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Dowel Hole Telegraphing

8/22/19       
Stewart Member

I've been doweling my cabinets together for a while and have never noticed this issue before - hoping someone has some insight as to what needs to be adjusted. The last couple of projects, my dowel holes are telegraphing through the finished ends (I do integrated finished ends). In all normal inside lighting, they do not show up but as soon as I take them out into the direct sun and angle them just right, there they are - sticking out like a sore thumb. My plywood (armor core with the mdf band right below the finished surface) finished end thickness is .725" and my dowel hole depth is .65" which allows a small gap of .047" so that my dowels don't bottom out. There was no debris left in the hole during assembly and glue is metered very carefully. Why is this showing up all of a sudden? On some units we were assembling today, I spot lighted the finished ends before assembly and sure enough, I can see them before the cases have even been squeezed together. What is going on here?

8/22/19       #2: Dowel Hole Telegraphing ...
Leo G Member

.075" is pretty thin. I assume the telegraphing is an indent and not a pucker.

Leave a bit more meat on the end panel and it should go away.

8/22/19       #3: Dowel Hole Telegraphing ...
Jared Emery

Just a thought, but if your dowels are too tight or not fluted enough you might be creating some hydraulic pressure with your glue and bulging out the ply. Another scenario is the MDF layer in that armor core is swelling from the water in your glue. I'd agree that your dowel holes are pretty deep.

8/23/19       #4: Dowel Hole Telegraphing ...
Stewart Member

Okay, so I noticed the dowel holes under spot light on this last batch before assembly - so, I know this isn't a hydraulic lock issue or mdf swell as the glue hadn't been applied yet. And, it is slightly convex - not sunken. So, I am wondering if I am just drilling too deep and somehow just now noticing (although that's a little hard for me to believe as we are all around these things from different angles through the process). Or, could my 8mm bit just be starting to dull enough to compress the mdf as it nears full depth causing enough tension for it to "pucker" as Leo put it?

8/23/19       #5: Dowel Hole Telegraphing ...
Leo G Member

If you've been at that depth all this time and not had the problem, a dull bit sounds like a pretty reasonable conclusion.

Or it might be that you are just noticing it and it's been happening all this time.

Simplest solution is change the bit, do a test and see if it's still an issue. If not you're good to go. If it still is then drill less deep and don't puncture the MDF outer band.

8/23/19       #6: Dowel Hole Telegraphing ...
Stewart

I'm just curious - how deep do you guys drill your face holes in 3/4" material and what kind of a gap are you leaving from the end of the dowel to the bottom of the hole?

8/23/19       #7: Dowel Hole Telegraphing ...
Larry Schweitzer Member

We almost never use ply so our settings may not translate. I checked several piles of material being run now. 3/4" melamine measured 0.755 +- 0.003. 8mm hole depth varied a bit with the thickness of the panel but .615 to .620". Dowels are inserted on a CNC bore & inset machine that is fairly consistent. Dowel stick out was from .495 to .500. When the cases are being assembled our glue injector is set so we don't get hydraulic lock. I. E. some air space. Cases are clamped in a Gannomat Concept Primus 90. We just happened to have some cases made last week with veneered MDF finished ends. I put a light on them & couldn't see any dowel telegraphing. So the least space we were leaving was 0.115".
Like Leo said, change your bits to see if that fixes the problem. Or leave a little more meat/thickness or air gap. There are slight variations in dowels also. Maybe it is just a case of all the tolerances/variations adding up.

8/23/19       #8: Dowel Hole Telegraphing ...
Alan F.

For a 19MM panel we do 15MM depth (30MM dowel /2), maybe you need to put a little more in the horizontal members for thinner materials.

We go a little deeper in horizontal members to account for glue space.

8/30/19       #9: Dowel Hole Telegraphing ...
Bruce H

I drill 16mm deep in a 19mm panel using a 30mm fluted dowel. I'd ask if you insert the decks with dowels and apply the end panel, or, the other way around? What are you clamping the joint with? How much glue are you putting in the hole and are you applying it to the side of the hole or in the bottom?

9/7/19       #10: Dowel Hole Telegraphing ...
Stewart Member

Yes, I do insert the decks with dowels (Gannomat logic) and then apply the finished end panel. Glue is metered into each face hole of the finished end and, yes, it is applied evenly to the sides of the hole - not the bottom.

9/7/19       #11: Dowel Hole Telegraphing ...
Bruce H

Looks right to me. Maybe try drilling a smidge deeper.

9/16/19       #12: Dowel Hole Telegraphing ...
Stewart Member

Okay, I just wanted to report back - I put a fresh bit in and adjusted my hole depth to make it slightly shallower. I spot lighted the finished side and so far, no telegraphing or "puckering". I'm amazed at what a problem a dull drilling bit can create. If only there was a way to keep track of how many holes each bit drills so I could have a better handle on changing them before this kind of thing happens...

9/16/19       #13: Dowel Hole Telegraphing ...
Oggie

Just drill a line of dowel holes in a piece of scrap board before starting a new project and examine the results. That will show you bad bits or incorrect setting (holes to deep).
Also, you may need to adjust hole depth for the material you use. I regularly use 3/4" plywood sheets but sheets from different manufacturers (although all are 3/4" in nominal) may differ 1/8" (or more) in actual thickness. Melamine boards not so much, but still somewhat.


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