The bearing on a router bit doesn't care what it runs against, as the outside race is for all intents and purposes 'stationary' compared to the inside race. If the bearing is well lubed and in good shape no issue running it against steel.
The only concern I would have using a steel template is that you could accidentally contact the cutter. I have nicked my wood and plastic templates by accident, and the cutter is spared. Templates can be fixed by bondo or other means, you run a carbide cutter into a steel template by accident and you are buying a new cutter.
That being said, if you used guide bushings against a steel template, there would be no issue. The guide bushing usually allows more clearance away from the bit than a bearing guided bit, therefore less chance of the bit contacting the template. (note I said LESS chance, not NO chance....)
Thanks for the reply. I ask about the steel because i have access to a laser machine at work. I wont use the steel templates all the time. but i want to use the steel ones to make plywood or mdf ones. I just didn't want the bearings blowing up on me.
Not all double sided tapes are equal. Some hold better than others. One problem with the lesser ones is that your pattern can creep under the sideways pressure of the router pushing against it. I like using hot melt glue in some of those cases. It holds pretty good against sideways pressure but will usually pop off easy enough when pried on. For paper patterns glued onto a template I like Lee Valley's Fish Glue. It is water soluble so a few spritzes of water on the pattern and wait a minute and you can peel the pattern off and wipe up the residue. Spray adhesive works too but it is more costly and you need mineral spirits to clean off residue. It is much faster than waiting for the fish glue to dry.
For working with paper patterns on the gears I've been working on since late-Nov., I covered the workpiece with blue painter's tape and then used spay adhesive to glue the pattern onto the blue tape. Once done, the tape peels off easily without leaving any residue. I've used that method more with scroll sawing, but it works just as well for bandsawing, sanding and routing.
I would be VERY careful about using such a "thin" layer between your workpiece and pattern if using a bearing or pin guided cutter. Very difficult to get the cutter height just right so it cuts only the workpiece without touching the pattern. I've used pieces of heavy card stock, ~1/16" thick between my work pieces and patterns, whether it has been using bearing guided or most recently, pin guided.
To connect or join the pattern with the workpiece when using pattern boards and the heavy card stock, I have used dowel pins mostly, but recently, when cleaning up the gear gullets and the tooth pattern on the pattern didn't match that of the hand-cut gears, I used undersized, low profile aluminum binder screws and used another lather of heavy card stock under the whole assembly as a spacer for the post heads.
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