View Full Version : Added another pulley to the motor cone pulley on my mill
12-18-2009, 07:13 PM
My Craftex knee mill has a slowest spindle speed of 270 RPM. I wanted to slow it down so I can use some larger diameter home made cutters. I wont be able to take deeper cuts but drill rod cutters and high speed steel should last better.
The motor cone pulley shaft bore extends over an inch past the motor shaft so I made a shaft that would fit into the cone pulley and expand when the bolt was tightened to keep it in place. I made a small pulley that fit onto that shaft. The intermediate and spindle pulleys have four grooves the motor only has three. The motor pulley can only drive three of the four intermediate pulley grooves. By adding the fourth pulley I was able to lower the spindle speed to about 160RPM.
12-18-2009, 07:21 PM
12-18-2009, 07:37 PM
Thats a nice little job, really like the expanding adaptor, the belt set up is familiar as its the same as my pillar drill and a slower speed would be handy on that too so i might copy your work if you dont mind,
12-18-2009, 07:52 PM
awsome at the expanding adapator, I was wondering how you attached that tip on the bolt before I realised.. you just turned the head off to make it, awsome.
+1 on the expanding arbor!
12-19-2009, 01:06 AM
For what I do with my mill, I can live with the lowest speed. The problem is that there is a gap in the speed range that's a bit bothersome. I'd like to find a way to eliminate the gap. I'll have to do some figuring to see if I can adapt your solution to this problem. Off hand, I'm not sure it's that simple.
Seems like a long time back, maybe mid '90s, there was an article in one of the V.P. mags where a fellow added another jack shaft located on the right side of the belt cover to solve that problem, but I haven't been able to track it down.
12-19-2009, 06:53 AM
If you want to improve it more, fix a brake disc (rotor) - as large as possible to the top of the spindle pulley to act as a flywheel.
12-19-2009, 07:21 AM
While that may sound like a good idea, the motors rotar allready acts as a flywheel, and I believe attaching a large mass to that small shaft extention could be very dangerious, not to mention get in the way of the belt cover.
as is, if that pully comes loose, its not that heavy or spining with enough momentium to likey bust through that belt cover.
12-19-2009, 09:44 AM
gearedloco you are right there is a gap in the speeds it goes from 490RPM to 950RPM and this pulley will not help. However if I were to remove the intermediate pulley and run a long belt from the motor to the spindle pulley I would gain 758, 663 784 and 907RPM. The first three would fill the gap nicely but each would require a different belt.
12-19-2009, 10:17 AM
The best improvement you can make is to change the motor and fit a VFD. I very seldom change belt positions, doing so only for large fly cutters or very small end mills or drills, so that I am not lugging or overreving the motor to get the spindle speeds I want. I routinely power tap down to 4/40 without drama. Your job is an excellent way of getting a slow speed, but fully variable speeds are even better, regards David Powell.
12-22-2009, 10:36 AM
A VFD and a motor change might happen later on right now I am saving for some more tooling for my lathe and mill.
I stopped by Kaman Bearing on the way home from work yesterday and they had a B60 belt. I don't even have to remove the intermediate pulley.
This will give me 660 RPM filling the gap between 490 and 950 RPM.
According to my calculator 660 RPM is the correct speed for a 1/2" HSS end mill cutting mild steel.
12-22-2009, 11:15 AM
Most of these motors are made to run at either 50 or 60 Hz with a corresponding difference in speeds. Is it possible for a 60 Hz System to be changed to 50 Hz by the use of some fancy circuitry, being switchable from 60 to 50 and back, there by increasing the range of speeds
12-22-2009, 11:25 AM
loose nut: If by 'fancy circuity' you mean 'a VFD' then yes.
if by fancy circuity you mean.. some random cobbled togethor parts.. no
12-22-2009, 07:29 PM
Neat adapter,going to file that one away.