Planer thicknesses smoothness as sandpaper grit level?

[RedMist]

Slightly vague question for which I apologise but I'm basically thinking out loud here.

I am happy with the results from my planer thicknesser, one of these

the wood comes out pretty much smooth as glass. Roughly speaking what sort of level of grit in sandpaper is it equivalent to? I've no experience with the higher number sandpaper grits.

 

[custard]

That's an interesting question, I've never thought of it in those terms.

Strictly speaking I guess there's no real equivalence, the planed surface will consist of series of minute scallops that the knives cut as the board goes through the machine. But putting that on one side and assuming a slow feed rate and sharp knives then I'd guess somewhere around 240-320 grit? Like I say, I'm trying to look past any knife ripple/scalloping and judge the underlying surface, if you applied finish straight to a machine planed surface it's look dog rough, but between the ripples it can actually be very smooth..

 

[n0legs]

That's a good question =D>
I'll ask a man I know.

 

[RedMist]

To put it another way, I have some planed hardwood boards that have ripple in them, what level of grit sandpaper should I use to remove the ripple prior to finishing with Danish Oil?

 

[Fitzroy]

This is fundamentally a geometry/trigonometry question. Each pass of the blade takes a circular cut out of the woodwork with a radius equal to the cutter block + blade extension, assume 0.1m. The blade speed is huge in comparison to the board speed, say 40m/s (120ft/s) blade speed vs 0.05-0.1 m/s (10-20ft/min) so passes the board effectively instantaneously, however for a two cutter block rotating at 5000rpm a cutter only passes the board every 1 / 2 / (5000/60) = .006s in this time the board can move forwards .0003m - 0.0006m (0.3mm - 0.6mm). In theory a point of wood as high as cutter rises 0.3mm - 0.6mm away from its lowest point could pass under the blade untouched by the cutter. We can solve for the height based on pythagorus, height of ripple = 0.1 - sqroot(0.1^2-.0003^2) = 0.45microns - 1.8microns (30microns is 320 grit). This seems small so perhaps the compressibilty of wood effects the outcome, or my maths is wrong.

From what I recall scallops I have seen from my p/t seem to be more in the order of 1-3mm wide depending on feed speed. With the same size cutter block these would translate into scallops from 5 to 45microns deep, with 30microns equating to 320grit, custard looks close to spot on. With a larger diameter cutter block the scallops would be shallower.

Regard

Fitz.

 

[transatlantic]

Wouldn't it just be the grit size used to sharpen the blades?

 

[RedMist]

Looking now at the boards I was happy with, I can see the ripple effect. It seems more pronounced on boards that once I had got them to the required height I left the blade height the same and I passed the boards through a few more times to `clean` up the board (may not be a good idea?).

So the correct procedure to get rid of the ripple is to sand them ( I have no hand plane ability). Would a mouse style electric sander and a grit of 240-320 do the job?

Am planning on using Danish Oil to finish these hardwoods.

 

[custard]

Would ... a grit of 240-320 do the job?

You'd be a lot faster and the job will look a lot better starting with 80 grit and working through the grits to 240.

 

[woodbrains]

Would ... a grit of 240-320 do the job?

You'd be a lot faster and the job will look a lot better starting with 80 grit and working through the grits to 240.

Hello,

Custard is right on here. It might sound counterintuitive to start with a coarser grit and seemingly ruin what looks quite presentable already. But if you don't hand plane (and I think you should learn, it makes things quicker in the long run)or remove a lot of material with coarse abrasive, you will only take the tips of the peaks from the scallops down to the lowest point. While this might sound exactly what you want to do, you in fact have to take the surface lower than that. The planer essentially beats the living daylights out of the wood surface, compressing the fibres. If you don't get lower than the compression, preferably with a plane :lol: all the scallops will magically reappear with moisture from the air or the finish.

Mike.

 

[profchris]

No 80 scraper plane? That would be my weapon of choice, and quicker even than power sanding through the grits I reckon. There's a small learning curve to sharpening it, but almost none to using it.

 

[RedMist]

Wow I'm having my eyes opened here, thanks all for the help so far!

For sanding, would this sequence of grit be ok? 80, 120 then 240?

 

[woodbrains]

Wow I'm having my eyes opened here, thanks all for the help so far!

For sanding, would this sequence of grit be ok? 80, 120 then 240?

Hello,

I might put 180 in there,it is a big leap from 120 to 240.

Mike.

 

[bugbear]

That's an interesting question, I've never thought of it in those terms.

Strictly speaking I guess there's no real equivalence, the planed surface will consist of series of minute scallops that the knives cut as the board goes through the machine. But putting that on one side and assuming a slow feed rate and sharp knives then I'd guess somewhere around 240-320 grit? Like I say, I'm trying to look past any knife ripple/scalloping and judge the underlying surface, if you applied finish straight to a machine planed surface it's look dog rough, but between the ripples it can actually be very smooth..

I think part of the problem here is words.

"Smooth" is OK in everyday use. Everybody knows what it means...

But a polished Henry Moore statue is smooth, or a fluted marble column. But they're not flat.

The key missing factor here is scale - smooth means (when you dig a little deeper) flat on a very small scale. As you move up the scale, the word (should) change, perhaps to "texture" and then "shape".

A wooden sculpture, made with a sharp tool, will have a shape (the overall design), a texture (the pattern of cuts), and a surface quality (the result of a single cut).

Returning to the output of the planer, we might say that we have a smooth surface, and a scalloped texture.

(in the world of controlled metalwork, these concepts have been formalised, and are measurable)

BugBear

 

[ED65]

( I have no hand plane ability).

That's easily remedied

If you have any specific problems with getting good results planing we can help you figure them out.

If you have problems with getting consistent results don't let that hold you back, you don't have to be able to plane to an absolutely perfect surface every time, even some pros don't try to do this (quite a few in fact, including Paul Sellers). Flattening/smoothing the surface with a plane as best you can and then scraping and/or sanding to finish off is very commonly done. And 99 times out of 100 after finishing nobody could detect the difference between such a surface and one finished off by planing only.

 

[custard]

Flattening/smoothing the surface with a plane as best you can and then scraping and/or sanding to finish off is very commonly done. And 99 times out of 100 after finishing nobody could detect the difference between such a surface and one finished off by planing only.

I'm not sure I agree with that. I can tell the difference with one glance from the other side of the room! And everyone can tell a difference the moment they run their fingers across the surface. Don't forget how tactile wood is, most people can't resist touching wooden furniture surfaces, it's like we're hard wired to hold or stroke wood, which is why these distinctions may be subtle but they're still important.

 

[RedMist]

Hmm, the thought of learning planing appeals to me. The Stanley 80 scraper seems magical too. I fundamentally can't comprehend however how something the size of a plane could get a board flat when the board is maybe 8 times the width of the plane itself...

off to youtube i go !

 

[ED65]

Flattening/smoothing the surface with a plane as best you can and then scraping and/or sanding to finish off is very commonly done. And 99 times out of 100 after finishing nobody could detect the difference between such a surface and one finished off by planing only.

I'm not sure I agree with that. I can tell the difference with one glance from the other side of the room! And everyone can tell a difference the moment they run their fingers across the surface. Don't forget how tactile wood is, most people can't resist touching wooden furniture surfaces, it's like we're hard wired to hold or stroke wood, which is why these distinctions may be subtle but they're still important.

Not sure if you missed the threads or the individual comments, this same has been argued here a number of times in the last couple of years (not sure if it's the most recent time but it came up during one of the mammoth threads about hand planing about a year ago). I've seen similar debates elsewhere and FWIW I've never seen good evidence presented on the planing > sanding end of the argument. Well planed > badly sanded certainly, but not over any possible quality of sanded surface.

Just to emphasise if needed: this is after finishing.

In the naked wood it can be extremely easy to see the difference between a planed surface and one finished by sanding, as you say it's obvious from across a room. But as soon as the first coat of finish goes on most or all of that difference vanishes (and the more coats of finish go on the smaller any difference should become).

As for a tactile difference, that's harder to argue one way or the other of course. But speaking for myself with a film finish I can't tell them apart because I'm feeling finish, not wood, and there's no textural difference to transmit through that.

 

[ED65]

Hmm, the thought of learning planing appeals to me. The Stanley 80 scraper seems magical too. I fundamentally can't comprehend however how something the size of a plane could get a board flat when the board is maybe 8 times the width of the plane itself...

off to youtube i go !

Don't neglect here though. There is tons of planing experience to draw from here, and a few of the posters here can give you info and tips that'll trump most of what you'd find on YouTube.

Not the YouTube is all bad of course, it's just that as with anywhere like that the quality is all over the map and it's likely that most of it is bad (Sturgeon's Law).

 

[custard]

to emphasise if needed: this is after finishing.

In the naked wood it can be extremely easy to see the difference between a planed surface and one finished by sanding, as you say it's obvious from across a room. But as soon as the first coat of finish goes on most or all of that difference vanishes (and the more coats of finish go on the smaller any difference should become).

I think you're getting mixed up.

Any surface texture is always way more obvious with a finish than in the white.

 

[bugbear]

Not the YouTube is all bad of course, it's just that as with anywhere like that the quality is all over the map and it's likely that most of it is bad (Sturgeon's Law).

Sturgeon's Law applies on here too...

BugBear