Gallery, Projects and General > Project Logs
Building a milling machine
chipenter:
one part cement to 5 parts aggrigate by volume , I would recoment 10mm aggrigate flint or granite for waterproof , and vibrated with say a hammer drill on the outside of the shuttering will make the wet cement almost flow and fill all the corners .
NormanV:
So, no sand?
chipenter:
sand yes comes with the ten mm aggrigate or ballest sometimes called grano for hard floors .
Pete W.:
Hi there, Norman,
If you have a branch of B&Q or Wickes near you, you should be able to find a 'How To' leaflet on concreting. Otherwise, try Google.
The type of aggregate available will vary a bit according to your location. For instance, up the Thames valley, it's usually pit ballast from gravel-pits on the flood-plain. In South Devon, where my parents lived after they retired, it used to be gritty stuff rejected by the Cornish china clay industry while here in East Hampshire, some builders' merchants supply aggregate dredged from the sea bed. It gets washed and graded (aka sieved) to separate different grain sizes. In other parts of the country it might be crushed stone or even ex-demolition crushed concrete. It all depends on the local geology. If you ask your local supplier I'm sure they will explain what is common in your area.
When I lived in Essex, I used to use 'as dug' ballast which is everything from ¾" down (except that it was washed to remove the clay) so that was coarse plus fine combined. Some recipes will call for the coarse and fine constituents separately - you combine them during the mixing.
You need enough fine aggregate (sand and fine gravel) to almost fill the spaces between the coarse aggregate, otherwise you'll need to add more cement. I agree with Jeff's advice about the aggregate to cement ratio but it isn't too critical, you don't need a laboratory balance to weigh the ingredients! (Well, actually, I expect you'll find most recipes measure by volume, not weight.) Actually, a builder's shovel is a recognised measure in some older tables of weights and measures. I'd suggest that for your quantities, a domestic coal shovel will do fine.
If you're mixing by hand, you turn it over three times dry and then three times wet, adding the water little by little. If you're using a mixer, you need to add at least some of the water first.
You shouldn't add too much water, else you'll get shrinkage. If you're going to vibrate as Jeff suggested, it should almost seem too dry as you put the mix into the mould (shuttering) and the vibration will mobilise it. (Have you seen that video of liquifaction of the soil beneath a building foundation during an earthquake?!?) If it doesn't mobilise, you can always tip it out and add a little more water, mix and re-pour. However, you mustn't let it dry out for at least three days. The chemical reaction of the concrete setting requires available water until the concrete has cured, so visit it regularly with the watering can or keep it covered with wet sacking and in the shade.
Once it's cured and really dried out, there might be some slight shrinkage but you could maybe introduce some polyester or epoxy resin into the cracks between the concrete and the metal.
NormanV:
I have now fitted the knee (I think that is the right name for it) and am pleasantly surprised how freely it slides up and down the column and lock without any shake. There is a block of wood under it to keep it in position, the next job is the screw that will raise and lower it. I am planning to use a 28mm acme threaded rod that is sold as a screw for a woodwork bench vice. After considering various geared methods of operating it I have settled on a ratchet mechanism to do it. It may be slow but it is within the cost restraints.
Thank you for the advice on concrete, I may do that soon but must be careful not to do it before I am finally certain that I won't need to dismantle anything.
Here's the screw and a pic of the machine as it now stands.
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