What Size Belt Do I Need?

[leatherisfun]

I bought a speed reducer with 3", 6" and 9" pulley. I want to install it on my Juki 1541s. However I don't know what size belt I will need to make this work. Can someone advise me about what size belts I will need please?

Thanks in advance.

[dirtclod]

Pull a string around them if their all ready on the machine them measure the string and you will have the length.

[Colt W Knight]

I would install the pulleys, and adjust the motor so that it sits in the middle of its adjustment. Then run a string around the pulleys to get the belt size. You can order any belt you need from McMaster-Carr if you don't have a local supply.

[leatherisfun]

Haven't installed it as yet. Want to handle it once, pulley and belts at the same time.

[SARK9]

>>Want to handle it once, pulley and belts at the same time.<<

No one knows where you will locate your reducer, how much adjustment is has, or where any of the pulleys will end up on your setup. The motor-to-reducer distance and belt length is not very forgiving in terms of adjustment, since the motor's relationship to the reducer is mostly in the horizontal plane rather than the vertical. You have to nail that length fairly accurately for both belts to tension properly. I doubt if anyone here can guess which belts you need.

I've made several reducers for myself; the diameter of the large pulley and exactly where it mounts tended to be totally arbitrary. The handwheel-to-reducer belt is usually somewhere around a 3L420 (which is frequently the "stock" length on a machine), while the servo-to-reducer can be anywhere from 3L280 to 3L340. My favorite method is to take a broken 3L450 I have, thread it through the pulley grooves with the adjustment ranges of both centered, tension it as hard as I can by hand, then mark the lap point. Measure the mark to the other end on both pulley runs and its *usually* within your range of adjustment.

If you enjoy math problems, you can also ballpark calculate the lengths based on the projected center-to-center distance and the diameters in each pulley pair, then correct for the angles created by the pair's diameter differences and the arc segment remainders from the first point of contact to the vertical centerlines.

Plan B: Buy a big sack of 3L belts from 28" to 44". Good luck!

-DC

[Northmount]

Using a string gives you the wrong length. Belt length should be measured at the top of the pulley where the belt rides, not in the bottom of the groove. Bottom of the groove will be too short.

You could draw out the mounting positions and size of each pulley on a piece of poster board. Then measure with a cloth tape. Or if you remember any of your geometry from school, you can calculate the length of the belts. Half the circumference of each of the 2 pulleys the belt will go around, plus 2 times the distance from centre to centre of each pulley will give the belt length. You have to know where you are placing each pulley for either of these methods to work.

Tom

[machinehead]

Have you considered using Link Belt? It is kinda pricey, but can save you time and aggravation. Most sewing machines and speed reducers use a 3L belt. There are different brands to choose from so search for the best price as it can vary considerably.

[leatherisfun]

I'll install the pulley later today and use northmount's method to measure. I'll report back.

[leatherisfun]

Installed the pulley which took quite a bit of work, more than expected. Had to extend the slot in the table accomodate the new position of the belt from the head. Then drilled new holes in the table to move the motor to line up with the 9" diameter pulley.

To get the correct belt measurement, I cut the current belt and used that to get new sizes required. New belts have been ordered. There is room on the pulley to increase the tension to tighten both belts.

[leatherisfun]

Belts came in today, installed and all is well. I used 39" and 34" belts which fit perfectly on the 3" and 9" pulley respectively. Only tried a few inches of practice stitches which looked beautiful. Even nicer was being able to go as slow as my 441 clone.

[dirtclod]

Good deal, glad you have it up and running.