Tips for a "perfect" platter face?

[Dave Mount]

Since I got interested in exotic woods I've found myself turning a lot more platterish pieces because I generally tend toward larger rather than smaller work, and it's easier (and cheaper) to find wider pieces of exotic woods in 1-2" thicknesses than more bowl-type thicknesses.

One thing I find challenging on platters is getting a finish cut that doesn't show and "rings" when viewed in raking light. I'm not talking about tearout, I'm talking about *really* subtle valleys or hills that show up as rings in reflection. And I really mean subtle -- one I can't feel with my fingers will still show up in raking light if the piece has a shiny finish, but they're too subtle to cast a shadow when the piece is still unfinished and on the lathe.

My finish cut is a bevel-rubbing push cut with a u-flute bowl gouge with a steep and blunt grind (aka bottomfeeder); while I'm of course trying to maintain a consistent sweep, the swing across a platter face is only a few degrees, so any hesitation or tiny flinch will create an issue. I don't have this problem with bowls, which just seem to be a little more forgiving. Maybe that's because there's more arc and you're moving the gouge handle more, and it's easier to make a smooth movement when there's more overall movement.

After the last gouge cut I feel for imperfections and use an NRS to deal with those, but as I said above, I've found that the finished work can show rings even when I couldn't feel anything with my fingers. I made an NRS out of a flat/square scraper and put just a super gentle curve on the edge thinking it would rub off the high spots; it's helpful, but not a sure way to a perfect curve. I've thought about doing finish sanding off the lathe using a 5" random orbit sander and a fairly coarse grit to try to get some sanding action that's not concentric with the ridges/valleys, but that seems like such a brute force approach. I know JKJ uses hand scrapers off the lathe, which might be an option, but I haven't tried that to date.

Below are some pictures if the kind of pieces I'm talking about. None of these pictures were intended to capture the reflections, though some may have had them (it's generally something I'm avoiding showing in a photo!). L to R, leopardwood (and back side), sapele, and a wood that was sold to me as "oticica" but I've not been able to find any literature on a wood by that name that looks like this (would love to know if anyone thinks they know what it is; very dense, very hard, fair amount of silica blunting, and it's definitely not Honduran or African mahogany, padauk, or sapele, all of which would be reasonable guesses from the picture). Thanks as always to JKJ for the squarish platter pattern, I just love using it, and people love the result far more than a round platter.

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Be interested to hear if someone has the silver bullet.

Best,

Dave

[Edward Weber]

After the last gouge cut I feel for imperfections and use an NRS to deal with those, but as I said above, I've found that the finished work can show rings even when I couldn't feel anything with my fingers. I made an NRS out of a flat/square scraper and put just a super gentle curve on the edge thinking it would rub off the high spots; it's helpful, but not a sure way to a perfect curve. I've thought about doing finish sanding off the lathe using a 5" random orbit sander and a fairly coarse grit to try to get some sanding action that's not concentric with the ridges/valleys, but that seems like such a brute force approach.

Dave

IMO
Your NRS may be crushing or bruising some fibers and not others, leaving the rings you mentioned.
I often use a ROS on large platters in order to blend a smooth dish or dead flat bottom. There is nothing wrong with sanding as a shaping tool if the gouge and scraper won't give you the result you want.

[Jim Morgan]

Same problem here - subtle rings that didn't show up until well into finishing. Buffing across the rings helped, but didn't get rid of them completely.

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[Dave Mount]

Ed-- Hadn't thought of crushing fibers. I'm usually finishing with a negative rake scraper as sharp as I can get it and as lightly as I can apply it which I wouldn't think would bruise. . .though the heel of the gouge that preceded it might be a culprit. And thanks for the push to just go for the ROS.

Jim-- That doesn't seem like much of a flaw to me, but at least you have that incredible piecework to distract! That's more patience than I'll ever have, nice work.

Sharp convexities are hard because they're often cut without bevel support and NRS can be hard to bring around that sharp curve without making new grooves. If you don't see the problem until after finishing, then sanding techniques are too late to help, but I've found on a sharp convex curve a sanding block can help fair the curve, strange as that sounds. I use PSA rolls for general use sandpaper and stick a piece of coarse paper on a flat scrap of wood, then "roll" that block back and forth around the convexity with the lathe running fairly slowly -- need to keep it moving so you don't create a flat. While a flat block nominally sands a flat, by keeping it moving you can actually create a fair curve because the flat surface always looks for the high spot and you gradually bring the high spots down to the low spots. Once the "rings" are gone using coarse paper on a block, I go through the finer grits with soft backing (fingers or a foam backing pad) to blend and refine. That's helped me anyway, YMMV.

Best,

Dave

[Brice Rogers]

With a NR scraper, it is the burr that does the cutting. The burr lasts ... maybe ... 20 seconds.

Consider using the cabinet scraper to remove the tooling marks. Maybe JHK will opine.

[Dave Fritz]

Sometimes I use an old chalk board eraser with sandpaper over it. It helps level out the sanding and avoids the paper from cutting deeper into the softer growth rings, esp. in woods like ash. Use a real light touch.

[Kevin Jenness]

Your photos show very clean work without visible ripples. I am sure they exist, but I doubt you can achieve the surface you want with edge tools only. An NRS with a frequently renewed edge may get closest, perhaps polished and burnished for a finer cut, but at some point you have to track down the renegade "rings" with abrasives.

At that point it's largely a matter of the shape and hardness of the backer pad, and that will be determined by the flatness of your surface and the particular wood you're working. Uneven textured wood like ash will need a harder pad to avoid accentuating problems. Unless the surface is perfectly flat the backer will have to have some level of curve or flexibility, so it's a matter of experiment to find the right one. Some options are felt, leather, foam, cork, alone or in combination. I have a 5" round plastic foam velcro hand pad that works well, I often use a 5" ros also - it has pads available in different densities. I do most sanding with the lathe turned off and usually the final grits are with a random orbit sander when possible.

A cabinet scraper can be useful for levelling but it's important to vary the angle relative to the grain direction to avoid chatter.

[John K Jordan]

...
A cabinet scraper can be useful for levelling but it's important to vary the angle relative to the grain direction to avoid chatter.

I do use NRS just after the finish cut (a burnished burr lasts a LOT longer than one from the grinder) but I've never found ANYTHING better than the hand scrapers for removing circular ripples, tearout, or other defects - IMO they are far, far better (and much quicker) than trying to remove them by sanding. They will also quickly remove any little center humps, difficult to remove even with NRS. Here are a few of the many scrapers I use, most I ground from rectangular cabinet scrapers, two from StewMac:

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For bowls and platters I grind my NRS like this, same bevel on both sides, 60-deg included angle, use an extra fine diamond hone to remove the grinding burr before burnishing the cutting burr. I grind a short flat on the ends which to simplify making the surface perfectly flat. Like all NRS, these are held horizontal and flat on the tool rest.

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Three things I find important:
- Take the piece off the lathe when scraping and final sanding. I'll hold it with my knees if necessary but almost always leave the piece in the chuck and fasten the chuck on the carving and finishing stand from Best Wood Tools.
- Use good lighting for this, meaning one or two point source lights used at a glancing angle. May have to turn off the overhead lights.
- Dampen the surface with something to make any surface defects more visible, whether smooth ripples or sanding scratches.

If the surface is the matte, bare sanded wood, defects like ripples can be invisible even with good glancing lighting but if made glossy they are easily seen. I wipe on naphtha since it dries quickly and leaves no residue. While the surface is wet, looking at different angles shows surface irregularities well. When it starts to dry, any sanding scratches left over from a coarser grit show up since the scratches hold the moisture longer than the sanded surface making them a little darker.

I do have to pay attention to the grain when scraping, either scrape with the grain or at some angle, never against the grain. The scrapers must be kept sharp with a proper burnished burr.\\

After scraping, I can usually start with 400 grit or finer paper.

I tend to sand by hand but sometimes use pneumatic ROS, 1" or 3" depending on the surface curvature. When sanding by hand I usually use a "soft sanding block", an eraser with the sandpaper wrapped around.

sanding_soft_block.jpg

BTW, here is the carving and finishing stand in use by a student using the 3" ROS on her "small squarish dished platters". Since the piece is not removed from the chuck it can easily be returned to the lathe for additional smoothing with the NRS if needed.

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JKJ