Profile Cutting Cutters and their Bearings
I have two CMT extension arbours and as I use the shown piece of 10mm aluminium as my router plate then I need to be able to get more cutter height and the extension arbours allow that, I have seen a few comments that have said that router plates do not need to be bolted down, I would never allow that and this plate is held down with 8mm stainless steel bolts, my 4mm ¼ Carbi-Tool rounding over cutter is shown in photo 1 and is seen peeking up through the plate, it is fitted to the ¼ collet “CMT Extension Arbour”, this small cutter comes with its own bearing and as this cutter never really has that much heavy load on it then this cutter works very well as it is and I use it for both “Straight Work and Profile Following” (I have also said that these small bearing do not last forever, no bearing does as spinning them at Router Speed is nominally faster than their rated maximum speed and I have often been amazed at how much hammering these tiny bearings can take before they cry “enough”, bearings run at router speed do have to be replaced) but what can be done with the 32mm full bullnose cutter in photo 2 as that has no built in bearing?
The full bullnose cutter is shown with the ½ inch CMT Extension Arbour and beside it is a JAF bearing that has a nominal ½ hole in the centre. JAF only have a few bearings that have a ½ inch hole but I was very happy to find them as I had tried many ½ inch ID bearings to see if they would slip onto the ½ inch cutter shafts and others that I found never did, It seems that bearing manufactures have a +/- tolerance and the manufacturers never go “oversize” so if the tolerance of a particular bearing is less strict then that makes it undersize, or if the plus or minus is larger with a bearing manufacturer then it is always “undersize and never oversize” and being that, then they may be able to be pressed onto a ½ inch stub, but they will not slip onto a ½ inch router cutter freely or without being loose, I was told that Japanese Bearing Manufacturers were very exact and the +/ - variation was far less and I found that to be true, the JAF bearing will not be the only ones that will slip onto a router cutter shaft, but I stopped looking for any others when I found that they would slid on very snugly.
Photo 3 shows the extension arbour assembled with the bearing on the shaft of the 32mm bullnose cutter and photo 4 shows it mounted in the router table.
This cutter is the most dangerous cutter that I have and it will rip the hand off any careless user, it is very dangerous, it is so large that it will not pass through the hole in the router plate, so I fit it into the router from the top and I “fully lock off the plunge feature of the router” as it would be a total disaster if the router opened out, while the cutter was running, however with a bearing fitted between it and the extension arbour then the bearing lets me rest on that bearing as I run fully shaped, yet fully rounded over components and the jig that I use with this cutter is a whole story on its own, were I not able to fit the bearing this way then I would be restricted with this cutter and it would be worthless to me, I would not be able to use it on curved parts and I would only be able to use it with a fence and on straight parts, that is not what I bought it for as I use the Router Table as a Profile Shaper, I cut the item just a small amount over size on the band-saw, then lock the item into the suitable jig and I let the cutter take away the small excess and finish it to size in one operation and that only leaves sanding.
Making a jig that has a built in “profile pattern” that will rest on a heavy bearing and then running the jig that holds the workpiece past the cutter, as the cutter brings an item to its finished size, and profile, is what a Profile Shaper does, it is advanced Jig making. It is an issue that the bearing and the cutters are not the same diameter, or 1 to 1, however they never normally are so the jig is made so that the pattern has to be offset or set back by whatever the difference is, that is that if the bearing is 32mm and the cutter cuts at 28mm then the jig has to be set back 4mm so that the finished size is correct. I do have several single and double bearing flush trim bits that are normally not larger than ½ inch and they have the bearing or twin bearings on the top of the cutter, the same as the small 4mm rounding over cutter in photo 1 but I do not like to lean onto and load up a bearing that is at the top of a high speed cutter that is also well up out of the Router Table and then also load up the shaft of the ½ inch cutter with the weight above the cutter, there is an issue with the cutter length ratio in regard to where the bearing is placed height wise and where the top of the cutter will cut so I have found that flush trim bits will only work some of the time. I normally sit the bearing hard up as there is normally a very nice lip that will stop the bearing creeping up however there have been times when I have needed the cutter to be higher so I have uses a ½ stop collar above the bearing as doing that lets me get the cutter higher.
There are some 19mm cutters that have a ¼ shaft and they also have the bearing between the shaft and the cutter but I have not seen any where the cutter length is also long enough for what I do, that is that even by lifting the cutter/bearing up a long way, up to the very underside of the workpiece, then the available cutting length is still not long enough and the Profile pattern is too close to the workpiece, and again, I do not like to load up a heavy 19mm cutter that has a ¼ shaft anyway, This will be more clear when I post the photos of the finished “Profile Copier” I did say before and will again, that this is very dangerous to have a large high speed cutter sticking up a long way out of the Router Table, I still have all my fingers because I am very careful.
Photo 5 shows the same arbour and bearing but this time with a 19mm straight double fluted Carbi-Tool cutter and photo 6 shows it mounted, this is the rig that I use for square edge profile cutting and I do also use other double fluted cutters including up to 30mm, this is not the cutter that I will use for the 12 sided Lathe Tools as I will need a longer one for that job, I will be able to sneak the profile pattern up and just under the new handle blanks but at this minute I think that I will need a working cutter length of over 60mm from the bearing to the top of the cutter.
I do have some solid tungsten spiral flute cutters that are sweet cutters and they have always cut very cleanly so I was happy to see that the JAF bearings will go onto them as well as they go onto the other ½ inch cutters that I have. This type of cutting puts a very big load onto the bearing but a big bearing like this can carry that load however I am still very careful to not load up the cutter with too much weight and to not over heat these bearings as a Router Table is not a Spindle Moulder, Spindle Moulder’s normally have a low speed race bearing that is not attached to the cutter head so they do not spin at Spindle or Router speed. This rig set up works very well, the CMT ½ inch extension arbour and the solid JAF bearing mounted onto the shaft of the cutter, but below the cutting, the extension arbour can lift the rig high enough to reach up to the workpiece height that I have to reach, and in regard to the new Tool Handles, then once that overall height is known then I will set the height of the Profile Pattern so the bearing will rest onto it or, the height of the cutter will be set by the needs of the new Rotating and indexed Profile Copier and then the Profile Pattern’s height will be set by the height of the bearing. Bearing onto pattern and cutter onto the new handles, that will all work fine and the last thing is that as the “Profile Pattern attached to the Router Copier” needs to be fully supported and resting on the “Bearing with the cutter”, all the time from “Before it touches the workpiece to after it leaves the workpiece” so then the profiler pattern needs to have “run-in and run-out portions built in”, that way the run-in part of the Profile Pattern can be moved up into contact with the bearing and then run in gently to contact the workpiece cleanly and that the bearing will stay in contact with the profile pattern until well after the cut is done and contact ceases, I will show photos of that.
The new box is being made so that the Profile Pattern can be changed for a different one, that different Profile Pattern may also be set at a different height, to suit whatever is being made, multi-sided Objects will get cut with the workpiece fixed via an indexing wheel with the required number of indexed stations and round objects can be copied one after another with the chuck rotating. I did see a U-tube Video of a bouncing Router Copier where the workpiece rotated and the Router was going up and down on what appeared to be a Hockey Strap type Spring, it is my opinion that that is not the way to make a Router Copier but me seeing that video was interesting, that device could make copies of Chair Legs or other Round Components however this new Router Copier of mine will work perfectly and be a lot safer, as always I have a lot to do and making this Jig is being done in my spare time so it will still be a bit of time before I can finish it. NGM