Diamond paste on MDF - Not for me

[Patrick Chase]

As I've mentioned a few times in other threads I use diamond pastes on iron and/or mild steel plates for some lapping jobs, particularly flattening chisel backs.

After seeing all of the posts from people suggesting MDF as a substrate for diamond paste I decided to give it a go. I tried every paste I have on hand: Norton water-based paste (45, 15, and 0.25 um), DMT oil-based paste (6 and 1 um) and PSI oil-based paste (45, 15, 6, and 1 um).

I was initially impressed with diamond on MDF, but noticed that the cutting started to slow down markedly within the first minute. The resulting surface finish was also finer than I would expect from the same size diamond particles on iron. I suspect that the diamond particles are receding into the relatively soft MDF such that their cut depth decreases - this is a known issue with basically all abrasives on compressible media (paper, cloth, wood, MDF, etc). This effect was present for all of the pastes I tested, but maybe a little worse for the Norton aqueous ones. This may be related to why people get such great results with the ubiquitous green lapping compound on strops even though it contains much larger calcinated alumina grains along with the 0.5 micron ZrO2. If the alumina particles initially cut fast but then recede, then you'd get nice speed at the start and a smooth finish at the end. I'm not a fan of that behavior with something as costly as diamond paste though.

Once the cutting slowed down I checked flatness with a straightedge, and found that I could see light where I'd been flattening my chisel. It wasn't severe (maybe 1/2 mil at the point when I stopped) but it was a lot more degradation than I'm used to seeing with grey iron or mild steel. Again the aqueous pastes seemed a little worse, perhaps reflecting MDF's hygroscopic nature. This isn't an automatic showstopper because MDF is cheap and plentiful, though as with the deceleration concern cost is an issue - In order for diamond paste to be economical I need to be able to use a given charge of paste for a long time.

The MDF does have some compliance and therefore does better when you want to polish a very slightly out-of-flat surface. Steel and iron are totally unforgiving that way - you have to get it dead flat on a coarse paste before you try to polish.

All in all I'll be sticking with iron and mild steel honing plates.

[Bruce Haugen]

I just got my cast iron block back from the local two-year college machine tool program. They didn't charge anything for surface grinding that block flat to a half thou, both sides. So now I can hone nearly anything on that 3 X 12 cast iron slab.

[Bruce Wrenn]

I finish polish my chisels using Tormek paste on MDF. For flattening, I use diamond plates, or wet dry sandpaper.

[John Kananis]

I use the Norton water-based paste on MDF and really enjoy it. That said, I've had a few of those plates on my Lee Valley wishlist for a while - maybe its time to pull the trigger.

[Bruce Haugen]

I use the Norton water-based paste on MDF and really enjoy it. That said, I've had a few of those plates on my Lee Valley wishlist for a while - maybe its time to pull the trigger.

The nice thing about diamond paste on cast iron is that it easily handles the A2 irons on my LV planes. For other irons and chisels, green compound on mdf really does the trick.

[Brian Ashton]

After seeing all of the posts from people suggesting MDF as a substrate for diamond paste I decided to give it a go. I tried every paste I have on hand: Norton water-based paste (45, 15, and 0.25 um), DMT oil-based paste (6 and 1 um) and PSI oil-based paste (45, 15, 6, and 1 um).

SNIP

Got anyone with a tablesaw you don't particularly like? Take the piece(s) of MDF full of diamond over to there house/shop and ask them to cut it down for you... Good way to use the scraps up and tick someone you don't like off

[Patrick Chase]

The nice thing about diamond paste on cast iron is that it easily handles the A2 irons on my LV planes. For other irons and chisels, green compound on mdf really does the trick.

Also the HAP40 PM HSS in one of my sets of chisels. Yet another useful purchase inspired by one of Derek's reviews.

Diamonds get a good edge with high-carbide-content alloys like HSS because they sharpen the carbides instead of knocking them out of the edge. Diamond and CBN are the only common abrasives that are hard enough to do that. IMO A2 is low enough in carbides that you can get a perfectly good edge with good stones, but the diamond paste certainly isn't hurting you :-).

I also use 3M film (675L, 661X, 663X, 668X) on hard steels. I tend to use the films if I don't have really tight flatness requirements, and the plates/paste otherwise.

[Patrick Chase]

Got anyone with a tablesaw you don't particularly like? Take the piece(s) of MDF full of diamond over to there house/shop and ask them to cut it down for you... Good way to use the scraps up and tick someone you don't like off

Oooh, not nice. Not nice at all :-).

[Jon McElwain]

A granite surfacing block is near the cost range of a sheet of MDF. Is this not a good option for sharpening or flattening?

[Patrick Chase]

A granite surfacing block is near the cost range of a sheet of MDF. Is this not a good option for sharpening or flattening?

I sometimes use granite surface plates to lap with SiC powder, though always with a sacrificial plastic laminating sheet on top.

I don't do the same with diamonds for a few reasons:

1. I use diamond paste for critical flattening, so that rules out the laminating film

2. Without the laminating film granite is too hard which means it will wear quickly. Lapping preferentially wears the harder material faster than the softer one. At Mohs=7 granite is much harder than either iron or mild steel, and getting uncomfortably close to the tools it's supposed to be lapping. I prefer that my surface plates stay flat.

3. Though flat those blocks are not particularly smooth. For example the surface of the block will telegraph through 3 mil polyester lapping film. I mostly use diamond paste in finer grits, and that's exactly where this becomes an issue.

4. Isolation. With loose lapping media like diamond pastes you need to be really careful about cross-contamination. Lapping on a single large block is undesirable

[Lenore Epstein]

A granite surfacing block is near the cost range of a sheet of MDF. Is this not a good option for sharpening or flattening?

That's not my observation. Where do you find a certified $20 granite surfacing block?

And Patrick--where do you get flat bits of mild steel? The Google tells me what it is, how it's used, and it looks like it's sold in large quantities for commercial use, but I can't find anyone selling smaller pieces of it at retail. Or maybe things like toolsforjapan's or japanwoodworker's kanabans or Veritas's honing plates are actually mild steel.

[Bruce Haugen]

And Patrick--where do you get flat bits of mild steel? The Google tells me what it is, how it's used, and it looks like it's sold in large quantities for commercial use, but I can't find anyone selling smaller pieces of it at retail. Or maybe things like toolsforjapan's or japanwoodworker's kanabans or Veritas's honing plates are actually mild steel.

not Patrick, but most cities of a reasonable size have metals dealers. They generally cut it to size, too. Or you can try online dealers like Online Metals, Speedy Metals, etc.

I prefer cast iron to mild steel because the diamond crystals seem to embed themselves into the surface more easily.

[Patrick Chase]

That's not my observation. Where do you find a certified $20 granite surfacing block?

And Patrick--where do you get flat bits of mild steel? The Google tells me what it is, how it's used, and it looks like it's sold in large quantities for commercial use, but I can't find anyone selling smaller pieces of it at retail. Or maybe things like toolsforjapan's or japanwoodworker's kanabans or Veritas's honing plates are actually mild steel.

The Veritas plates are mild steel.

For cast iron you either have to order from an online metal dealer as Bruce says, or procure your lapping platest through a machine shop (they know where to get metal). I have a friend who runs a machine shop...

[Bruce Haugen]

The Veritas plates are mild steel.

For cast iron you either have to order from an online metal dealer as Bruce says, or procure your lapping platest through a machine shop (they know where to get metal). I have a friend who runs a machine shop...

Or, you can work at a utility where they are junking out one of these https://upload.wikimedia.org/wikiped...wer_backup.jpg

except that ours was bigger, about 5000 HP. The cast iron I got came from an access port cover, 3/4" thick and free?

[Jim Koepke]

Or, you can work at a utility where they are junking out one of these https://upload.wikimedia.org/wikiped...wer_backup.jpg

except that ours was bigger, about 5000 HP. The cast iron I got came from an access port cover, 3/4" thick and free?

I used to work at DeLaval Enterprise Engine Division where we made such beasties. Long before my woodworking days began in ernest.

We didn't make an 18 cylinder model that I recall. Did make a 20 cylinder version.

jtk