Why couldn't a woodworking router be converted into a belt grinder?

scotchleaf

scotchleaf

Joined
Oct 23, 2006
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I've got an extra router, which I believe to be variable speed. Could it be used as the motor for a grinder?
 
WAY too much RPM, and a variable speed motor of the type used in a router would not be able to provide enough power when slowed down for belt-grinding purposes and would toast itself quickly. That's why it takes extra $$ to set up a real variable speed grinder via 3 phase motor and VFD or DC motor and drive. It just takes that type of set up to provide enough torque to the belt without burning things up.

If you want to go the salvage parts route, I've heard of people scavenging the DC motors/controllers from old treadmills and rigging something together, but it likely won't be ideal or very powerful.

--nathan
 
Exactly my thoughts silver. The motor just would not produce enough torque at low rpm to run a grinder for very long, if at all, without frying. The power rating in a router is also not remotely accurate or relative to grinder motors. Just like my 6hp shop vac. It says 6hp but if it was, not only would it have to cost far more, but you would never be able to run it on a wall outlet if it was.
 
As others said to much RPM and not enough torque. If you want to scrounge the parts for a knife belt grinder old treadmill motors will work fine if they are 1hp or larger, use step pulleys and link belt so get different speeds..

For the best deal in a two wheel grinder I know of, Go here. www.cootebeltgrinder.com one of these and a 1 1/4hp treadmill motor, step pulleys and link belt and I had my first real knife grinder. I purchased the 8" contact wheel 2 x 72"..
 
Why couldn't you gear it down with a pulley drive? Like something off of a drill press.
 
I don't think it would even be practical to try to gear it down plus the drive shaft is too small. 2 inches is about as small as you could go as a drive pulley that would fit a belt properly. Routers usually run around. 24 000 rpm, this means to get a driven shaft speed of the typical 3450 rpm motor, the driven pulley would have to be roughly 14 inches in diameter. And, as was stated, the actual power just is not there, regardless of how it is geared.
 
To some extent, the actual speed of rotation is immaterial; lt's the belt speed that is important and you can just fit a much smaller drive wheel to get what you need. I don't think 2" as a minimum diameter to work with a belt is necessarily correct; there are plenty of small-wheel attachments in use at much smaller diameters.

Having said that, a router would still be a poor power unit for a belt grinder. The variable speed range is usually only about 3:1. They tend to be tool-rated rather than continuously-rated, usually have unsealed motors with lots of airflow through them (not a problem with wood dust, but electrically conductive steel dust could get quite exciting) and the bearings don't seem to be designed for the sort of radial loading that a belt system would impose.

If it's going begging though, you could mount it in a table and use it as a poor-man's small wheel attachment with abrasive sleeves and holders.

http://www.pferdusa.com/products/204i/204i02P.html

http://www.pferdusa.com/products/204i/204i03/204i0301P.html
 
The metal dust makes sense. That would be a deal breaker. I have seen some pretty creative table saw setups though. Using a small primary and a pretty big secondary pulley. Not saying it worked well, but it worked. Gotta love hillbilly engineering!
 
From an engineering POV:
1) The bearings are made for low load. They would not last long at all under the side load of a drive wheel.
2) The drive wheel would be have to be very small, That would make the belt run very slow.
3) As a drive wheel gets smaller, it has less surface contact with the belt. This lowers the friction, and causes slip. When a load was applied to the belt ( as in grinding) a 2" or smaller drive wheel would just turn while the belt stayed still.
The torque is very low on these type motors. They are intended to turn a small mass router bit at a very high speed....not deliver high torque at a low speed. Gearing one down would not help.
4) This is the biggest one - Router motors are usually in RATED HP...not delivered HP. Just because it says 3.5HP doesn't make it more powerful than a Baldor 2HP grinder motor. It has a small fraction of that power, and a ghost of the torque. Power and torque come from the number of windings, the size of the wires in the windings, and the size of the armature. In a tiny router motor these are not present.

These and many more reasons are why a 5HP shop vac or a 3HP router won't run ANY shop equipment other than the one they are installed in.
 
I had an old pulley belt set up once , using a washing machine motor. Experimented a little with belt length and mounting set ups..and of course, it wasnt osha approved with that open belt I had running!
 
Thanks everyone! I had a feeling that wasn't the right solution. I have an old 3/4 hp GE motor I might try.
 
A belt grinder motor needs to be powerful enough to provide good grinding. A 1HP is the normal minimum, and 2HP is the normal max. 3/4HP is the bare bottom for a well make grinder doing lighter work. Get a good quality 1750RPM motor made to run shop equipment if it is going to be that small.
 
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