Hello all, I am new here and I Need some professional advice. Until recently, our company has built commercial cabinets using a pocket screw system. We are in the process of switching over to a doweling operation and have acquired the proper machinery to execute our goal. The issues arises in the quality of our product when we use our new system. The majority of the cabinets built with dowels are coming out with misaligned faces and a minute few are coming out near perfect. We are cutting our parts on a Felder H10 16 38 nested CNC, in which the doweling operations are done first and then the parts are cut to size. We edge band our parts on a Felder Tempora 60.08 which is freshly calibrated by yours truly. Our horizontal boring is done by a Homag D200 which drills and inserts the dowels. From there everything is sorted and put into a case clamp for final construction. I have worked on this issue for 4 months, most leads tend to point to my CNC machine.
- I've measured the compression bits with calipers to make sure they are set right in the CNC control.
-I've had Felder out to do a overhaul on the machine and check it for square and look for faults.
- I've checked Microvellum for any settings that may be causing an issue and found nothing.(our engineer is amazing at this program)
- our horizontal boring machine has been calibrated and is practically brand new.
- I've even tried to see if our dust hose (which is 10 inch and 15 foot long) is pulling the CNC out of alignment slightly during operation.
I've hit the end of my knowledge base of this subject and would greatly appreciate some input on the subject.
Thank you,

Why would you go back to dowels ? Were you having problems with the pocket screws ?

We are returning to dowels to increase production capacity. I wasn't the one who ultimately made the decision to switch on this but I am the primary one tasked with getting it to work.

Instead of guessing where the problem could be, why not just use digital calipers and find out exactly where it is?
Cut some parts and drill holes. Do not edgeband.
Dry fit parts (without glue) and find those that produce misaligned faces.
For the faces to be flush, dowel holes need to be at the exact distance from the front edge, for both vertical (drilled on CNC in your case) and horizontal (drilled on Homag) holes.
Measure which one are not and you'll know where to start troubleshooting.

Im with Oggie, run some parts dry, no banding, and see whats up. You said though that some come out ok and others dont? To me that sounds like running a batch of identical cabinets some cut and dowel together good and some dont? If thats the case the issue should be pretty easy to track down. Either parts in some part of the nest are being cut improperly or there is some operator error in the edge boring.

If all is good there you on to the bander which would only be an issue if your running pre-mill.

4 months would seem you'd know if the first and the hundred and first part are coming off the CNC identically, and if so you know its in the next step.

We fought this for a while as well. Like the other said, test parts with no banding. The biggest help we found was adjusting the bit diameter in the cnc.

Do a square test on the cnc, Cut a 100mm x 100mm square x15mm deep in a scrap piece. Measure that with calipers. If its plus or minus the 100mm that it should be it will affect the doweling. Adjust the bit diameter in the cnc tooling till it is cutting exactly 100.00mm x100mm on the caliper. Doing this with every bit changed helped dramatically

Down and dirty way to check if your CNC is the problem. Take matching pair of machined sides insert some dowels (no glue) in one side, now put other side onto dowels. You will easily be able to detect if there is an alignment problem. You can do the same thing for horizontal boring by using two cabinet bottoms.

We just had in issue with cabinet vision and I was teaching my guys how to troubleshoot problems
Write things down to keep track of your steps
Run test parts
Check that they are the size they are supposed to be
Check parts are square
Check part thickness matches material thickness in your software

If part is correct size move on to holes. If not troubleshoot why part size is off

Measure your holes with calipers
Are they where they should be?

Make changes and repeat till you find problem

Make sure your software guys are actually looking at their code! We had 2 issues that literally came down to me yelling at software guys HAVE YOU EVEN LOOKED AT YOUR CODE IN THE POST?
Nope
Another thing. You can’t have both true and false answer to same question

Check the accuracy of the drill block to the spindle. Cut a square and drill a hole in the centre. Measure all 4 dimensions. We adjust to 0.001.

If the spindle was squared up recently this may need to be adjusted.

Are the drills in all machines running true?

Is there dust buildup on the location fixtures on the Homag?

Set the tops and bottoms 1mm back from the sides - the difference between 0.0 mm and 0.5mm is obvious, the difference between 0.5mm and 1mm is unnoticeable.

I set up my dowel system right from the get go as I figured to go CNC and gain the production advantages, dowel assembly was a must. And you can't beat dowel assembly for speed in my opinion. I do add an assembly screw between the dowels on a stretchers just in case of glue failure on a two dowel joint, but other than that all dowel only in the joints.

I think dropout is on the right track and you should start with the drill block and make sure it is alligned to the spindle correctly. There is an offset that the cnc uses to tell it where the router head is in reference to the drill block. If the refference is off in any of the four directions you will get a missalignment. and you could have two missalignments that add up to a perfect allignment.

The way that I set mine was to make a 1/4" x 1/4" x on a panel and then make a hole with a 1/8" bit right in the center of the x. make sure that you place the 1/8" bit in the drill block in the same location where you will place your 8mm bit for dowels. The small hole in the 1/4" x 1/4" cross makes it easy to see where and by how much to adjust. Keep tweaking the offsets till the block alligns with the spindle. Then run the pattern 5-10 times on different spots on the table to determine accuracy on repeatability.

Once this is working well you can go to the boring machine and start checking it. I have had machines that were not perfectly parallel to the table all along the bore path and while this did not affect the flush front to back it would through the flush side to side off some.

I started with a maggi 21 spindle, then an accusytems H23 and was able to get acceptable results with both but not perfect every time. The overlay doors and hinges and slides of the euro construction system was always enough to make everything look perfect after doors and drawers were on.

We drill for 9.5 off the bottom with out banding.

Therefore our doweler is registered to drill off the exterior of all case parts.

The software cuts 1/2mil off for wall ends. None for the base and tall cabinets.

Hope this helps

I think you need to examine your part holding. It would be impossible for some cabinets to be correct and some not if the program is correct and the machine has been checked like you say... drilling first then profiling might make the part move slightly depending on your vacuume and tool pressure ... just a thought... sometimes it's the simple things we overlook ..