turn the outer rim as well as facing the throwing surface. With the piece held by the spigot, it rang like a bell while I was facing the outer section, the resulting chatter is visible in the photo with the bevel gears in the post above. Yesterday I realised I could now grip it by the outer rim again, took another skim across the face and now got a nice surface. The centre of the casting is a bit porous.
   
The two capscrews are to act as locating pins for 'bats', apparently all the cool kids in pottery use these- a 'bat' is a disc of plastic or masonite that is placed on the throwing head, it has holes to engage these pins, the pot is made on the bat and the bat is lifted off the throwing head along with the pot, it can be put back on for later reworking. The things you learn. 10" pin spacing is apparently a standard size for bought bats.

The photo of the casting in my earlier post, with the casting in the sand, shows the part of the mold that collapsed where the excess needed to be machined out. I planned to mount the thing on my RT so I could follow the radius as well as the spokes. Went to the trouble of mounting the RT on the mill, put the disc on top and realised the disc is the same size as the RT and the RT slots don't go all the way to the rim, the centre hole is blind, in short I had no way of holding the thing down to the RT. I dismounted the RT and clamped the disc to the table and did an ugly job of gouging out the extra material, really this is just to avoid any gross imbalance.
   
Took me a while to figure out how I was going to cut a keyway in the blind bore of the throwing head, I welded a boring bar to a piece of tool steel long enough to allow the nose of the shaper ram to clear the rim while the tool went into the bore. Drilled a hole (random drill it chosen- about 3/8) at an angle to intersect the bore right at the end, to give the slotting tool somewhere to finish the stroke. Clamped the spigot in the shaper vice, with an improvised jack in the other end of the jaw. All this setup, along with grinding the 1/4' slotting tool all took about an hour and a half. The cut took less than 5 minutes. Gotta love the shaper.
   
   

[Pete O]

Made a hub for the concrete flywheel and welded some bar onto it for reinforcing and to increase weight near the perimeter
   
and cast the concrete, it was cast on a plywood disc laid on a nice level section of the floor and the shaft plumbed to the vertical to minimise runout.
   

When the concrete was firm, I removed the shaft so I could cut the keyways.
I used my not-quite-finished sharpening jig to sharpen a 1/4" x3" side and face cutter to put a keyway in the 25mm shaft, first time I've had a chance to make a cut with a cutter dressed on this jig, very happy with the result, the cutter was cutting on all teeth and made a nice job, although it was actually .235" wide at the cutting edge so I had to take an extra pass on each side of the cut.

   
   

I made a test assembly and gave it a run, I added the seat mount to the frame and attached the chain derailer / tensioner from the bicycle.
   

Had a couple of issues to sort out; there were a couple of tight spots in the bevel gears, I did some dressing with a file but couldn't get rid of the tight spots completely. I set the gears up so there is minimal clearance at the tightest teeth. The bevel gears are quite noisy under power, I think this is inherent in the parallel-tooth bevel, just have to live with it.
The drive works well and the ratio of the bicycle sprockets I used seems spot-on, I pedaled it up to speed and used my analogue RPM gauge on the throwing head which showed 250 rpm, exactly what I had aimed for after my pottery research. The flywheel stores a lot of kinetic energy and keeps the wheel spinning for a long time once pedaled up to speed.
There was a distinct wobble from imbalance in the flywheel. I decided to approach it like a big surface grinder wheel.
   
There was a definite heavy point that the wheel kept settling to, I tried removing weight by drilling holes near the perimeter but that was a very inefficient way to remove mass so instead I added weight to the opposite point by glueing some 6mm steel offcuts to the underside, there's about an inch of clearance to the frame under the flywheel. Didn't take too much to get it to the point where there was no consistent point that it wanted to settle at.
   

I disassembled and gave the frame a coat of paint- Ford tractor blue.
   

All assembled ready for handover. Six adjustable feet so the throwing head can be leveled. The yellow masking tape is there to protect the enamel which is still soft. Seat height and pedal height are adjustable, once it is all adjusted to fit the owner, I'll cut the chain to length and get rid of the tensioner.
   
   

I presented it to my daughter last night, only 4 days late for her birthday. It's going to have to be dismantled again to transport it to her place, getting that 90kg flywheel into her garage and assembled again might be interesting. Anyway, a fun project, a lot of hours in it, I was worried it might turn out to be a white elephant but the end result is very functional and she was ecstatic.

[TomG]

Looks really nice, Pete.
I've seen them with foot powered wheels, but never with pedals. The tractor seat really makes it.

Tom

[Pete O]

Thanks Tom, I really appreciate that. The video that I linked at the start of this thread is the only example of a pedal-powered wheel that I have seen, I really admire the guy for the original idea although I think I've improved a little on his prototype.
I've been keeping the tractor seat for something special, given that there are childhood memories attached to it for all my kids. I was glad that it worked on the pottery wheel.

[Pete O]

The potters wheel got it's first use yesterday; I was planning on disassembling it and moving it into my daughter's garage but she has just been offered a new job that will necessitate a move so it will have to stay in my shed until she is in her new location. She got hold of some clay and a few tools and came around and spent a couple of hours, there seems to be quite a bit of skill in this pottery business and she is a rank beginner but she couldn't get the smile off her face. It was nice to see the thing actually works, I was worried I may have been building a white elephant but it seems to be a winner.
   
   
I took a bit of video but I don't know how to attach that here.

[Roadracer_Al]

Do pottery wheels spin the other direction below the equator? :)

Good job!

[Pete O]

(04-21-2018, 02:15 PM)Roadracer_Al Wrote: Do pottery wheels spin the other direction below the equator?  :)

Good job!

Thanks Al;
Coriolis effect notwithstanding, as far as pottery wheels go, the world is divided through the longitudinal plane rather than the lateral one. The eastern way is to rotate the wheel clockwise, whilst we westerners rotate them anticlockwise (which is the English or Australian equivalent of 'counterclockwise').