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?

9 thoughts on “SP-15 Belt is loose again!

  1. Dave Seat - April 28, 2016

    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.

  2. Katie Harper - April 28, 2016

    Thanks for all the suggestions. We have made a temporary fix. Dave Seat was here yesterday, and he drilled out the current holes to make them larger, allowing us to pull the motor away from the cylinder and thus tightening the belt. I will also explore the idea of the adjustable belt, and we might even be able to disassemble the press and fix the slots permanently over the summer. But this fix is working beautifully for now.

    Thanks again!

  3. Justin Turcotte - April 27, 2016

    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.

  4. Katie Harper - April 23, 2016

    Neither one of our SP-15 presses will allow movement of the drum cylinder when the motor is off, so we have to clean it by holding a rag to it with the motor on. Since we cannot move the cylinder by hand, can you suggest a better method? Thanks.

  5. The Arm NYC - April 23, 2016

    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.


  6. Lad Boyle - April 9, 2016

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

  7. Katie Harper - April 8, 2016

    I forgot to mention that the bolts holding the motor had not come loose, so while that was a good idea, it proved to not be the cause here. The previous belt did show some signs of wear, but I think it’s still too loose. The other SP-15 has a gear belt with teeth and is much tighter.

  8. Katie Harper - April 8, 2016

    I just replaced the belt and the new one is better but still loose. I can turn the drum cylinder by hand, which I should not be able to do. Dave Seat is due here later this month, so perhaps he can offer a solution short of taking the press apart and putting in slots instead of holes. Meanwhile, I’m wondering if we could perhaps replace the pulley with a slightly larger one? That would seem to take up slack in the belt.

  9. Lad Boyle - April 5, 2016


    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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