Hobby project

[tonyfoale]

[QUOTE=albertq;255185]

Ok now I think understand, the grinding spindle will hang horizontally below the cross plate so as to clear grinding wheel.

The spindle will not be below the cross plate it will be about "wheel radius - 15 mm" ABOVE the bottom of the cross plate. On the face of the cross plate there will be a pair of horizontal linear rails, 28 mm thickness, onto which will fit the third (X axis when configured as a mill) granite slab of 22 mm thickness. So the outer face of this slab will be 28 + 22 =50 mm away from the outer face of the horizontal slab (Z axis when configured as a mill). The grinding head will mount on the third slab and the wheel and guard will overhang to one side. 50 mm + the radius "spindle to the base of the grinding head" gives ample clearance for the wheel and safety guard.

I'll make a sketch and post it. Unlike your excellent post I have no physical drawings or sketches, although I do have mental pictures of it all.

[albertq]

Imagination and mental pictures are all you really need Tony. I'll watch you create it with interest.

[tonyfoale]

Imagination and mental pictures are all you really need.

I have have no shortage of those, but here is a paper picture. My mental pictures have straighter lines.

Click for full size.

Since the video with rough sawn wood I have milled the individual wood sections square. Then I milled the assembly where it matters. The wooden mockup has been useful for checking out how I can fit the final metal version in the mill for alignment and machining. I did not size the thing based on what I could machine but the sizing came from the size of the magnetic chuck plus some overrun. With a large flycutter in the mill I can just cover it where necessary. A function of luck.
For now I will have a rest from the physical side and concentrate on designing and making the controller and writing the software. Then I'll be able to check powered movements.

Setup alignment.

Needs controller and software to test.

The bearing housing and motor mount are what I had and they fit. For the final metal version they will be combined into a single piece housing. That will ensure concentricity and there will be less setup needed.

[mwmkravchenko]

Looks like something that you could pour out of high strength concrete and have quite the rigid tool. The gantry uprights could have integrated compression rods if you were worried, or you could alternatively mix in a fibrous binder.

Been thinking along similar lines for a CNC mill and possibly lathe.

Mark

[carl blum]

Hi: Looks like a very good start! Here are my suggestions: Mount the ball slides as far apart as possible, would make the table more repeatable and stable. Look at adding flood coolant, it makes a huge difference by keeping the work cool and flushing the chips away. When I grind without coolant I often get burn marks.
The concrete bed and frame is a valid idea, some modern machines use epoxy/granite frames, I have epoxy/granite surface plate that was once certified.
Carl. (ps: I designed grinding machines at work)

[tonyfoale]

Looks like something that you could pour out of high strength concrete and have quite the rigid tool. The gantry uprights could have integrated compression rods if you were worried, or you could alternatively mix in a fibrous binder.

Mark

I did mention in the video that my original thoughts were to use epoxy/granite, for the frame, which I regard as superior to concrete. Neither epoxy granite nor concrete are very rigid. Just look at their Young's modulus. Both rely on steel for rigidity. For rigidity where do you get the best results from the steel? You get the best results when the steel is at the surface. Just consider their I, moments of inertia. Hence my choice of steel tube filled with epoxy granite. In addition it is so much easier to make.

[tonyfoale]

Hi: Looks like a very good start! Here are my suggestions: Mount the ball slides as far apart as possible, would make the table more repeatable and stable. Look at adding flood coolant, it makes a huge difference by keeping the work cool and flushing the chips away. When I grind without coolant I often get burn marks.

All valid points which are in the plan.

The concrete bed and frame is a valid idea, some modern machines use epoxy/granite frames, I have epoxy/granite surface plate that was once certified.
Carl. (ps: I designed grinding machines at work)

I have a thicker plate of solid granite which I am still considering as the base on top of epoxy granite filled steel tubes.
What is/was the benefit of an epoxy granite surface plate over the more usual solid granite plate?
(PS. I did not design grinding machines at work) So please outline using your experience, for the benefit of us all, just what features you have found to influence surface finish.

[michaelmacnz]

I did mention in the video that my original thoughts were to use epoxy/granite, for the frame, which I regard as superior to concrete. Neither epoxy granite nor concrete are very rigid. Just look at their Young's modulus. Both rely on steel for rigidity. For rigidity where do you get the best results from the steel? You get the best results when the steel is at the surface. Just consider their I, moments of inertia. Hence my choice of steel tube filled with epoxy granite. In addition it is so much easier to make.

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OH YES .... SOOOO... much easier.. AND for looks, Why not add stick on "Carbon Fiber" signwriters vinyl ? (HeHe Dad's joke)

[tonyfoale]

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OH YES .... SOOOO... much easier.. AND for looks, Why not add stick on "Carbon Fiber" signwriters vinyl ? (HeHe Dad's joke)

I did consider that but the coefficient of vinyl thermal expansion does not match that of the steel base.

[mwmkravchenko]

Just a bit of information that is well explained and practical. There are quite a few more useful videos in this channel. I've mixed and poured epic amounts of concrete. I learned a fair bit watching some of these videos.

Mark