The bearings determine the roller dimensions to a degree. I already knew I was going to have them approx 50mm diameter by 250mm long, hence me knowing an approximate size for the bearings. But armed with the bearings I can now determine how the rollers must be turned to suit the bearings. Any good fitter & turner will be able to turn the rollers to suit and have them fit beautifully

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The shaft of the roller must sit inside the bearing snugly, but also the centre of the bearing is the part that turns and so you need clearance so that end of the roller does not rub against the whole fact of the bearing, just the centre. I chose a step of 1mm, ie. just enough to provide clearance. You can see the ‘step’ that provides the clearance in this picture;

Now you can see we have our shaft dimensions for 3 of the ends. The handle shaft is slightly different as it must be long enough to poke through the frame and provide enough clearance to crank the roller. Also, we need a way to attach a handle to it. I decided a thread on the end is very versatile, but more on the handle a bit later.

The only thing left now with the rollers is what diameter and their surface roughness. After talking with a few people I decided that a 2" or 50mm roller would be easy to turn and still give a good crush, and that knurling the surface with a light 20tpi would give enough grip without mangling the grain

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So now you have to have the rollers made. This I leave up to you, but you will need at least a sketch of your design and supply the bearings with the stock to the machinist for the best fit.The next step is to decide on how to mount the rollers. I wanted to be able to at least adjust them after they were mounted, plus also leave open the possibility of adding quick adjustment later. The bearing mount that I came up with was to use a piece of water pipe cut to the width of the bearing and welded to a piece of plate steel;

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Note the bearing just sits proud, otherwise the rollers would rub. You need a large clearance hole for the bearing centre, and the small hole is for the bolt to clamp it to the frame. I used a small grub screw which you can just see in that 3rd picture but some loctite bearing adhesive would also work fine. I painted them up with some leftover killrust sexy green (ok, it's really heritage green) enamel paint.

On to the frame. I had some old packing timber that I decided to try out my frame idea on before investing in some hardwood. My idea was to cut a channel into the ends of the frame for the mounting plates to sit securely into. I have a Triton workcentre which was ideal for the job. You'll want to do both ends as a single piece as it's easier and safer (I fear mightily the 9" circular hand remover, er saw).

I simply set the depth of the table saw to the depth of the mounting plates and cut down the centre. I then adjusted the fence out by a bit more than a saw blade width eg 4mm, and cut it again, reverse the stock and cut again, repeat until with of channel = width of plates. Clean up the channel with a chisel and check that plates are snug but can slide along channel reasonably well. Then cut the piece in half. BTW, the beer was opened after I finished for the day - remember it's hard to brew one handed, so don't mix beer and sharp stuff.

Next, put one frame end in a clamp with the channel facing up. Put 2 of the bearing mounts into the middle of the channel. Put the bearings onto the short shafts of the rollers and place them upright into the bearing holders. Move the rollers together to approximately the crush size you will be using, and remove rollers and mark the mounting holes. Drill these holes slightly larger than your bolt size, eg. for a 8mm bolt, drill 9mm, this gives you 2mm adjustment. Mark the hole for the handle shaft and drill this with about 2mm clearance.

Bolt the bearing mounts in place. Put the remaining 2 bearings on the rollers and put them back in bearing mounts, but this time with the handle shaft through the hole you drilled for it. Put the bearing mounts on top of the other 2 bearings and sit the other frame end on top of them. Turn the whole thing over, adjust roller gap and mark and drill the mounting holes for the remaining mounts.

Now all that is required is to measure up the sides of the frame and cut pieces to suit. I bolted the whole thing together using coach bolts,and it's quite strong. The wood I used is a bit soft really and I have to do the mounting/adjustment bolts up very tight and it crushes the frame a bit too much.

The only thing left is a handle. I used a piece of steel bar and welded a 16mm nut on the end. Drill a hole in the other end for the handle.

For the handle I drilled down the middle of a wooden file handle and used a long 10mm bolt. You can see in the picture below how the handle is assembled. A washer at either end of the wood allows for nice smooth movement.

The prototype fully assembled. I used it for a while like this with a simple cardboard hopper.

In making a wooden hopper I needed a way to keep the grains from falling out the ends of the rollers. The simplest method was a couple of pieces of felt cut to suit the roller curves. The felt is held in place purely by the hopper so that it can be taken out and dusted if needed.

The hopper is very simple. I used a 900 x 450 sheet of 12mm craftwood. I cut along the 900mm length, at a width of 225mm. Then cut that piece in half to get two 450mm x 225mm sections which form the 'V' of the hopper. The remaining wood is cut in half for the sides, and trimmed  to suit the V. Note the V needs to extend past the sides by the depth of the rollers from the top of the mill, about 40mm in my case, so that each half of the V sits just barely off the top of a roller.

The gap at the narrow end of the V is set by measuring the distance between the two roller axes. Thus the grain will be fed nicely into the centre of the rollers. This hopper holds about 9kg of grain. The nice thing about this design was that I can easily get my hand to the non-driven roller and give it a tweak, as sometimes it doesn't grip the grain at the start of the crush with a small roller gap. I probably should have had the rollers machined with a slightly coarser knurl in hindsight.

Here you can see the sort of crush I get. Currently the gap is approximately 1mm, and I'll probably reduce that to 0.9mm when I make the hardwood frame. It leaves the husks very much intact but crushes the centre up well enough. I don't have any trouble mashing even 60/40 wheat beers.

It really cranks thru the grain well, and my 6yo girl takes great delight in 'helping' me and she has no trouble turning the handle on her own. I get a tremendous amount of satisfaction out of using something I built myself everytime I brew.