Diamond paste question

Re: Diamond paste question

Todd Stock

>Start with couple of BB sized applications, and go from there.

not the best substrate

bill tindall

>The best substrate is cast iron, but I have had good success with acryllic (plexiglas). I wish someone would sell cast iron paltes (Joel?) They are simple to make and not costly if ordered from cast iron supplier and ground flat several at a time.

On something porous like MDF, or a hard wood, the diamond will bury in the soft substrate resulting in two disadvantages. One, you will need to use more paste and second it will cut like a smaller grit size because the particles are more buried.

Ideally the substrate should be soft enough for the diamonds to just embed in, and the lubricating property of cast iron is an advantage. A light viscous lub. on acrylic works OK.

Re: not the best substrate

Wendell @ Murphy, Tx

>Thanks for the advice Bill. I'll keep my eyes peeled for some cast iron plates in the future. Right now I want to try it out first before making a big investment in substrates.

Do you use a honing guide with the diamond paste? I usually use an eclipse style guide when I sharpen. I am wondering if I should be concerned with grit contaimination on the roller with the diamond paste. What do you think?

Wendell

Re: not the best substrate

paul womack

>Intriguing. A metallurgist on oldtools recommended paper, long ago.

As you say, it seem "obvious" that the diamonds will just disappear into it, and yet he was getting good results.

http://nika.frontier.iarc.uaf.edu/~cswingle/archive/get.phtml?message_id=64524#message

BugBear (who is always doubtful of "obvious" and "common sense", because there are manu wonderful, intriguing, counter intuitive things in this wonderful world)

MDF 'n' diamond? Maybe not the best...

David Barnett

>...but damned good and plenty cheap and easy to get.

You're right, of course, that cast iron is a fine substrate, but then not all cast iron is equal, either. Meehanite is considered best by several lap makers, although iron from MSC works nicely, too, if you enjoy scrapers, prussian blue, and surface plates.

Iron is not simply always the best substrate for diamond abrasive, however. It really depends on what you're lapping, honing or polishing. I use diamond on copper, zinc, tin, acrylic (lucite, perspex, plexiglass), and ceramic, which allows me to facet and polish sapphire/ruby, topaz, emerald, and so on.

I wouldn't dismiss MDF outright, though. Experience proves otherwise, and this has been bourne out in numerous articles and tests.

Counterintuitive, yes. One would suppose "ideally", as you say, that partial embedment would be the key, and it's easy to assume that MDF fails in this regard. But apparently the resins that bond the fibers in MDF accomplish this very thing. Surprised me, too.

So while it isn't 'best'; grooved Meehanite laps with all that lovely lubricating graphite, on edge tools MDF and diamond are nevertheless 'good enough'.

Now wait a minute!

Don Thompson - Cutler Ridge, Florida

>Don't run off. ;-)

"I use diamond on copper, zinc, tin, acrylic (lucite, perspex, plexiglass), and ceramic"

Why so many different substrates? Which do you use for what?

easy way to flaten your cast iron piece

bill tindall

>Any large machine shop will have a Blanchard grinder. This affair will accomodate a bunch of cast iron pieces and for $25 (local pricing) both flatten them all at once as well as leave the occasional deep scratch that can be an advantage for a cast iron plate.

There is a good business opportunity awaiting someone interested in supplying already cut and flattened cast iron plates. In quantity they could be manufactured for a few dollars each and sold for considerably more. The cast iron is available as cast bar stock of the right cross section to make the plates.

more information

bill tindall

>I hollow grind. 15 micron on acryllic or cast iron removes 60 or 80 grit grinder scratches with but a few strokes. One can go directly from 15 to 1 micron for edge completion suitable for most work, so only two sizes are needed for this procedure, and hence, only two plates. (others go to an even smaller diamond size for demanding work)

Only a few strokes are needed, and at a few, it is easier to keep things aligned for hand guiding. I no longer use a jig. Cross contamination can be an issue.

With MDF I don't know how one deals with the accumulation of grinding grunge. With the nonporous acryllic( $12 per sq ft at MSC for 1/2 ") or cast iron I wash it off with the lubricant I used for honeing- mineral spirits in the case of cast iron.

There are a lot of people using diamond now. Maybe it is time for a good airing of other's experience with substrates, lubricants, cross contamination, , grit sizes used, etc.

Re: easy way to flaten your cast iron piece

Wendell @ Murphy, TX

>So is the problem with MDF due to the softness or the porous natural of the material? Would it help to seal it with a coat or two of something like polyuerethane?

Bill, do you have some pointer to source of cast iron bar stock? Should I just look under "metals"

in the phone book?

Wendell

Re: easy way to flaten your cast iron piece

Fred Krow

>I have obtained several 5 x 12 bars of Ductile Iron and had them surface ground flat. Ductile Iron is much more stable than ordinary Cast Iron. The old foundrys in the Eastern US would make a casting and store it outdoors for about one year to settle down and stress relieve. Today they use a large furnace and much shorter time period.

http://www.metal-technologies.com/ductile.asp

http://www.metal-technologies.com/gray.asp

http://www.ductile.org/

http://www.ductile.org/didata/default.htm

http://www.key-to-steel.com/Articles/Art93.htm

http://www.castingsource.com/tech_art_ductile.asp

Regards,

Fred Krow

Yeah, but...

David Barnett

>I've always heard ductile iron's different molecular/crystalline structure makes rather poor laps. Au contraire? Does it have the same spheroidal graphite lubricating properties?

Cleavage planes and drag. (Tad OT)

David Barnett

>Which is a teaser topic if ever, heh. Don, all I can think is that I so overwhelmed you with my substrate flood you gave up on the the rest of that sentence. Most of my lapping, cutting, grinding is not tool steel but hard gemstone; up to about 9 Mohs. It can get kinda complex and solid state physics, voodoo and astrology may all become involved, or so it seems. Has to do with crystal structure, cleavage planes (bet you don't have one of those in your collection), and how some abrasives/grits will fracture various crystal presentations (different substrates have unique drag and embedment characteristics at a given rpm), leading to that mysterious phlogiston of the gem faceting world called "Beilby Flow".

Anyway, Bill's right. Iron's great, acrylic works when you're hand lapping (rotary laps can heat up badly with diamond). MDF works, and I sometimes use copper for hand lapping and polishing, but copper's also good for coarser grits, as well. File folders are great for graver stropping, and ceramic with spray diamond and pencil graphite's outstanding for tungsten carbide graversl. Puts a nice polish on any spare Burmese rubies you might have lying about, too.

Really, get some diamond, try it on whatever. It's a cheap thrill for someone like me. Without a life, that is, apart from tool fetishism.

Re: substrate - laminate

Barry Va Beach

>Wendell, I tried mdf once or twice and agreed with those that posted that the paste sinks in too quickly. I bought several cast iron plates form Japan Woodworker and the diamond keeps "alive" much longer. Recently though I used the back of a laminate floor ( like pergo but it wan't pergo). The back was flat and the diamond seemed to last longer than on MDF - I assume because the back is sealed. The cost was right since I only used a cutoff. So I quess that sealing hte mdf would help ( if it didn't fuzz up) but think you would be better off with a more durable surface - like cast iron or laminate.

Corian works, too.

David Barnett

>

Re: substrate - laminate

Wendell @ Murphy, TX

>So would plastic laminate work? I have a sheet laying around that I could use to coat my MDF blocks.

Wendell

Re: substrate - laminate

David Barnett

>Don't know. Corian has acrylic content.

I remember an article in FWW where the woodworker preferred hard maple to MDF. FWW had an online 'tips' video on the subject, although that was some time ago.

copper

bill tindall

>flat copper can be had in the form of circuit board blanks.

Re: Yeah, but...

Fred Krow

>I did not consider your points David. My main reason for selecting Ductile Iron was dimensional stability. Interesting viewpoints, I will research further.

Regards,

Fred Krow

Re: Ductile Iron Lapping Plate

Fred Krow

>I found some references for use of Ductile Iron in commercial lapping plates.

http://www.prhoffman.com/lapping-plate.htm

http://www.processresearch.com/silicon.htm

I believe the Shapton Compact Lapping System plate is also Ductile Iron.

Regards,

Fred Krow

Glad to find this out. Thanks!

David Barnett

>Great links. Learned something useful. Next time I make an iron lap I'll just have to try it. Thanks!