Sanding Veneer to Thickness
From contributor F:
I have a few suggestions. I am going to make the assumption that you are speaking of sanding individual leaves of shop made, resawn veneer. I have a nice resaw and have refined a set of fences, jigs and setup that allows me to saw veneer at .03125" (1/32") with great consistency and accuracy using a 3" stellite skip tooth bandsaw blade.
I would first rule out the Performax type machines because of the cantilevered drum design. I would say, though, that if I had one and was willing to learn about its quirks, I am sure I could get it to do the job satisfactorily as to prepping to lay up leaves of veneer for pressing, which I also am assuming is your end goal.
However, I have gotten good results sanding veneer to a consistent thickness with a planer\molder style machine that has a solid steel sanding head that can be installed in place of the molder or planer cutter heads.
The thing about a lot of machines is that they are not always sent from the factory with the fussy, caliper wielding craftsman in mind. They are generally set up to give good visual results to someone using a tape measure and burning an inch.
If you have any of those sanders that you mentioned using but were unhappy with, I suggest tuning and adjusting the parallelism of the sanding head and the table.
My machine is a sheet metal housing clad RBI planer/molder/sander/etc. The sheet metal housing aside, it has a solid steel bed and has solid enough support for the cutter head, and a well made enough elevation system to do what it is supposed to do well.
Most machines of this nature are capable of having adjustments made to the elevation mechanism of the machine that will fine tune the bed to head parallelism. After you have a machine that is properly adjusted, you must learn to work within the capabilities of sandpaper. Sandpaper does not work the same as a planer knife, in that with sandpaper, you cannot set the machine to a given elevation and then send two leaves of veneer through the machine that have greatly differing thicknesses and expect them to emerge on the outfeed side of the machine being exactly the same thickness.
The work needs to be done as slowly as the sandpaper's capabilities allow. At times I have been on projects that have required me to resaw large quantities of veneer. I found it to be much more efficient with those kind of quantities to take the veneer to someone who rents time on a wide belt sander. The typical scenario is you call the guy, make an appointment, and then tail off on the sander while he operates and feeds the veneer into the machine.
The wide belt machine brand that I recommend is Timesaver. With these machines, nothing is required but to lay a leaf of veneer right on the belt and let it go through. I did once have a bad experience with an off brand machine that would kick back a leaf of veneer every third or fourth sheet. It was a long time ago and it may just have been a poorly set up machine, but just the same, I recommend Timesaver.
Lastly, keep in mind that the resaw phase of making the veneer will set the stage for how easily the sanding phase goes. Saw the leaves as accurately as you possibly can.
Also, I have been able to get such a good smooth pattern of band saw mark on my sawn veneer that I was able to get away with sanding only one side of each leaf. If you do this, be sure to flip every other leaf over from the way it was flitched before sanding so that you can still bookmatch the sanded faces when you lay it up.
From contributor F:
Oh, and by the by, the last time I rented time on a Timesaver, the owner/operator charged me $60 an hour. It took us about 30 minutes to sand a large pile of 11.25" wide by 10 foot long veneer and at one dollar a minute, it was worth every penny of the $30.00 I paid him.
From contributor D:
The reason your material varies in thickness is a problem inherent in many sanders, and very prominent in drum sanders. Just because the thickness gauge reads .250 doesn't necessarily mean anything that goes through the machine will come out .250.
Unlike a planer, which will cut to the dimension set (as far as its capabilities, hp, etc), a sander has a lot of work to do in a very short period of time. If the material is wide, thickness will be reduced much less than with a narrow part. The current crop of quasi-hobby drum sanders all deflect (both drum and platen) and will have more slop than industrial drums or wide belts.
This give is probably accounted for in the machine's design since the typically underpowered drum sanders would stall, slip, load paper or trip breakers more frequently without a little give on thicker material or with too large a bite. Coarser wraps, slower feed, and more patience may help make things more consistent. A wide belt or industrial drum will also do it without the need for so much patience.
From contributor S:
Is this a production question or a hobby question? If it's a high production question, then... To get thickness consistency, you need to abrasively plane the veneer to the desired thickness. To do that you need a specialized sander that has a flat feeding belt and vacuum. Be ready to spend six figures.
There is a way to do it on a cheap sander, but you need to change the feed belt to a high durometer, high stiction flat belt and you need to place a roller immediately below the sanding head in order to raise the feed belt ever so slightly so as to create a specific contact point. All of this sounds easier than it really is.
As for the inconsistent thickness that you are getting now, you can not just sand with a 120 grit and think that you can control the thickness. You need a 60 grit belt on a hard drum in order actually remove substantial amount of material and plane the veneer to a certain thickness. This will leave you with a fairly rough veneer that needs to be sanded again to make it smooth.
Then of course you run into other problems like heating the veneer and drying it to a crisp. Splitting it. And on and on. To get around that, you need to back the veneer. And that's another category of fun and games.
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