DIY Surface grinder

A fast ticket to ridicule, according to some bod trying to do it on YouTube, but what care I? :joker:

I had this notion that 30mm round rail bolted to RSJ's might just be rigid enough. I looked at what was available and went for 230x75 parallel flange channel at 25 kg/meter. The rails are all 50cm long.
Attachment 24719

I machined aluminium blocks to connect rail to RSJ. These fit inside the channel. There's a thin slice of channel draped over one of my blocks in the picture.

The idea is that misalignment is irrelevant, it is twist and flex that must be overcome. Do we agree?

I guess the YouTube channel you are referring to is ‘physics anonymous’ ? They are trying to build a homemade grinder but there has not been an update for a while.

I’ve been thinking about your question of whether alignment is relevant and it feels wrong but maybe you are right and it does not matter.

On the stiffness then as you say that will matter as the work piece will be pushed away rather than being ground and the effect will be different depending on where the table is on the rails as they are stiffer at the ends of travel. So the workpiece would not be flat but would be dished in the middle. Any reason you did not go for supported rail or linear profile rail?

Good question. I reasoned that profile rails and supported rails conform to whatever you bolt them to, but round rails have their own built in straightness. By bolting the X and Y blocks either side of the same plate, I think I have defined a flat XY plane and I can grind the table square to that.

The tricky bit is cutting the inside of the RSJ channel flat and square where the rails connect. There is no sensible reference surface anywhere, tolerance seems to be about 1.5mm. I am hoping for consistency.

I got a wonderful gadget from RDG Tools, a sort of spring loaded centre. This held the m30 reamer amazingly square and true when finishing the end supports. I can slide all 6 onto the same pair of rails and they happily slide about and butt up against each other. I was not expecting that, good tool.

Tried adding some RSJ's, not cut to length yet.
Attachment 24737
I tried cleaning them with a knotted wire brush on my angle grinder and they laughed at me.
Attachment 24736
I might need to take them over to Newhaven and get them shot blasted, getting fed up with washing my hands every 5 minutes.

Before you spend any more time and money i would look at Dronsfield Eagle manual surface grinders (i paid £250 for mine) or Herbert made some small machines. If you have more space a Jones and Shipman 540 is best value. It may take a while for to find one on Ebay that suits your purpose. Even the small machines are 300Kg plus.

What size and orientation of wheel is planned?

I was thinking to use those Norton, white wheels, 6 or 8 inches diameter in 2 widths.

Rotating around the Y axis as per industry standard Jones and Shipman 540. 2800rpm.

That wheel overhang detemines the useable Y travel. I can have up to 300mm, less the wheel width, but I don't think I am quite that brave. OTOH, the more it sticks out the greater the stiffening torque on those linear bearings.

My angle grinder has now burnt out trying to descale this stuff. Ordered a replacement and a bigger, slower one. More Watts, less frantic...

Attachment 24740

More delays. The 9" angle grinder arrived with a broken plug and has to go back.

However I fitted the gusset plates so my Z axis now stands erect.

Attachment 24767

Thanks to the wonders of CNC the holes laser cut in the 12mm plates line up perfectly with the holes I drilled and threaded in the RSJ.

Next comes the bit I have been putting off. Boring the spindle bearing housing using my little ML10. It's 19cm long. I can't chuck it so it looks like a face plate job.

Taking a bit longer than expected. I keep losing tools, screws, bearings and stuff then waiting for the postman to replenish me...

http://www.robinhewitt.net/sg6.jpg

Quote:

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Originally Posted by Robin Hewitt

Good question. I reasoned that profile rails and supported rails conform to whatever you bolt them to, but round rails have their own built in straightness.

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So your second surface grinder build will use profile rails?

Oh , yes, very good :untroubled:

Here are a few questions I am pondering...

One of the best features of CNC surface grinders is that once you diamond dress the stone you know the exact height of it above the chuck. Is that information worth preserving for the next session? I'm wondering if the ON/OFF switch should apply a precision brake to the Z screw before cutting the power.

Do I need to seal all the workings dust tight or will the wipers already fitted on the linear bearings and screws suffice?

Do I need to machine the inside of the RSJ flat, to square off the rails, or will the rolled stel consistency compensate for the rolled steel innaccuracy?

The coolant/grinding wheel/ground metal, produces a very fine grinding paste so if wipers did work it would not be for long.
This is the minimum spec machine in terms of safety and ability to grind. It may be cheaper to buy a complete machine that needs a rebuild and fit motors on the handwheels. I paid 250 for mine and magnetic chucks on there own will not cost much less.
https://www.google.com/search?q=dron...1ZWXccBbiMtKM:

Colin, I don't think you quite understand what is going on.
I don't actually need a surface grinder.
I want to play with a surface grinder.
Making it to my own design is merely the icing on the cake.
I do this for fun :very_drunk:

Motor fits on okay. No vibes when it hangs from the screw, gentle vibes when I prop it. Weird.

Now waiting for the 20mm rail which is the grinder shaft, the 30mmx2 nuts and left hand die for securing the stone, the stepper motors/drivers etc., and the time to fit it all together.

Attachment 24890

What clearance bearings are you using?

No idea. Do you think it matters? I will be running them in an oil bath.

Quote:

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Originally Posted by Robin Hewitt

No idea. Do you think it matters? I will be giving Quick Extender Pro a shot and running them in an oil bath.

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Are you expecting issues when you get to fitting it all together?

Assembly is easy.
I am expecting 'issues' when I grind my first, large, flat surfaces and then put them face to face with a smear of engineer's blue.
Question is, will I be able to correct it?
It is not easy to get your head around a lack of flatness and see through it to a probable cause and solution.
I will either succeed or become bored and do something else :grumpy:

£370 worth of Japanese stepper technology arrived on Tuesday and I am still fondling it. I get a stiffy from just reading the spec sheets :love-struck:

Not happy. Got the wrong steel for the wheel arbor, horrible to cut, tears (rhymes with hairs) and smears...
Attachment 24978
and some chinese bloke sold me the worlds crappiest nuts at over 4 quid each
Attachment 24979
If I put that on a thread it would rip it to pieces. They are going to cost him over 4 quid each in return postage if he makes me send them back.
:tranquillity:
Whatever.
I have bought M30x2 l/h taps and die and I am ordering EN1A freecutting leaded steel from GLR. A s/h M20 spiral flute reamer is on it's way and I am doing circuit boards to hook an STM32F407 cpu to the steppers :peaceful:

Looking Good!

Progress tortuously slow, new spindle nose in leaded steel, thread a bit raggety, will have to do.

Laying out circuit boards for the controller, just reached the DRC stage -yawn-

Attachment 25051