Drive belt for SB9 lathe

[jpigg55]

I recently had a drive belt break. Actually, the splicing pulled out.
Luckily, I had another belt that came with it, but figured I should either get a new one or repair the old one.

The lathe is a SB9A with under-drive with the standard flat, cone pulleys. I've seen a variety of options people have used from Quik link belts to serpentine belts with poly groove pulleys like in this thread: https://www.machinistgazette.com/index.php?topic=412.msg2627#msg2627

A spliced belt is the easiest way to go and re-lacing the broken belt might be an option (although I'd need to purchase a splicing kit) since it should still be long enough after cutting off the damaged area, but thought I ask if there may be other/better options.

The spare belt is a cloth style vs leather and is a bit too wide, but works.
I just wanted to get a spare belt, should the need arise. Would rather be in the "Have it and not need it" vs the "Need it and not have it" category.

[Jake Parker]

Can the belt be easily serviced if it were solid, or does it need to be threaded through the head stock and then laced together?

If it were serviceable I would go with a serpentine belt on the existing pullys. Yes, there will be a very small contact area at the end of each of the groves, but the belt material itself has IMO 100% more traction than the old leather belt.
There would be less stretching and the new belt would be more impervious to oils, cutting fluids and coolants.
And if your worried about belt breakage, I use old serpentine belts for lifting straps for loads in the 400# > range with no worries.

Just my $.02

[jpigg55]

No, not easily serviceable. Putting a serpentine belt on would require head stock disassembly.
Do-able, but not sure where to find short serpentine belts locally and didn't want to order online and get the wrong size that's too short or long.

[woodchucker]

there's not need to groove for a serpentine belt. I have a serpentine belt on my sb9a... but mine is not an under powered, mine is behind the lathe.


So you could replace it with a serpentine belt. you would need to cut it for the under unit. Then glue it back together. I think that the flexible CA glue would probably hold it... just cut it and reglue. The best way to cut it is a skarf joint. It gives lots of glue area, and provides a more flexible less stressful joint. You would buy a longer belt and use a belt sander to create the skarf... I would probably freeze the belt to stiffen it to work more easily. You may even want to put it in water before freezing.. since the belt should be good for freezing temps... That would make it work easier I would think... I like the serpentine belt, it has a good amount of grab compared to the leather. Doesn't make noise when it hits the lacing...


https://en.wikipedia.org/wiki/Scarf_joint

[chips and more]

I could be blowing smoke out my a**. And I have not tried it, but would if I had the need. How about using polyurethane flat belting, the type used on conveyors and the like? You would just cut to length and then fuse together with say a hot knife. I have been using the 4mm round stuff on watchmaker lathes since day one with complete success.

[jpigg55]

If I go with a serpentine belt, think I'd opt to disassembling to install vs cut & glue.
More work, but I'd think it would add longevity to the belt.

[jpigg55]

If I go with a serpentine belt, think I'd opt to disassembling to install vs cut & glue.
More work, but I'd think it would add longevity to the belt.

Scratch that. I was watching a couple YouTube videos about replacing belt with serpentine belt.
Even Mr Pete said headstock disassembly was a royal pain.
Seems a lot of people went the cut and glue method and are very happy with it.

[woodchucker]

the headstock is easy to take the spindle out of and put back in... nonsense about it being a pain.


What I think is tough is your drive is underneath... so that's a pain...
But the spindle is a few minutes work out, and a few more back in...
I use all thread and a piece of pvc tubing with an aluminum end cap to pull it back in... makes it real simple.

[Terrywerm]

If I go with a serpentine belt, think I'd opt to disassembling to install vs cut & glue.
More work, but I'd think it would add longevity to the belt.

Scratch that. I was watching a couple YouTube videos about replacing belt with serpentine belt.
Even Mr Pete said headstock disassembly was a royal pain.
Seems a lot of people went the cut and glue method and are very happy with it.

Mr Pete may be very knowledgeable, but he lacks drive when a challenge arises and prefers to take shortcuts. Every shortcut has its pros and cons, but shortcuts leave a part of the journey unseen. I was recently watching a video of his where he built the PM model dynamo. During that build he completely skipped over a couple of steps simply because he didn't see the need and didn't want to go through the set up to properly complete the part. When he built the Stuart Progress engine he completely skipped the piston rod gland because he felt that it would be too difficult too make. There have been a number of shortcuts he has taken, particularly on model engines and such, that a real modeler would not even consider.

I know, this is all based on my opinion, but I always felt that a large part of modeling a working machine was to see your way through the challenges that come up and figure out how to replicate as much of the original as possible.

Anyway, my point is that there are ample instances where he skips over things that are a bit more challenging, so I wouldn't put too much stock in his statement about the headstock disassembly being a PITA. I have never disassembled the headstock of a South Bend of any kind, so I am no expert there, but I have had the headstock of my Logan 10" apart and it wasn't that bad. I am running a multi-groove (serpentine) belt on there and love it.

I guess it is also important to remember that everyone has their own opinion of what they consider too much work compared to the end result, so to each their own.


 

[jpigg55]

One thing he mentioned was the need to re-alignment of all the bearing/bushings during reassembly.
Since I've never pulled one apart, I wasn't sure what this involved or if it was even of concern. I'd hate to end up with a misalignment between the headstock and tailstock for a belt change.

Not even sure if a serpentine belt is available in the proper width and length, although I suspect there is since people have done it.
It would also require disassembly of the under-drive to get the belt over the bottom cone pulley.

Guess it boils down to if I decide all the extra work would be worth it vs just cutting and splicing the new belt.

[woodchucker]

so as far as I know, there are only 2 different types of bearings for the sb9.


Cast Iron built into the headstock... That's what I have, mine is a war time lathe.  And bronze sleeved bearings, which I wish I had... I have more slop than I want, and replacing the sleeves if I had them would make her new again.


There is no aligning them. They go into the bore..


I think Mr. Pete must be describing ball bearings with a race. But I can't imagine that they are hard to align. You have practically no tolerance when it comes to those.  Unless you don't seat the race.

[4GSR]

One key thing to keep in mind if you decide to pull the spindle.  Make sure the woodruff key that keys to the bull gear is on top dead center or 12 o'clock position.  Any other position, the key can drag thru the bearing damaging it. 

I need to someday pull the spindle on mine to replace the poly groove belt I run.  My dad grooved the pulleys to accept a J-series Poly Groove belt almost 55 years ago.  I wear out a belt about every 15-20 years.  Not bad IMO.  No belt slippage either.

Ken

[jpigg55]

Decided to go with the glued scarf joint belt, mostly because my auto mechanic gave me a free serpentine belt.
It's too long to use without cutting to size and probably long enough to make 2 belts.

The FREE part is what tipped the scales.

[dlane]

I went with this guy AL Bino flat belts, I went with the green one has worked good