Variable speed runs too fast

AGCB97

H-M Supporter - Diamond Member
H-M Lifetime Diamond Member
Joined
Apr 22, 2016
Messages
965
I have a variable speed Powermatic drill press that runs too fast. It is a belt type (like a snowmobile belt). I checked the motor speed and it is only off by ~50 RPM but the lowest the spindle will run is ~350 RPM. According the manual it should be 80 RPM.

Would a worn belt cause this? Seems to me I remember that when a snowmobile belt was worn, low speed (torque) suffered but high speed was higher than normal.

Any thoughts?

Thanks
Aaron
 
Hi Aaron- a worn belt would give a slower speed, not higher. That's such a big discrepancy there must be a misprint or something else is going on
How are you checking the speed?
Can you post a picture of the drive setup?
Mark
 
You might provide the model number, the ones I looked up showed a speed range of 250-3000. The mechanical variable speed versions use a form of the Reeve drive, so a set of pulleys that change diameter as the two halves of the pulley either squeeze together or widen. Often one is spring loaded, the newer Powermatic have an intermediate transfer pulley with two stacked adjustable pulleys one to the motor and the other to the spindle to give more adjustable. If a belt is worn or the tension adjustment is incorrect, the pulley will not be able to climb up the pulley to the larger diameter and this would limit your low speed setting. I would remove the cover and look at the drive while adjusting the speed, on the low speed the belt should be at the outermost diameter of the adjustable pulley. Some of the older models have an adjustment screw to set the belt traction to adjust the belt speed ratio.

Some machines may also use a 2 speed motor, so would need to have some more specific information and maybe a picture or two.
294624
 
Does the motor look original, or has it been replaced? The machine could have been supplied with an 1140 RPM
motor which was later replaced with a 1720 RPM unit.
 
Sounds like perhaps the Reeves drive isn't pinching together enough at the low speed setting which would hold you at a too-high speed. Check that.
Mark
 
It's a 1725 RPM motor but am sure it's original. There were 3 on a table with consecutive serial numbers. I'm checking the RPM with a handheld digital tach. Maybe the manuals I looked at were for a different model. This is a 1200 with power down feed. I can get about 150 RPM by turning down the VFD frequency and still seems to have good power.
Thanks for the replies.
Aaron
 
Yes....a worn belt will affect speed. I tached my Bridgeport with a worn belt and got 5100 rpm on the top end when it should normally be 4200.
 
I have a variable speed Powermatic drill press that runs too fast. It is a belt type (like a snowmobile belt). I checked the motor speed and it is only off by ~50 RPM but the lowest the spindle will run is ~350 RPM. According the manual it should be 80 RPM.

Would a worn belt cause this? Seems to me I remember that when a snowmobile belt was worn, low speed (torque) suffered but high speed was higher than normal.

Any thoughts?

Thanks
Aaron
You say you checked the motor speed. Did you check the speed according to the tag on the motor or check according to the manufacturer’s manual specs.
Only reason I’m going down this road is I’m wondering if maybe the original motor was a 1700 rpm motor but somewhere along the line someone put a 3400 rpm motor on the drill.
 
Motor tag says 1725 and digital tach reads close to that also. I guess I mistakenly read the specs for the electronic variable speed model which has a lower speed range that the belt drive model which I have.
Aaron
 
Back
Top