Sanding red wood slab leaves a wavy surface..help!

Hi guys,

First post and first project so go easy haha.

I purchased an amazing Californian red-wood slab for a desk project im currently undertaking and have run into a few problems.

First of all the slab is 15mm ticker on one end than it is the other. To fix this i have built my own router sled and have tested it on an off cut, seems to do the job fine for milling the slab to be an equal thickness all the way through. Pictures attached.

The second problem i am currently trying to fix is that when it comes to sanding, using a rectangular orbital sander, after a couple of passes the surface becomes wavy. Meaning that where the aging lines are, are the peaks and in between them are slight valleys, so the aging lines are obviously harder/ denser than the rest of the timber.

If anyone has experienced this before please let me know how you've combated this as i want to finish this project as fast as possible!

Cheers.
Attachment 418204Attachment 418203

Hi weekendman,
You will have trouble sanding redwood like other soft timber because of the hard and soft nature of the grain the narrow dark lines are hard and the wide are soft so when sanding you sand hollows in the soft between the hard you will need to find a drum sander to put it through or try a belt sander sanding with the grain as opposed to an orbital. The sled looks good and should do a good job on the thickness.
Regards Rod.

:whs:

It's like cedar; the trick is to do as little sanding as possible. Starting from a flat surface, the more you sand the worse this variation will become.

It's also advantageous to start with as high a grit as you can get away with, but knowing what that is for any given piece takes a bit of experience... if you have an offcut you should be able to work it out without too much effort.

How clean did your router jig leave the surface? Much tear-out? perhaps you could buzz another mm or two off it to bring it black to flat then use large(ish) hand sanding blocks rubbing with the grain to finish? (I mean a 1/3 or 1/2 sheet of paper wrapped around a flat piece of wood... NOT one of the rubber or foam 'painters blocks' that conform to the surface. The latter make thngs even worse. DAMHIKT.)

It involves a bit more elbow grease, but properly done shouldn't take any more time to run a few grits than an electron burner. Honestly!

Thanks for the replies guys,

I have recently found a service on gumtree that someone is offering for their drum sander. However my question with that is, would the surface not turn out wavy like the previous times i've sanded? And im not 100% sure if the machine would only have one grit or would pass down through grits.

As for the router jig, if i go slow and steady enough without putting undue pressure on the sled the machining comes out fairly decent. I am using a 1 inch straight edge bit with 2 blades. I have tried sanding with 80 grit paper stuck to a small 200x40x90mm piece of hardwood in a cross hatching pattern, The surface turns up fairly rough with visible sanding lines but when running my fingers over, still turns out very slightly wavy. Maybe ill try taking another 1mm off the surface and sand with the grain this time.

Cheers!

A scrapper maybe?


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I would use the router and take off 0.25mm with the grain with the router set at it's fastest setting, the other alternative would be to make up a large hand sanding sled similar to the gyprock sanders.

Conifers like Redwood have seasonal growth. The summer growth is fast, so the timber is soft, the late-in-the-season wood going into Autumn "late-wood" is dense and hard. Any sanding tends to emphasise the growth pattern.

There are large double-drum sanders that can run two different grits - coarse on the first drum and finer on the second drum. However, if the wood is resinous (as conifers often are) you might get some resistance/outright refusal from any drum sander owner/operator as that writes of a sanding belt very quickly.

You could hand plane it smooth with a long plane as long as the blade is very sharp, or else find someone with a wide-enough thicknesser, preferably one equipped with a spiral cutterblock.

Hand Plane, Really, REALLY sharp hand plane. Got a lot of Western Red Cedar which I want to use for box making (liners) and the only way to get it satisfactorily flat is hand plane.

Another 'step out of the box' idea is to not worry about the undulating surface of the timber in the desk. Celebrate the innate nature of the timber rather than try to fight it. Most desks these days are not for writing on anyway, so do not need to be perfectly flat. If a perfectly flat area is required then inset a flat material on the writing area. Antique desks often had leather (or fabric like oil cloth) inserts to provide a good writing surface. For an absolutely flat surface that still keeps the beauty of the timber showing you could put some glass on top (secure with mirror corners) or inset a smaller piece of glass in the critical-flatness area.

If the drum sanding service you are talking about is the one in Cheltenham then go for it. At that price it's a lot better then mucking around and it should come out flat. Drum sanders dont allow the undulations to form.

that machine is a twin belt, the rear one probably being 120 or 180 grit. You'll still need to sand it a bit by hand or Ros, maybe 240 and 360. Use new, high quality paper and because it's sharp you will be less inclined to oversand the soft grain. The undulations are made worse when people overwork the surface with dull paper.

We did a redwood job recently at work and it came out dead flat from our wide belt sander. It's a twin head calibrating sander, which means a steel first head and hard rubber second head. We're in Moorabbin if you haven't sorted it out already.

Sorry for the late reply guys, i do appreciate the suggestions! As im writing this post i currently have the desk finished and could not be happier.

To close things off and for anyone else having this problem, here is how i battled it.

For a janky setup the router jig did the job, where was a small amount of tear out but i could live with it. After testing multiple ways of sanding i found the solution. I first sanded the slab by hand with 80 grit paper stuck to a block of hard wood about 220x80x20mm, then stepping down to 120 paper still stuck on the block. Following that i then went and bought a single action orbital sander and hit the slab with 180 grit to finish off the sanding. Now i have to say that this method was not perfect, the slab was still minutely wavey but this is as good as i was gong to get it.

I then beveled the edge with a small router and finished the slab with epoxy, this was the best option in my opinion as 1) The slab is being used for a desk and dries rock hard 2) It has self leveling capabilities so even fine waves would be sorted. For anyone wanting to see the final product i have attached a couple photos.

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Quote:

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Originally Posted by weekendman

Thanks for the replies guys,

I have recently found a service on gumtree that someone is offering for their drum sander. However my question with that is, would the surface not turn out wavy like the previous times i've sanded? And im not 100% sure if the machine would only have one grit or would pass down through grits.

As for the router jig, if i go slow and steady enough without putting undue pressure on the sled the machining comes out fairly decent. I am using a 1 inch straight edge bit with 2 blades. I have tried sanding with 80 grit paper stuck to a small 200x40x90mm piece of hardwood in a cross hatching pattern, The surface turns up fairly rough with visible sanding lines but when running my fingers over, still turns out very slightly wavy. Maybe ill try taking another 1mm off the surface and sand with the grain this time.

Cheers!

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I've had this problem and the drum sander fixed it no problem.

Ripper job in the end!

Looks fantastic! Great job.

I hope that you have also sealed the under-surface. The sapwood (light coloured timber) of many timbers, including Redwood, is susceptible to many pests and fungi. You need to seal on all surfaces. BTW, the epoxy finishes are not proven to last, they may well do, but there is no current emphasis on longevity.