Cutting Rosettes with a CNC Router
Hold-down is the big challenge. Here are a half dozen suggested solutions. October 8, 2005
I have a client that would like some fir rosettes and plinth blocks. Any tricks to holding and making these? I have a 58E Northwood with 15 hp spindle and 5'x8' vac table.
Sounds like the perfect candidate for the old "leave an onion skin and then run it through the wide belt face down to remove said onion skin" trick.
You can create a pod type of table by creating a gasket on the surface of your spoil board. Outline where your part goes with some 1/8" thick (1/4 or 1/2" wide) weather stripping or similar material, then drill a hole (3/8" or so) through the MDF spoil board inside your gasketed perimeter, making sure to drill into one of the air passages and not the table itself. This will allow the vacuum to pull the part directly, giving you great hold. Just be sure not to let any dust or wood chips get through the hole, as they will quickly clog the filter in your vacuum pump. When done, fill the hole with Bondo and pull up the weather stripping if it is a one time run. If you plan on doing the same run in the future, you may consider making a dedicated spoil board. I have done as many as 25-30 gasketed parts on a spoil board at one time and they all hold great. The only drawback is the setup time.
I've done these both ways. I have dedicated PVC vac pod type fixtures that cut 4 blocks at a time. I've also held down approximately 12" x 24" blanks (any normal method works well here) and not cut all the way through. This cuts 12 to 18 blocks at a time depending upon size, and is my preferred method.
We have vac pod hold down rather than through vacuum, so I either use the pods or screw the large blanks down to the MDF spoilboard table. We have to leave about 1/4" at the bottom so the board stays stiff. As such, we have to band saw the blocks apart and sand the edges. It's still much faster than precutting the blocks for the 4 at once fixtures.
If this is an ongoing thing, why don't you look at a small dedicated automatic rosette machine instead of tying up your CNC on small ticket items that are a problem to run?
I agree with the above. If this is not ongoing business, I would run from this project. If it is, you can buy a dedicated rosette machine with hopper feed for about $4500.00 that I think will produce about 10 parts a minute. Unless there is some intricate 3D carving that you can charge good money for, you're not going make money on your CNC. Rosette cutters also require very slow RPMs.
I have done quite a few rosettes on the router, primarily because it works much better than drill press type cutters in difficult woods. As you probably know, fir is one of those difficult woods. I simply use a classical plunge bit with the innermost cut on a radius, which leaves the common small dimple, then plunge out a little further and deeper to create a common looking bullseye. My setup is to s4s the stock in longer lengths, say 2-3 feet, and simply cut the rosette on one end of board, flip it, run it again, set the next board up, then cut to length on a chop saw. A few small locating cleats and a toggle clamp as close to the end but out of the way secures them. You can actually produce these fairly quick for special projects, though I wouldn't want a steady diet of them.
The Mikron R200 Automatic Rosette Machine will do 300 to 1000 blocks an hour. It turns at 7500rpm. It's quick and easy to set up and you don't have to stand there - you can do something else while the machine is running your block. No jigs required.
Come on - there is no other source for fir, hemlock, or green leaf fruitless mahogany rosettes, but you're not going to let that force you from a good job. Particularly if you have a machine that can do them quite easily and you sure as hell wouldn't spend $4000.00 to make 10, 50, or even 500 rosettes. Grab a bit, spend a couple of hours, step out of the box, and git 'er done.
We make rosettes as we need them on our PTP. Just made some today! I wrote a parametric program a couple years ago that lets us enter the finish size of the rosette in DY and the length of your stock in DX. We use a board about 1/4" wider than finished size and long enough to cut all the rosettes we need. The program starts by cutting the rosette pattern in the center of each block. We have a dedicated rosette cutter. Then we use a down spiral carbide bit to work down the length of the board, cutting between the rosettes, leaving about 1/16" skin. The program will only cut as many rosettes as will fit on the board (DY). Next, it climb cuts the inside and outside edges for exact width and to clean up any blowout from previous cuts. We can also "profile" the edges if needed. After taking off the PTP, we use a chop saw to separate the blocks and then kiss them on the edgesander to remove what's left of the 1/16 skin. This works pretty well. Can make a couple or 20 pretty quickly.
I just recently had to make 35 rosettes that were pretty detailed. I tried everything - I made them on the lathe with a Grizzly rosette head in the tail. I have a Weinig grinder, so I made the knife myself. I also made a faceplate so you could center each one with only two screws. The only material that would not tear was ultralight fibre. It was a pain, but they came out great. I charged $10.00 each, but it was not enough.
Rosettes are our type of (small) thing. With the onion skin thing, you have to do secondary processing. With weather stripping, if the gasket is 1/2" wide and the rosettes are 2" wide, you will have lost one half of your vacuum surface area before you start to cut. I think that 1/8" is too thick - you get too much of a Jell-O effect on the material being cut. Another contributor advises screwing down the large blanks, but you have a vacuum system you want to employ, and vacuum setup is quicker and less cumbersome than clamping and bolting. Others want you to purchase another machine.
We sell zone board cover. It is a foam sealant cut to the exact width of the fir (or any other board foot material) that you are buying. Zone board cover allows the operator to design a custom rosette gasket using his current CAM program and cut a custom rosette gasket using his current 58E Northwood CNC router. Setup time is quick, approximately 2 times the cycle time for cutting the rosette. Cutting small parts does not have to be a big headache.
It sounds like you are saying you can hold a typical 3" x 3" rosette blank in place for machining with the zone board cover material. It seems hard to believe you wouldn't get some shifting and/or twisting due to cutting pressure. Could you also make a 1 or 2 pass perimeter cut to bring an oversize blank down to size after profiling the face?
Pin nail your product to a backerboard. We do that for small items (MDF drawerfronts, wood bar doors).