Help with flat belt tracking

[RCPDesigns]

When restoring my Cincinnati Cutter Grinder I need to turn down the cone pulley on the spindle due to the pitting from rust. I couldn't tell if it was original crowned or not. While researching how to turn a crown on a pulley I read that only the drive pulley should be crowned. As such, I didn't put a crown on the cone pulley there was one on the pulley on the motor. I read this on the Internet so it must have been true.
However... I'm having tracking problems. In one direction the belt moves to the front of the spindle. In the other direction it moves towards the rear. I've checked the alignment of all other parts and I feel like they are good. The belt only stops moving one direction or the other when it encounters an obstacle. If I turn the drive pulley by hand it appears to track OK.

I'm sure there are all kinds of possibilities but I'm hoping that the clue that it wants to track in one direction or another based on the rotation will lead to a likely solution.

My gut tells me the Internet was wrong and I need a crown on the spindle cone pulley as well. I know my Hendey machine tools all have crowned pulleys.

Assuming that I do need to crown the pulley does anyone have tips for doing so on a lathe without special attachments?

Thanks!

 

[L Vanice]

It is quite easy to turn cast iron and other metals with hand-held chisels. Woodturning chisels can be found with HSS or even carbide blades, enabling turning at higher speeds than possible with carbon steel blades. Some metal lathes had T-rests available as factory options, but it is pretty simple to improvise a rest. Hand turning is the easiest way to make curved surfaces like a pully crown on a manual lathe. You can get very nice smooth curves with hand tools, but I sometimes use a little electric belt sander for the final finish. Look up Milwaukee Bandfile. There are also various makes of air-powered belt sanders.

Larry

 

[Lester Bowman]

Being someone who has restored plenty of antique engines I have found almost invariably the drive pulley is flat while the driven pulley is crowned.

 

[atomarc]

IMHO..you don't need an actual 'crown' on the pulley, you only need to taper each edge a smidgen. This will make the belt center on that pulley. If it acts as you have described above, it usually means that the pulleys are not aligned with each other. Use a straight edge and make sure they're aligned..and I'm not talking parallel, but aligned, if that makes sense.

Stuart

 

[JST]

I don't see that there is any problem with crowning both. The drive on my flat belt lathe is crowned on both and it tracks very well.

It may be that you do not "have to" crown both, but that may likely be in ideal circumstances. Crowning both does not seem to have any downside.

Does anyone have a reason why crowning both will cause problems?

 

[Tom A]

I don't see that there is any problem with crowning both. The drive on my flat belt lathe is crowned on both and it tracks very well.

It may be that you do not "have to" crown both, but that may likely be in ideal circumstances. Crowning both does not seem to have any downside.

Does anyone have a reason why crowning both will cause problems?

The only thing I can think of, might be the belt wriggling around a bit, if the 2 crowns aren't exactly the same shape - Fighting each other, if you will. In most cases though, it probably wouldn't make any difference.

 

[jim rozen]

There's a lot going on with flat belt alignment. Check all of these to see how they affect tracking:

1) axial alignent - shift one set of sheaves along the spindle axis with respect to each other, what happens?

2) angular alignment, vertical plane. The two shafts have to be parallel when viewed from above. Rotate one set of sheaves around the vertical axis and see the effect. In a bench lathe this means hold the headstock foot still and move the tailstock leg forwards and backwards on the bench.

3) angular alignment, horizontal plane. Rotate one shaft around a horizontal axis. Bench lathe: shim the tailstock leg up or down.

Both sheaves can be crowned.

 

[enginebill]

Both pulleys should be crowned. Flat drive pulleys are for tight and loose pulleys. Doesn't matter if each crown is different. I think the crown is 1/8" per foot but you can look it up in Machinery's Handbook which really gives you all the information that you need.

 

[dundeeshopnut]

Have you tried reversing the belt's direction of travel on the pulleys to see if it creeps the same way? A belt that is spliced or stretched so one edge is slightly longer will often try to run off the pulleys no matter the alignment.

 

[M.B. Naegle]

While having a crown can help, In my experience miss-alignment is 90% of flat-belt tracking issues. Even worn pulleys can be made to track correctly with the right positioning. IMO, I wouldn't worry about trying to get geometrically perfect flay pulleys unless there was no ability to adjust them at all, or they had a LOT of wear. I've had a couple machines that had castings out of square from the factory that required a little shimming under the motor to get it back to square. Square isn't necessarily a geometric thing either. You can start that way, but often might need to push it one way or the other if the belt is a little stretched on one side.

Crowns and tapers behave differently on flat belts. With a crown, the belt wants to center over the crown, but with a taper from misalignment or wear (and think of the taper as both axis together, not just a taper on one pulley), the belt wants to track downhill.

On your machine, It's likely as simple as adjusting the twist between the motor and the spindle and adding some shims under a couple of feet on the motor. I'd start with the motor and spindle as aligned as you can get them, and if the belt is crawling to one side, shim the motor so that the motor shaft is a little higher on that side. If it seems to be staying put but is just riding close to the edge of the pulley, you might need to play with where the motor pulley mounts on the shaft.

IMO old flat-belts are great cause you can "make" them work despite wear and in a pinch replace them with lots of different materials, but they are high maintenance compared to modern V-belts, cog and serpentine belts.

 

[jim rozen]

I think the take-away here is you can set these up so they look and measure perfect, but they still will track off to the side. Just do the experiments mentioned and you'll see
that one or more of the adjustments (axial alignment, vertical twist, and horizontal twist) will resolve the tracking issue.

 

[RCPDesigns]

Have you tried reversing the belt's direction of travel on the pulleys to see if it creeps the same way? A belt that is spliced or stretched so one edge is slightly longer will often try to run off the pulleys no matter the alignment.

When the direction of rotation is reversed the belt creep changes direction as well. Might that be a splice issue?

 

[RCPDesigns]

While having a crown can help, In my experience miss-alignment is 90% of flat-belt tracking issues. Even worn pulleys can be made to track correctly with the right positioning. IMO, I wouldn't worry about trying to get geometrically perfect flay pulleys unless there was no ability to adjust them at all, or they had a LOT of wear. I've had a couple machines that had castings out of square from the factory that required a little shimming under the motor to get it back to square. Square isn't necessarily a geometric thing either. You can start that way, but often might need to push it one way or the other if the belt is a little stretched on one side.

Crowns and tapers behave differently on flat belts. With a crown, the belt wants to center over the crown, but with a taper from misalignment or wear (and think of the taper as both axis together, not just a taper on one pulley), the belt wants to track downhill.

On your machine, It's likely as simple as adjusting the twist between the motor and the spindle and adding some shims under a couple of feet on the motor. I'd start with the motor and spindle as aligned as you can get them, and if the belt is crawling to one side, shim the motor so that the motor shaft is a little higher on that side. If it seems to be staying put but is just riding close to the edge of the pulley, you might need to play with where the motor pulley mounts on the shaft.

IMO old flat-belts are great cause you can "make" them work despite wear and in a pinch replace them with lots of different materials, but they are high maintenance compared to modern V-belts, cog and serpentine belts.

I tried shimming the motor and the belt still went forward regardless of what I did. I even shimmed the opposite of what I thought... still went forward. Flipped the belt over... still went forward. Reversing the direction of rotation caused the belt to creep backwards. As such, clockwise rotation belt goes forward. Counter-clockwise rotation belt creeps backwards. No rotation belt stays centered.

 

[M.B. Naegle]

I tried shimming the motor and the belt still went forward regardless of what I did. I even shimmed the opposite of what I thought... still went forward. Flipped the belt over... still went forward. Reversing the direction of rotation caused the belt to creep backwards. As such, clockwise rotation belt goes forward. Counter-clockwise rotation belt creeps backwards. No rotation belt stays centered.

The directional reverse may indicate a twist between the two axis. Looking at your pictures, do you still have the T-slot rails between the motor and the head casting? Is there a way to twist the motor in relation to the mounting plate? It might only be an 1/8" that makes the difference.

I missed if you're using composite rubber belt or leather, but might also help to pre-stretch the belt. If it sat or ran one way for awhile, you can stretch it square between a couple pulleys or round drops and leave it there for a week or two and re-set it's shape.

 

[M.B. Naegle]

This video was posted awhile back, but offers a good visual for how a belt behaves over crowns and inclines.

 

[MilGunsmith]

In my experience with the NJAEMC museum, we have more trouble with short belts tracking. The long ones, like when we hook up an old tractor to a corn grinder, seem to stay on better and those are harder to align.

 

[michiganbuck]

Q: (Assuming that I do need to crown the pulley does anyone have tips for doing so on a lathe without special attachments?)

You might make a chuck-held stub mandrel, it would be a just-fit to your pulley ID and taper bigger perhaps + .002 in a one-inch length... so the mandrel would get too big for the pulley bore closer toward the chuck.

You put on your pulley and turn a number of steps getting bigger towards the center of your pulley..Then turn the pulley around and do the other side, towards the bigger diameter. *You only want to turn toward the greater diameter in your stub mandrel because turning towards the smaller diameter will /may slide the part off the mandrel.

After making these steps going large toward the middle you can file and abrasive paper the steps to become a nice radius. You do the filling the same way so the pressure is toward the gain diameter in your mandrel. For safety, some guys would bring the empty tailstock to be only .002 away from the part so it
can't go that way...and get loose.

Guess I would mark 3/8" in the pulley center and then mark each 1/8" or so and take .005 more to each line, turn it and do the same again.// or make steps that make the crown radius you choose. yes dray a map of it so not to get confused.

OH! file test your pulley first to see that is soft enough to turn.

Here is a website on pulley crown.
Crowned Pulleys — Which Option is Right for You? | Sparks Belting

 

[michiganbuck]

A chuck-held stub mandrel like this will run dead true until you take it out of the chuck...so you don't want to whack the part on too hard.

 

[Rob F.]

When the direction of rotation is reversed the belt creep changes direction as well. Might that be a splice issue?

Did you reverse the motor or take off the belt and turn it around to re-install?
edit:
I see you answered this in later posts.

 

[enginebill]

A belt that is not straight will move from side to side.