Raised Panel Doors - Sanding and Knife Marks
Advice on sanding and finishing issues related to moulder knife marks in raised panel door profiles. September 18, 2014
Question (WOODWEB Member) :
We recently sent out a job and were called back by the contractor after the staining was done. There were some knife marks at the top of the profile and some at the lower part by the tongue on about ten doors. We have been fighting the corner issue for years. We are gluing the panels in hf press which get the panel pretty flat and then we are making a light pass with the wide belt before profiling on the shaper. We are running a new freeborn insert cutter on an SCMI shaper with a three roll feeder running face up with a back trimmer and a bearing. After making two passes the marks are random and very light in most spots but where noticeable after stain so we are re-doing these doors. I checked the spindal and the run-out is about tow thousandths. Like I said they are new cutters with a new rub bearing and good strong pull at the dust hood to keep the table free of chips. Iím at a loss here so any help would be greatly appreciated.
From contributor J:
If you don't want knife marks, you need to sand them. There are profile sanders for this, but you still need to hand sand some if you want a quality product. Who is telling you to stain right off of the shaper? Are you doing any further sanding after the widebelt?
From the original questioner
Yes we run everything through the wide belt after assembly and follow up with a Festool random orbit sander. Iím talking about the panel profile only. Yes I would agree a shape and sand would produce a quality door.
From contributor A:
I'm assuming the corner issue is uneven thickness of cut at the corners. Three wheel powerfeeds are tough. It doesn't matter if it was made by NASA or some Italian maestro. Four wheelís are an improvement. Belt feeders are the best for things like raised panels where millimeters of vertical movement are noticeable. Every surface should be sanded before staining. That is woodworking 101. The end grain of raised panels is always an issue. Pre-sealing with shellac prevents over darkening.
From Gene Wengert, forum technical advisor:
A bit of technical info: When machining wood that is quite dry, the fibers often get pushed down rather than cut off (on a microscopic level). We need to cut these fibers off, which is what sanding does. If not cut, the difference in staining and light reflection will show up and look like knife marks, etc. You need to use sharp sandpaper (which means fresh) to cut these fibers. So, change paper or discs much more often, especially in this dry weather which means the fibers are a bit stronger.
From contributor S:
Sand the panel hips before you assemble the doors. Use good, sharp paper and it only takes a few minutes a panel. If you're getting bad cuts at the corners, you may have: planel stock that is not flat, too much pressure on the powerfeed, a dip in the shaper table (which can be brought on by too much prolonged pressure with a feeder. I saw a Martin that was dished 1/32" once).