We have an older Weinig Profimat 23E - 5 head. If I am NOT running any grooves in the back of the molding, Can I just take all the bottom material off with the first head and leave the 5th head off in these cases?
Is there any practical reason for removing another 1/2 mm from the bottom with the last knife?
Same question with our flooring - we run face down and to the back groove with the number 4 top head. We hand-plane and sand the face anyway, so is there any reason to remove another 1/2mm from the face with the last #5 knife?
My thought is for most of the time to not use the #5 head unless I am back grooving something run face up - there fore to leave that last table in the same plane as the middle tables.
The last bottom cutter head is very important. The purpose is to remove any lubrication used on bed plates prior to the last bottom cutter head, if lubrication is left on the wood it might affect the finishing process, if bed plate lubrication is not used then you can expect faster wear of the bed plates of your machinery, it can also cause feed issues while milling.
There is generally a .020" shim under the outfeed bed plate, it takes .020" of cut to create enough wood chips to keep the moulding knives cool.
Milling flooring face down is a good option because it allows two cutter heads to mill the face of the lumber creating a superior product, your flooring milling process is a bit different so I understand the question.
Many folks use a carbide insert spiral head on the first bottom cutter head and a straight planer knife on the last bottom cutter head eliminating and blend lines left from the first bottom spiral leaving a better looking finished product.
I hope this helps
All the best
In that (or similar) case only, there is probably no need for it. But on all others, the last bottom "finishes" the product, which should be run face-down whenever possible.
FWIW, we run a specific head on the last bottom of our moulder that runs flooring. It has a very shallow gullet, which allows the chipbreaker to actually function as a chip breaker on the thin 0.020" chip being removed at that position. "Typical" heads are designed to remove more material and must have a deeper gullet or burning will occur because it will fill with material before its ejected. Even challenging grain such as we see on character grade material comes out almost mirror smooth.
In the end, it's your machine and your product. There is no "right" or "wrong" way of doing anything as long as you and your customers (and OSHA, EPA, DEP, etc) approve.
There are a couple of things to think about as to the use of the last bottom cutterhead. If you maintain a sharp edge on the first bottom cutter and your runs are short, then I do not use my last bottom all of the time. If I allow the first bottom to have minor nicks and to cut rough stock, then the last bottom will help provide a better finish. With the table lubricant that I use there is no concern about the last bottom head. This lubricant evaporates quickly and leaves no residual.
I will state that in most cases I do run the last bottom to improve the finish and to help assure a tighter tolerance in the thickness.
To me using the last bottom head takes away the reference point. You don't use a jointer to finish thickness. That first bottom head creates that ref point. I used mine for primary back relief and notching. That bed lube will evap.
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