Have fun! ISO dropout dimensions are:-

Axle-front/top hole 78.11mm
Axle-rear/bottom hole 39.9mm
Caliper mount hole to hole 51mm

ha! you guys are funny! 🙂 the technical stuff doesn’t get the better of me as i leave that side of it to Tom!

Tom makes his own drop outs, primarily for aesthetic reasons, but also because he wants to make the entire frame as opposed to buying the parts from for example paragon machine works etc.

i don’t claim to be an expert on the design process and dimensions but in very basic terms, the drop outs work. there is enough movement in the slotted disc mount holes to accommodate the movement of the rear axle etc.

This should help explain (if the Demon works like this) – Bianchi with 30mm of wheel movement using 15mm of disc bolt movement.

I’d imagine you start drawing axle to horizontal slot. The angle / position of the other slot sorts itself out (intersection of 51mm and 78.11mm arcs).

I make my own because bought ones are never the shape I want. My CNC plasma cut option is rather less pretty than Tom’s CNC machined – but being cheap and lazy means £20 for 3 pairs suits me fine 🙂

I’d already found those dimension elsewhere, but wanted the angles.

Anyway, I’ve done the drawing, and I can now see how the sloping holes manage to accommodate a 25mm fore/aft movement of the axle, with just 13mm fore/aft movement of the lower disk mount slot.
I based the drawing on a rough measurement of the upper disk mount slot on the photo provided in the initial post (I made it about 42 degrees.)

Based on this, my drawings make the top slot about 12mm long, which is close enough, considering the inaccuracies of my drawing.

However, this is with the rear of the lower slot directly above the axle – which, obviously, isn’t the case in the Demon dropouts. If I try to move the lower slot backwards, to where it looks like it is on the Demon dropout, then the length of the upper slot shortens to 7mm.

The common factor though, regardless of the lower slot position, is that the center of the line between the bolts is at a different distance from the axle, depending on the position of the bolts in the slots. This could possibly cause minor issues if the pads were not fully in contact with the rotor – and have worn unevenly – leaving rough edges in contact with the rotor when the wheel is moved.

I may be overthinking this, and I’m willing to defer to the experience of the frame builder – I just had to get some level of understanding of the geometries involved.

Going to pour myself a large drink now.

</geek>

EDIT: Just saw your new post, and it confirms your assertion that the 25 mm to 13mm movement thing work, but also strengthens my suspicions that the orientation of the caliper changes too.

EXTRA EDIT:
In your picture, is the rear hole, in the circular adapter, one of the caliper mounting holes? If so, where is the other one?

Now my head hurts…. 🙂

The extra hole in my little jig thing isn’t anything to do with disc mounting. I can’t quite remember why it is there……. You can see the hole where the axle goes, and you can see the two bolts where the caliper bolts on.

With mine, I guess you could say the caliper orientation changes – but only relative to the frame / seatstay. But it DOES NOT change relative to the disc – they both just rotate about the axle. The pads still sweep the same portion of the disc and the disc still passes through the same bit of caliper.

You can spin the horseshoe thing round anywhere you want and bolt the caliper on – pointing out underneath the frame if you must – the caliper is still the same relative to the disc.

Sorry OP! Enjoy riding it. And smile at this whenever you adjust the back wheel 🙂

Ah, I can now see how the horseshoe keeps everything in line, relative to the rotor – but this may not be the case with the Demon dropout, depending on the presence/absence of an equivalent to your horseshoe.

Totally off topic but what are those tyres like?

the tyres are fast, 29×2. think they were the first in the country in that size, i’ve had them 18 months, they were sourced by Don Walker, the guy that runs the North American Handmade Bicycle Show, they only just came out around the time the bike was on display there before being finished and painted, i like them as they feel comfortable on the road and they are fast rolling, they are now available from Extra Uk as they are the new importer for Maxxis tyres, they previously apparently weren’t brought in.