View Full Version : Bridgeport Style Vari-Head question
02-03-2008, 11:59 AM
Ok so i have a gate profitmill which has a vari-speed head that I'm assuming really is just a copy of the Bridgeport vari-speed head...anyway theres this lil setscrew in between the spindle and the motor housing on the top of the head with a locknut on it so I'm assuming its adjustment, but is it belt tension or belt alignment?
Well that was question number one, and no. 2 is has anyone got diagrams for the internals of these heads? the power downfeed has given up, and its reacting like a gear is slipping on a shaft as if its stripped a key or something similar, so a basic idea of the internals before i pull it apart would be good.
and last but not least, i've never had to replace a belt on the machines like this ive used before but now its my main machine im thinking i should have a spare belt handy so where do you get vari-speed belts from for bridgys and the clones?
02-03-2008, 12:38 PM
I don't know about the screw but I suggest you don't mess with it untill you get a manual for the mill. On a Vari drive there is no tensioning device except the spring in the Vari drive pulley. The spring pushes the two pulley halves together and keeps the belt under tension.
Also, DON'T move the speed wheel unless the motor is running. If you do and then start the motor it can and may snap the belt in half. The belts are expensive and not easy to replace. What ever happens is not good so don't move the speed control wheel.
02-03-2008, 12:59 PM
The spring pushes the two pulley halves together and keeps the belt under tension.
Also, DON'T move the speed wheel unless the motor is running. If you do and then start the motor it can and may snap the belt in half. The belts are expensive and not easy to replace.
You got that right! heh i still have bruises from replacing the belt after changing out the motor, the springs on those pulleys are incredibly strong got one hell of a bruise when taking them apart, was already aware about the speed change issue, and theres a really big sticker on the front of the mill to remind me:D ....on the upside i did figure out a real easy way to replace the belts without taking everything apart, the only thing i needed to do was loosen the motor mount bolts a little.
I had a closer look inside the inspection plates earlier and the screw bears against a floating plate on the spindle end so it appears to be alignment, granted i have no need to adjust it anyway, just was really bugging me not knowing what is was for sure:rolleyes: as it is i cant really afford the down time to recondition the head at the moment either so im just laying out a plan to do it when things quiet down a little.
02-03-2008, 01:10 PM
The plate is a travel limit for the spindle sheave.
02-03-2008, 05:13 PM
As Beckley said, its a travel limit for the VS adjustment. I think you adjust for the upper speed limit with that, but I don't recall for sure. You may want to take a look on the web and download one of the .pdf copies of one of the bridgeport mill manuals out there. I would include a link, but am lacking my list links on this PC.
02-03-2008, 05:42 PM
Just found a manual for a vari bridgport head mill, i had links before but lost them now found them again so i've taken a look through and found out most of what i needed to know.
also found a link to a rebuild of one of the step pulley heads complete with a ton of pics including the power down feed and i think has answered my own question about the down feed problem on mine. ill take a crack at fixing it tomorrow and see how i go if not ill be back to ask more questions.
That screw on top helps to set the the speed plate rpm to the correct speed.
Rum machine in high gear speed turned down to 500 RPM put RPM gage in spindle and adjust screw till you reach 500Rpm on gage. Then you speed dial will be set to right RPM.
02-04-2008, 12:13 AM
When considering buying a spare drive belt, make sure which belt edge angle you have. My understanding is most if not all of the BP clones have a different angle than a real BP. I found this out by buying the wrong one on my Alliant mill and the pulleys chewed up the belt edges because they didn't conform.