Questions re: DIY box style speed reducer

[shelr1]

I would like to build a DIY "box style " speed reducer. I understand the concept pretty well, I am thinking of a 3:1 reduction using a 6: OD and 2" OD pulley. My first question is, if you use 2 fixed pillow block bearings to support the shaft, how do you allow for adjusting the belt tension between the reducer and the sewing machine? I thought of use a 2 bolt flanged bearing and making one of the mounting holes slotted, would need to have same setup on both bearings does that seem like it would work? Also, I see a lot of 6" pulleys rated for 4L belts and I want to use 3L, can a 3L belt work well with the larger 4L pulley? I have seen some pulleys rated for 3L and 4L that's what I'm hoping to do.

[AlZilla]

I don't have a design for you but I do have a caution. I've been working to reduce a 111w153 by putting a bigger hand wheel on it.

One thing I've learned is that hardware store pulleys aren't really very well balanced.

I'm probably just going to end up with a servo. I could probably balance those pulleys well enough by using the same process we used decades ago to "balance" motorcycle tires.  But it's reached the point of more work than I care to put into it.

[toxo]

3 hours ago, AlZilla said:

I don't have a design for you but I do have a caution. I've been working to reduce a 111w153 by putting a bigger hand wheel on it.

One thing I've learned is that hardware store pulleys aren't really very well balanced.

I'm probably just going to end up with a servo. I could probably balance those pulleys well enough by using the same process we used decades ago to "balance" motorcycle tires.  But it's reached the point of more work than I care to put into it.

Not knowing where you are doesn't make helping you any easier. As I said before, I changed my handwheel, pulley and belt for less than £40. For the big wheel look for "taperlock" whatever the size of the big wheel, The taperlock bush is the same. I've never had a pulley wobble. The speeds we are talking about means that if the bore of the pulley is slightly bigger than the shaft pad it out with a piece of baked been tin or whatever.

[shelr1]

The 2 pulleys I am using for this speed reducer are straight bore,  common bore sizes are 1/2" or 5/8"  or 15mm depending on the shaft that is selected. They can be keyed or set screw but typically a taper bore is not used in this application. If using a quality shaft and pulley the fit is not a problem as far as run out or balance is concerned.

[Garyak]

An idle/tensioner pulley. Since you’re talking diy, find an old domestic machines with the spring loaded lift assist. I had to make one for my 145w. 

[kgg]

4 hours ago, shelr1 said:

My first question is, if you use 2 fixed pillow block bearings to support the shaft, how do you allow for adjusting the belt tension between the reducer and the sewing machine?

The belt for:

i) the large pulley is gets it's tension by the adjustment bolt on the servo motor frame

ii) The small pulley gets it's tension by adjusting the vertical distance in relation to the hand wheel pulley.

The advantage of the cantilever reducer pulley over the a system where you support a shaft between to bearings is the ease at which belts can be readily change. I am doing a hybrid of both where I am using a shaft supported by two pillar block bearings that cantilevers the reducer bearing off the cross bracing on the tables K-leg.

Here is a couple of sketches that may give you some ideas. The first is just a front view showing a poor representation of the cylinder arm on top of the table. The second shows the placement on the cross brace where it will have two bolts through the cross brace. The third is of the pillow block bearings mounted to a flat plate with a slot  cut out to allow the reducer pulley to move which would give tension on the belt from the small pulley to sewing machines hand-wheel.

kgg

Edited May 11, 2023 by kgg

[shelr1]

kgg, thank you for the info. Yes it is the vertical tension between the hand wheel pulley and the small pulley I was asking about. I do like your idea of the cantilever arrangement for the shaft/pulley. I am putting this on a flat bed machine,  just need see how that fits my machine.  I do like the easy access to the belts on your design. Garyak, I appreciate your design idea, it reminds me of a belt tensioner on a car, and pretty easy to adjust.

[dikman]

Possible out-of-balance pulleys shouldn't be an issue if using a servo as the speeds are generally not fast enough to cause a problem. I have quite a few various size (generic) pulleys I've bought off ebay and none of them have had balance problems.

[shelr1]

I'm making progress. This is pretty close to kgg's design. 

[kgg]

8 minutes ago, shelr1 said:

This is pretty close to kgg's design.

Yep, that's damn close. Nicely done. That arrangement should help tame the clutch motor. The next step maybe to replace the clutch motor with a servo motor. A couple of questions:

i) What sewing machine are you installing this on? ii) speed reducer shaft diameter, large pulley size and the motor pulley size. I'm assuming the motor speed is 1750 rpm.

kgg