Planing Warp out of Wood Flooring Stock

It requires hand labor, but you can use a moulder to straighten warped stock up to a point.June 28, 2013

We are manufacturers of hardwood flooring in India. Can anyone guide us on how we can straighten the warped wood pieces on a four side moulder? We have four side moulder with seven spindle arrangement. When we set the first surface planing spindle we are unable to straighten the warped piece as the spindle doesn't takes out warpage, but only planes the piece.

Forum Responses
(Solid Wood Machining Forum)
From contributor O:
Typically the stock is prepped by a Straight-Line Ripsaw - SLR or a Gang Ripsaw. This establishes one straight edge, and then the width is established from that first edge, making a straight blank of consistent width. Some molders do have infeed edgers that can remove about 3/8" of concave/convex edge. These machines have long infeed tables 5' or longer.

From the original questioner:
Thanks. I am not talking about the width part, I am talking about the thickness part.

From contributor O:
It will depend on the volume you wish to process, but a top/bottom planer will take out a lot of warp and get lumber to a consistent thickness for molding. Or a single head planer can be used to flatten a bit and get consistent thickness. The best practice is to minimize/eliminate warp by drying the stock properly and wood selection. Not all woods will make moldings.

From contributor F:
Contributor O pretty much covered it. I used to feed a six head molder and found in general warped stock in equaled warped stock out. It did have the ability to take a bit of warp out on thick pieces, but in general the feed pushes the stock flat as it enters the machine and so unlike a jointer doesn't really make it too much flatter. For most moldings we left well enough alone. If we needed something to be flat we would often have to face it on the jointer and follow up with a pass through the planer - very time consuming. Although I haven't run one you may also want to look into a machine like the Oliver Straight-O'-Plane which is supposed to get wood reasonably flat in one pass.

From Dave Rankin, forum technical advisor:
A moulder, if it has a long infeed table, is designed to take the warp out of wood.

Here are the limitations:

1. The longest piece that can be straightened is no longer than the infeed table.

2. The side pressure rollers and the overhead pressure rollers before the first bottom head need to be moved out of the way so they do not touch the wood.

3. The amount of warp or bow must be taken off of the bottom head. So if you have 3mm or 1/8" of warp then set the infeed table to remove at least that much material.

4. The wood is then hand feed, 1 piece at a time, until the rollers after the first bottom begin to feed the material.

5. It is difficult to do this and run end to end with the material. This is the reason most people do not attempt to do this. If you can run one piece at a time and then reset the infeed table for each additional piece then you can straighten material.

From contributor J:
You can use stress relief in wood to help you in some cases. Pre-plane your blanks. Using the bed adjustment on you moulder make sure the most material is being taken of the top (hump) of the blank. If you use a two sided planer to pre plane you can do the same with that. Providing everything cleans up, yes you can flatten bowed boards by milling them. Often you might need to separate the flat from the bowed and run different table settings for each.

From contributor J:
We run moldings daily. The best way to flatten lumber is with a two sided stratoplaner. You can use you're molder, and without hand feeding ! You need to back off the air pressure on your feed roller before the first bottom cutter, but you must keep steady pressure on the roller after the bottom cutter. If your lumber is real bad, and you have a good rip saw , gang rip before you plane as a narrow board flattens much easier in a planer than a wide one.