Author Topic: Flat Belt Reversing Mechanism  (Read 4959 times)

Offline rspringer

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Re: Flat Belt Reversing Mechanism
« Reply #30 on: August 06, 2018, 06:04:09 AM »
You will still need the center idler.  With out it will be like going from forward to reverse with out using a clutch.  The belt will be on counter rotating shafts at the same time.  Kind of like my daughter driving a straight shift, you can force it but it ain't gonan be pretty.

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #31 on: August 07, 2018, 12:35:04 AM »
One of the major disadvantages of working at "scale model" level, is that some things simply don't scale down that well and still remain functional. I am finished all of the parts for this project except for the end plates that support the shafts.  (I have to buy some material.)  My plan is to manually push or pull the shifter to left or right by hand to see how well the belt moves as I slide it from one pulley to another. On a full size rig, I would have a long lever, pivoted at the bottom and a link from the lever to the end of the slider mechanism. The belt can only be moved from side to side while it is running under power between pulleys. I was able to find this animation on YouTube which is "sorta/kinda" like what I am trying to do, except it isn't reversing.

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #32 on: August 07, 2018, 01:33:42 PM »
-I got some more insight into that neutral center pulley. This set-up was used to drive the cable drum on the carriage of sawmills.  As soon as a board was cut off by the mainsaw you could go quickly from foreword to reverse to retract the carriage. However, when the carriage got to the load end, the belt was moved onto the neutral pulley so the carriage paused while another log was loaded, or the log being cut could be "dogged over" the width of a board and then the belt was moved from the neutral pulley over to the one which advanced the carriage into the saw.--Belts used on a large line shaft driven shaper didn't need a pause at either end of the stroke, so shapers only had a forward and reverse pulley side by side with no neutral pulley between them.---- Brian

Offline Dan Rowe

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Re: Flat Belt Reversing Mechanism
« Reply #33 on: August 07, 2018, 02:16:00 PM »
Belts used on a large line shaft driven shaper didn't need a pause at either end of the stroke, so shapers only had a forward and reverse pulley side by side with no neutral pulley between them

Brian, a shaper does not need a reverse but it most defiantly needs an idle pulley to stop the machine. Putting something into the vise on a moving shaper is not something I want to think about.

Dan
ShaylocoDan

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #34 on: August 07, 2018, 02:29:09 PM »
Okay Dan--Ya got me. Somebody on a different forum had posted a huge flat belt driven shaper. It was wailing back and forth like crazy, driven by a belt which to me appeared to shift between two pulleys only. they must have had some means of disengaging the drive from the shaper, but I didn't see it.---EDI EDIT--There are three pulleys. i just didn't see that before.---Brian
« Last Edit: August 07, 2018, 02:33:37 PM by Brian Rupnow »

Offline Kim

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Re: Flat Belt Reversing Mechanism
« Reply #35 on: August 08, 2018, 05:16:19 AM »
Even if you didn't want to stop the machine, it seems like a center 'neutral' pulley would be necessary.  Otherwise, as the belt transitioned from one direction to the other, there would be a not-insignificant amount of time when the belt would be trying to drive both ways at the same time - forward and reverse.  That seems bad.  If nothing else, it would cause excessive wear on the belt because one side or the other (or both) would have to be slipping during the transition.

Just seems like the neutral middle is necessary to me in all cases.

Kim

Offline ChuckKey

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Re: Flat Belt Reversing Mechanism
« Reply #36 on: August 08, 2018, 09:14:20 AM »
Pedantry corner: as the table moves rather than the tool, that thing is a planer.

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #37 on: August 09, 2018, 02:06:39 AM »
Just got home from a great 2 day mini vacation. Wife and I drove over to Peterborough and spent the afternoon telling lies and drinking wine with a good friend I worked with for five years in the zinc die casting business. Him and his wife were great hosts and a good time was had by all.---Now, as to the mechanism--I have thought about the "over center spring loaded toggle" for an automatic reverse function. However, I tried that on a different reversing mechanism using gears and a rack this past year, and it failed rather miserably. If the moving parts had enough momentum to let them coast  the last bit of stroke, the toggle would have worked fine. However, at small scale and relatively light weight, as soon as the toggle was moved almost to the tipping point, the moving components stopped and just sat there.-Fully disengaging one gear from the rack, but not tipping over far enough to engage the reverse turning gear with the rack. I tried many adjustments and refinements of this system, then decided it wasn't going to work. I will do some thinking on Miners quadrant gear solution, but first I have to buy some material tomorrow and finish the two sideplates and assemble this thing to see it work. Sometimes just seeing a new mechanism work will inspire me with solutions to further progress.

Offline Steamer5

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Re: Flat Belt Reversing Mechanism
« Reply #38 on: August 09, 2018, 02:04:51 PM »
Hi Brian,
 Keep at you will crack it!
Thanks for posting the video of the planner, many years ago while visiting a friend at an engineering & foundary works I got to see a planner chomping away on two full length railway rails cutting the taper for points, it was getting towards the end of the cut & from memory was moving a significant distance. This was a rather large machine.

Cheers Kerrin
Get excited and make something!

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #39 on: August 10, 2018, 07:53:08 PM »
Here we have the first full assembly. I have some serious rework underway with the belt shifting mechanism, and the belt is a little looser than I would have liked, but we are underway.

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #40 on: August 10, 2018, 10:14:19 PM »
Its hard to tell by looking at a 3D model how big or small something is going to be. The shafts on this thing are only 3/8" cold rolled steel. I just finished getting the gear train all sorted out, and it is working as I had intended. Tomorrow I will remake the belt shifter mechanism. I couldn't get the two 1/4" rods which support the belt shifter any closer to the pulley because the idler gear was in the way. Today I decided to go with an offset belt shifter to keep the side guide rollers as close to the pulley drum as I can get them.

Offline zeeprogrammer

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Re: Flat Belt Reversing Mechanism
« Reply #41 on: August 10, 2018, 10:56:36 PM »
I keep  :popcorn:
It's an interesting project...the type that I think will be useful to me at some point.


What's the story on that huge can of e-clips?  ;D
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #42 on: August 10, 2018, 11:31:11 PM »
Carl--Good question about the e-clips. Ever since I started making model size machinery, e-clips were horrible nasty little things that were hard to hold onto, and hard to install without flying across the room, never to be seen again, or even worse, into your eye. I finally broke down and bought two spring loaded insertion tools and 100 of 1/8" e-clips and 100 3/16" size e-clips. They live in that big cocoa can which is stored on a shelf in my shop unless I actually are using them. The insertion tools are expensive, (about $60 each) and only work on one specific size of e-clip. They are wonderful!!!  I should have bought them ten years ago.

Offline Brian Rupnow

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Re: Flat Belt Reversing Mechanism
« Reply #43 on: August 11, 2018, 12:16:45 AM »
It seems to be a bit of an art to get exactly the right center distance between the pulleys. Built as per my original design, the belt is just a bit too slack, and will slip on the pulleys instead of transmitting power. This picture shows the mechanism with four flat washers 0.055" thick between the one endplate and the sideplates, and this seems to make the belt a bit too tight.  I'm starting to feel a bit like Goldilocks. Tomorrow I will try it with some 0.030" spacer washers.

Offline Johnmcc69

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Re: Flat Belt Reversing Mechanism
« Reply #44 on: August 11, 2018, 01:12:44 AM »
A belt tensioner in the assembly would be slick. Especially if it took the tension off the belt when "shifting" it. Just a thought...

 John