Replies

1. 
   hammer1 | Sep 21, 2007 02:47am | #1

   I think you would be asking for trouble. Most bits won't cut at that low a speed, they'll just jam. There may be another way to accomplish what you want, depends on what it is. Chuck one in a drill press and you'll see what I mean, be careful and real, real slow.

   Beat it to fit / Paint it to match

2. 
   RickL | Sep 21, 2007 02:48pm | #2

   Tell us more on the application. An end mill is better at that rpm. The easiest way is to mount a chuck or collet on a jackshaft. Are you putting lateral presure on the bit? If so, I don't recommend a drill press unless the chuck is threaded on. Posting with the application is far more useful than specifying a certain need. Other more pertinent options can be suggested. Your original intent may be so far off base in your application.

1. 
   Rooftree | Sep 21, 2007 06:46pm | #4

   Thanks for all the replies so far. I guess I should have given more info.The application is a smasher of small plastic parts. The parts will be fed into a hopper with a router bit inside. When the motor is turned on, the parts will be smashed. It's a little like an in-sink garbage disposer. Although the application does not involve routing in any way, I'm using a router bit because its size, strength, effectiveness, and price are just right. By the way, I'm using a panel raising bit that's 3.25" diameter. To keep the design simple and the costs as low as possible, I'd like to use a router motor to drive the bit. But even dialed down to 10,000 RPM, it's way too noisy. My options are to use a single-speed router with a speed control unit, or a common AC induction motor that operates around 3500 RPM.If I go with a common AC induction motor, I need to find a way of attaching the router bit. So I'm stuck trying to find a fitting that can couple a router bit to a motor shaft. It looks like the motor will have a keyway on the shaft. But I could probably get one with a D-flat.Any ideas?

1. 
   saschafer | Sep 21, 2007 07:23pm | #5

   Since concentricity and all that good stuff is irrelevant in your application, just have a machine shop make you a small coupler of mild steel, about 1" Ø and 2" long. Have them drill a hole in one end to fit the motor shaft, and one in the other end to fit the router bit. Add four #10-32 tapped holes on the sides for setscrews, two for the motor shaft and two for the router bit. When viewing the coupler end-on, the setscrew holes within each pair should contact the shaft at 90° positions (see attached sketch).

   Do you already have a working prototype using the router bit?

   -Steve

    

   
1. 
   Rooftree | Sep 21, 2007 07:34pm | #6

   Steve,Thanks! After seeing your idea I feel a little embarrassed - I should have thought of that. Sometimes the simplest solutions are the hardest to create. Nice work!The only concern I have now is potential loosening of the set screws. I can install them with Locktite. But a year from now when the bit needs to be replaced, I'm not sure if the service person can be counted on to use it. I'll have to give this some more thought.Mike

2. 
   RickL | Sep 21, 2007 07:44pm | #7

   As one who repairs and builds machines I really think you are approaching it all wrong. You should be looking at plastic grinders, granulators and shredders for inspiration.

   So what are you doing with the shredded plastic?????

   The chuck is a really simple thing. Boring a piece of round stock to fit a motor shaft and boring the other end to fit the router bit is a quick simple thing for a metal lathe. A couple of set screws adn some tapping and it's done. At that rpm you don't have any balance issues.

1. 
   Rooftree | Sep 21, 2007 08:29pm | #8

   I'm happy to report that in most cases the plastic will be recycled.I've looked at a cross-section animation of a plastic grinder online, so I have a modest undertanding of their construction. But I've never seen one in person. I'm pretty much stuck with the basic configuration of the machine. And since it's working so well (other than the noise), I'm reluctant to go off in a different direction.

2. 
   [email protected] | Sep 21, 2007 08:30pm | #9

   I agree, I would be looking more towards something more like a pack of saw blades similar to a dado set with four-tooth chippers, but with something to limit the bite.  The blades sold for cutting hardi board come to mind. 

   A lot of it would depend on the plastic involved.  If it is a phenolic resin, or a ploycarbonate such as Lexan, the machine will have far different issues than if it is something soft like polyethylene. 

3. 
   alanplanesaw | Sep 21, 2007 02:59pm | #3

   Rooftree,

   Although I am not an engineer, router bits are designed to cut at high rpm.  They don't work as designed at slow speeds.  A common mistake is to put them in a shaper.

   Shapers have much larger bits, and the rpms are much slower.  You can put a router bit in a shaper, but the performance and results are not as designed.  And, safety is a major issue.

   Alan - planesaw