Working with Resawn Moulding Blanks
From contributor W:
One of the things I learned about resawn lumber the hard way is that you have to use it right away or it will tend to cup pretty bad. For example: if we were resawing a 3 1/2" paneling out of 4/4 for the moulders with a finish product thickness of .343 and I let the resawn lumber sit overnight on the shop floor it would almost be unusable. The wider and thinner the resawed piece the worse it is. I think this happens because you are only opening one side of the grain of the board when you resaw to new drying forces.
From contributor J:
There are a few profiles that we run that we have to resaw hard maple. Every time the two halves bow toward each other due to stress relief, some to the point we can't use. In most cases the profile is so thin they can still be used. Try a small order and see how it works out.
From contributor F:
Here are some tips on running resawed lumber I've learned over the years. Make sure the lumber has been conditioned in the kiln to relieve stress. Do a prong test before ripping or before resawing to make sure there is not stress or case hardening. That will minimize the "face bow". Specify "no tentions" on your P.O when you order from a sawmill. If buying from a distributor, make them understand that you will send it back if it has not been conditioned.
Since you will have some face bow anyway, it's better to run the resawed face "down" when moulding so that the pieces don't jump on top of each other. When running beveled patterns with the resawed face down, you will have to take an extra 1/6" off with the #2 head (inside head) because the top edge of the board will not be touching the fence. That is because the edge is not 90 degrees to the resawed face.
When running beveled patterns, adding to the width of the rip allows more clearance in the thickness. Draw it out on a piece of paper and you will see that as the rip size gets wider, you have more clearance on the thickness. If you are trying to finish at .500 and the resawed blank is only .580, you need to rip wider and you won't lose as many pieces due to skip on the face.
My rule of thumb is to have the blank at least .100 (one hundred thousandths) thicker than you want to finish and even then that requires a nice smooth resawed face so that you only have to take about .030-.040 with the first bottom head. I've always run Baker resaws in order to get the tight tolerances and smooth resawed face.
After the resaw, band the resawed blanks just like you would a unit of moulding you are getting ready to ship. The wood will only cup and bow if it is allowed to. Let it sit around loose in a cart and it will be difficult to feed throught the moulder. I always surface my blanks before resawing them. On 4/4 lumber, I hit and miss to 1". That way when the two pieces come out of the resaw, they are the same size (if I set the resaw up correctly) and can be put into the same buggy and fed through the moulder one after the other.
Otherwise, if you resaw blanks that vary in thickness, then the bottom piece (on a horizontal resaw) will always be the same and the top piece will always vary in thickness and you will have to set the moulder pressure elements and feedwheels differently for the bottom piece than you do the top piece. You can bet that the top piece will not feed very good and you will wind up with burn marks and skip. I guess that's enough, good luck with the resawed blanks. If you are selling to distributors, you have to resaw 4/4 and 5/4 to meet their price demands.
Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?
Have you reviewed the related Knowledge Base areas below?