DIY surface grinder

[Colin Barron]

On Colin Barron Said:

Have a look on face book, a manual feed Eagle for £500 with a magnetic chuck or a Jones and shipman 540 for £1500 which is much better but heavier.  Spend the time you would have spent on rebuilding a machine that will be rigid and give a decent level of precision.

Unfortunately I live in the opposite end of the continent. Anything heavier than books or small tools is too expensive to ship.

Today I opened the alchemy lab. I made a concrete recipe with ratio 1:1:1.5 (cement, sand, gravel). The result should be a high strength concrete (C40). Also I added 2% plasticizer.

In the second sample I add also polypropylene fiber (SikaFiber PPM12). The recommended usage is 0.6kg for one cubic meter of concrete. When I scaled the quantity for my small batch I got to many 0 after decimal point. So I add 10g of fiber. This proved to be way to much. The mix was no longer homogenous.

 

Also I refined the test method to evaluate different concrete recipes. I used a large piezo transducer as a vibration sensor. It’s high impedance is a good match for the oscilloscope input.

I made some tests with a piece of concrete I found in the garden. I discover that if I hit the block the results are not very consistent. Instead, if I suspend a weight and then I drop it the repeatability is perfect. Bellow are two consecutive tests:

And this is the whole process:

The only problem is that the results are very sensitive to location of the piezo sensor. I’ll do more tests when the two samples are cured.

 

[Sonic Escape]

On Sonic Escape Said:

On Colin Barron Said:

Have a look on face book, a manual feed Eagle for £500 with a magnetic chuck or a Jones and shipman 540 for £1500 which is much better but heavier.  Spend the time you would have spent on rebuilding a machine that will be rigid and give a decent level of precision.

Unfortunately I live in the opposite end of the continent. Anything heavier than books or small tools is too expensive to ship.

Today I opened the alchemy lab. I made a concrete recipe with ratio 1:1:1.5 (cement, sand, gravel). The result should be a high strength concrete (C40). Also I added 2% plasticizer.

In the second sample I add also polypropylene fiber (SikaFiber PPM12). The recommended usage is 0.6kg for one cubic meter of concrete. When I scaled the quantity for my small batch I got to many 0 after decimal point. So I add 10g of fiber. This proved to be way to much. The mix was no longer homogenous.

 

Also I refined the test method to evaluate different concrete recipes. I used a large piezo transducer as a vibration sensor. It’s high impedance is a good match for the oscilloscope input.

I made some tests with a piece of concrete I found in the garden. I discover that if I hit the block the results are not very consistent. Instead, if I suspend a weight and then I drop it the repeatability is perfect. Bellow are two consecutive tests:

And this is the whole process:

The only problem is that the results are very sensitive to location of the piezo sensor. I’ll do more tests when the two samples are cured.

 

A lightweight grinding machine which can produce quality work has yet to be built.

[Sonic EscapeParticipant @sonicescape38234]

I give up trying different concrete recipes. The best mix is 1:1:1.5 + plasticizer. This result is a very hard concrete that has also low viscosity. The other combinations either developed cracks of were too soft.

Now I’m thinking about a way to build relatively complex formworks without too much effort. Last year I had one cubic meter of blue clay from my well but unfortunately I throwed it away. It would have been very useful for making molds.

I think I solved the spindle problem. I was considering the option to build one from scratch. But the idea of doing an internal taper does not appeal to me unless there is no alternative. Next I wanted to use a semi-universal dividing head. But I’m not sure if it will not complain if I’ll spin it so fast. In the end I remember that I have a spare milling head. It is compatible with my two mills.

It is MT5 and has a runout of 8μm. Not that it would matter in this application. All I have to do is to find an MT5 blank arbor with soft end to hold the wheel.

I’ll remove the 90 degree gear inside the milling head and I’ll add a pulley directly on the main arbor. This thing is overkill for this application. It has around 60kg. I think the whole grinder will weight a few hundred kg in the end…

 

[Sonic EscapeParticipant @sonicescape38234]

I made a basic 3D model of the SG just to have an idea about the dimensions. I assumed the magnetic chuck is 400x150x50mm. The spindle is the one from the previous post and the grinding wheel is 30cm in diameter. The yellow piece represent the chuck + a 100mm thick concrete slab that will move along the X axis. Blue is moving along the Y axis over the red base. The stack looks tall but it includes also the space required by the linear guides.

The problem is how to connect the spindle. If I want to have some 40cm maximum clearance between the grinding wheel and the magnet chuck then I’ll need a large vertical support block connected to the red base. This one alone would weight >200kg. Not a problem for my workshop crane but still … something doesn’t look right

[Colin BarronParticipant @colinbarron94178]

Try putting Jones and Shipman 540 into google or facebook marketplace and this will show you tried and tested methods.

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