SP-15 Belt is loose again!

Seems like we just replaced the V-belt on our SP-15, the one with the newer Baldor motor. It is already loose again. The last time we had belt issues, Lad Boyle wrote about a process he had for removing the bottom plate, the plate the motor sits on. I think this was so my machinist could make slots for the motor instead of holes, which we have now. The slots would allow us to move the motor slightly to tighten the belt. Am I remembering this correctly? Is it normal for such belts to become loose after only a few months?

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Dave Seat
8 years ago

Belt tight now. Simple fix was to enlarge the 1/4″ holes to 3/8″ so there was enough play to move the unit back to tighten the belt. Then we used fender washers to take up the difference in the holes. All better now.

Justin Turcotte
Justin Turcotte
8 years ago

I’m not sure if you have figured out the belt issue on your sp-15 yet but here is my two cents. I’m guessing the original motor assembly had slots to take up the slack. It is not often that a v belt system has no adjustment. Having someone put slots in the mount is the best way to cure your issue. Belts always stretch out. What Dan said about cleaning is correct, the harder you make that system work the faster the belt wares out. I have known some people to “bump” the switch until the cylinder is in a good spot for cleaning. A larger drive pulley on the motor may solve the belt tension for a little while but the faster speed will cause other components down the line to wear out faster. If machining slots isn’t an option you could use an adjustable v belt system. They come in many different sizes. I have used them on machines for years and not had to make an adjustment. The benefit of these is when your belt breaks you can simply change out the broken link.
Best of luck with your press.

The Arm
8 years ago

A question:
Do you clean your ink drum by running the motor and holding a rag against the drum? I have seen people do this and, on an SP-15, it stretches the belts and wears them out prematurely. The chain-driven presses seem to tolerate it (and some manuals like the 219 even state it as correct), but it also stresses the motor unnecessarily. If this is part of your cleaning regimen, you may want to consider cleaning the drum while the press is turned off.


Lad Boyle
8 years ago

A slightly larger pulley will make the drum turn a bit faster

Lad Boyle
8 years ago


You are correct that I suggested the mounting holes in the plate be slots so you have a little bit of play to increase or decrease the tension on the belt by sliding the motor backwards or forward.

Not sure how to gauge how tight the belt needs to be – certainly, it can be too tight and obviously, too loose.

If you had it set with a reasonable amount of tension and then it loosened, there are two possibilities. 1) the belt stretched and now the tension needs to be reset. OR 2) the bolts holding the motor allowed it to slip. If this is possible, were the motor mount bolts tightened using lock washers? If not, you might add locked washers. This prevents the nuts from slipping on the bolts.

Maybe someone else has other ideas. I’ve not had the problem so i am guessing about problem and solution.


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