How to calculate drive wheel size?

If a shaft is turning at about 800rpm and you want to use a drive wheel to friction spin a 12" disk at 30rpm what size should the drive wheel be?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Pete Macke wrote:

Have you seen the carnage when such questions were asked previously? Are you /mad/?
Ok, assuming the drive wheel was at the very perimiter of the 12" wheel, the size would be 12*(30/800) or about 0.45", ballpark 1/2" category unless it is rocket science, in which case I recommend other means...
PK
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sue lol.. glad someone knows how to do this.
-- Log

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

the edge of the disk. Finding a small drive gear should be doable. I could probably fashion one out of round bar myself.
OR I could put a flexible rack on the inside rim ( think record turntable to picture this) and reduce the speed of my drive to around 200 RPM this would mean I could use a bigger and probably better drive gear with less chance of failure.
A nice course tooth flexible rack about 1/2 to 3/4 wide would be perfect. Except I don't know where you would find such a critter.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Pete Macke wrote:

By rack I assume you mean the toothed thingy that make up the connecting part of a gear. If you application is not high torque, consider plain friction drive. You can also certainly consider belt drive; often much easier to do in a custom situation. The drive end in this case, being only 1/2", will be troublesome; you would need to use a leather belt I think. Perhaps a two-step process - an intermediate idler wheel such as found on many drill presses.
PK
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That's absolutely correct, which leads to the next step of deciding how to actually accomplish this "friction spin" process, and how to start & stop the contraption since the mass (wieght) of the 12" disk is a consideration, as well as just what sort of load you're planning to put on this disc (since that's going to cause slippage, etc.) A good starting place would be to put some sort of rubber rim on your 12" disc, and just lay the shaft against it. If this works for your application, great, but don't be surprised if it doesn't. In all probablilty, you're probably going to have to use a v-belt arrangement and a jackshaft (idler pulley arangement) to get the necessary torque transmittal in conjunction with the rather substantial speed reduction you need (dropping 800 rpm to 30 rpm).
BJT

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Previous carnage:
http://groups-beta.google.com/group/rec.woodworking/browse_thread/thread/97a3b786eaa1a85c/540520d0aba5b142?q=DP+speed+formula%3F&_done=%2Fgroups%3Fq%3DDP+speed+formula%3F%26&_doneTitle ck+to+Search&&d#540520d0aba5b142
And:
http://groups-beta.google.com/group/rec.woodworking/browse_thread/thread/e551211401202b06/9aa311e3f1efbfd8?q=slower+drill+press&_done=%2Fgroups%3Fq%3Dslower+drill+press%26&_doneTitle ck+to+Search&&d#9aa311e3f1efbfd8
--
Alex
cravdraa - at - yahoo - dot - comment
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.