Author Topic: Flat Belt Reversing Mechanism  (Read 5105 times)

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Flat Belt Reversing Mechanism
« on: August 02, 2018, 09:17:25 PM »
With the end of every project, I declare that I've had enough machining, and I'm going to take a break for a couple of months. Then I lay in bed at night, and it isn't sugar plum fairies that dance thru my head---it's machinery!! One of the things that fascinates me is how they shifted flat belts pulleys into reverse on the old lineshaft machinery. I've seen pictures of it but never have seen it done in "real life". I just happen to have a small flat belt, about 5/8" wide x 0.100" thick that I scavenged from somewhere, and time on my hands. So--I spent this morning modelling a flat belt reversing mechanism.   In the attached picture, the power is input to the beige colored counter-shaft in the lower left hand corner. This will make the gear which meshes with it rotate in the opposite direction and carry the green pulley closest to that gear and the shaft it rides on with it. However, the belt is at the other green pulley on the far side from the yellow gear, so what's going on here?

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #1 on: August 02, 2018, 09:18:47 PM »
If we look at the mechanism from the other side, we see that since there is an idler gear between the countershaft gear and the driven pulley gear, the green pulley on the far side will always be rotating in reverse to the first pulley we seen over by the input end of the countershaft. And in the picture as shown, the pulley will be driving the flat belt and the pulley at the far end.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #2 on: August 02, 2018, 09:19:45 PM »
Now there is a trick here at the end with three pulleys. The center pulley and shaft which it rides on are not driven from either side. The center pulley and shaft just free-wheel. The two outside driven shafts are hollow. The shaft with the center pulley on it is supported by the two outer driven shafts, but it is not keyed to them. The center pulley and it's shaft free-wheel. The second picture posted is actualy a section taken thru the 3-pulley shaft, to show how this is arranged.


Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #3 on: August 02, 2018, 09:22:16 PM »
This picture shows the belt shifted to the center pulley which is the neutral position. Since no power is being transmitted to the shaft which supports the center pulley, the belt will not be driven.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #4 on: August 02, 2018, 09:22:57 PM »
So, what mechanism is used to move the belt into one of it's three possible positions? (note that the pulley at the far end has the same overall length as the three shorter pulleys combined) The belt shifter mechanism. This shifter mechanism can be moved by means of a lever, a screw, or even finger power in this case. It is guided in it's travel by matching holes in the two side frames. Since the top run of belt and the bottom run of belt are moving in opposite directions, the bronze colored rollers which contact the sides of the belt must be able to revolve independently, one clockwise, the other counter-clockwise.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #5 on: August 02, 2018, 09:23:40 PM »
And here is a final picture, in which the belt has been moved to the opposite side pulley from the very first picture posted, so the belt will be rotating in the opposite direction from the very first picture posted.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #6 on: August 02, 2018, 09:24:31 PM »
Will I actually build this?--The answer is "probably".  I never have much "real work" in the summer time, and although my good wife and I have some small day trips planned this summer, that is still going to leave me with a lot of time on my hands.---Brian

Offline crueby

  • Full Member
  • *****
  • Posts: 9189
  • Rochester NY
Re: Flat Belt Reversing Mechanism
« Reply #7 on: August 02, 2018, 10:04:54 PM »
Very slick setup, it would be a neat addition to your 90 degree drive unit.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6742
  • Surrey, UK
Re: Flat Belt Reversing Mechanism
« Reply #8 on: August 03, 2018, 06:56:20 AM »
Seems a lot of work for what a tumbler reverse would do with far less parts.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #9 on: August 03, 2018, 04:48:05 PM »
One of the first things I had to do was to measure the true center to center of the belt when it was on the pulleys. I made up all four of the pulleys this morning, then took two into the machine shop. I zeroed out the quill using my DRO with the long pulley clamped in my vice, then locked the y axis and moved the table in the x axis until I could get the belt on both pulleys. The height of the quill was lowered to match the pulley in the vice. Then it was simply a matter of cranking the table in the X axis until I felt that the belt had proper tension on it. The center to center turned out to be 5.167".

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #10 on: August 03, 2018, 07:33:55 PM »
One thing about turning--It goes fast.

Offline Dan Rowe

  • Full Member
  • ****
  • Posts: 749
  • Dripping Springs TX USA
Re: Flat Belt Reversing Mechanism
« Reply #11 on: August 03, 2018, 08:08:24 PM »
Brian, if the belt stretches after a bit of use the only way to fix it is to add shims to the side plates. If you rearranged the plates you could use slotted holes to allow for belt stretch.

Dan
ShaylocoDan

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 5248
  • Barrie, Ontario Canada
Re: Flat Belt Reversing Mechanism
« Reply #12 on: August 03, 2018, 09:37:31 PM »
Dan--This thing isn't going to see enough use for the belt to stretch. The belt was salvaged from an old vacuum cleaner with 90,000 miles on it. If it was ever going to stretch it probably happened a long time ago.

Offline Gas_mantle

  • Full Member
  • ****
  • Posts: 1335
  • North Yorks - UK.
    • My Youtube channel
Re: Flat Belt Reversing Mechanism
« Reply #13 on: August 03, 2018, 09:48:46 PM »
Slightly off topic but going back to the subject of reversing output.

I know little about traction engines but am curious as to how they operated. I appreciate they had the usual Stephenson reversing gear to enable forward or reverse travel but having seen that a lot of engines seem to have spur gears after the crank I was under the impression they could also be reversed through gearing independently of the crank direction ?

Am I missing something here  :headscratch:
« Last Edit: August 03, 2018, 09:53:38 PM by Gas_mantle »

Offline ChuckKey

  • Full Member
  • ****
  • Posts: 88
Re: Flat Belt Reversing Mechanism
« Reply #14 on: August 03, 2018, 10:35:13 PM »
I know little about traction engines but am curious as to how they operated. I appreciate they had the usual Stephenson reversing gear to enable forward or reverse travel but having seen that a lot of engines seem to have spur gears after the crank I was under the impression they could also be reversed through gearing independently of the crank direction ?

No. The valve gear does the reversing. The spur gears provide a reduction gear to the wheels.

Typically an agricutural engine will have two speeds and road engines three. It is not a good idea to try to change gear on the move.

Some engines have three shafts (crankshaft, countershaft, and axle) so the wheels turn in the same direction as the flywheel. Others have four shafts so the flywheel and wheels turn in opposite directions.

Pull the pin out of the wheel hub to disconect the drive to use the axle mounted winch drum. Swap the normal pin for a long one to lock the differential.