Doweling on a Point-to-Point CNC

      CNC routers can be tweaked for accurate dowel boring, but a dedicated boring machine is a better way to go. August 8, 2008

Question
I am trying to utilize dowel construction with my Busellato CNC. I find that parts do not align. Is it possible to get perfect joints using the CNC? If it is, what is the quickest way to calibrate the machine?

Forum Responses
(CNC Forum)
From contributor S:
I haven't run a Busellato in a while, but from what I can remember you need to go to parameter offsets and calibrate the machine from every work field. This shouldn't take long, but you need patience for it. Cut a board 24" x 24" and make a hole program with an 8mm bit at 12 mm from the edge. This will give you a measurement of 8mm from edge to hole once the machine is calibrated correctly.



From Brian Personett, forum technical advisor:
Yes, it is possible - we do it every day. What contributor S said. The horizontal units can be somewhat tricky; I would give DMG a call.


From contributor M:
Yes, it is possible. There are parameters for every tool onboard that can be tweaked. You will probably want to start with aligning all your pins first. Depending on the model, that should not be hard, especially if you have a dial indicator. I have done this on several machines. That said, if you are drilling horizontal holes for dowels, offline line boring machines, or better yet, dowel inserters are the way to go. Do yourself a favor and call DMG for proper alignment procedures. They can talk you through it and ultimately save time. Oh, and back up all current parameters in case you screw up or get caught by the typo gremlin.


From contributor J:
Each of the individual tools on the machine can be calibrated to function within the manufacturer's specifications. You also want to write your programs referencing from the face of the panel instead of using s/2, due to the fact that panels vary in thickness.


From contributor I:
All of the advice above is correct about parameters and tweaking them for the tools to be as accurate as possible. If you have designed in small reveals (0.5mm) I would say go for it! However, if you are shooting for flush construction, in my opinion you are wasting your time. Why? Because flush is the hardest to do the way you are approaching it.


From contributor E:
We have a Busellato B1 and I am perfectly happy with it. We assemble all our cabinets with 8mm dowels. But I really feel that to do it correctly you have to do the horizontal on another machine. We use a HPJ from AccuSystems. Both machines make for a very accurate box.


From contributor B:
I confirmat all of my construction using my Busellato, but I must say my Ayen skb 50 is much more accurate and faster. The only thing that saves me is the fact that you can move the panels slightly with the rubber mallet. I can understand your frustration!


From contributor C:
I have a Busellato Jet Optima P2P machine and have been using the machine for horizontal drilling with great results. I am doing a sizing cut on all my panels. I cut my parts 4 mm larger on the saw, then trim all parts to final size on the Busellato. This takes away all registration issues and my joints line up properly. I have had a few minor issues with some plywood that is not flat, and it warps past the pods - this can be corrected by putting the pods right next to the edge of the material, but you have to be careful as the trimming/sizing cut is a through cut and will cut the pods. I used to have a Gannomat construction boring machine for horizontal drilling, but since I am doing the sizing cut on the CNC I leave the panel on the machine and do the horizontal drilling, and no longer needed the Gannomat.

Another benefit of sizing on the CNC is that the edge quality is much better than with the saw, no scoring blade and edgebanding goes on much better, eliminating the need for an edgebander with pre-mill in my shop. I also find that my panels are straighter since the tension in the panel is removed by the saw, then squared by the CNC.

I also reference the height as a fixed number not the s/2. I am getting great results this way, but there is a time penalty in trimming on the CNC. I was in Europe last Fall and visited a number of shops there. All of them used either the edgebander (with squaring track feed) or a CNC to trim the panels after being cut on a saw. All the shops that I visited said that the surface from the saw was not good enough to edgeband. After seeing the quality of their product I was convinced of that. For my shop, quality of the final product is paramount and a few extra seconds to trim the panel means more for the end product than the time it takes to do the trimming cut.

My machine is quite new and was set up properly by the tech, so the horizontal drills are aligned, but even with proper alignment the trimming/squaring cut is paramount in my opinion.



From contributor K:
There are other parameters to consider other than pin alignment. We have a Busellato 1999 Optima 90 and a Busellato 2002 Jet 4002. One uses Winner 90 software and the other uses Genesis (basically the same). We always would program using s/2 without any difficulties, although we bought an Omal dowel inserter for multiple reasons. Main reason is that it is difficult to dowel 4" wide spreaders on the Busellato, plus with a dowel inserter, you're always referenced from the bottom, plus it's very handy for mitering frames and seaming and for dowelling drawer boxes. Plus it's fast!

As for referencing horizontal drilling in the Busellato, check a few things. First, are the pods in good shape and not slightly different in height due to different pads or maybe replaced housings? The pods must be exactly the same height in order to drill horizontally with success. Pod placement and drill speed are also very important. Also check the belt tension on the dc motors because you will get backlash that will throw things off, especially on the z- axis. There is a socket head nut below the head which you can use to check this.

But even when our machines were running perfectly, it is still very hard to get perfect flush joints. Even with our dowel inserter, it's hard to get perfection. This is just the way it is unless you're using pre-milling in your programming or maybe a flatbed router.



From contributor L:
We run parts everyday on our Rover 321. We get perfect joints regularly. When they aren't, I look at the machine rails and see if they need resurfacing or if we need to change some bits out. Your machine may need to be aligned completely, or just in the horizontal drilling aspect. Start at the pins for and drill in at x and y at 54mm the offset needs to be equal. Use an 8mm bore - checking for depth is paramount. I always use MDF scrap for this. You will need to adjust your machines' parameters.

Second, you need to route a flattening/corrective amount off of your pods or work rails so that the machine is level. Make the correction in the machine parameters.

Third, on an edge bore program, tell the machine to drill at 9mm and not exactly half of your panel. Trust me - this will make alignment of the parameters easier and the drill/construction routines faster.

Make sure you are using a quality set of dial calipers to check alignment; a cheap set will not repeat a measurement.



From contributor H:
Dial or digital calipers are a good starting point, but it's difficult to measure holes without the proper attachment. They arenít really a necessity. Trial and error fit will be required to get the joints flush, both on the edges and surfaces.

However, I've found that it's easier to go with a "shadow reveal." Even if the machine is accurate, and unless you machine the edges with your router, you're at the mercy of your operator's ability to properly locate the part every time. Not to mention that he cleans any sawdust away from and fully tightens any stops that may need to be moved for various size panels. And the pods must be kept clean between loading and unloading panels.



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