Taper Introduced by Edgebander Premill

      A discussion of the milling accuracy and adjustment tolerances of an edgebander with premill heads. December 2, 2010

Question
We have a Holz Her 1321 edgebander with milling heads. We cut our parts to size, then remove the thickness of the banding with the milling heads. We change from melamine to plywood to MDF, from applying solid strips to PVC banding. We change the bander back and forth a lot.

Our problem is consistency. Our parts often come out with a taper of up to 1/32" in a 3' piece. This makes the joints of our cabinets look terrible. Is this normal? We spend hours trying to set the bander up. When we get it set up good, we have to change to something different and fight the process all over again. Should an edgebander be able to change regularly and still keep a decent tolerance of say +/- .008 from one end to another, or am I asking too much?

Forum Responses
(Cabinetmaking Forum)
From contributor J:
Maybe you could do the math (add or subtract edge thickness) at the saw, i.e. 1mm, 3mm, 15mm, etc., then leave the bander to remove a fixed amount, say 3mm, to clean and prep the edge. Every crank or movement introduced after the machine is dialed in brings error. 3mm removal with pre-mill station should clean up any chipping or square issues. Maybe you require more width/length tolerance, but I'd get it at the saw, and leave the bander settings untouched as much as possible.



From the original questioner:
Thanks, but we cut all our parts on a CNC nested router and use banding that varies in thickness. Changing our programs accordingly for different banding widths is involved. Sometimes the banding on the bottom edge of a wall cab is different than the face banding. I'm trying to find out if our bander is normal or if we need a major tuneup.


From contributor R:
Sounds like it could be some very simple things that need adjustment. First off, clean your track thoroughly, especially buildup on the underside. Then check the squareness of your infeed fence. Worth a try.


From contributor C:
Why are you pre-milling off the CNC? This is unnecessary. The cut should be smooth and square. I think you should turn the pre-mill off. The bander needs a cleaning and tuneup and the infeed needs to be aligned.


From contributor S:
Because he wants to remove the PVC thickness at the edgebander, not at saw or router.


From contributor C:
Well, okay. But in the grand scheme of expenses, the labor and sharpening will add up and add up. Why sharpen two items when one is enough?


From contributor P:
If you are spending that much time and energy adjusting the machine, it would pay you to get Wayne Korbler or Lee Johnson in to your shop to correct this problem. It may be that a fence has moved or something else that is not a normal adjustment. Regardless, your problems are not normal for a bander.


From contributor Y:
Too many variables to provide a simple answer, but it certainly sounds like your bander is way out of adjustment. As mentioned above, I would call Lee Johnson. Get your bander right and your life will be much easier, however you choose to process your parts.


From contributor I:
I think you are taking off too much at the pre-mill. .5mm is best, or ask you rep. The purpose of pre-milling is not to compensate for banding thickness, but to create an optimal surface for applying glue and banding. CNCs are known to make less than ideal gluing surfaces, so do not turn off the pre-mill.

There is definitely something wrong. When I read your post I thought "definitely a saw issue," until you said you cut out on CNC. But you should confirm that your parts are square off the CNC before overhauling the bander. CNCs do go out of whack.

The only part of the bander that can change the squareness of the panel is the pre-mill. If the pressure to the milling unit cylinders is too low, or you are removing too much material, they could be deflecting under a difficult cut. This would also create an inconsistent problem that would not show up on every cut. If your infeed fence is out of alignment, this would cause the taper, but it would do it on every panel, not sometimes. If you have a bad section of feed chain or a few bad pads in the same spot of the chain, this could cause the intermittent issue. Finally there is operator error. Everything in the edgebander floats, so slight misalignments while feeding do not usually cause a problem. Except the pre-mill! This requires perfect alignment or the panels will be tapered. The operator needs to be very certain that the work piece is fed in straight. Always push in at the rear edge of the piece as the feed belt grabs it.

If your parts are good before the edgeband, and bad after, the only thing that could cause this is the pre-mill. I would start by only removing .5mm. I do not see why this is difficult for you to do. Just make sure you are using the correct banding in the material list and it is correctly measured.



From contributor W:
I would have to agree, you're removing too much at pre-mill. I don't have a bander with pre-mill, but gather it is used to produce a chip-free, square, freshly milled panel edge, in preparation for edgebanding. I would think you could hit that in a .5-1mm range.

As far as different band thickness, that should be easily compensated for in the router, leaving only a panel height and glue height adjustment at the edgebander, no? The less monkey fiddling with adjustments at the bander, the better.



The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor E:
Contributor I is on the right track. I think we are as usual in situations like this, trying to diagnose too deeply. I have 29 years of experience working on HH edgebanders and have encountered many odd issues and usually find that most issues are simple but the solution is sometimes illusory.

The giveaway to this problem is that the problem varies from panel to panel. First, I would watch panels of several lengths travel into the machine without anything touching the edge of the panel past the in-feed fence. Move everything back away from the panel's edge, including the glue station, and watch to see if the panel moves away from the in-feed fence. If not then the in-feed fence is aligned to the conveyor. If it does move away then the fence is not aligned and there is a procedure for aligning the fence, but is too detailed to go into in this message. However, if your machine was properly set up then the in-feed fence should have been pinned into position when installed. I would contact Holz-Her technical service and ask them to assist you in the proper method of squaring the fence and/or aligning the conveyor chain.

My thoughts are that you do not have enough downward pressure on the upper beam rollers - the front end panel is being pushed away from the pass line by the side pressure of the glue station or the pressure rollers and trimming less on the front than on the rear panel. I have seen this on other machines. There should be 2.8 to 3 mm of compression of the upper rubber beam rollers throughout the entire length of the machine. You can check this by raising the beam and placing 6" x 12" panels on the conveyor pads and then lowering the beam down until the rollers just touch the top of the panels. The rollers should touch all at the same time. Take note of the reading of the beam position on the mechanical digital, or if fitted with a servo controlled, the beam on the screen. This number minus 2.8 to 3 mm should equal the panel thickness.

Extremely dull cutterheads or too much speed on thick stock removal can cause this as well. Cutterheads that dull or too much speed will usually cause chipping.



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