Grinders

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Written by Kirk Mclean

Part of this material I used in the 20 hour granite course I taught at Pratt. Most of the info is from Tom Urban's workshop at Camp Brotherhod, some from a workshop by Don Ramey that Hank Nelson organized at my place years ago. If you find anything useful, please add it to the article - Kirk

Grinders: 

4-5 inch dry-cut diamond blades designed to run at about 10K RPM, which is speed of right angle grinders.  For sufficient power, look for high 6 amp range or greater.  Hitachi and DeWalt models hold up well. For variable speed, recommend Metabo or Makita.  Avoid Bosch or Milwaukee.  Larger blades (7-8 inches) run about 5K RPM, which is speed of 7-inch grinders or worm drive circular saws. Worm drive saws can be set up to run wet, keep blades cooler.

Grinder maintenance:  Blow out grinders 2x daily.  Blow outside, inside, and then blow out while running.

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Grinder Blades and Diamonds

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Written by Tracy Powell

Some thoughts on diamond blades

If you only get one.....

which one will do you the most good?

For the sake of clarity, let's just talk about what you could get that would be most useful with any small electric grinder, rated for 4 1/2" or 5" blades, single speed, for a mix of hard and soft stones.   

I will try to offer my reasons for choosing one of the many kinds of diamond blades available, based on what different chores it can do, how versatile it is, and how affordable it is.  These are my opinions only, and I welcome being corrected by other carvers with more experience and knowledge.  I hope this exercise is useful to you.

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Polishing

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Written by Kirk Mclean

Preparation:

Polishing a surface will show up every dip and bump, so if you’re seeking a long, flowing curve or a flat area, locate highs and lows with fingers, mark, and remove with coarse diamond cup wheel before beginning polishing steps.  Sequence begins with fine diamond cup wheel (or 36-60 grit silicon carbide).  Move cup wheel rapidly in small circles so that you don’t burn stone.  Next step is 80 grit silicon carbide cup; again moving it rapidly. 

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Another use of Grinding Wheels - Hand Shaping

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Written by nwssa crew

On 19-Dec-09, at 2:29 PM, verena schwippert wrote: ..yes Dirk, but only under the sanding of particular type of stone you are working on. What is it ?  Its different for every kind of stone.
...yup it is. -- V

Silicon Carbide Shapers  - Right on, V!  Actually, those small pieces of silicon carbide work well for hardnesses from soft marble to hard granite. With each of those materials, hard rubbing with a piece conforming well to the surface produces

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Cup Wheel Grinding

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Written by Kirk Mclean

Part of this material I used in the 20 hour granite course I taught at Pratt. Most of the info is from Tom Urban's workshop at Camp Brotherhod, some from a workshop by Don Ramey that Hank Nelson organized at my place years ago. If you find anything useful, please add it to the article - Kirk

Diamond cup wheels:  extra-coarse, coarse, medium and fine.  Usually use coarse for shaping, jump to fine for beginning polishing.  Extra-coarse available from Gran Quartz.  For basins, wheels with curved edges available or use continuous instead of turbo to avoid digging in.  Must use guard on grinder with diamond cup wheels.

Silicon Carbide cup wheels:  used for masonry (avoid aluminum oxide ones for metal).  Grits range from 16 on up.  16-24 grit used for shaping, 80-120 grit in polishing process.  Can bevel edge with dressing tool to shape for interior grinding (basins) or undulating surfaces.  Will wear to match radius of surface.  Use at lower speed  (2-3000 RM) because larger mass creates more torque.

Glazed Diamond Segments

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Written by NWSSA member

When using a diamond core drills, drilling stone,  I found out that often the rate of drilling would slow, even when applying more pressure. The problem would continue to get worse, especially when drilling dense stone such as basalt.

The sintered diamond tips had become glazed. 

Although oriented to "concrete" this link (which just well could be called "hard stone vrs soft stone sintered diamond blades") provides an article with images that show what's happening so you can tell what the problem is. 

How to "fix" the mismatch between stone hardness and sintered matrix can be found at this link (Image linked from the situp.com.au site)

The take away from 'glazed diamonds' is that "dressing a diamond tool" is something you may need to do, and that you may need a different "dressing stone" for each of your blades/cores/cupwheels. 

(Some manufactures claim their tools do not need dressing, because of propietary techniques, maybe the NWSSA veterans can shed light on this topic)

Air Hammers

Details

Written by Kirk Mclean

Part of this material I used in the 20 hour granite course I taught at Pratt. Most of the info is from Tom Urban's workshop at Camp Brotherhod, some from a workshop by Don Ramey that Hank Nelson organized at my place years ago. If you find anything useful, please add it to the article - Kirk

(Does someone have other/better photos? )

Pneumatic hammers

Sources: 

• Trowel & Holden
• Bicknell Supply
• Cuturi
• Japan

Types:

• D (Dallet) long stroke 3/4 “, 1 inch.  Used for removing lots of stone.  More impact, vibration.
• B short stroke 1/2, 3/4, 1 inch.  Less vibration, used for detail.
• Bantam-fine detail, lettering
• Many carvers use 3/4D, control impact by amount of air.

Air consumption:

• 4 CFM-1/2 & 3/4;
• 6 CFM-1”

• For 1" hammer a whip connection (see photo)is recommended so as not to beat up the coupler. It is likely that once you put a whip on one then you'll find yourself putting them on all.
• Control air flow to hammer with an adjustable valve (stop cock). Note valve handle is small enough so as to not get caught on everything yet big enough to easily turn it without fumbling.

Chisel diameter:

• B & D take 1/2” shank,
• Bantam smaller.  Many European chisels fit Bantam.

• 4 pt square or 5pt round:  stone removal 
• 9 pt: stone removal, final shaping 
• cup, criss-cross, axe:  finish. 
• Rippers, long 4 pt: Deeper carving.  NOT used like toothed chisel. 

Carving chisels:

• roughing have heavy profile, finishing a bit thinner. 
• Limestone thinner and wide
• Granite requires carbide blade set into steel. 
  
  • Avoid wedge insert (marble blade), tends to pop out. 
  • DO NOT pry on chisel, let it do work.

Safety:  Vibration, noise, dust & chips.

• Usual eye, hearing and breathing protection.
• Wear padded gloves, grip gently.
• DO NOT grip tightly, lean into stone.
• Take frequent breaks  from work.

Air hammer care:

• If sticking soak in kerosene overnight. 
• Or, add WD-40, run, then put in white spindle oil (10 SAE). 
• Oil hammers before and after use. 
• Run at low speed for minute before putting under load.
• Running hammer full speed without chisel can damage it.

Splitting Granite

Details

Written by Kirk Mclean

Granite is removed either by impact or by abrasion, not by carving through the stone. Stone will break and carve more easily in one direction, known as the “grain”.  Slabs are usually sawn so grain runs long way, thus breaking is across the grain

Granite tends to split towards an edge.  The closer you are to an edge with splitting tool, the more the crack tends to run to the outside rather than down through the stone.

Depending upon the situation and piece of stone, three techniques can be used: "Plugs and Feathers", "Saw Cuts and Weges", and " Pitching"

(Anyone have photos of feathers/wedges and pitching tools they are willing to contribue/post)

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