Drive pulley for the live coal loader in Brooks

[Bob]

David has been building a beautiful coal loader for Brooks, WV, modeled after one on the Clinchfield. He came up with an ingenious air-powered method of filling an overhead hopper with dyed walnut shell grit from Horrible Freight.

There will be a long conveyor that loads coal from below the hopper over to the loader itself. For this David needed a drive pulley.

I won't go into the tribulations experienced in the early work. I volunteered to try to make an improved pulley to drive an elastic waistband belt with a Pittman gear motor.

I made two practice pieces that taught me a lot about how to NOT go about the project.

After some trepidation, I cut a long piece of aluminum and set about mangling it. First up, I worked to get it to run as true as possible in a Sherline scroll chuck. Aluminum is soft so alignment can sometimes be brought to true using subtle persuasion.



After taking a skim cut on the end of the rod, the next step was to locate the center of the material for a 1/4" hole to mate with the Pittman gear motor. This is done with a "center drill."



The conical indentation helps an ordinary drill to find a near perfect center. I used three stubby screw machine drills to start the hole and enlarge it.



Drill bits are not very accurate and they usually cut oversize holes. I ordered a 1/4" chucking reamer to make a precise hole with about 0.001 clearance on the motor shaft (measured.)



It turned out that with the Sherline rotary table mounted in their adjustable angle plate, there wasn't enough work volume left to mill the part. What's a mother to do? Order their right angle mount that takes up a lot less space on X axis.

To make accurate grooves in the pulley, I needed to prove that the rotary table after adjustments ran square to the machine. First I make sure it is square to the X axis.



Next, test for square against the Z axis.



On to part 2

[Bob]

Part 2.

Now that we know the axes are squared, we need to find where we are dead center over the target. Sorry, but the image hosting won't accept videos. For this step I used a Starrett edge finder.

After putting two "end of cut" grooves on the pulley using the lathe, it was back to the mill. A carbide 60 degree mill-drill was chosen to make grooves every 20 degrees.

At the start:



After learning a few things not to do, and considering the very long unsupported length of the part, I chose to make very light cuts, only 0.005 deep. Most cuts were made with oil to reduce vibration. Remember, the Sherline mill isn't a full-size machining center. Have patience, grasshopper!

Starting the cuts:



One to go:



Off the rotary table and back on the lathe after a bit of cleaning up. Here's where the barrel profiling began. Sorry, but I got tired and didn't take any photos of the profiling operation.

Today, Mar 31 2022 the part ran a belt well. There are a few residual coal particle management issues to deal with, but I'm sure the loader will work well and be a lot of fun to operate.

[Bob]

O'tay, Pankey!

David reported via text that the belt now runs smoothly without side guides for an attempt to keep coal particles from running under the belt.


Then he added a scraper at the top end, inside the loader, to scrape off coal that attaches under the belt.


WIN!

Well done, David!

I love it when a plan comes together!

[Craig]

I love it when a mill comes together!!

Nice work Bob!!!

[Big Train James]

Bob,
I'm curious if you are intending the grooves in the shaft for a specific type of timing belt?  I have toyed with the idea of developing a low profile drive, drawing inspiration from the work that Jay Criswell has done with the gearmotors and timing belts.

One issue is the size of components, the readily available timing belt pulleys from SDP/SI have large flanges on either side of the cogged section, to keep the belt from wandering.  Said flanges increase the overall diameter of the pulley by a decent amount.  I have always thought about milling the pulley teeth directly into a drive shaft, seeing your example makes me think it's feasible.  And if done correctly, the belt can be constrained from drifting along the length of the shaft.

Jim

[Bob]

Craig -

The grooves are not for a timing belt, but rather to drive a piece of elastic waistband material that Katy sewed together to form a loop. Same deal as the original live coal loader on 1.0.

David tried a couple of times putting sandpaper on crowned filed thread spools, but the belt always wrapped around them and jammed the new mechanism. Coarse sandpaper grit bit into the belt and wrapped it around. Finer sandpaper didn't move the belt reliably.

The grooves I milled were sharp enough to drive the belt but not so sharp that they grabbed the belt to cause it to wrap around. The barrel shape was first turned with the Sherline lathe cross slide and later profiled with mill files.

With belt drives, the critical bit is not shoulders on the drum to prevent the belt from wandering off, but rather to produce a pickle barrel shape on the end rollers with a crown in the center. That is what actually keeps the belt running true on-center.

Timing belt technology is quite different. Keeping the shaft axes shaft square is what matters. Not so much with a crowned belt.

Bob

[Bob]

Well, David's original A&O top roller for the Brooks loader beltway didn't always roll smoothly. It worked great for a while, but fiction eventually stalled the belt. Harrumph.

The next project was a poorly-photographed upper roller assembly using ball bearings. First photo, the roller that occasionally had too much friction.



A couple surplus ball bearings on hand. Could they work in a redesign?



So I turned an aluminum roller assembly on the lathe, drilled through for a central brass axle shaft and ball bearing pockets on each end. Here we see one end of the roller being precision bored. The outer race of the bearing just barely fit.



At this point I just wanted to get the thing finished, so I mostly stopped taking photos. Here in a photo I called "Steamroller" we see the nearly finished assembly before milling two Photoshopped 15 degree angles in a scrap block of Nylon to kick particles stuck to the underside of the belt to either side and down into the hopper. Both ball bearing inner races are just proud of the roller, and M2 screws hold both ends of a brass shaft in place.



After machining the V, I added a shim brass scraper to the milled V upper side to knock off stained ground walnut shell "coal" particles that stuck to the bottom of the belt. Sorry, no more photos. I wish I had taken more, but the hour was late and I was tired.

The initial report from the mothership is that the roller works great and that the loader shovels coal faster than a noob operator may be able to handle. David suggests that a belt feed speed control would be helpful. Now I'm looking for a solution.

[Bob]

Found another couple of photos on my phone. The roller assembly will plug into the end of the beltway, which is enclosed in PVC tubing. Coal falls down to a funnel that delivers it to an awaiting car. The belt is made from elastic waistband material.



Making a mess on the mill, trimming the nylon block to length.



The finished roller, prior to adding a 0.005" brass coal scraper to the V groove. The purpose is to remove particles that work their way under the belt, causing them to fall to either side of the belt and into the delivery hopper.